Food Chemistry 179 (2015) 85–93

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Quality assessment of noodles made from blends of rice flour and canna starch Yuree Wandee a, Dudsadee Uttapap a,⇑, Santhanee Puncha-arnon a, Chureerat Puttanlek b, Vilai Rungsardthong c, Nuanchawee Wetprasit d a

Division of Biochemical Technology, School of Bioresources and Technology, King Mongkut’s University of Technology Thonburi, Bangkhuntien, Bangkok 10150, Thailand Department of Biotechnology, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand Department of Agro-Industrial, Food, and Environmental Technology, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand d Department of Biotechnology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand b c

a r t i c l e

i n f o

Article history: Received 18 November 2014 Received in revised form 22 January 2015 Accepted 24 January 2015 Available online 31 January 2015 Keywords: Rice noodles Canna starch Dietary fiber Short-chain fatty acids Butyric acid

a b s t r a c t Canna starch and its derivatives (retrograded, retrograded debranched, and cross-linked) were evaluated for their suitability to be used as prebiotic sources in a rice noodle product. Twenty percent of the rice flour was replaced with these tested starches, and the noodles obtained were analyzed for morphology, cooking qualities, textural properties, and capability of producing short-chain fatty acids (SCFAs). Crosslinked canna starch could increase tensile strength and elongation of rice noodles. Total dietary fiber (TDF) content of noodles made from rice flour was 3.0% and increased to 5.1% and 7.3% when rice flour was replaced with retrograded and retrograded debranched starches, respectively. Cooking qualities and textural properties of noodles containing 20% retrograded debranched starch were mostly comparable, while the capability of producing SCFAs and butyric acid was superior to the control rice noodles; the cooked noodle strips also showed fewer tendencies to stick together. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The rice noodle—produced from rice flour or rice flour mixed with other components, such as cassava starch, modified starch or hydrocolloids—is one of the most popular varieties of Asian noodles, and is widely consumed throughout Southeast Asia (Bhattacharya, Zee, & Corke, 1999; Hormdok & Noomhorm, 2007). Rice noodles are high in carbohydrates and calories but low in dietary fiber (DF) and resistant starch (RS) (Puwastien, Raroengwichit, Sungpuag, & Judprasong, 1999). Presently, consumers are more concerned with the health effects of DF as well as RS in carbohydrate-rich foods. Accordingly, various aspects related to DF/RS – for example, potential sources, digestion and fermentation, physiological effects, qualities of food products, acceptability by consumers, etc. – have been extensively researched. A number of studies related to noodle qualities have investigated the potential of adding fiber sources to noodles made from wheat. However, much less information is available regarding rice noodles, perhaps due to the more severe effect of DF on their textural qualities. According to the report of Srikaeo, Mingyai, and Sopade (2011), noodles made from rice flour replaced with 20% ⇑ Corresponding author. Tel.: +66 2 470 7754; fax: +66 2 452 3479. E-mail address: [email protected] (D. Uttapap). http://dx.doi.org/10.1016/j.foodchem.2015.01.119 0308-8146/Ó 2015 Elsevier Ltd. All rights reserved.

unripe banana flour, canna flour or commercial modified corn starch had significantly higher RS content (2.5%, 3.6% and 8.8%, respectively) than noodles made from rice flour only (1.0%). Recently, Wandee et al. (2014) showed that rice noodles incorporated with 15% cassava pulp and 5% pomelo peel contained much higher total dietary fiber (TDF) content (14.4%) than the control (3.0%), while their textural properties were comparable. However, there have been no reports on the physiological effects and fermentability of rice noodles enriched with DF/RS, either in vivo or in vitro studies. RS is the total amount of starch and the products of starch degradation that are not digested in the small intestine and pass into the colon, similar to dietary fiber (Englyst, Kingman, & Cummings, 1992; Topping & Clifton, 2001). RS is fermented by colonic microflora, producing short-chain fatty acids (SCFAs) and gas (H2, CO2 and CH4). The fermentation rate and relative molar ratio of SCFAs are dependent on the amount and type of RS (Annison & Topping, 1994). SCFAs – mainly acetic, propionic and butyric acids – are absorbed and metabolized in various organs, leading to different physiological effects. Butyric acid is completely metabolized in the colonic epithelial cells, and therefore has been shown to play an important role in the maintenance of colonic health (Topping & Clifton, 2001). In vitro studies as well as animal studies indicate that butyric acid has the potential to reduce risk factors that are

