Food Chemistry 128 (2011) 284–291
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Effect of acid concentration and treatment time on acid–alcohol modified jackfruit seed starch properties Himjyoti Dutta a, Sanjib Kumar Paul a, Dipankar Kalita a, Charu Lata Mahanta a,⇑ a
Department of Food Processing Technology, School of Engineering, Tezpur University, Assam, India
a r t i c l e
i n f o
Article history: Received 12 August 2010 Received in revised form 7 January 2011 Accepted 2 March 2011 Available online 9 March 2011 Keywords: Jackfruit seed starch Physicochemical properties SEM XRD FTIR
a b s t r a c t The properties of starch extracted from jackfruit (Artocarpus heterophyllus Lam.) seeds, collected from west Assam after acid–alcohol modification by short term treatment (ST) for 15–30 min with concentrated hydrochloric acid and long term treatment (LT) for 1–15 days with 1 M hydrochloric acid, were investigated. Granule density, freeze thaw stability, solubility and light transmittance of the treated starches increased. A maximum decrease in the degree of polymerisation occurred in ST of 30 min (2607.6). Jackfruit starch had 27.1 ± 0.04% amylose content (db), which in ST initially decreased and then increased with the severity of treatment; in LT the effect was irregular. The pasting profile and granule morphology of the treated samples were severely modified. Native starch had the A-type crystalline pattern and crystalline structure increased on treatment. FTIR spectra revealed slight changes in bond stretching and bending. Colour measurement indicated that whiteness increased on treatment. Acid modified jackfruit seed starch can have applications in the food industry. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Starch is a natural semicrystalline biopolymer of D-glucose. The starch molecule is composed of linear amylose and branched amylopectin fractions responsible for its crystalline and amorphous properties, respectively. Acid modified (or acid-thinned) starch is used in different food uses (Atichokudomchai, Shobsngob, Chinachoti, & Varavinit, 2001; Chun, Lim, Takeda, & Shoki, 1997; Hoover, 2000) and also in the paper and textile industries (Beninca et al., 2008). Acid modification causes degradation of starch without damaging the basic granular size and structure (Lawal, Adebowale, Ogunsanwo, Barba, & Ilo, 2005), although some change in the surface morphology is observed. Basic physicochemical properties of starch viz. crystallinity, viscosity, swelling power and solubility, thermal and textural properties are however changed. In addition, the formation of various limit dextrins occurs due to hydrolytic cleavage of the polymeric chains of the starch molecules (Robyt, Choe, Fox, Hahn, & Fuchs, 1996; Yiu, Loh, Rajan, Wong, & Bong, 2008). Acid preferentially attacks the amorphous regions, leading to increased relative crystallinity of the starch and then attacks the more crystalline sections at a slower rate at a later stage (Biliaderis, Grant, & Vose, 1981; Chun et al., 1997; Genkina, Kiseleva, & Noda, 2009). Atichokudomchai, Shobsngob, and Varavinit (2000) found a decrease in the amylose content and an increase in relative crystallinity with an increase in the extent of hydrolysis in cassava starch hydrolysed with hydrochloric acid. According to Biliaderis, ⇑ Corresponding author. Tel.: +91 3712 267008x5702; fax: +91 3712 267005. E-mail address: [email protected] (C.L. Mahanta). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.03.016
Maurice, and Vose (1980), the hydrolysis of the amorphous zones allows the reorganization of the segments of the chains and the formation of a more crystalline structure. However, Amaya-Llano, Martinez-Bustos, Alegria, and Zazueta-Morales (2008) reported a decrease in the relative cystallinity of maize starch and an increase in Jicama starch with similar hydrolysis conditions, which was attributed to the higher amylose content of the maize starch. Somashekarappa, Somashekar, Singh, and Ali (1999) reported significant changes in the microcrystalline properties of different starches with different types of acid-treatments. Fox and Robyt (1992) confirmed from their studies that the mechanism of hydrolysis of starch granules suspended in alcohol involves the hydrolysis of glycosidic bonds with the water inside the granules. Lin and Chang (2006) observed a slow and a rapid degradation stage during acid–methanol treatment for the starches studied. The type of alcohol and acid concentration influences the degree of polymerisation of the alcohol–acid modified starches (Yiu et al., 2008). Jackfruit (Artocarpus heterophyllus Lam.) is an important naturalised plant of Southeast Asia. Boiled and cooked jackfruit seeds are consumed by people as a part of their diets in different parts of the world. It is a rich source of starch. The dry basis starch content in jackfruit seeds after removal of the spermoderm as found by Tulyathan, Tanuwong, Songjinda, and Jaiboon (2002) was around 77.76%. Different works (Bobbio, El-Dash, Bobbio, & Rodrigues, 1978; Tulyathan et al., 2002) suggested two types of granule shapes in jackfruit seed starch. Jackfruit seed starch has not been considered and exploited as a potent source of starch. Only a few published articles are available on this material. Native jackfruit seed starch was compared with different physically and chemically
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modified commercial starches in terms of their physicochemical properties by Mukprasirt and Sajjaanantakul (2004). Work of Tulyathan et al. (2002) gave the native X-ray diffraction and Brabender viscosity curve patterns. Tongdang (2008) compared a few properties of the starch with that of three different Thai aromatic fruit seed starches. A systematic study of acid modified jackfruit seed starch is not reported so far. The aim of the present study was to investigate the effect of rapid and slow alcohol–acid hydrolysis on the physicochemical, structural, morphological and structural properties of jackfruit seed starch.
to the acid hydrolysis treatment time (min), respectively. In the long-term process, acid hydrolysis took place by treating the sample with 1 M hydrochloric acid in absolute alcohol at 27 °C for 1, 5, 10 and 15 days with thorough shaking every 6 h. The rest of the process was carried out similarly as was done in the short-term process, and the modified starch samples were marked as LT1, LT5, LT10 and LT15 according to the acid hydrolysis treatment time (days), respectively.
2. Materials and methods
Starch recovery after hydrolysis was calculated by the following formula.
