Effect of Sorghum Flour Addition on In Vitro Starch Digestibility, Cooking Quality, and Consumer Acceptability of Durum Wheat Pasta Imran Khan, Adel M. Yousif, Stuart K. Johnson, and Shirani Gamlath

Abstract: Whole grain sorghum is a valuable source of resistant starch and polyphenolic antioxidants and its addition into staple food like pasta may reduce the starch digestibility. However, incorporating nondurum wheat materials into pasta provides a challenge in terms of maintaining cooking quality and consumer acceptability. Pasta was prepared from 100% durum wheat semolina (DWS) as control or by replacing DWS with either wholegrain red sorghum flour (RSF) or white sorghum flour (WSF) each at 20%, 30%, and 40% incorporation levels, following a laboratory-scale procedure. Pasta samples were evaluated for proximate composition, in vitro starch digestibility, cooking quality, and consumer acceptability. The addition of both RSF and WSF lowered the extent of in vitro starch digestion at all substitution levels compared to the control pasta. The rapidly digestible starch was lowered in all the sorghum-containing pastas compared to the control pasta. Neither RSF or WSF addition affected the pasta quality attributes (water absorption, swelling index, dry matter, adhesiveness, cohesiveness, and springiness), except color and hardness which were negatively affected. Consumer sensory results indicated that pasta samples containing 20% and 30% RSF or WSF had acceptable palatability based on meeting one or both of the preset acceptability criteria. It is concluded that the addition of wholegrain sorghum flour to pasta at 30% incorporation level is possible to reduce starch digestibility, while maintaining adequate cooking quality and consumer acceptability. Keywords: consumer acceptability, cooking quality, in vitro starch digestibility, pasta, sorghum

Introduction

S: Sensory & Food Quality

on sensory attributes (Prabhasankar and others 2009; Baiano and others 2011; Verardo and others 2011; Fares and Menga 2012). Sorghum [Sorghum bicolor (L.) Moench] is a cereal crop that is underutilized for human consumption in many developed countries. However, sorghum addition may improve the health properties of pasta as sorghum contains a combination of beneficial components, including resistant starch (Dicko and others 2006; Ragaee and others 2006) and polyphenolic antioxidants (Awika and Rooney 2004; Dykes and Rooney 2006; Khan and others 2013). To date the consumption of food products made from sorghum alone (for example, bread, cookies), are less popular than those made from more conventional cereals such as refined wheat due to the bitterness and astringency produced by the phenolic compounds in sorghum (Kobue-Lekalake and others 2007; Abdelghafor and others 2011), hence alternative products using sorghum as a partial ingredient are likely to be more desirable. This is illustrated by the findings of a recent study of Yousif and others (2012) in which red sorghum flour (RSF) and white sorghum flour (WSF) incorporated into flat bread at 40% of flour weight significantly reduced the in vitro starch digestibility of the flat bread without major impact on sensory acceptability. However, acceptability parameters for pasta are quite different compared to flat bread and may require different substitution levels of RSF and WSF. To date, there is no such equivalent study that determined the effect of sorghum flour incorporation on in vitro starch digestibility, cooking quality, and consumer acceptability of pasta. Therefore, this study was conducted with the objective to elucidate the effect MS 20131736 Submitted 11/21/2013, Accepted 5/19/2014. Authors Khan, of RSF and WSF addition to pasta on these attributes.

Pasta is the 2nd most consumed food worldwide after bread. However, in terms of health benefits pasta is considered superior to bread as it exerts favorable effects on the human body, including inducing low postprandial blood glucose and insulin responses as compared to white bread (Aston and others 2007). After the Food and Drug Administration (FDA) recommendation in 1940s for pasta enrichment with nondurum wheat ingredients (Marconi and Carcea 2001), extensive research has been conducted to enhance its nutritional quality and to optimize the levels of addition of nondurum wheat ingredients into pasta through instrumental and sensory evaluation techniques. Wood (2009) found that durum wheat in pasta can be substituted with chickpea flour up to 30% incorporation level without affecting its sensory attributes. More recently, Aravind and others (2013) showed that with the addition of commercial resistant starch type II or III up to 20% level into pasta it is possible to reduce its starch digestibility without affecting cooking quality and sensory attributes. Reducing starch digestibility of foods is important because it can help to lower energy intake and postmeal blood glucose levels and hence may provide protection against the development of obesity and type 2 diabetes (Barros and others 2012). Similarly other legumes, cereals and seaweed have been successfully incorporated into pasta to enhance its nutritional properties with no or minimal effects