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involved in the development of colorectal cancer (inhibiting proliferation while increasing differentiation and apoptosis) (Brouns, Kettlitz, & Arrigoni, 2002). Canna starch, a kind of starch extracted from rhizomes of the edible canna plant (Canna edulis Ker.), is mostly used for preparing transparent starch noodles, a traditional food of Southeast Asia. High resistance of canna starch granules to enzyme hydrolysis has been reported by Hung and Morita (2005), Srichuwong, Sunarti, Mishima, Isono, and Hisamatsu (2005), and Puncha-arnon, Puttanlek, Rungsardthong, Pathipanawat, and Uttapap (2007). Canna starch and its derivatives have been reported to contain a significant amount of RS. Native, acetylated, hydroxypropylated, octenyl succinylated, and cross-linked canna starches gelatinized at 100 °C for 10 min were found to contain 20.8%, 33.8%, 43.5%, 51.3% and 35.3% RS, respectively (Juansang, Puttanlek, Rungsardthong, Puncha-arnon, & Uttapap, 2012). Wandee, Puttanlek, Rungsardthong, Puncha-arnon, and Uttapap (2012) prepared retrograded starch (RS type 3) from canna starch by gelatinization and then stored the gels at different times and temperatures. Under suitable conditions, the thermally stable RS fraction in canna starch could be increased from 1.9% to 16.8%. Bernabé, Srikaeo, and Schlüter (2011) reported that fermentation of raw canna starch with fresh human feces as inoculum produced significantly higher total SCFAs and butyric acid compared with banana, potato, mung bean and taro starches. However, there has been no information on the quality and fermentability of rice noodles incorporated with canna starch and its derivatives. Therefore, this study aimed to assess the potential of canna starch and its derivatives (retrograded, retrograded debranched, and crosslinked) as sources of DF in dried rice noodles. 2. Materials and methods 2.1. Raw materials Commercial rice flour containing 22% amylose (dry weight basis; dwb) was purchased from Patum Rice Mill and Granary Public Co. Ltd., Pathum Thani, Thailand. Eight-month-old rhizomes of edible canna plants were obtained from the Rayong Field Crops Research Center, Rayong, Thailand; the starch was isolated according to a procedure described by Puncha-arnon et al. (2007). Amylose content of canna starch determined according to the method of Jayakody and Hoover (2002) was 23.9% (dwb). Cross-linked canna starch (CL) was prepared following the method of Emrat (2007), using 0.2% w/w sodium trimetaphosphate as a cross-linking agent. Retrograded canna starch was prepared by autoclaving starch at 121 °C for 120 min and then storing gel at 4 °C for 3 days (Wandee et al., 2012). A similar procedure, except that gelatinized starch was debranched with pullulanase enzyme (64 PUN/g starch) for 24 h prior to storage, was used to obtain retrograded debranched canna starch. 2.2. Dried noodle preparation 40 g (dwb) of flour mixes were prepared by mixing rice flour with 20% of native, retrograded, retrograded debranched, or cross-linked canna starches. Water was then added to each flour mix to obtain a slurry with a concentration of 40% w/v. 30 ml of slurry was spread evenly on a stainless tray (11.4  21.6 cm) and steamed for 1 min. Each noodle sheet was peeled from the tray and dried at 70 °C for 15 min. The noodle sheets were stacked, covered with cheesecloth and allowed to rest for 3 h at room temperature, then cut into strips 3.0 mm wide. The noodles were further dried in a hot-air oven at 40 °C until the moisture content decreased to 10–12%. Dried noodles were packed in polyethylene bags and kept at room temperature for further quality investigation.

2.3. Analyses of noodles 2.3.1. Determination of water absorption index In order to obtain information on the ability of each raw material to absorb water, single-component flour/starch (100%) was used to prepare noodles using the procedure described above. It was found that noodles could be produced from a slurry of rice flour, native canna starch or cross-linked starch at a concentration of 40% w/v; however, slurries of retrograded and retrograded debranched starches were too thick, and concentrations of only 15% for retrograded starch and 30% for retrograded debranched starch could be used for noodle sheet formation. The water absorption index of the noodles obtained was determined according to the method of Anderson, Conway, Pfeifer, and Griffin (1969), with a slight modification. Dried noodles were cut into small pieces (3– 5 cm length), ground with a Pulverisette 14 variable-speed rotor mill (Fritsch, Idar-Oberstein, Germany) and sieved through a 106 lm screen. A noodle powder sample (0.5 g, dwb) was added to 15 ml of distilled water in a centrifuge tube, then vigorously mixed with a vortex mixer before placing in a shaker at 30 °C for 30 min. After centrifugation at 1127g for 15 min, the supernatant was carefully removed and the sediment was weighed.