2.1. Isolation of starch Jackfruits were collected from two trees of west Assam, India. The ripened fruits were cut open manually with a sharp knife and the seeds were taken out from the bulbs. The jackfruit seeds were washed well with tap water to remove the outer cohesive layer and dried at 30 °C in a tray dryer for two days. The arils were removed manually and the thin brown spermoderms of the inner seeds were lye-peeled using a 0.6 M potassium hydroxide solution for 3 h at room temperature to expose the pale white cotyledons. Starch from jackfruit seed cotyledons was isolated by a method modified from the methods of Mukprasirt and Sajjaanantakul (2004) and Bobbio et al. (1978). The cotyledons were washed several times with distilled water to completely remove any traces of alkali on the seed surfaces. They were then wet ground in a blendor (Philips juicer mixer grinder HL1632) with distilled water (1:3, seed to water) for 2 min. The crushed mass was then passed through a standard sieve of size 200 lm. The filtrate was centrifuged at 2000 rpm for 4 min in a centrifuge (Hettich Zentrifugen EBA 21) and the collected residue was resuspended in a 0.5 M solution of sodium thiosulfate (1:1, residue to solution) for 36 h, with stirring at regular intervals in order to remove any protein fractions adhering to the starch granules. The suspension was centrifuged at 3000 rpm for 5 min. The brown layer formed at the top of the white residue was carefully scraped off. The residue was then neutralised with 0.1 M hydrochloric acid and washed two times with distilled water. It was further washed two times with 50% ethanol to remove any ions. The material was then collected, dried under vacuum at 30 °C, ground in a laboratory grain mill (Fritsch Pulverisette 14), passed through 100 lm sieve and stored at 4 °C for further analysis. 2.2. Chemical composition of isolated starch Estimation of moisture, protein, fat and total starch in the isolated starch material was carried out following the AOAC (2005) protocols. 2.3. Acid modification Two sets of acid–alcohol modifications viz. one short-term with concentrated acid and the other, long-term with dilute acid, were carried out following a modified method of Yiu et al. (2008). In the short-term process, the starch was suspended in concentrated hydrochloric acid and 70% alcohol (1:2 v/v), and was allowed to hydrolyse in a shaking water bath at 45 °C for 15, 22 and 30 min. The solution was immediately neutralised after each treatment initially with 1 M sodium hydroxide and finally adjusted to pH 7.0 with 0.1 M sodium hydroxide, washed 3 times with ultra pure water, centrifuged at 4500 rpm for 15 min, dried and further processed as followed during isolation of native starch. The modified starch samples were marked as ST15, ST22 and ST30 according
2.4. Recovery yield
Recovery yieldð%Þ ¼
Dry weight of starch after hydrolysis Dry weight of starch before hydrolysis 100
2.5. Granule density The granule densities of the native and acid-hydrolysed starch samples were determined using the liquid displacement method mentioned by Ogungbenle (2007) for some legume starches. 2.6. Degree of polymerisation The degree of polymerisation (DP) was calculated by dividing the total carbohydrate (AOAC, 1990) with the reducing sugar estimated by the copper sulphate method, described by Lane and Eynon (1923), using glucose as the standard. 2.7. Amylose content The total and soluble amylose contents of all the native and modified samples were determined by the method of Sowbhagya and Bhattacharya (1979). 2.8. Swelling power and solubility A starch suspension was prepared using 5 g starch (db) in 15 ml distilled water in a centrifuge tube and heated for 30 min at 55, 65, 75, 85 and 95 °C with stirring every 2 min. The samples were then cooled to room temperature before centrifuging at 5000 rpm for 15 min. The supernatant was collected and dried at 40 °C to constant weight. The swelling power was calculated as gram of swollen starch per gram of dry sample and the solubility as the percentage of the dried supernatant to the original dried sample. 2.9. Light transmittance Light transmittance of starch suspensions was measured by a modified method of Perera and Hoover (1999) for measuring turbidity. A 2% aqueous starch suspension was heated in a boiling water bath for 1 h with constant stirring. The suspension was cooled for 1 h at 30 °C and then stored at 4 °C. Light transmittance was determined at 640 nm against a distilled water blank with a UV–VIS Spectrophotometer (Cecil Aquarius 7400) every 24 h, for 6 days. 2.10. Freeze–thaw stability The freeze–thaw stability of the gelatinized starch was measured by the method of Kaur, Singh, and Singh (2004) with some modifications, to determine the retention of stability of the gelatinized starch after repeating cycles of freezing and thawing. An
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aqueous suspension of starch (5%, w/w) was heated at 95 °C in a shaking water bath for 1 h. The paste was weighed (exactly 20 g each) into previously weighed polypropylene centrifuge tubes and the tubes were closed tightly. The paste was centrifuged at 1000 rpm for 3 min to remove free water (supernatant). Alternate freezing and thawing was performed by freezing at 18 °C for 24 h and thawing for 4 h at 30 °C, followed by centrifugation at 4500 rpm for 25 min. A total of eight freeze–thaw cycles were performed. The weight of water separated after each cycle was taken as the extent of syneresis and expressed as the percentage of water separated.
%Syneresis ¼
2.15. FTIR spectroscopy The infra-red spectra for all the samples were obtained with a FTIR spectrometer (Nicolet Impact 410) equipped with KBr optics and a DTGS detector. The equipment was operated with a resolution of 2.0 cm1 and scanning range of 4000–370 cm1. 2.16. Statistical analysis
Water separatedðgÞ 100 Total weight of sampleðgÞ
All the experiments were carried out in triplicate. Tests of significant differences between means were determined by Duncan’s multiple range test at a significance level of 0.05 using SPSS 11.5 (SPSS Inc., USA).
2.11. X-ray diffraction Wide angle X-ray diffractograms were obtained with an X-ray diffractometer (Rigaku Miniflex) with a k value of 1.54040 operating at 30 kV acceleration potential and 15 mA current with a copper target. The scanning range was 2–30° of 2h values with a scan speed of 8° 2h/min. The diffractogram patterns were evaluated according to Zobel (1964). The percentage crystallinity was determined according to Singh, Ali, Somashekar, and Mukherjee (2006).
%Crystallinity ¼
Lab Ultrascan Vis). The result was expressed as L⁄, a⁄, b⁄ using native starch as reference.
Area under peaks 100 Total area
2.12. Starch granule size, structure and morphology and tissue histology
3. Results and discussion 3.1. Chemical composition of jackfruit seed starch The jackfruit seed starch had 11.3% ± 0.03 moisture, 0.4% ± 0.02 protein (db), 0.2% ± 0.00 fat (db) and 99.2% ± 0.04 starch (db). The isolated starch had negligible protein and fat contents. 3.2. Recovery yield
Native and modified starch granules were observed with a Scanning Electron Microscope (JEOL 6993V) operating at an acceleration voltage of 15 kV and 1500 magnification. The location of the granules in transverse sections of the seeds was studied at 300 magnification.
The recovery of starch after acid modification decreased with increasing the treatment time (Table 1). The recovery was comparatively higher in the long-term modification process carried out using 1 M hydrochloric acid than the short-term process using concentrated hydrochloric acid. However in both the cases, the yield was more than 73%.
2.13. Pasting properties
3.3. Granule density
The pasting profiles of starches were recorded using a Rapid Visco Analyser (RVA Starchmaster2, Newport Scientific Instruments). The viscosity profiles were recorded using starch suspensions (10% w/w; 28 g total weight). The Std1 profile of Newport Scientific was used, where the samples were held at 50 °C for 1 min, heated from 50 °C to 95 °C at 12.16 °C/min, held at 95 °C for 2.30 min, cooled from 95 °C to 50 °C at 11.84 °C/min, and held at 50 °C for 2 min. The peak viscosity (PV), hot paste viscosity (HPV), cold paste viscosity (CPV), breakdown (BD) and setback (SB) were recorded. HPV = minimum viscosity at 95 °C, CPV = final viscosity at 50 °C, BD = PV HPV and SB = CPV HPV.
The differences in the densities of the modified starch granules are attributed to their surface damage caused by mild and strong acids, hence inversely related to the recovery yield (Table 1). Its increase was higher in the short-term modified samples (1.32 ± 0.05 in native starch to 1.44 ± 0.03) than the long-term modified samples (up to 1.40 ± 0.03). The comparatively greater damage to granule shapes and sizes in case of short-term treatments may be attributed to the concentrated acid.
2.14. Colour measurement
The DP for native starch was 3180. The DP was lowered on acid modification with short term treatments showing greater effect than long term treatments (Table 1). DP appeared to be influenced by treatment time and acid concentration.
The colour of all samples was compared by analysing the samples in a Colour Measurement Spectrophotometer (Hunter Color-
3.4. Degree of polymerisation
Table 1 Recovery yield, granule density, total and soluble amylose and DP values of native and acid-modified jackfruit seed starch.
a
Parameters
Native
ST15
ST22
ST30
LT1
LT5
LT10
LT15
Recovery yield (%)a Granule density (g/cm3)a Total amylose (%)a Soluble amylose (%)a DPa
100.00f 1.293a 27.12f 4.70a 3483.0h
81.33d 1.390cd 15.92a 12.49c 2813.5c
77.50c 1.413de 19.50b 17.89e 2699.5b
73.22a 1.443e 21.56c 20.02g 2607.2a
86.32e 1.320ab 22.94e 11.98b 3036.6g
81.58d 1.337b 22.24d 16.80d 2990.6f
78.11c 1.353bc 23.15e 18.96f 2930.3e
76.49b 1.403de 22.53d 20.32g 2831.0d
Means with the same superscript do not differ significantly from one another (P > 0.05).
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(b) Native ST15 ST22 ST30 LT1 LT5 LT10 LT15
25
Swelling power (g/g)
20
15
Native
24
ST15 22
WSI%
(a)
ST22
20
ST30
18
LT5
LT1 LT10
16
LT15
14 12
10
10 8
5
6 0
4 50
60
70
80
90
100
50
o
60
70
80
90
100
o
Temperature ( C)
Temperature ( C)
Fig. 1. (a) Swelling power and (b) solubility curves of acid modified jackfruit seed starch.
3.5. Amylose content
3.6. Swelling power and solubility
In both type of modifications, the milder treatments i.e. ST15 and LT1 and LT5 showed a rapid decrease in the amylose contents, which was significantly different from the native starch (Table 1). This is because of the rapid initial degradation of amylose by acid. The amylose percentage increased thereafter for ST22, ST30 and LT10, respectively, which may be attributed to the loss of amylopectin fractions on continuous acid attack. However, a minor fall in the amylose percentage was again observed for LT15. This irregular rise and fall in the amylose content for the long-term process indicated a possibility that the amylose and amylopectin are distributed in the granules in such a fashion that the weak acid was able to degrade the fractions separately at different stages. Another possibility is that the degraded amylose fractions recrystallized themselves in a form that was more resistant to the acid, while retaining their native amorphous characteristics.