Yousif, and Gamlath are with School of Exercise and Nutrition Sciences, Deakin Univ., Burwood, Victoria 3125, Australia. Author Johnson is with Food Science and Technology Program, School of Public Health, Faculty of Health Sciences, Curtin Univ., Perth, Western Australia 6845, Australia. Author Khan is with Dept. of Human Nutrition, Univ. of Agriculture, Peshawar, Khyber Pakhtunkhwa 25120, Pakistan. Direct inquiries to author Gamlath (E-mail: [email protected]).

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Materials and Methods Raw materials Durum wheat semolina (DWS) was purchased from Manildra Mills (Tamworth, NSW, Australia). Red and white sorghum R  C 2014 Institute of Food Technologists

doi: 10.1111/1750-3841.12542 Further reproduction without permission is prohibited

Effect of sorghum flour addition . . .

Pasta preparation Details of the pasta preparation method have been described previously (Khan and others 2013). Briefly, formulations consisting of 100% DWS (control) or by replacing DWS with 20%, 30%, and 40% substitution levels of either RSF or WSF were prepared and mixed with water (35 to 40 mL per 100 g of flour as determined for each formulation by previous trials; Khan and others 2013) to obtain a homogenous dough. The dough was sheeted and cut into pasta strips (length 25 cm, width 0.6 cm, and thickness 0.2 cm) through a pasta machine (Atlas, model 150, Padova, Italy). The obtained samples were dried in open air at ambient temperature to moisture level of ࣘ10%. Pasta cooking quality Optimum cooking time. The optimum cooking time was determined according to AACC approved method 66-50 (AACC 2000). Pasta was considered as cooked when the central starch white core in the pasta strands disappeared after squeezing them between 2 glass slides. All tests were performed in duplicate. Water absorption. Each pasta sample (10 g) was cooked to its optimum cooking time and then drained for 2 min. Water absorption was determined as [(weight of cooked pasta − weight of uncooked pasta) / weight of uncooked pasta] × 100 (Gelencser and others 2008). Duplicate measurements were performed for each pasta type and the mean values were obtained. Swelling index. The swelling index of cooked pasta (weight fraction of water in the cooked pasta) was evaluated according to the procedure used by Cleary and Brennan (2006). Briefly, each whole pasta sample (10 g) was cooked to its optimum time, drained for 2 min and then dried in a laboratory oven (Thermoline Scientific, model TO-235F, Wetherill Park, NSW, Australia) at 105 °C to constant weight. Swelling index of cooked pasta was determined as (weight of cooked pasta − weight of cooked dry pasta) / weight of cooked dry pasta. Duplicate measurements for each pasta type were performed. Dry matter. Dry matter of cooked pasta (2 replicates per sample) was determined after drying the samples in a laboratory oven (Thermoline Scientific, model TO-235F, Wetherill Park, NSW, Australia) at 105 °C to constant weight, expressed as (weight of cooked dry pasta / weight of cooked pasta) × 100, as described in the AACC approved method 44-15A (AACC 2000).

Hunter Valley, Md., U.S.A.) to pass 100% through a 0.5-mm screen. The ground samples were stored at 4 °C in the dark.