Water absorption index ðWAI; g=gÞ ¼

wet sediment weight dry sample weight

2.3.2. Cooking quality analysis Cooking time of noodles was determined according to the AACC (1995) method for spaghetti, with a slight modification. Dried rice noodles (5 g) were cut into 5-cm lengths and cooked in 200 ml boiling distilled water in a covered beaker. Optimum cooking time was determined by removing a piece of noodle every 30 s and pressing the cooked noodle between two glass slides until the white, hard core of the noodle strand disappeared. At least five measurements were performed for each sample. Cooking weight and cooking loss of starch noodles were measured according to the AACC method (1995), with a slight modification. At least five replications were done for each measurement. Dried rice noodles (1.0 g) were cut into small pieces (3–5 cm in length) and boiled in 30 ml water until completely cooked. The cooked noodles were then filtered through a nylon screen, rinsed with distilled water, drained for 1 min, and immediately weighed. Cooking weight was determined from the difference between noodle weights before and after cooking, and expressed as the percentage of g cooked noodle/g dried noodle. Cooking loss was determined by evaporating to dryness the cooking water and rinse water in a pre-weighed glass beaker in a hot-air oven at 105 °C, and was expressed as the percentage of solid loss during cooking. 2.3.3. Textural profile analysis The texture of a 10-cm length of cooked noodle was measured using a texture analyzer (EZTest EZ-S-50N; Shimadzu, Tokyo, Japan) equipped with a pair of noodle elongation jigs (No. 17; Shimadzu). A 15 N load cell was applied to measure the tensile strength of noodles at an elongation speed of 60 mm/min. The initial distance between clamps was set at 10.0 cm. From the force– displacement curve (mm), measurements of tensile stress (N/ mm2; Pa) and elongation (%) were generated using the texture analysis software (Trapezium 2 version 2.24). At least 15 strands of noodles were measured for each sample. 2.3.4. Total dietary fiber (TDF) analysis TDF content of rice noodles was measured using a TDF assay kit (Megazyme International Ireland, Wicklow, Ireland), following AOAC method 985.29 (AOAC, 2000). Dried noodles were cut into

Y. Wandee et al. / Food Chemistry 179 (2015) 85–93 Rice flour

Canna starch

Retrograded starch

Retro-debranched starch

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100% Rice flour noodle

20% Native canna starch noodle

20% Cross-linked starch noodle

20% Retrograded starch noodle

20% Retrograded debranched starch noodle

Fig. 1. Morphologies of raw materials and upper surface of noodles made from rice flour and rice flour substituted with 20% native, cross-linked, retrograded, and retrograded debranched canna starches.

small pieces (3–5 cm length), ground with a Pulverisette 14 variable-speed rotor mill (Fritsch, Germany) and sieved through a 106 lm screen prior to analysis. Samples were gelatinized with a heat-stable a-amylase (pH 6, 100 °C, 30 min) and then enzymatically digested sequentially with protease (pH 7.5, 60 °C, 30 min) and amyloglucosidase (pH 4.5, 60 °C, 30 min) to remove protein and starch. TDF was precipitated with ethanol, and after washing and drying, the residue was weighed. TDF ð%Þ ¼

sample residue  protein from residue  ash from residue  blank sample weight  100

2.4. In vitro fermentation 2.4.1. Pre-digestion of noodle samples Prior to in vitro fermentation, all noodle samples were digested by in vitro enzymatic digestion according to the method of Englyst et al. (1992), with modifications. Briefly, 10 g of noodle powder was added to 200 ml water in an Erlenmeyer flask. The suspension was heated at 80 °C for 5 min and then placed in a water bath at 37 °C for 10 min to equilibrate. Sodium acetate buffer (0.1 M, pH 5.2, containing 4 mM CaCl2) was added and the mixture was shaken well by hand. Alpha-amylase (9000 U/g starch; Sigma A-3173) and amyloglucosidase (75 U/g starch; Sigma P7545) were

then added and the flask was incubated at 37 °C for 2 h in a shaking water bath. Undigested residue was recovered, washed twice with distilled water and freeze-dried. Duplicate dried samples were pooled and ground in a mortar, passed through a 106 lm sieve, and used for in vitro fermentation. 2.4.2. Preparation of inoculum and fermentation medium The inoculum was prepared from fresh cecum of three healthy pigs obtained from Fresh Meat Processing Co., Ltd. (Nakhon Pathom, Thailand). The cecal contents were pooled, weighed and mixed with sterile medium in a ratio of 1:1 (w/w). The mixture was homogenized in a household blender for 1 min and strained through four layers of cheesecloth. The fermentation medium was composed of 2.5 g trypticase peptone, 125 ll micro-mineral solution (132 g/L CaCl22H2O, 100 g/L MnCl24H2O, 80 g/L FeCl26H2O and 10 g/L CoCl26H2O), 25 ml buffer solution (4 g/L (NH4)HCO3 and 35 g/L NaHCO3), 125 ml macro-mineral solution (5.7 g/L Na2HPO4, 6.2 g/L KH2PO4 and 0.6 g/L Mg47H2O), 1.25 ml resazurin solution (0.1% w/ v) and 33.5 ml reducing solution (6.25 g/L cysteine hydrochloride, 6.25 g/L Na2S9H2O and 40 ml 1 M NaOH) in 1 L of medium (pH 7.2). 2.4.3. In vitro fermentation In vitro batch fermentation was conducted according to the method of Lebet, Arrigoni, and Amadò (1998), with a few modifications. Fermentation was performed in triplicate for each noodle sample. One hundred mg of pre-digested noodles was added to