The swelling power and solubility measurements were carried out at different temperatures between 55 and 95 °C (Fig. 1a and Fig. 1b). Both parameters were found to increase with increase in temperature, the increase being drastic above the gelatinization temperature. However, the solubility increased and the swelling power decreased with the severity of acid treatments, which was also reported by Lawal and Adebowale (2005) in his work with Jack bean starch. The amylopectin fraction is primarily responsible for granule swelling and amylose acts as a diluent (Tester & Morrison, 1990). In addition to amylose, the bonds of amylopectin are weakened and gradually break with increasing temperature, resulting in increased solubility. The damage of amylopectin by acid can be attributed to the decrease in the swelling power of the granules. A negative correlation of the swelling power with the amylose content was observed by Singh, Singh, Isono, and Noda (2010), which indicated the suppression of granules swelling in the presence of amylose.
86 84
Native
82
ST15
80
ST22
78
ST30
76
LT1
74
LT5
72
LT10
70
LT15
68 66 64
(b) Native
70
ST15 ST22
60
ST30 LT1
50
% Syneresis
% Transmittance at 640nm
(a)
LT5 LT10 LT15
40
30
62
20
60 58 56
10
54 52
0
50 48 0
1
2
3
Time (days)
4
5
6
0
1
2
3 4 5 6 7 Number of freeze-thaw cycles
Fig. 2. (a) % Transmittance and (b) freeze–thaw stability of acid modified jackfruit seed starch.
8
9
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3.7. Light transmittance The % transmittance at 640 nm of the native starch was the lowest, followed by short term samples and the long term samples, as seen in Fig. 2a. This behaviour of acid treated starch samples may be attributed to the decreased tendency towards retrogradation after modification. However, the % transmittance of the native, as well as the modified starch pastes, decreased with the time of storage at 4 °C, though irregularly. The leaching of amorphous regions during acid thinning enhances the bond formation between the amylopectin molecules, and thus can decrease its light transmittance (Lawal, 2004) upon storage. The results revealed that the acid concentration and the time of treatment had different extent of changes in the amylose and amylopectin molecules that caused varied tendencies towards gelatinization and retrogradation. 3.8. Freeze–thaw stability The % syneresis shown by the starches increased with increasing the acid treatment time (Fig. 2b). The native starch showed very little syneresis after the third freeze–thaw cycle. Sharp increases in the % syneresis were observed in the case of ST15 and ST22 in the first two cycles and only in the first cycle in the case of ST30. However, the extent of this increase in syneresis decreased in consecutive cycles with many other samples levelling off. The samples from the long-term process exhibited distinct increases, although they were not as prominent as the short-term samples. The study revealed that the stronger acid caused greater changes in the bonding patterns, which resulted in lowering of the water holding capacities by the granules during continuous freezing and thawing. 3.9. Crystalline structure after acid modification The native jackfruit starch granule exhibited the typical A-type X-ray diffractogram of starch with peaks at 2h values near 15 (peak 1), 18 (peak 2) and 23 (peak 3) (Zobel, 1964). The pattern did not change in the starch with different acid–alcohol modification treatments. However, the peak intensities showed distinct variations for the native and the short and long-term processed samples (Fig. 3a). Loss of crystallinity was more evident in the long-term process and in both treatment types, in accordance with the changes in the amylose contents of the samples (Fig. 3b). In the case of the short-term process, the crystallinity first increased from native to ST15 indicating a loss of amorphous structure due to
3.10. Starch granule size, structure and location in the seed tissue SEM of a transverse section of jackfruit seed revealed that all the types of starch granules in the seeds were present as clusters in the cells separated by well defined membranes (Fig. 4a). These cells that housed the starch granules were made up of proteins, which were found to stain bluish purple with bromocresol blue. The SEM pictures of the isolated starch granules revealed basically four types of structures viz. round, dome-shaped, trigonal and tetragonal (Fig. 4b). The sizes of the granules ranged from 6– 12 lm. The largest granules were dome-shaped while the smallest ones were observed to be the trigonal ones. All four types were however present in equal proportion throughout the area taken for magnification. The acid degraded the surfaces of the starch granules (Fig. 4c–i). The extent of visible degradation increased with increasing the time of treatment. The extent of surface degradation was more severe in case of the short-term process compared to the long-term process. The native structures of the granules were retained in ST15 and ST22, but in ST30 some of the granules lost their native morphology. In the long-term process, however, the native structures of the granules were retained
(b) 28
LT15
Amylose content
LT10
26
Intensity
ST30 ST22 ST15
Amylose content (%)
LT5 LT1
Crystallinity
24
84 80 76 72
22 68 20 18
Native
64
Crystallinity (%)
(a)
amylose hydrolysis and the concentration of amylopectin in the sample, but again decreased for ST22 and ST30, indicating a loss of crystalline amylopectin and an increase in the amylose fractions due to the progressive acid attack. However, in the long-term process, although an initial increase in crystallinity (LT1 and LT5) followed by a decrease (LT10) similar to the short-term process was observed, another hike in the crystallinity was observed. This indicates a probability that the amylose and amylopectin fractions are arranged in the starch granules in such a conformation that the acid can degrade different portions separately, or there may be a formation of some non-amylose crystalline portions due to the reorganization of the hydrolysed chains that are more resistant to further slow acid-hydrolysis. Minor changes in the peak intensities were also observed in the different samples under the same set of procedures, and therefore changes in % crystallinity were also found. A change in the peak structure was prominent in peak 2 (2h value near 18) than the other two peaks. The % crystallinity was observed to be inversely related to the amylose content of the acid modified starch, as can be seen from Fig. 3b. Only in LT10 and LT15 the % crystallinity was found to be lower than what their amylose content suggested. The amylopectin content, therefore, was found to influence the peak intensities.
60 56
16 5
10
15 20 2 Theta
25
30
52 0.0 Native ST15 ST22 ST30 LT1 LT5 LT10 LT15 Samples
Fig. 3. (a) X-ray diffractogram of native and acid-modified jackfruit seed starch and (b) relationship of % crystallinity with the amylose contents upon acid modification.
H. Dutta et al. / Food Chemistry 128 (2011) 284–291
289
Fig. 4. SEM pictures of (a) transverse section of jackfruit seed; (b) native; (c) ST15; (d) ST22; (e) ST30; (f) LT1; (g) LT5; (h) LT10; and (i) LT 15. Arrow marks (;) indicate shapes of starch granules [in (b)] and a higher degradation of flat surfaces of granules by acid [in (d) and (i)].
throughout the treatments. An interesting fact noticed in both cases was that the flat surfaces of both the dome-shaped as well as the trigonal-shaped granules got more affected by the acid as distinct depressions were observed (Fig. 4c–i). 3.11. Pasting properties Pasting properties are dependent on granule swelling, friction between swollen granules, amylose leaching, starch crystallinity
and chain length of starch components (Singh, Sodhi, & Singh, 2009) and the extent of molecular breakdown and degree of gelatinization (Hagenimana, Ding, & Fang, 2006). The RVA results revealed a significant influence of acid concentration and hydrolysis duration on the jackfruit seed starch (Table 2). The viscosity values of acid treated starch samples were far lower than those of the native starch and the viscosity values were significantly different. The decrease in the magnitude of the peak viscosity (PV) might reflect a greater degradation and gelatinization of
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Table 2 Pasting properties and Hunter colour values of native and acid-modified jackfruit seed starch.
a
Properties
Native
ST15
ST22
ST30
LT1
LT5
LT10
LT15
RVA PV (cP)a HPV(cP)a BV (cP)a CPV(cP)a SV (cP)a
3483g 2658g 824g 5073f 2440g
46c 35c 10a 74b 39c
27b 10b 17c 38a 28b
17a 3a 14b 27a 23a
1747f 1307f 440f 2432e 1124f
217e 68e 151e 295d 227e
98d 46d 50d 203c 155d
19a 4a 15bc 32a 26ab
Colour L⁄a a⁄a b⁄a
90.59a 1.13f 6.37f
91.96ab 1.05e 5.22e
92.35ab 0.92b 4.11b
92.89ab 0.86a 3.92a
92.07ab 1.03d 5.34f
92.54ab 0.99c 4.71d
93.13ab 0.91b 4.27c
93.51b 0.86a 3.94a
Means with the same superscript do not differ significantly from one another (P > 0.05).