Proximate and dietary fiber analysis of cooked pasta Moisture content was determined in a conventional oven at 105 °C until the weight of the samples remained constant (AOAC 1997). Protein content was determined by the Kjeldahl method (AACC 2000) with nitrogen-to-protein conversion factors of 5.7, 5.81, 5.86 and 5.92 for control, 20%, 30%, and 40% sorghum containing pastas, respectively. These factors were calculated based on the conversion factor of 5.7 for durum semolina and 6.25 for sorghum flour, respectively. Ash and fat content were measured by AOAC methods 923.03 and 920.85, respectively (AOAC 1997). Total dietary fiber was determined by AOAC method 985.29 (AOAC 1997), using Sigma-Aldrich total dietary fiber assay kit (TDF-100A, Sigma-Aldrich, St. Louis, Mo., U.S.A.). All analyses were performed in duplicate. In vitro starch digestibility The in vitro rate of starch digestibility was determined on freeze dried cooked samples by the method of Sopade and Gidley (2009). Briefly, 500 mg ground sample of each pasta type was mixed with 1 mL of porcine α-amylase (Sigma A-3176). Within 30 s 5 mL pepsin solution (Sigma P-6887; 1 mL/mL 0.02 M HCl) was added to the sample, followed by incubation at 37 °C in a reciprocating water bath for 30 min. The mixture was then neutralized with 5 mL 0.02 M NaOH. Thereafter, 25 mL 0.2 M sodium acetate buffer (pH 6) was added followed by 5 mL pancreatin (Sigma P-1750)/amyloglucosidase (Sigma A-7420) mixture and the shaking action of the water bath commenced. This was taken as time zero and was not interrupted until time 120 min. At 0, 20, 45, 60, 90, and 120 min an aliquot (10 μL) of digested sample was taken for free glucose determinaR tion using a glucometer (AccuCheck , Roche Diagnostics, Castle Hill, Australia). Total starch was determined by assay kit, KTSTA 04/2009 (Megazyme Intl., Wicklow, Ireland) which is based on the amyloglucosidase/α-amylase method (AOAC Method No. 996.11). Digested starch (DS) (g/100 g dry starch) was calculated for all time points separately using Eq. 1 (Sopade & Gidley, 2009). DS =

0.9 × G × 180 × V W × S [100 − M]

(1)

where G = free glucose (mM/L), V = volume of final mixture (mL), 180 = glucose molecular weight, W = sample weight (g), S = total starch content of sample (g/100 g dry sample), M = moisture content of sample (g/100 g sample), and 0.9 stoichiometric constant. Digestion curves of DS (g/100 g dry starch) compared with time of digestion (min) for each sample, corrected for baseline value (time zero) were constructed. Rapidly digestible starch (RDS) (g/100 g dry starch) was calculated by substituting G in Eq. 1 with (G20 − G0 ), indicating free glucose value at 20 min minus free glucose value at 0 min. Similarly, slowly digestible starch (SDS) Preparation of samples for chemical composition and in (g/100 g dry starch) was calculated by substituting G for (G120 − vitro starch digestibility determination Samples for the determination of chemical composition and in G20 ) in Eq. 1. Measurements were performed in duplicate. vitro starch digestion were prepared by the method of GallegosInfante and others (2010a). Briefly, cooked pasta samples were Texture profile analysis frozen in liquid nitrogen, freeze-dried in a laboratory freeze-drier Textural parameters of cooked pasta were determined using a (Flexi-DryTM , model FD-3-55D-MP, FTS Systems, Stone Ridge, Texture Analyser TA-XTplus (Stable Micro Systems, Godalming, N.Y., U.S.A.) and ground using a sample mill (Black and Decker, Surrey, UK), calibrated for a load cell of 25 kg. The TA-XTplus Vol. 79, Nr. 8, 2014 r Journal of Food Science S1561

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grains were obtained from Lochabar Enterprises (Tara, QLD, Australia) and Queensland Dept. of Agriculture Fisheries and Forestry (Cooper’s Plains, QLD, Australia), respectively. The whole grains were milled to flours as previously described (Khan and others 2013). The proximate and dietary fiber composition of the raw materials (g/100 g db, ± standard deviation [SD]) (Khan and others 2013) was as follows: protein, DWS 13.43 ± 0.22, RSF 10.05 ± 0.02, WSF 11.77 ± 0.04; fat, DWS 0.67 ± 0.10, RSF 2.57 ± 0.31, WSF 1.52 ± 0.17; ash, DWS 1.19 ± 0.05, RSF 1.18 ± 0.07, WSF 1.57 ± 0.08; total dietary fiber, DWS 4.61 ± 0.72, RSF 9.00 ± 0.56, WSF 6.46 ± 0.60.