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8 ml of fermentation medium in a 20 ml serum bottle. The bottle was sealed with a butyl rubber stopper and aluminum cap and the headspace was flushed with N2 for 3 min to maintain anaerobic conditions. The sample was then hydrated overnight at 4 °C. After equilibrating in a water bath at 37 °C for 1 h, 2 ml of inoculum was added to each bottle and the headspace was flushed again with N2 for 1 min. The bottles were incubated in a shaking water bath (50 strokes/min) at 37 °C. Samples of the fermented broth (0.5 ml) were taken at 24, 36 and 72 h and immediately placed in a freezer at 20 °C to stop fermentation. A control containing no sample was used as a blank; inulin, which is a completely fermentable substrate, was used as a reference. 2.4.4. Analysis of short-chain fatty acids SCAF analysis was carried out by high performance liquid chromatography (HPLC). The frozen fermentation broth was rapidly thawed in warm water, centrifuged at 12,522g at 4 °C for 30 min and filtered using a 0.45 lm nylon syringe filter. 20 ll of sample was injected into a Shimadzu HPLC system consisting of a LC-20AD pump, RID-10A refractive index detector, VertiSep OA 8 lm HPLC column (7.8  300 mm), and a computer with a data analysis software program (CLASS-VP). The sample was analyzed in isocratic mode using 0.005 N sulfuric acid as a mobile phase at a flow rate of 0.8 ml/min. The column temperature was steadily maintained at 50 °C. Acetic, propionic and butyric acids were used as external standards. 2.5. Statistical analysis Analysis of variance (ANOVA) was performed using Duncan’s multiple range test to compare treatment means at p < 0.05. If not specified, all tests were carried out with three replications. 3. Results and discussion 3.1. Water absorption of single-component noodles Water absorption capacity has a major impact on cooking qualities and textural properties of noodles. The water absorption index (WAI) of noodles made from single-component rice flour was 7.3 g/ g. Noodles made from single-component cross-linked canna starch exhibited the highest WAI (8.2 g/g), followed by those from native canna starch (6.8 g/g), retrograded canna starch (5.4 g/g) and retrograded debranched canna starch (2.8 g/g), respectively. The high WAI of cross-linked starch noodles was attributed to reinforcement of intermolecular bonding of starch molecules inside starch granules by cross-linking with phosphate ester bonds; hence, the granules had greater ability to swell. On the other hand, the low ability to absorb water of noodles made from retrograded debranched starch was likely due to the highly ordered structure that occurs during incubation of debranched starch under certain conditions. These results suggested that partial replacement of rice

flour with cross-linked canna starch or retrograded debranched canna starch would have a significant impact on cooking qualities and textural properties of rice noodles. 3.2. Morphology of dried noodles Fig. 1 shows the morphologies of raw starches and the upper surface of dried noodles made from rice flour and rice flour with 20% canna starch or its derivatives, as observed by light microscopy. Rice starch granules had a much smaller size (2–10 lm) as compared with the canna starch granules (10–100 lm), and some of them were clumped together into small lumps. The size and shape of cross-linked canna starch granules were identical to those of the native starch (figure not shown). Retrograded and retrograded debranched starches exhibited a non-granular structure with irregular shapes and rough surface. The particles of retrograded starch had relatively larger size as compared with retrograded debranched starch. As shown in Fig. 1, distinctive surface morphologies were observed among the different noodles. One hundred percent rice flour noodles had a rough surface, with some bubbles distributed throughout. A similar morphology was found for noodles made from rice flour incorporated with retrograded debranched starch, but with some different features in that the noodles containing retrograded debranched starch displayed a rougher surface, much fewer bubbles and numerous small pores. Noodles made from rice flour with native and cross-linked canna starches had a number of swollen rice starch granules embedded in a smooth surface; canna starch granules were not observed. The surface of noodles made from rice flour with retrograded starch was rougher than those containing native and cross-linked canna starches, but smoother than noodles with retrograded debranched starch; relatively large pores were also found on the surface. These appearances are related to the composition as well as the physicochemical properties of the individual starches. The rough surface of rice flour noodles was attributed to the swollen, unbroken rice starch granules protruding from the smooth matrix of completely gelatinized starch granules. Rice flour had high gelatinization temperature (73.2 °C, as determined by a differential scanning calorimeter) (Puncha-arnon & Uttapap, 2013) and high pasting temperature (93.5 °C, as determined by a rapid visco analyzer) (Wandee et al., 2014); therefore, some granules still remained in granular form after steaming. The rougher surface of noodles when 20% of rice flour was replaced with retrograded debranched starch was likely due to the low ability of retrograded debranched starch to absorb water. Less moist retrograded debranched starch particles would impede heat transfer to the rice starch granules, and hence reduce the extent of rice starch gelatinization. Also, small pores that appeared on the noodle surface were possibly caused by a difference in water-holding capacity of the two components in the steamed noodle sheet. Pores were generated in the high water holding areas when the noodle

Table 1 Cooking qualities, textural properties and TDF content of noodles made from rice flour and rice flour substituted with 20% canna starch and its derivatives. Noodle sample

Cooking time (min)

Cooking weight (%)

Cooking loss (%)

Tensile strength (mN)

Elongation (%)

Rice flour (control) Native canna starch Cross-linked starch Retrograded starch Retrograded debranched starch

3.0 3.5 3.5 3.5 3.5

132.1b 157.8a 155.0a 156.1a 139.9b

1.3d 1.6c 1.5c 1.8b 2.7a

173.9c 213.8b 242.5a 161.1c 166.5c

80.1b 81.9b 110.0a 84.3b 64.3c

TDF (%, dwb) Experiment

Calculation

3.0d 4.0c 3.9c 5.1b 7.3a

3.8 2.6 2.5 3.9 5.2

Values with different superscripts in a column differ significantly (p < 0.05). Values of cooking qualities and TDF are the mean of triplicate determinations, while the values of textural properties are the mean of ten determinations.