starch. Among the acid hydrolysed starch samples, LT1 displayed a viscosity profile much higher than all the acid treated samples but substantially lower than the native starch. All acid hydrolysed samples displayed a lower peak viscosity (17-1749 cP) compared with the native (3483 cP). The reduction in PV by acid treatment may be attributed to an increase in hydrolysis of amorphous regions and the production of low molecular weight dextrins (Singh et al., 2009). This also indicated the presence of polymeric chains, which was also corroborated by the degree of polymerisation values (DP). HPV is influenced by the rate of amylose exudation, granule swelling, and competition between exudated amylose and remaining granules for free water, while CPV is largely determined by the retrogradation tendency of the soluble amylose upon cooling. Depending on the acid concentration and hydrolysis time, both HPV and CPV were affected. HPV varied between 3 and 35 for short term treatment and 4 to 1307 cP for long term treatment. CPV ranged from 27 to74 cP and from 32 to 2432 cP for short term treatment and long term treatment, respectively. BD, which is the measure of susceptibility of cooked starch granule to disintegration and SB, which is measure of recrystallization of gelatinized starch during cooling, also decreased with acid treatment. A similar decrease in pasting viscosities upon acid treatment of corn starch was reported earlier by Sandhu, Singh, and Lim (2007), Wang, Truong, and Wang (2003) and Singh et al. (2009), in acid thinned sorghum starch. The range of CPV values observed in the study makes it suitable for using this starch as fillings in confectionery items by the food industry. 3.12. Colour measurements The colour of all the samples was white and close to each other (Table 2). The L⁄ value for all samples was near to 90, which may be interpreted as more or less perfect white. The values increased with the treatment time, irrespective of the acid concentration. Yellowness, indicated by positive value of b⁄, decreased with the treatment time. This increase in whiteness and decrease in yellowness may be due to the washing out of residual starch pigments upon acid treatment (Mukprasirt & Sajjaanantakul, 2004), as well as the washing steps followed to neutralise the acid. The L⁄, a⁄ and b⁄ values of acid modified starch were significantly different from the native starch. 3.13. FTIR spectroscopy The native spectrum pattern of starch (Iizuka & Aishima, 1999; Irudayaraj & Yang, 2002) shows ten peaks between 3700 and 800 cm1. In our study, all characteristic peaks were observed in the native as well as the acid modified starch samples. Distinct changes in peak intensities were however observed in the modified samples, which were predominant in the LT15 and ST30 samples.
Slight but gradual changes in the positions of the peak between 2970 and 2910, corresponding to the stretching vibration of C–C– H bond were observed. The study revealed changes in the bonding characteristics of the jackfruit seed starch upon acid–alcohol treatment. The changes were affected significantly by the acid concentration and predominantly by the treatment time. 4. Conclusions The properties of acid modified starches depend on the acid concentration and hydrolysis. The effect on the physicochemical properties was more severe in short term treated starch than in long term treated starch. The properties of acid modified starches from jackfruit seed starch were significantly different from native starch. The increase in syneresis during freeze thaw cycles was stabilised after the initial 2–3 cycles for both treatments. Of the four types of starch granules observed, acid preferentially attacked the dome shaped and trigonal shaped granules. Long term treatment caused greater loss of crystallinity than short term treatment; however, the crystallinity was regained when treated for a longer duration. Pasting properties showed a drastic loss in viscosity and the very low HPV and CPV indicates the possibility that acid thinned jackfruit starch can be utilised in confectionery fillings. Work of Tulyathan et al. (2002) revealed that jackfruit seeds may serve as a potent source of starch as the recovery yield from the extraction process was about 77%, which is more than the starch content of maize (around 70%), the highest employed source meant for commercial starch extraction. However, most of these jackfruit seeds do not undergo any utilisation. Acid modified jackfruit seed starch has a promising scope for utilisation in confectioneries, paper and textile industries and for making gum candies because of the peculiar changes in viscosity and other properties developed due to thinning by the acid. References Amaya-Llano, S. L., Martinez-Bustos, F., Alegria, A. L. M., & Zazueta-Morales, J. de J. (2008). Comparative studies on some physico-chemical, thermal, morphological, and pasting properties of acid-thinned jicama and maize starches. Food Bioprocess Technology, doi:10.1007/s11947-008-0153-z. AOAC (1990). Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Inc.: Arlington. AOAC (2005). Official Methods of Analysis, 18th ed. Association of Official Analytical Chemists, Inc.: Arlington. Atichokudomchai, N., Shobsngob, S., Chinachoti, P., & Varavinit, S. (2001). A study of some physiochemical properties of high crystalline tapioca starch. Starch/Starke, 53(11), 577–581. Atichokudomchai, N., Shobsngob, S., & Varavinit, S. (2000). Morphological properties of acid modified tapioca starch. Starch/Starke, 52(8–9), 283–289. Beninca, C., Demiate, I. M., Lacerda, L. G., Carvalho Filho, M. A. S., Ionashiro, M., & Schnitzler, E. (2008). Thermal behavior of corn starch granules modified by acid treatment at 30 and 50 °C. Eclética Química, 33(3), 13–18. Biliaderis, C. G., Grant, D. R., & Vose, J. R. (1981). Structural characterization of legume starches. II. Studies on acid-treated starches. Cereal Chemistry, 58, 502–507.
H. Dutta et al. / Food Chemistry 128 (2011) 284–291 Biliaderis, C. G., Maurice, T. J., & Vose, J. R. (1980). Starch gelatinization phenomena studied by differential scanning calorimetry. Journal of Food Science, 45, 1669–1680. Bobbio, F. O., El-Dash, A. A., Bobbio, P. A., & Rodrigues, L. R. (1978). Isolation and characterization of the physiochemical properties of the starch of jackfruit seeds (Artocarpus heterophyllus). Cereal Chemistry, 55, 505–511. Chun, J., Lim, S., Takeda, Y., & Shoki, M. (1997). Properties of high crystalline rice amylodextrins prepared in acid–alcohol media as fat replacer. Cereal Foods World, 42, 813–819. Fox, J. D., & Robyt, J. F. (1992). Modification of starch granules by hydrolysis with hydrochloric acid in various alcohols and the formation of new kinds of limit dextrins. Carbohydrate Research, 227, 163–170. Genkina, N. K., Kiseleva, V. I., & Noda, T. (2009). Comparative Investigation on acid hydrolysis of sweet potato starches with different amylopectin chain-length. Starch/starke, 61(6), 321–325. Hagenimana, A., Ding, X., & Fang, T. (2006). Evaluation of rice flour modified by extrusion cooking. Journal of Cereal Science, 43, 38–46. Hoover, R. (2000). Acid-treated starches. Food Reviews International, 16, 369–392. Iizuka, K., & Aishima, T. (1999). Starch gelation process observed by FT-IR/ATR spectrometry with multivariate data analysis. Journal of Food Science, 64(4), 653–658. Irudayaraj, J., & Yang, H. (2002). Depth profiling of a heterogeneous food-packing model using step-scan Fourier transform infrared photoacoustic spectroscopy. Journal of Food Engineering, 55, 25–33. Kaur, L., Singh, N., & Singh, J. (2004). Factors influencing the properties of hydroxypropylated potato starches. Carbohydrate Polymers, 55, 211–223. Lane, J. H., & Eynon, L. (1923). Determination of reducing sugars by means of Fehling’s solution with methylene blue as internal indicator. Journal of the Society of Chemical Industry, 42, 32–36. Lawal, O. S. (2004). Composition, physicochemical properties and retrogradation characteristics of native, oxidized, acetylated and acid-thinned new cocoyam (Xanthosoma sagittifolium) starch. Food Chemistry, 87, 205–218. Lawal, O. S., & Adebowale, K. O. (2005). Physicochemical characteristics and thermal properties of chemically modified jack bean (Canavalia ensiformis) starch. Carbohydrate Polymers, 60(3), 331–334. Lawal, L. S., Adebowale, K. O., Ogunsanwo, B. M., Barba, L. L., & Ilo, N. S. (2005). Oxidized and acid thinned starch derivatives of hybrid maize: functional characteristics, wide-angle X-ray diffractometry and thermal properties. International Journal of Biological Macromolecules, 35, 71–79. Lin, J., & Chang, Y. (2006). Molecular degradation rate of rice and corn starches during acid–methanol treatment and its relation to the molecular structure of starch. Journal of Agricultural and Food Chemistry, 54(16), 5880–5886.