Effect of sorghum flour addition . . . settings were as follows: pretest speed of 1.0 mm/s, test speed of 1.0 mm/s, posttest speed of 10.0 mm/s, and trigger force of 0.05 N. A 35-mm cylinder probe (ref. P/35, Stable Micro Systems) was used that compressed 4 strands of pasta at a constant deformation rate (1 mm/s) to 70% of the initial pasta thickness. Each test sample was compressed 2 times, each compression being followed by decompression. The probe was held stationary for 10 s between the end of 1st compression and start of 2nd compression. From texture profile analysis curves, parameters of hardness, adhesiveness, springiness, and cohesiveness were calculated (Epstein and others 2002). The 1st peak force was termed hardness, and the negative area of the curve during the retraction of the probe was termed adhesiveness, representing the work required to pull the probe away from the sample. Cohesiveness was calculated by dividing the area of the 2nd compression cycle by the area of the 1st compression cycle. Springiness was defined as the rate at which a compressed sample went back to its uncompressed form after the compression force is removed, calculated by dividing the distance of the 1st half of the 2nd compression cycle by the distance of the 1st half of the 1st compression cycle. At least 10 individual pasta strands were tested for each sample.

Table 1–Proximate and dietary fiber composition of control and sorghum-containing pasta samples (% db). Sample Control 20% RSF 30% RSF 40% RSF 20% WSF 30% WSF 40% WSF

Protein

Fat

Ash

Total dietary fiber

13.05 ± 0.16a 12.81 ± 0.10a 11.96 ± 0.48bc 11.57 ± 0.19c 13.02 ± 0.16a 12.75 ± 0.10ab 12.59 ± 0.29ab

0.52 ± 0.05d 0.79 ± 0.03b 0.81 ± 0.11b 1.29 ± 0.03a 0.56 ± 0.03cd 0.71 ± 0.07bc 0.78 ± 0.08b

1.27 ± 0.08abc 1.16 ± 0.08bc 1.16 ± 0.07bc 1.09 ± 0.01c 1.41 ± 0.16a 1.36 ± 0.09ab 1.31 ± 0.15abc

5.10 ± 0.11e 6.11 ± 0.12b 6.24 ± 0.09b 7.15 ± 0.13a 5.47 ± 0.15d 5.79 ± 0.17c 6.18 ± 0.10b

Values are expressed in means ± SD (n = 2). Means in the same columns with different letters are significantly different (P < 0.05, LSD test). RSF, red sorghum flour; WSF, white sorghum flour.

a randomized order. The pasta samples were evaluated for acceptability of color, flavor, texture (in mouth), and overall acceptability using the 9-point hedonic scale (1 = dislike extremely and 9 = like extremely) (Meilgaard and others 2007). Two preset criteria as explained by Clark and Johnson (2002), with some modification, were used to determine the acceptability of sorghum-containing pastas for the purposes of this study. RSF or WSF-containing pasta was considered acceptable if: (i) the mean sensory score for overall acceptability was equal to or greater than 6.0, representing “like slightly” on the 9-point hedonic scale and (ii) the estimated population mean ratings for overall acceptability of the RSF or WSF-containing pasta was no lower than 1 rating category below that of the control pasta; that is, if the lower 95% confidence interval for the mean difference (sorghum-containing minus control) lies above −1.0.