Y. Wandee et al. / Food Chemistry 179 (2015) 85–93

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3.3. Cooking qualities Cooking qualities of noodles made from rice flour and rice flour incorporated with 20% of canna starch and its derivatives are summarized in Table 1. Cooking time, cooking weight and cooking loss of noodles made from rice flour were 3.0 min, 132.1% and 1.3%, respectively. Noodles made from rice flour replaced with canna starch and its derivatives had slightly longer cooking time (3.5 min) and higher cooking loss (1.5–2.7%). The increase in cooking loss of noodles containing retrograded and retrograded debranched starches was due to the heterogeneous nature of the mixing components. Although the noodles incorporated with canna starch and its derivatives displayed statistically higher cooking loss values than the control, the magnitude of difference (less than 1.4%) was negligible in practical terms. According to the Chinese and Thai standards for starch noodles, cooking loss should be less than 10% and 9%, respectively (Lii & Chang, 1981; Sisawad & Chatket, 1989). Except for the noodles incorporated with retrograded debranched starch, cooking weights of noodles with canna starch and the other two derivatives (155.0–157.8%) were significantly higher than the control. Cooking weight values of the noodles were consistent with the morphologies of the noodles as shown in Fig. 1, i.e., noodles with a higher degree of gelatinization could absorb more water. An increase in cooking weight of noodles prepared from a blend of rice flour and canna starch (80:20) has also been reported (Qazi, Rakshit, Tran, Ullah, and Khan (2014). Noodles incorporated with retrograded debranched starch had comparable cooking weight to rice flour noodles. This result differed from studies by Aravind, Sissons, Fellows, Blazek, and Gilbert (2013) and Sozer, Dalgıç, and Kaya (2007) in which pasta replaced with 20% of commercial resistant starch type 3 (Novelose 330™) and spaghetti enriched with 10% of resistant starch type 3 had higher cooking weight than the control. 3.4. Textural properties

Fig. 2. Concentrations (mmol/L) of acetic acid ( ), propionic acid ( ) and butyric acid ( ) produced from 100 mg of inulin and indigestible residues of various rice noodles after 24 h (a), 48 h (b) and 72 h (c) fermentation.

sheet was dried. The smoother surface of noodles containing retrograded starch, as compared with noodles made from pure rice flour, indicated that retrograded starch facilitated the gelatinization of rice starch. Retrograded starch is formed by incubation of gelatinized starch under specified conditions. During this process, the intact amylose and amylopectin molecules can re-associate by H-bond formation. However, the molecular association was not as strong as in the case of retrograded debranched starch, due to the highly branched nature of the starch molecules; therefore, it can be more easily gelatinized by steaming and thus promote the gelatinization of surrounding rice starch granules. Native and cross-linked canna starch also accelerated rice starch gelatinization because the gelatinization temperatures of native (70.4 °C) and cross-linked canna starch (69.9 °C) (Emrat, 2007) were lower than that of rice flour.

As shown in Table 1, tensile strength and elongation values of rice noodles were 173.9 mN and 80.1%, respectively. Tensile strengths of noodles replaced with native canna and cross-linked starches (213.8 and 242.5 mN, respectively) were significantly higher, whereas those of noodles with retrograded and retrograded debranched starch (161.1 and 166.5 mN, respectively) were comparable to the control. Elongation values of noodles supplemented with canna starch and its derivatives were inconsistent. Noodles made from rice flour, rice flour with native canna starch and rice flour with retrograded starch had similar elongation values (80.1%, 81.9% and 84.3%); noodles containing retrograded debranched starch had a significantly lower elongation value (64.3%), while noodles with cross-linked starch (110.0%) displayed much higher elongation. The effect of the second starch component on the textural properties of rice noodles was quite complicated, since it would depend on several factors such as the pasting behavior of each starch, interaction and compatibility of the two starches, water absorption and retrogradation abilities of each starch, etc. The highest tensile strength and elongation was found in rice noodles containing cross-linked canna starch; this was most likely due to the high degree of gelatinization of both starches, resulting in a homogeneous mixture of disrupted starch granules stabilized by cross-linked covalent bonding. Hydrogen bonding between starch molecules formed during incubation of noodle sheets could also provide a gel network that strengthened the structure of the noodles. On the other hand, the heterogeneous structure of noodles containing retrograded debranched starch – due to incomplete disruption of starch granules, many small pores, and less association of leached amylose – would contribute to their having the lowest tensile strength among the tested noodles.