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Mukprasirt, A., & Sajjaanantakul, K. (2004). Physico-chemical properties of flour and starch from jackfruit seeds (Artocarpus heterophyllus Lam.) compared with modified starches. International Journal of Food Science and Technology, 39, 271–276. Ogungbenle, H. (2007). Effect of chemical modification on starch of some legume flours. Pakistan Journal of Nutrition, 6(2), 167–171. Perera, C., & Hoover, R. (1999). Influence of hydroxypropylation on retrogradation properties of native, defatted and heat moisture treated potato starches. Food Chemistry, 64, 361–375. Robyt, J. F., Choe, J., Fox, J. D., Hahn, R. S., & Fuchs, E. B. (1996). Acid modification of starch granules in alcohols: reactions in mixtures of two alcohols combined in different ratios. Carbohydrate Research, 283, 141–150. Sandhu, K. S., Singh, N., & Lim, S. T. (2007). A comparison of native and acid thinned normal and waxy corn starches: physiochemical, thermal, morphological and pasting properties. LWT: Food Science and Technology, 40, 1527–1536. Singh, V., Ali, S. Z., Somashekar, R., & Mukherjee, P. S. (2006). Nature of crystallinity in native and acid modified starches. International Journal of Food Properties, 9, 845–854. Singh, S., Singh, N., Isono, N., & Noda, T. (2010). Relationship of granule size distribution and amylopectin structure with pasting, thermal, and retrogradation properties in wheat starch. Journal of Agricultural and Food Chemistry, 58, 1180–1188. Singh, H., Sodhi, N. S., & Singh, N. (2009). Structure and functional properties of acid thinned sorghum starch. International Journal of Food Properties, 12(4), 713–725. Somashekarappa, H., Somashekar, R., Singh, V., & Ali, S. Z. (1999). Microcrystalline parameters in native and acid-modified starches. Bulletin of material science, 22(4), 805–810. Sowbhagya, C. M., & Bhattacharya, K. R. (1979). Simplified determination of amylose in milled rice. Starch/Stake, 31, 159–163. Tester, R. F., & Morrison, W. R. (1990). Swelling and amylosization of cereal starches. I. Effects of amylopectin, amylose and lipids. Cereal Chemistry, 67, 551–557. Tongdang, T. (2008). Some properties of starch extracted from three Thai aromatic fruit seeds. Starch/Starke, 60(3–4), 199–207. Tulyathan, V., Tanuwong, K., Songjinda, P., & Jaiboon, N. (2002). Some physicochemical properties of jackfruit (Artocarpus heterophyllus Lam.) seed flour and starch. Science Asia, 28, 37–41. Wang, Y. J., Truong, V. N., & Wang, L. (2003). Structures and rheological properties of corn starch as affected by acid hydrolysis. Carbohydrate Polymers, 52, 327–333. Yiu, P. H., Loh, S. L., Rajan, A., Wong, S. C., & Bong, C. F. J. (2008). Physiochemical properties of sago starch modified by acid treatment in alcohol. American Journal of Applied Sciences, 5(4), 307–311. Zobel, H. F. (1964). X-ray analysis of starch granules. In R. L. Whistler (Ed.), Methods in carbohydrate chemistry, IV (pp. 109–113). London: Academic Press Inc..
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Food Chemistry journal homepage: www.elsevier.com/locate/foodchem
Effect of acid concentration and treatment time on acid–alcohol modified jackfruit seed starch properties Himjyoti Dutta a, Sanjib Kumar Paul a, Dipankar Kalita a, Charu Lata Mahanta a,⇑ a
Department of Food Processing Technology, School of Engineering, Tezpur University, Assam, India
a r t i c l e
i n f o
Article history: Received 12 August 2010 Received in revised form 7 January 2011 Accepted 2 March 2011 Available online 9 March 2011 Keywords: Jackfruit seed starch Physicochemical properties SEM XRD FTIR
a b s t r a c t The properties of starch extracted from jackfruit (Artocarpus heterophyllus Lam.) seeds, collected from west Assam after acid–alcohol modification by short term treatment (ST) for 15–30 min with concentrated hydrochloric acid and long term treatment (LT) for 1–15 days with 1 M hydrochloric acid, were investigated. Granule density, freeze thaw stability, solubility and light transmittance of the treated starches increased. A maximum decrease in the degree of polymerisation occurred in ST of 30 min (2607.6). Jackfruit starch had 27.1 ± 0.04% amylose content (db), which in ST initially decreased and then increased with the severity of treatment; in LT the effect was irregular. The pasting profile and granule morphology of the treated samples were severely modified. Native starch had the A-type crystalline pattern and crystalline structure increased on treatment. FTIR spectra revealed slight changes in bond stretching and bending. Colour measurement indicated that whiteness increased on treatment. Acid modified jackfruit seed starch can have applications in the food industry. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Starch is a natural semicrystalline biopolymer of D-glucose. The starch molecule is composed of linear amylose and branched amylopectin fractions responsible for its crystalline and amorphous properties, respectively. Acid modified (or acid-thinned) starch is used in different food uses (Atichokudomchai, Shobsngob, Chinachoti, & Varavinit, 2001; Chun, Lim, Takeda, & Shoki, 1997; Hoover, 2000) and also in the paper and textile industries (Beninca et al., 2008). Acid modification causes degradation of starch without damaging the basic granular size and structure (Lawal, Adebowale, Ogunsanwo, Barba, & Ilo, 2005), although some change in the surface morphology is observed. Basic physicochemical properties of starch viz. crystallinity, viscosity, swelling power and solubility, thermal and textural properties are however changed. In addition, the formation of various limit dextrins occurs due to hydrolytic cleavage of the polymeric chains of the starch molecules (Robyt, Choe, Fox, Hahn, & Fuchs, 1996; Yiu, Loh, Rajan, Wong, & Bong, 2008). Acid preferentially attacks the amorphous regions, leading to increased relative crystallinity of the starch and then attacks the more crystalline sections at a slower rate at a later stage (Biliaderis, Grant, & Vose, 1981; Chun et al., 1997; Genkina, Kiseleva, & Noda, 2009). Atichokudomchai, Shobsngob, and Varavinit (2000) found a decrease in the amylose content and an increase in relative crystallinity with an increase in the extent of hydrolysis in cassava starch hydrolysed with hydrochloric acid. According to Biliaderis, ⇑ Corresponding author. Tel.: +91 3712 267008x5702; fax: +91 3712 267005. E-mail address: [email protected] (C.L. Mahanta). 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.03.016
Maurice, and Vose (1980), the hydrolysis of the amorphous zones allows the reorganization of the segments of the chains and the formation of a more crystalline structure. However, Amaya-Llano, Martinez-Bustos, Alegria, and Zazueta-Morales (2008) reported a decrease in the relative cystallinity of maize starch and an increase in Jicama starch with similar hydrolysis conditions, which was attributed to the higher amylose content of the maize starch. Somashekarappa, Somashekar, Singh, and Ali (1999) reported significant changes in the microcrystalline properties of different starches with different types of acid-treatments. Fox and Robyt (1992) confirmed from their studies that the mechanism of hydrolysis of starch granules suspended in alcohol involves the hydrolysis of glycosidic bonds with the water inside the granules. Lin and Chang (2006) observed a slow and a rapid degradation stage during acid–methanol treatment for the starches studied. The type of alcohol and acid concentration influences the degree of polymerisation of the alcohol–acid modified starches (Yiu et al., 2008). Jackfruit (Artocarpus heterophyllus Lam.) is an important naturalised plant of Southeast Asia. Boiled and cooked jackfruit seeds are consumed by people as a part of their diets in different parts of the world. It is a rich source of starch. The dry basis starch content in jackfruit seeds after removal of the spermoderm as found by Tulyathan, Tanuwong, Songjinda, and Jaiboon (2002) was around 77.76%. Different works (Bobbio, El-Dash, Bobbio, & Rodrigues, 1978; Tulyathan et al., 2002) suggested two types of granule shapes in jackfruit seed starch. Jackfruit seed starch has not been considered and exploited as a potent source of starch. Only a few published articles are available on this material. Native jackfruit seed starch was compared with different physically and chemically
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modified commercial starches in terms of their physicochemical properties by Mukprasirt and Sajjaanantakul (2004). Work of Tulyathan et al. (2002) gave the native X-ray diffraction and Brabender viscosity curve patterns. Tongdang (2008) compared a few properties of the starch with that of three different Thai aromatic fruit seed starches. A systematic study of acid modified jackfruit seed starch is not reported so far. The aim of the present study was to investigate the effect of rapid and slow alcohol–acid hydrolysis on the physicochemical, structural, morphological and structural properties of jackfruit seed starch.
to the acid hydrolysis treatment time (min), respectively. In the long-term process, acid hydrolysis took place by treating the sample with 1 M hydrochloric acid in absolute alcohol at 27 °C for 1, 5, 10 and 15 days with thorough shaking every 6 h. The rest of the process was carried out similarly as was done in the short-term process, and the modified starch samples were marked as LT1, LT5, LT10 and LT15 according to the acid hydrolysis treatment time (days), respectively.