S: Sensory & Food Quality

Color measurement The color of uncooked and cooked pasta was measured using a Minolta chroma meter (Minolta, CR-410, Osaka, Japan). Pasta samples were placed in the sample cup for measurement and the color readings expressed by Hunter L∗ , a∗ , b∗ values (10 replications per sample). L∗ values describe black to white (0 to 100); a∗ values describe redness (positive) and greenness (negative) and b∗ values describe yellowness (positive) and blueness (negative). The change in color due to sorghum addition was determined by calculating the color differential index (E) using Eq. 2: Statistical analysis  Results are presented as mean ± SD. One-way analysis of variE = (L)2 + (a )2 + (b )2 ance (ANOVA) was used to compare the effect of pasta for∗ ∗ mulation on proximate and dietary fiber composition, RDS and where L : L ∗sample − L ∗control; a : a sample − a control; and SDS levels, cooking quality attributes, and consumer acceptability ∗ ∗ b : b sample − b control . (2) scores. All analyses were carried out using SPSS statistical software version 20 (SPSS Inc., Chicago, Ill., U.S.A.). Statistically significant According to the Handbook of Colour Science (Yamauchi differences among means were tested using Fisher’s least significant 1989), E is an index for determining visual color differences (LSD) post hoc test at P < 0.05. and is described in terms of related values as follows: (0 to 0.5, trace difference); (0.5 to 1.5, slightly noticeable; hard to detect Results and Discussion with the human eye); (1.5 to 3.0, noticeable; detectable by trained people); (3.0 to 6.0, appreciable; detectable by ordinary people); Proximate and dietary fiber composition of pasta Results obtained on proximate and dietary fiber composition (6.0 to 12.0, large; large difference in the same color category) and of cooked pasta are presented in Table 1. Pasta protein content (larger than 12, extreme; another color category). decreased significantly (P < 0.05) in 30% and 40% RSF pastas Consumer sensory evaluation of pasta compared to the control pasta. This pattern can be related with Sensory evaluation was performed on cooked pasta by an un- the protein dilution effect produced by the RSF used in this study, trained consumer panel (n = 50), 23 males and 27 females; 20 which has previously been reported to have lower protein content to 57 y old (mean ± SD = 29.3 ± 7.8). Ethical approval for the than DWS (Khan and others 2013). The fat content increased study was granted by the Deakin Univ. Faculty of Health, Human significantly (P < 0.05) in all sorghum-containing pastas in comResearch Ethics Advisory committee. Panel members were re- parison to the control pasta, while ash content did not change cruited via advertisement at Deakin Univ., Melbourne, Australia, with the addition of both RSF and WSF. This pattern in fat conthrough which they were informed of the types of pasta used in tent can be related with the previously reported higher fat content the study. Panel members were staff and students of the Univ. and of the RSF and WSF used in this study compared to the DWS were selected based on lack of allergy to gluten protein. (Khan and others 2013). Total dietary fiber significantly (P < 0.05) Pasta samples were cooked for the optimum cooking time with- increased in all sorghum-containing pastas in comparison to the out the addition of salt, drained, and kept warm until serving. Pan- control pasta with the highest value being observed for 40% RSF elists assessed pasta samples (10 strands per sample) for consumer pasta mirroring the previously reported higher level of total dietary acceptability while seated isolated in sensory booths. The samples fiber in the RSF used in this study than the WSF and DWS (Khan were served in plastic plates, labeled with random 3 digit codes, in and others 2013). These results are also in agreement with those S1562 Journal of Food Science r Vol. 79, Nr. 8, 2014

Effect of sorghum flour addition . . . of Yousif and others (2012) who observed decrease in protein and Table 2–RDS and SDS values of control and sorghum-containing increase in total dietary fiber content of flat bread incorporating pasta samples (g/100 g dry starch). RSF and WSF. Samples RDS SDS 23.27 ± 0.92a 15.23 ± 0.38d 11.91 ± 0.33e 10.70 ± 1.03e 20.15 ± 0.29b 18.00 ± 0.45c 16.23 ± 0.59d

Control 20% RSF 30% RSF 40% RSF 20% WSF 30% WSF 40% WSF

37.56 ± 0.38ab 36.27 ± 0.23ab 36.67 ± 0.98ab 36.44 ± 1.50ab 36.96 ± 0.48ab 37.66 ± 0.34a 36.10 ± 0.72b

Values are expressed in means ± SD (n = 2). Means in the same columns with different letters are significantly different (P < 0.05, LSD test). RDS, rapidly digestible starch; SDS, slowly digestible starch; RSF, red sorghum flour; WSF, white sorghum flour.

soluble fiber which in comparison to insoluble fiber has the ability to decrease enzyme accessibility to food in the small intestine by delaying gastric emptying due to its higher viscosity and gel forming properties (Pi-Sunyer 2002). The decrease in starch digestibility of sorghum-containing pastas may also be attributed to the inhibitory effect of sorghum polyphenolics on digestive enzyme activity (Mkandawire and others 2013) and interaction of sorghum polyphenolics with starch molecules (Barros and others 2012). The RDS values found in 40% RSF or 40% WSF pasta in the present study were lower than those reported in flat bread incorporating RSF or WSF at the same level (Yousif and others 2012). These differences could be attributed to the more compact structure of pasta, which is responsible for the reduced enzymatic susceptibility of starch in pasta. On the other hand the open structure of flat bread allows high accessibility to starch hydrolysis enzymes, resulting in high levels of RDS (Cavallero and others 2002). Given the relation between in vitro and in vivo starch digestion rates (Vonk and others 2000), it would be anticipated that the addition of sorghum flour into pasta would lower its glycemic index.