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Table 2 Amounts of indigestible residue (g/50 g noodles), total SCFAs and butyric acid (mmol/50 g dried noodles) in noodle products. Sample

Indigestible residue (g/50 g noodle)

100% Rice flour 20% Native canna starch 20% Cross-linked starch 20% Retrograded starch 20% Retrograded debranched starch

6.8 ± 0.5 7.6 ± 0.3 8.1 ± 0.1 7.8 ± 1.5 10.4 ± 0.2

Total SCFA (mmol/50 g noodle)

Butyric acid (mmol/50 g noodle)

24 h

48 h

72 h

24 h

48 h

72 h

12.5d 14.4c 15.7b 14.7c 17.0a

15.3e 17.8d 19.8b 19.1bc 25.6a

16.4d 19.9c 21.6b 21.6b 28.2a

2.5e 3.1d 3.6b 3.4c 3.8a

3.3e 4.1d 4.6b 4.4b 7.4a

3.4d 4.4c 4.8b 4.7b 7.8a

Values with different superscripts in a column differ significantly (p < 0.05). Values of total SCFAs and butyric acid are the mean of triplicate determinations, while the values of indigestible residue are the mean of duplicate determinations.

3.5. Total dietary fiber content Total dietary fiber (TDF) contents of uncooked rice noodles made from rice flour and rice flour incorporated with canna starch and its derivatives are shown in Table 1. Incorporation of canna starch and its derivatives resulted in a significant increase of TDF content, from 3.0% to 7.3%. The highest TDF content was found in noodles containing retrograded debranched starch (7.3%), followed by retrograded starch (5.1%), while TDF contents of noodles containing canna starch or cross-linked starch were comparable (4.0%, 3.9%). In Table 1, the TDF values calculated from the fiber contents in raw materials are also given in parentheses. The experimental TDF value of noodles made from rice flour was slightly lower, while those of noodles with canna starch and its derivatives were significantly higher than the calculated values. This indicated that noodle processing could increase or decrease TDF, depending on the raw material source. The increase of TDF in noodles supplemented with canna starch and its derivatives was most likely due to the high retrogradability of canna starch. High retrogradation of canna starch is thought to be due to the combined effect of the following factors: considerably high amylose content (about 30%; Puncha-arnon et al., 2007); small size of amylose molecules (1600 dp), with low value of the average number of branch chains; and high value of the average chain length of amylopectin (Thitipraphunkul, Uttapap, Piyachomkwan, & Takeda, 2003). The results were opposite to our previous study on noodles incorporated with cassava pulp and pomelo peel (Wandee et al., 2014), in which the experimental values were lower than their corresponding calculated values. In those cases, part of TDF might be heat-unstable and could be destroyed by noodle processing, especially during the steaming step. 3.6. In vitro fermentability of noodles Noodle products were subjected successively to in vitro digestion with a-amylase and amyloglucosidase, and the indigestible residues were recovered and subsequently fermented by an in vitro batch system using pig cecal content as inoculum. Concentrations of SCFAs produced from 100 mg of indigestible residue of inulin, rice noodles and rice noodles containing canna starch and its derivatives after 24, 48 and 72 h fermentation are shown in Fig. 2. Inulin is a long-chain prebiotic consisting of a linear series of ß-(2 ? 1) fructose units, and typically has a terminal non-reducing glucose (GFn). According to the report of Roberfroid (2004), inulin is slowly but completely fermented, so it was used as a reference in this study. As shown in Fig. 2a, fermentation of inulin for 24 h produced the lowest SCFAs (9.6 mmol/L), followed by noodles containing retrograded debranched starch (16.3 mmol/L), while fermentation of the rest produced comparable amounts of total SCFAs (18.5–19.4 mmol/L). Slower fermentation of noodles containing retrograded debranched starch, as compared with other canna starch samples, was due to the highly ordered structure of retrograded debranched starch.