2. Materials and methods
Starch recovery after hydrolysis was calculated by the following formula.
2.1. Isolation of starch Jackfruits were collected from two trees of west Assam, India. The ripened fruits were cut open manually with a sharp knife and the seeds were taken out from the bulbs. The jackfruit seeds were washed well with tap water to remove the outer cohesive layer and dried at 30 °C in a tray dryer for two days. The arils were removed manually and the thin brown spermoderms of the inner seeds were lye-peeled using a 0.6 M potassium hydroxide solution for 3 h at room temperature to expose the pale white cotyledons. Starch from jackfruit seed cotyledons was isolated by a method modified from the methods of Mukprasirt and Sajjaanantakul (2004) and Bobbio et al. (1978). The cotyledons were washed several times with distilled water to completely remove any traces of alkali on the seed surfaces. They were then wet ground in a blendor (Philips juicer mixer grinder HL1632) with distilled water (1:3, seed to water) for 2 min. The crushed mass was then passed through a standard sieve of size 200 lm. The filtrate was centrifuged at 2000 rpm for 4 min in a centrifuge (Hettich Zentrifugen EBA 21) and the collected residue was resuspended in a 0.5 M solution of sodium thiosulfate (1:1, residue to solution) for 36 h, with stirring at regular intervals in order to remove any protein fractions adhering to the starch granules. The suspension was centrifuged at 3000 rpm for 5 min. The brown layer formed at the top of the white residue was carefully scraped off. The residue was then neutralised with 0.1 M hydrochloric acid and washed two times with distilled water. It was further washed two times with 50% ethanol to remove any ions. The material was then collected, dried under vacuum at 30 °C, ground in a laboratory grain mill (Fritsch Pulverisette 14), passed through 100 lm sieve and stored at 4 °C for further analysis. 2.2. Chemical composition of isolated starch Estimation of moisture, protein, fat and total starch in the isolated starch material was carried out following the AOAC (2005) protocols. 2.3. Acid modification Two sets of acid–alcohol modifications viz. one short-term with concentrated acid and the other, long-term with dilute acid, were carried out following a modified method of Yiu et al. (2008). In the short-term process, the starch was suspended in concentrated hydrochloric acid and 70% alcohol (1:2 v/v), and was allowed to hydrolyse in a shaking water bath at 45 °C for 15, 22 and 30 min. The solution was immediately neutralised after each treatment initially with 1 M sodium hydroxide and finally adjusted to pH 7.0 with 0.1 M sodium hydroxide, washed 3 times with ultra pure water, centrifuged at 4500 rpm for 15 min, dried and further processed as followed during isolation of native starch. The modified starch samples were marked as ST15, ST22 and ST30 according
2.4. Recovery yield
Recovery yieldð%Þ ¼
Dry weight of starch after hydrolysis Dry weight of starch before hydrolysis 100
2.5. Granule density The granule densities of the native and acid-hydrolysed starch samples were determined using the liquid displacement method mentioned by Ogungbenle (2007) for some legume starches. 2.6. Degree of polymerisation The degree of polymerisation (DP) was calculated by dividing the total carbohydrate (AOAC, 1990) with the reducing sugar estimated by the copper sulphate method, described by Lane and Eynon (1923), using glucose as the standard. 2.7. Amylose content The total and soluble amylose contents of all the native and modified samples were determined by the method of Sowbhagya and Bhattacharya (1979). 2.8. Swelling power and solubility A starch suspension was prepared using 5 g starch (db) in 15 ml distilled water in a centrifuge tube and heated for 30 min at 55, 65, 75, 85 and 95 °C with stirring every 2 min. The samples were then cooled to room temperature before centrifuging at 5000 rpm for 15 min. The supernatant was collected and dried at 40 °C to constant weight. The swelling power was calculated as gram of swollen starch per gram of dry sample and the solubility as the percentage of the dried supernatant to the original dried sample. 2.9. Light transmittance Light transmittance of starch suspensions was measured by a modified method of Perera and Hoover (1999) for measuring turbidity. A 2% aqueous starch suspension was heated in a boiling water bath for 1 h with constant stirring. The suspension was cooled for 1 h at 30 °C and then stored at 4 °C. Light transmittance was determined at 640 nm against a distilled water blank with a UV–VIS Spectrophotometer (Cecil Aquarius 7400) every 24 h, for 6 days. 2.10. Freeze–thaw stability The freeze–thaw stability of the gelatinized starch was measured by the method of Kaur, Singh, and Singh (2004) with some modifications, to determine the retention of stability of the gelatinized starch after repeating cycles of freezing and thawing. An
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aqueous suspension of starch (5%, w/w) was heated at 95 °C in a shaking water bath for 1 h. The paste was weighed (exactly 20 g each) into previously weighed polypropylene centrifuge tubes and the tubes were closed tightly. The paste was centrifuged at 1000 rpm for 3 min to remove free water (supernatant). Alternate freezing and thawing was performed by freezing at 18 °C for 24 h and thawing for 4 h at 30 °C, followed by centrifugation at 4500 rpm for 25 min. A total of eight freeze–thaw cycles were performed. The weight of water separated after each cycle was taken as the extent of syneresis and expressed as the percentage of water separated.
%Syneresis ¼
2.15. FTIR spectroscopy The infra-red spectra for all the samples were obtained with a FTIR spectrometer (Nicolet Impact 410) equipped with KBr optics and a DTGS detector. The equipment was operated with a resolution of 2.0 cm1 and scanning range of 4000–370 cm1. 2.16. Statistical analysis
Water separatedðgÞ 100 Total weight of sampleðgÞ
All the experiments were carried out in triplicate. Tests of significant differences between means were determined by Duncan’s multiple range test at a significance level of 0.05 using SPSS 11.5 (SPSS Inc., USA).
2.11. X-ray diffraction Wide angle X-ray diffractograms were obtained with an X-ray diffractometer (Rigaku Miniflex) with a k value of 1.54040 operating at 30 kV acceleration potential and 15 mA current with a copper target. The scanning range was 2–30° of 2h values with a scan speed of 8° 2h/min. The diffractogram patterns were evaluated according to Zobel (1964). The percentage crystallinity was determined according to Singh, Ali, Somashekar, and Mukherjee (2006).
%Crystallinity ¼
Lab Ultrascan Vis). The result was expressed as L⁄, a⁄, b⁄ using native starch as reference.
Area under peaks 100 Total area
2.12. Starch granule size, structure and morphology and tissue histology
3. Results and discussion 3.1. Chemical composition of jackfruit seed starch The jackfruit seed starch had 11.3% ± 0.03 moisture, 0.4% ± 0.02 protein (db), 0.2% ± 0.00 fat (db) and 99.2% ± 0.04 starch (db). The isolated starch had negligible protein and fat contents. 3.2. Recovery yield
Native and modified starch granules were observed with a Scanning Electron Microscope (JEOL 6993V) operating at an acceleration voltage of 15 kV and 1500 magnification. The location of the granules in transverse sections of the seeds was studied at 300 magnification.
The recovery of starch after acid modification decreased with increasing the treatment time (Table 1). The recovery was comparatively higher in the long-term modification process carried out using 1 M hydrochloric acid than the short-term process using concentrated hydrochloric acid. However in both the cases, the yield was more than 73%.
2.13. Pasting properties
3.3. Granule density
The pasting profiles of starches were recorded using a Rapid Visco Analyser (RVA Starchmaster2, Newport Scientific Instruments). The viscosity profiles were recorded using starch suspensions (10% w/w; 28 g total weight). The Std1 profile of Newport Scientific was used, where the samples were held at 50 °C for 1 min, heated from 50 °C to 95 °C at 12.16 °C/min, held at 95 °C for 2.30 min, cooled from 95 °C to 50 °C at 11.84 °C/min, and held at 50 °C for 2 min. The peak viscosity (PV), hot paste viscosity (HPV), cold paste viscosity (CPV), breakdown (BD) and setback (SB) were recorded. HPV = minimum viscosity at 95 °C, CPV = final viscosity at 50 °C, BD = PV HPV and SB = CPV HPV.