70 Control Digested starch (g/100g dry starch)

60 20% RSF 50 30% RSF 40 40%RSF 30 20%WSF 20 30%WSF 10 40%WSF 0 0

20

40

60 Time (min)

80

100

120

Figure 1–Starch digestogram of control and sorghum-containing pasta samples. Values are means ± SD of duplicate samples at each time point. RSF, red sorghum flour; WSF, white sorghum flour.

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In vitro starch digestibility of pasta The addition of both RSF and WSF into pasta decreased the rate and extent of in vitro starch digestion compared to the control pasta, as indicated by lower response curves in the digestogram (Figure 1). The 40% RSF pasta exhibited the lowest values of DS while the control pasta exhibited the highest values at each time point. This was confirmed by the RDS and SDS values which are presented in Table 2. ANOVA demonstrated that all sorghum-containing pastas had lower levels of RDS (P < 0.05) than the control, but did not differ in their SDS levels. In addition, pasta samples with higher percentages of RSF and WSF showed significantly (P < 0.05) lower levels of RDS with significant lower levels (P < 0.05) in the RSF compared to the WSF-containing pastas at the same substitution level. Interaction between sorghum endosperm proteins (kafirins), which are mainly formed by intermolecular disulphide crosslinking (Chandrashekar and Mazhar 1999) and starch granules has been studied extensively as a main factor that influences sorghum starch digestibility (Ezeogu and others 2008; Taylor and Emmambux 2010). Ezeogu and others (2005) found that cooking sorghum flour in the presence of a reducing agent (2-mercaptoethanol) improved flour starch digestibility by preventing or reducing disulphide-bonded polymerization of the kafirins, suggesting that sorghum proteins may act as a physical block to starch digestion. In contrast to the results obtained in the present study, Austin and others (2012) found increase in starch digestibility of soft and hard sorghum endosperm porridges with the addition of anthocyanin-rich black sorghum bran. However, in the current study, whole grain sorghum flour was used instead of bran. Sorghum bran has been shown to contain mainly insoluble fiber (Gordon 2001) while whole grain sorghum flour also contains

Effect of sorghum flour addition . . . Cooking quality of pasta The effects of the different levels of both RSF and WSF on pasta cooking quality parameters are shown in Table 3. Optimum cooking time did not change significantly (P ˃ 0.05) with the addition of either RSF or WSF and was only 1 min shorter for all sorghum-containing pastas compared to the control pasta. Mean values for water absorption and swelling index of all RSF and WSF-containing pastas showed no significant difference from the control pasta (P ˃ 0.05). Contrary to the results obtained in the present study, a decrease in these parameters of sorghumcontaining pastas was expected due to the hydrophobic nature of sorghum kafirin (Duodu and others 2003). On the other hand, an increase in these parameters of sorghum-containing pastas was expected due to the higher concentration of fiber in them (Table 1). It is therefore speculated that no significant changes in water absorption and swelling index of sorghum-containing pastas could be the result of the net effect of these 2 factors. The dry matter contents of pasta containing 30% and 40% RSF or WSF were significantly (P < 0.05) lower than the control pasta, possibly indicating increased loss of solids during cooking. Cooking loss is considered an important pasta quality parameter and was determined for the same pasta samples in a previous study (Khan and others 2013) in which pasta containing RSF or WSF exhibited higher cooking loss compared to control pasta. Decrease in dry