Extending the fermentation time to 48 h resulted in a significant increase in total SCFAs of inulin and noodles containing retrograded debranched starch (Fig. 2b). Noodles incorporated with all derivatives of canna starches produced significantly higher amounts of butyric acid (5.6–7.2 mmol/L) as compared with rice noodles (4.9 mmol/L) and noodles containing native canna starch (5.3 mmol/L) (p < 0.05); noodles with retrograded debranched starch had the highest amount of butyric acid (7.2 mmol/L). This circumstance was more pronounced when the fermentation time was extended to 72 h (Fig. 2c). The high concentration of total SCFAs was caused by high production of acetic acid. At this fermentation period, rice noodles produced the lowest amount of total SCFAs when compared with other substrates (p < 0.05). Total SCFAs from inulin still increased concurrently with increasing fermentation time, and propionic acid was found to be a major component. Fermentation of noodles containing retrograded debranched starch produced the highest amount of butyric acid (7.5 mmol/L), followed by inulin (6.2 mmol/L) and noodles incorporated with retrograded starch (6.0 mmol/L), respectively. After 72 h of fermentation, the molar ratio of acetic, propionic and butyric acids produced from noodles containing retrograded debranched starch was 41:31:28. These results were in agreement with a previous report, in that RS fermentation generally results in relatively higher butyric acid production, on the order of 20–28 mol%, compared with about 10–15 mol% for non-starch polysaccharides (Brouns et al., 2002). Therefore, in terms of fermentation products, retrograded debranched starch is a promising prebiotic source since it can produce high levels of SCFAs as well as high butyric acid. In humans, the highest fermentation activity is found in the proximal colon, and declines farther down the gastrointestinal tract as the availability of substrates decreases (Topping & Clifton, 2001). Therefore, the distal colon is the site with the most limited carbohydrate sources of carbon and energy for bacterial growth. This results in a decrease in SCFAs and an increase in undesirable (even toxic) compounds, such as phenol and NH3, in distal regions of the colon, resulting in a less healthy colonic environment (Macfarlane, Gibson, & Cummings, 1992). An easily fermentable substrate might be depleted rapidly at the proximal colon, whereas a substrate that is difficult to ferment could be excreted with feces; thus, substrates with an appropriate fermentation rate are preferable. In terms of fermentation rate, inulin would appear to be ideal since its fermentation was the lowest on the first day and increased continuously during the second and third days of fermentation. On the other hand, fermentation of the other substrates, except the residue of noodles containing retrograded debranched starch, reached nearly maximum values after the first day. Therefore, from the perspectives of both fermentation products and rate of fermentation, retrograded debranched starch is probably the most promising source of prebiotics. The fermentation rate of this substrate could be adjusted to a slower or faster rate by altering the production conditions, such as debranching level, incubation time and temperature, number of incubation cycles, drying rate and temperature, etc.

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Y. Wandee et al. / Food Chemistry 179 (2015) 85–93 Table 3 Cooking qualities, textural properties and TDF content of noodles made from rice flour and rice flour substituted with retrograded debranched starch at various levels. Noodle sample

Cooking time (min)

Cooking weight (%)

Cooking loss (%)

Tensile strength (mN)

Elongation (%)

TDF (%, dwb) Experiment

Calculation

Rice flour 20% Retrograded 25% Retrograded 30% Retrograded 35% Retrograded 40% Retrograded

3.0 3.5 4.0 4.0 4.0 4.0

132.1ab 139.9a 140.3a 139.5a 136.7ab 124.1b

1.3f 2.7e 3.0d 3.3c 4.1b 4.4a

173.9a 166.5a 137.8b 134.6b 131.0b 131.0b

80.1a 64.3b 55.2c 49.6 c 41.0d 39.2d

3.0e 7.3d 8.0c 9.4b 9.8b 10.6a

3.8 5.2 5.7 6.2 6.8 7.3

debranched debranched debranched debranched debranched

starch starch starch starch starch

Values with different superscripts in a column differ significantly (p < 0.05). Values of cooking qualities and TDF are the mean of triplicate determinations, while the values of textural qualities are the mean of ten determinations.

Fig. 3. Appearances of cooked rice noodles made from rice flour and rice flour substituted with retrograded debranched canna starch at various levels, after standing for 0, 10, 20, 30 and 60 min.

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3.7. Indigestible residues and SCFA production of noodles A survey on dietary intake of Thai adolescents in Bangkok (Uthang, 1990) revealed that the average intakes of dietary fiber were 7.32 g/day in men and 8.88 g/day in women. Many countries have recommended daily consumption of about 25–30 g of fiber in order to keep the bowels healthy. Table 2 shows the amount of indigestible residue, total SCFAs and butyric acid in one serving (50 g) of noodle products. The amount of indigestible residue of rice noodles, determined by in vitro-simulated upper intestinal tract digestion, was 6.8 g/50 g dried noodles; while for noodles incorporated with canna starch and its derivatives, the amounts were between 7.6 and 10.4 g/50 g dried noodles. These indigestible residues, consisting mainly of resistant starch and fiber, were assumed to be the substrate that passed into the colon. Thus, the amount of SCFAs produced would depend not only on the fermentability of an individual substrate but also its resistance to digestion in the small intestine. On the basis of one serving size, noodles containing canna starch and its derivatives produced higher amounts of total SCFAs and butyric acid than rice flour noodles. Noodles with retrograded debranched starch produced the highest amounts of total SCFAs and butyric acid. These results confirmed the potential of retrograded debranched starch as a prebiotic source. 3.8. Qualities of noodles incorporated with higher levels of retrograded debranched starch The results shown above revealed that incorporation of 20% retrograded debranched canna starch could increase TDF content of noodles and improve the nutritional benefits, in terms of increasing fermentability and butyric acid production, without adversely affecting the cooking qualities. It was also observed that cooked noodle strips made from only rice flour tended to stick together when kept for a long period, while noodles containing retrograded debranched starch did not. Therefore, it was presumed that addition of a higher level of retrograded debranched starch would not only increase the fiber content but also improve the quality and texture of cooked noodles when keeping after cooking. Accordingly, replacement of retrograded debranched starch in noodles at 25%, 30%, 35% and 40% was studied. The results of cooking quality, textural properties and TDF content of the noodles obtained are shown in Table 3. Cooking time of noodles with higher levels of retrograded debranched starch was extended to 4.0 min, while cooking weight was comparable to the control. Cooking loss was significantly increased with an increased amount of retrograded debranched starch; however, the cooking loss of noodles containing the highest level (40%) of retrograded debranched starch was still less than the limit specified by Thai standards for starch noodles. The results of textural properties of noodles clearly revealed that increasing levels of retrograded debranched starch had a significantly negative effect on strength and elongation of the noodles. Appearances of cooked noodles made from retrograded debranched starch at various levels during keeping at 25 °C for up to 60 min are shown in Fig. 3. When left to stand for 10 min, cooked rice flour noodles stuck together, and clumped into a lump of noodle strips when allowed to stand longer (30–60 min). Strips of noodles enriched with 20% retrograded debranched starch remained separate for up to 30 min but tended to stick together after that. Noodles containing higher levels of retrograded debranched starch did not stick together even after 60 min. The most important characteristics for cooked starch noodles are texture and mouth feel; they should remain firm, not sticky, after cooking, and exhibit high tensile strength, short cooking time and low cooking loss (Tan, Li, & Tan, 2009). Although the addition of retrograded debranched starch at levels higher than 20% possessed some benefits in terms