The differences in the densities of the modified starch granules are attributed to their surface damage caused by mild and strong acids, hence inversely related to the recovery yield (Table 1). Its increase was higher in the short-term modified samples (1.32 ± 0.05 in native starch to 1.44 ± 0.03) than the long-term modified samples (up to 1.40 ± 0.03). The comparatively greater damage to granule shapes and sizes in case of short-term treatments may be attributed to the concentrated acid.
2.14. Colour measurement
The DP for native starch was 3180. The DP was lowered on acid modification with short term treatments showing greater effect than long term treatments (Table 1). DP appeared to be influenced by treatment time and acid concentration.
The colour of all samples was compared by analysing the samples in a Colour Measurement Spectrophotometer (Hunter Color-
3.4. Degree of polymerisation
Table 1 Recovery yield, granule density, total and soluble amylose and DP values of native and acid-modified jackfruit seed starch.
a
Parameters
Native
ST15
ST22
ST30
LT1
LT5
LT10
LT15
Recovery yield (%)a Granule density (g/cm3)a Total amylose (%)a Soluble amylose (%)a DPa
100.00f 1.293a 27.12f 4.70a 3483.0h
81.33d 1.390cd 15.92a 12.49c 2813.5c
77.50c 1.413de 19.50b 17.89e 2699.5b
73.22a 1.443e 21.56c 20.02g 2607.2a
86.32e 1.320ab 22.94e 11.98b 3036.6g
81.58d 1.337b 22.24d 16.80d 2990.6f
78.11c 1.353bc 23.15e 18.96f 2930.3e
76.49b 1.403de 22.53d 20.32g 2831.0d
Means with the same superscript do not differ significantly from one another (P > 0.05).
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(b) Native ST15 ST22 ST30 LT1 LT5 LT10 LT15
25
Swelling power (g/g)
20
15
Native
24
ST15 22
WSI%
(a)
ST22
20
ST30
18
LT5
LT1 LT10
16
LT15
14 12
10
10 8
5
6 0
4 50
60
70
80
90
100
50
o
60
70
80
90
100
o
Temperature ( C)
Temperature ( C)
Fig. 1. (a) Swelling power and (b) solubility curves of acid modified jackfruit seed starch.
3.5. Amylose content
3.6. Swelling power and solubility
In both type of modifications, the milder treatments i.e. ST15 and LT1 and LT5 showed a rapid decrease in the amylose contents, which was significantly different from the native starch (Table 1). This is because of the rapid initial degradation of amylose by acid. The amylose percentage increased thereafter for ST22, ST30 and LT10, respectively, which may be attributed to the loss of amylopectin fractions on continuous acid attack. However, a minor fall in the amylose percentage was again observed for LT15. This irregular rise and fall in the amylose content for the long-term process indicated a possibility that the amylose and amylopectin are distributed in the granules in such a fashion that the weak acid was able to degrade the fractions separately at different stages. Another possibility is that the degraded amylose fractions recrystallized themselves in a form that was more resistant to the acid, while retaining their native amorphous characteristics.
The swelling power and solubility measurements were carried out at different temperatures between 55 and 95 °C (Fig. 1a and Fig. 1b). Both parameters were found to increase with increase in temperature, the increase being drastic above the gelatinization temperature. However, the solubility increased and the swelling power decreased with the severity of acid treatments, which was also reported by Lawal and Adebowale (2005) in his work with Jack bean starch. The amylopectin fraction is primarily responsible for granule swelling and amylose acts as a diluent (Tester & Morrison, 1990). In addition to amylose, the bonds of amylopectin are weakened and gradually break with increasing temperature, resulting in increased solubility. The damage of amylopectin by acid can be attributed to the decrease in the swelling power of the granules. A negative correlation of the swelling power with the amylose content was observed by Singh, Singh, Isono, and Noda (2010), which indicated the suppression of granules swelling in the presence of amylose.
86 84
Native
82
ST15
80
ST22
78
ST30
76
LT1
74
LT5
72
LT10
70
LT15
68 66 64
(b) Native
70
ST15 ST22
60
ST30 LT1
50
% Syneresis
% Transmittance at 640nm
(a)
LT5 LT10 LT15
40
30
62
20
60 58 56
10
54 52
0
50 48 0
1
2
3
Time (days)
4
5
6
0
1
2
3 4 5 6 7 Number of freeze-thaw cycles
Fig. 2. (a) % Transmittance and (b) freeze–thaw stability of acid modified jackfruit seed starch.
8
9
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3.7. Light transmittance The % transmittance at 640 nm of the native starch was the lowest, followed by short term samples and the long term samples, as seen in Fig. 2a. This behaviour of acid treated starch samples may be attributed to the decreased tendency towards retrogradation after modification. However, the % transmittance of the native, as well as the modified starch pastes, decreased with the time of storage at 4 °C, though irregularly. The leaching of amorphous regions during acid thinning enhances the bond formation between the amylopectin molecules, and thus can decrease its light transmittance (Lawal, 2004) upon storage. The results revealed that the acid concentration and the time of treatment had different extent of changes in the amylose and amylopectin molecules that caused varied tendencies towards gelatinization and retrogradation. 3.8. Freeze–thaw stability The % syneresis shown by the starches increased with increasing the acid treatment time (Fig. 2b). The native starch showed very little syneresis after the third freeze–thaw cycle. Sharp increases in the % syneresis were observed in the case of ST15 and ST22 in the first two cycles and only in the first cycle in the case of ST30. However, the extent of this increase in syneresis decreased in consecutive cycles with many other samples levelling off. The samples from the long-term process exhibited distinct increases, although they were not as prominent as the short-term samples. The study revealed that the stronger acid caused greater changes in the bonding patterns, which resulted in lowering of the water holding capacities by the granules during continuous freezing and thawing. 3.9. Crystalline structure after acid modification The native jackfruit starch granule exhibited the typical A-type X-ray diffractogram of starch with peaks at 2h values near 15 (peak 1), 18 (peak 2) and 23 (peak 3) (Zobel, 1964). The pattern did not change in the starch with different acid–alcohol modification treatments. However, the peak intensities showed distinct variations for the native and the short and long-term processed samples (Fig. 3a). Loss of crystallinity was more evident in the long-term process and in both treatment types, in accordance with the changes in the amylose contents of the samples (Fig. 3b). In the case of the short-term process, the crystallinity first increased from native to ST15 indicating a loss of amorphous structure due to
3.10. Starch granule size, structure and location in the seed tissue SEM of a transverse section of jackfruit seed revealed that all the types of starch granules in the seeds were present as clusters in the cells separated by well defined membranes (Fig. 4a). These cells that housed the starch granules were made up of proteins, which were found to stain bluish purple with bromocresol blue. The SEM pictures of the isolated starch granules revealed basically four types of structures viz. round, dome-shaped, trigonal and tetragonal (Fig. 4b). The sizes of the granules ranged from 6– 12 lm. The largest granules were dome-shaped while the smallest ones were observed to be the trigonal ones. All four types were however present in equal proportion throughout the area taken for magnification. The acid degraded the surfaces of the starch granules (Fig. 4c–i). The extent of visible degradation increased with increasing the time of treatment. The extent of surface degradation was more severe in case of the short-term process compared to the long-term process. The native structures of the granules were retained in ST15 and ST22, but in ST30 some of the granules lost their native morphology. In the long-term process, however, the native structures of the granules were retained
(b) 28
LT15
Amylose content
LT10
26
Intensity
ST30 ST22 ST15
Amylose content (%)
LT5 LT1
Crystallinity
24
84 80 76 72
22 68 20 18
Native
64
Crystallinity (%)
(a)
amylose hydrolysis and the concentration of amylopectin in the sample, but again decreased for ST22 and ST30, indicating a loss of crystalline amylopectin and an increase in the amylose fractions due to the progressive acid attack. However, in the long-term process, although an initial increase in crystallinity (LT1 and LT5) followed by a decrease (LT10) similar to the short-term process was observed, another hike in the crystallinity was observed. This indicates a probability that the amylose and amylopectin fractions are arranged in the starch granules in such a conformation that the acid can degrade different portions separately, or there may be a formation of some non-amylose crystalline portions due to the reorganization of the hydrolysed chains that are more resistant to further slow acid-hydrolysis. Minor changes in the peak intensities were also observed in the different samples under the same set of procedures, and therefore changes in % crystallinity were also found. A change in the peak structure was prominent in peak 2 (2h value near 18) than the other two peaks. The % crystallinity was observed to be inversely related to the amylose content of the acid modified starch, as can be seen from Fig. 3b. Only in LT10 and LT15 the % crystallinity was found to be lower than what their amylose content suggested. The amylopectin content, therefore, was found to influence the peak intensities.