80

Textural properties of pasta Textural properties of pasta are presented in Figure 2. The addition of both RSF and WSF significantly decreased (P < 0.05) the hardness of pasta at all levels compared to the control pasta. However, the hardness values did not differ (P ˃ 0.05) among all the sorghum-containing pastas. These results are in agreement with those of Cleary and Brennan (2006) who observed decrease in hardness of pasta incorporating barley fiber fraction. The decrease in pasta hardness is mainly associated with the disruption in protein-starch matrix induced by dietary fiber (Tudorica and others 2002) and reduction of gluten content (Wood 2009; Chung and others 2012). This may also be the reason of low hardness values of pasta in the present study, induced by higher level of dietary fiber (Table 1) and absence of gluten content in sorghum flour. Adhesiveness of pasta significantly decreased (P < 0.05) with the addition of both RSF and WSF. Although adhesiveness values showed a descending trend with increasing RSF or WSF concentrations, the values did not differ (P ˃ 0.05) among all the

a

70

b

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60

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b 0.0 Adhesiveness (N.s)

50 40 30 20 10 0

-0.2 -0.4 -0.6 -0.8

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S: Sensory & Food Quality

Hardness (N)

matter content following cooking has been previously reported by Cleary and Brennan (2006) in pasta containing barley fiber fraction. To sum up the results of the cooking quality parameters, it appears that the addition of both RSF and WSF into pasta did not affect the cooking quality parameters to a great extent.

abc

c

a

bc

c

0.8 0.6 0.4

0.2

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0.0

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Figure 2–Textural characteristics of control and sorghum-containing cooked pasta samples. Values are expressed in means ± SD (n = 10). Different letters above the bars within each graph indicate statistical differences (P < 0.05, LSD test). RSF, red sorghum flour; WSF, white sorghum flour.

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Effect of sorghum flour addition . . .

Sample

Cooking Water time (min) absorption (%)

Control 20% RSF 30% RSF 40% RSF 20% WSF 30% WSF 40% WSF

15.2 ± 0.4a 14.3 ± 0.4a 14.1 ± 0.3a 14.3 ± 0.2a 14.2 ± 0.4a 14.2 ± 0.3a 14.3 ± 0.4a

Swelling index

Dry matter (%)

1.99 ± 0.04ab 2.02 ± 0.03ab 2.05 ± 0.04ab 2.08 ± 0.04a 1.98 ± 0.02b 2.01 ± 0.06ab 2.08 ± 0.04a

39.42 ± 0.13a 38.98 ± 0.25ab 38.24 ± 0.31bc 37.52 ± 0.77c 38.47 ± 0.14abc 38.20 ± 0.66bc 37.64 ± 0.39c

Sample

L∗

(A) Uncooked pasta Control 75.36 ± 0.49a 20% RSF 63.57 ± 0.61b 30% RSF 60.56 ± 0.54d 40% RSF 57.88 ± 0.50e 20% WSF 64.16 ± 0.88b 30% WSF 62.30 ± 0.89c 40% WSF 61.05 ± 0.65d (B) Cooked pasta Values are expressed in means ± SD (n = 2). Control 79.21 ± 1.88a Means in the same columns with different letters are significantly different (P < 0.05, 20% RSF 64.62 ± 0.62b LSD test). RSF, red sorghum flour; WSF, white sorghum flour. 30% RSF 61.19 ± 1.51c 40% RSF 58.38 ± 0.95d 20% WSF 65.22 ± 1.33b sorghum-containing pastas. These results are in line with those of 30% WSF 63.82 ± 1.73bc Cleary and Brennan (2006) who observed decrease in pasta adhe- 40% WSF 61.09 ± 1.67c 158.11 ± 1.84a 159.82 ± 2.53a 161.95 ± 1.59a 161.75 ± 2.77a 158.41 ± 3.45a 159.04 ± 4.28a 160.16 ± 3.89a

a∗

b∗

࢞E

2.25 ± 0.21e 4.04 ± 0.25c 5.33 ± 0.19b 6.62 ± 0.13a 1.94 ± 0.14e 2.17 ± 0.14e 2.26 ± 0.18e

31.71 ± 0.49a 20.58 ± 0.71b 19.45 ± 0.28c 17.93 ± 0.24e 20.73 ± 0.28b 18.49 ± 0.18d 15.91 ± 0.11f

17.41 ± 0.72e 20.68 ± 0.64c 23.96 ± 0.54a 16.13 ± 0.46f 19.12 ± 0.70d 21.89 ± 0.59b