of TDF content and continued good appearance of noodles after standing, the detrimental effect on cooking and textural qualities was found to be unacceptable. Therefore, weighing the merits and demerits of these attributes, substitution of rice flour with 20% retrograded debranched starch would be the most suitable level for noodle production. 4. Conclusion This study demonstrated the potential of using canna starch and its derivatives to improve the qualities of rice noodles. Crosslinked canna starch can increase tensile strength and elongation, while retrograded debranched canna starch can increase TDF content and improve nutritional benefits in terms of increased butyric acid production. In vitro experiments revealed that noodles substituted with retrograded debranched canna starch exhibited a slow fermentation rate; therefore, these noodles are also expected to be slowly fermentable in vivo and will yield a certain amount of SCFAs along the distal colon. Due to the high TDF content, acceptable cooking qualities and textural properties, as well as good fermentability, rice noodles substituted with 20% retrograded debranched starch are recommended as an alternative food choice for health-conscious consumers. Acknowledgements The authors gratefully acknowledge financial support from: the Thailand Research Fund, via the Royal Golden Jubilee Ph.D. Program (for Miss Yuree Wandee); and the National Research Universities Project and Research Promotion in Higher Education, Office of the Higher Education Commission. References AACC (1995). Approved methods of the American Association of Cereal Chemists (9th ed.). St. Paul, MN: American Association of Cereal Chemists. Anderson, R. A., Conway, H. F., Pfeifer, V. F., & Griffin, E. L. (1969). Gelatinization of corn grits by roll and extrusion cooking. Cereal Science Today, 14, 4–12. Annison, G., & Topping, D. L. (1994). Nutritional role of resistant starch: Chemical structure vs physiological function. Annual Review Nutrition, 14, 297–320. Aravind, N., Sissons, M., Fellows, C. M., Blazek, J., & Gilbert, E. P. (2013). Optimisation of resistant starch II and III levels in durum wheat pasta to reduce in vitro digestibility while maintaining processing and sensory characteristics. Food Chemistry, 136, 1100–1109. Bernabé, A. M., Srikaeo, K., & Schlüter, M. (2011). Resistant starch content, starch digestibility and the fermentation of some tropical starches in vitro. Food Digestion, 37–42. Bhattacharya, M., Zee, S. Y., & Corke, H. (1999). Physicochemical properties related to quality of rice noodles. Cereal Chemistry, 76, 861–867. Brouns, F., Kettlitz, B., & Arrigoni, E. (2002). Resistant starch and the butyrate revolution. Trends in Food Science & Technology, 13, 251–261. Emrat, I. (2007). Modification of canna starch by cross-linking with sodium trimetaphosphate. M. Sc. thesis, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand. Englyst, H. N., Kingman, S. M., & Cummings, J. H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition, 46, S33–S50. Hormdok, R., & Noomhorm, A. (2007). Hydrothermal treatments of rice starch for improvement of rice starch noodle quality. LWT–Food Science and Technology, 40, 1723–1731. Hung, P. V., & Morita, N. (2005). Physicochemical properties and enzymatic digestibility of starch from edible canna (Canna edulis) grown in Vietnam. Carbohydrate Polymers, 61, 314–321. Jayakody, L., & Hoover, R. (2002). The effect of lintnerization on cereal starch granules. Food Research International, 35(7), 665–680. Juansang, J., Puttanlek, C., Rungsardthong, V., Puncha-arnon, S., & Uttapap, D. (2012). Effect of gelatinisation on slowly digestible starch and resistant starch of heat-moisture treated and chemically modified canna starches. Food Chemistry, 131, 500–507. Lebet, V., Arrigoni, E., & Amadò, R. (1998). Measurement of fermentation products and substrate disappearance during incubation of dietary fibre sources with human faecal flora. LWT–Food Science and Technology, 31, 473–479. Lii, C. Y., & Chang, S. M. (1981). Characterization of red bean (Phaseolus radiatus var. aurea) starch and its noodle quality. Journal of Food Science, 46, 78–81.

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