60 56
16 5
10
15 20 2 Theta
25
30
52 0.0 Native ST15 ST22 ST30 LT1 LT5 LT10 LT15 Samples
Fig. 3. (a) X-ray diffractogram of native and acid-modified jackfruit seed starch and (b) relationship of % crystallinity with the amylose contents upon acid modification.
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Fig. 4. SEM pictures of (a) transverse section of jackfruit seed; (b) native; (c) ST15; (d) ST22; (e) ST30; (f) LT1; (g) LT5; (h) LT10; and (i) LT 15. Arrow marks (;) indicate shapes of starch granules [in (b)] and a higher degradation of flat surfaces of granules by acid [in (d) and (i)].
throughout the treatments. An interesting fact noticed in both cases was that the flat surfaces of both the dome-shaped as well as the trigonal-shaped granules got more affected by the acid as distinct depressions were observed (Fig. 4c–i). 3.11. Pasting properties Pasting properties are dependent on granule swelling, friction between swollen granules, amylose leaching, starch crystallinity
and chain length of starch components (Singh, Sodhi, & Singh, 2009) and the extent of molecular breakdown and degree of gelatinization (Hagenimana, Ding, & Fang, 2006). The RVA results revealed a significant influence of acid concentration and hydrolysis duration on the jackfruit seed starch (Table 2). The viscosity values of acid treated starch samples were far lower than those of the native starch and the viscosity values were significantly different. The decrease in the magnitude of the peak viscosity (PV) might reflect a greater degradation and gelatinization of
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Table 2 Pasting properties and Hunter colour values of native and acid-modified jackfruit seed starch.
a
Properties
Native
ST15
ST22
ST30
LT1
LT5
LT10
LT15
RVA PV (cP)a HPV(cP)a BV (cP)a CPV(cP)a SV (cP)a
3483g 2658g 824g 5073f 2440g
46c 35c 10a 74b 39c
27b 10b 17c 38a 28b
17a 3a 14b 27a 23a
1747f 1307f 440f 2432e 1124f
217e 68e 151e 295d 227e
98d 46d 50d 203c 155d
19a 4a 15bc 32a 26ab
Colour L⁄a a⁄a b⁄a
90.59a 1.13f 6.37f
91.96ab 1.05e 5.22e
92.35ab 0.92b 4.11b
92.89ab 0.86a 3.92a
92.07ab 1.03d 5.34f
92.54ab 0.99c 4.71d
93.13ab 0.91b 4.27c
93.51b 0.86a 3.94a
Means with the same superscript do not differ significantly from one another (P > 0.05).
starch. Among the acid hydrolysed starch samples, LT1 displayed a viscosity profile much higher than all the acid treated samples but substantially lower than the native starch. All acid hydrolysed samples displayed a lower peak viscosity (17-1749 cP) compared with the native (3483 cP). The reduction in PV by acid treatment may be attributed to an increase in hydrolysis of amorphous regions and the production of low molecular weight dextrins (Singh et al., 2009). This also indicated the presence of polymeric chains, which was also corroborated by the degree of polymerisation values (DP). HPV is influenced by the rate of amylose exudation, granule swelling, and competition between exudated amylose and remaining granules for free water, while CPV is largely determined by the retrogradation tendency of the soluble amylose upon cooling. Depending on the acid concentration and hydrolysis time, both HPV and CPV were affected. HPV varied between 3 and 35 for short term treatment and 4 to 1307 cP for long term treatment. CPV ranged from 27 to74 cP and from 32 to 2432 cP for short term treatment and long term treatment, respectively. BD, which is the measure of susceptibility of cooked starch granule to disintegration and SB, which is measure of recrystallization of gelatinized starch during cooling, also decreased with acid treatment. A similar decrease in pasting viscosities upon acid treatment of corn starch was reported earlier by Sandhu, Singh, and Lim (2007), Wang, Truong, and Wang (2003) and Singh et al. (2009), in acid thinned sorghum starch. The range of CPV values observed in the study makes it suitable for using this starch as fillings in confectionery items by the food industry. 3.12. Colour measurements The colour of all the samples was white and close to each other (Table 2). The L⁄ value for all samples was near to 90, which may be interpreted as more or less perfect white. The values increased with the treatment time, irrespective of the acid concentration. Yellowness, indicated by positive value of b⁄, decreased with the treatment time. This increase in whiteness and decrease in yellowness may be due to the washing out of residual starch pigments upon acid treatment (Mukprasirt & Sajjaanantakul, 2004), as well as the washing steps followed to neutralise the acid. The L⁄, a⁄ and b⁄ values of acid modified starch were significantly different from the native starch. 3.13. FTIR spectroscopy The native spectrum pattern of starch (Iizuka & Aishima, 1999; Irudayaraj & Yang, 2002) shows ten peaks between 3700 and 800 cm1. In our study, all characteristic peaks were observed in the native as well as the acid modified starch samples. Distinct changes in peak intensities were however observed in the modified samples, which were predominant in the LT15 and ST30 samples.
Slight but gradual changes in the positions of the peak between 2970 and 2910, corresponding to the stretching vibration of C–C– H bond were observed. The study revealed changes in the bonding characteristics of the jackfruit seed starch upon acid–alcohol treatment. The changes were affected significantly by the acid concentration and predominantly by the treatment time. 4. Conclusions The properties of acid modified starches depend on the acid concentration and hydrolysis. The effect on the physicochemical properties was more severe in short term treated starch than in long term treated starch. The properties of acid modified starches from jackfruit seed starch were significantly different from native starch. The increase in syneresis during freeze thaw cycles was stabilised after the initial 2–3 cycles for both treatments. Of the four types of starch granules observed, acid preferentially attacked the dome shaped and trigonal shaped granules. Long term treatment caused greater loss of crystallinity than short term treatment; however, the crystallinity was regained when treated for a longer duration. Pasting properties showed a drastic loss in viscosity and the very low HPV and CPV indicates the possibility that acid thinned jackfruit starch can be utilised in confectionery fillings. Work of Tulyathan et al. (2002) revealed that jackfruit seeds may serve as a potent source of starch as the recovery yield from the extraction process was about 77%, which is more than the starch content of maize (around 70%), the highest employed source meant for commercial starch extraction. However, most of these jackfruit seeds do not undergo any utilisation. Acid modified jackfruit seed starch has a promising scope for utilisation in confectioneries, paper and textile industries and for making gum candies because of the peculiar changes in viscosity and other properties developed due to thinning by the acid. References Amaya-Llano, S. L., Martinez-Bustos, F., Alegria, A. L. M., & Zazueta-Morales, J. de J. (2008). Comparative studies on some physico-chemical, thermal, morphological, and pasting properties of acid-thinned jicama and maize starches. Food Bioprocess Technology, doi:10.1007/s11947-008-0153-z. AOAC (1990). Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Inc.: Arlington. AOAC (2005). Official Methods of Analysis, 18th ed. Association of Official Analytical Chemists, Inc.: Arlington. Atichokudomchai, N., Shobsngob, S., Chinachoti, P., & Varavinit, S. (2001). A study of some physiochemical properties of high crystalline tapioca starch. Starch/Starke, 53(11), 577–581. Atichokudomchai, N., Shobsngob, S., & Varavinit, S. (2000). Morphological properties of acid modified tapioca starch. Starch/Starke, 52(8–9), 283–289. Beninca, C., Demiate, I. M., Lacerda, L. G., Carvalho Filho, M. A. S., Ionashiro, M., & Schnitzler, E. (2008). Thermal behavior of corn starch granules modified by acid treatment at 30 and 50 °C. Eclética Química, 33(3), 13–18. Biliaderis, C. G., Grant, D. R., & Vose, J. R. (1981). Structural characterization of legume starches. II. Studies on acid-treated starches. Cereal Chemistry, 58, 502–507.
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