1.87 ± 0.33d 3.63 ± 0.60c 4.54 ± 0.88b 5.60 ± 0.86a 1.59 ± 0.45d 1.77 ± 0.60d 2.29 ± 0.58d

29.04 ± 1.77a 17.51 ± 0.65c 15.11 ± 0.66e 13.64 ± 0.31f 18.33 ± 0.16b 16.08 ± 0.63d 12.95 ± 0.55f

19.74 ± 1.97c 24.01 ± 2.20b 27.25 ± 1.89a 21.18 ± 1.96bc 23.03 ± 2.13b 26.28 ± 1.52a

siveness enriched with barley fiber fraction. However, contrary to Values are expressed in means ± SD (n = 10). our results, Aravind and others (2013) observed no changes in pasta Means in the same column for either section (A) or section (B) with different letters are significantly different (P < 0.05, LSD test). adhesiveness enriched with different types of resistant starch, while L∗ : lightness/darkness; ± a∗ : red/green; ± b∗ : yellow/blue. was calculated relative to the control pasta. Chillo and others (2011) observed increase in pasta adhesiveness E RSF, red sorghum flour; WSF, white sorghum flour. enriched with barley β-glucan. Cohesiveness is another important textural parameter and is an indicator of how the sample holds together upon cooking. which according to the Handbook of Colour Science (Yamauchi There was no statistical difference (P ˃ 0.05) between cohesiveness 1989) fall in the “extreme, another color” category. values of control and sorghum-containing pastas. These results indicate that all sorghum-containing pastas had similar tolerance to disintegration during cooking as control pasta. The addition of Consumer sensory evaluation of pasta both RSF and WSF to pasta had no major impact on its springiness. The hedonic sensory attributes of cooked pasta evaluated by a consumer panel are given in Table 5. Panel members assigned Color characteristics of pasta lower (P < 0.05) scores for color, flavor, texture (in mouth), Color measurements were performed on both uncooked and and overall acceptability for sorghum-containing pastas than the cooked pasta (Table 4). With the addition of both RSF and WSF, control pasta. For acceptability of color, the control pasta scored the color became darker (lower L∗ value). RSF addition signifi- in the range of “like moderately” while both RSF and WSFcantly increased (P < 0.05) the redness (higher a∗ value) whereas containing pastas scored in the range of “neither like nor dislike” WSF addition did not significantly (P ˃ 0.05) affect a∗ value. Both with the exception of 20% WSF pasta which scored in the range RSF and WSF significantly decreased (P < 0.05) the yellowness of “like slightly.” The main comment expressed by panelists re(lower b∗ value) at all incorporation levels. The change in these garding color of all sorghum-containing pastas was, “less yellow parameters of sorghum-containing pastas may be attributed to the in color.” The sensory data for color are consistent with the inpresence of colored phenolic compounds such as anthocyanins strumental color data in which control pasta scored significantly in sorghum flours particularly in RSF (Yousif and others 2012). higher (P < 0.05) for brightness and yellowness compared to all Change in pasta color parameters (decrease in L∗ and b∗ values sorghum-containing pastas. For acceptability of flavor, texture, and and increase in a∗ value) has previously been observed by Wood overall acceptability, the control pasta scored in the range of “like (2009) in pasta enriched with chickpeas flour and by Aravind moderately” while pastas at 20% and 30% incorporation levels of and others (2012) in pasta substituted with durum wheat bran and RSF or WSF scored in the range of “like slightly.” Pasta at 40% germ compared to pasta made from 100% semolina only. Dry pasta incorporation level of RSF or WSF scored in the range of “neither color is an important quality parameter from the consumer point like nor dislike.” The results on sensory attributes obtained in the of view (Wang and others 2004). However, in the present era, the present study are consistent with those of Yousif and others (2012) market for composite pastas, with added nondurum materials (that who obtained similar scores for color, flavor, texture, and overall actually are darker) has grown considerably (Gallegos-Infante and acceptability of flat bread incorporating RSF and WSF. Our results on sensory attributes (flavor and overall acceptability) also closely others 2010b). In addition to L∗ , a∗ , and b∗ values, E was also determined matched those obtained for pasta substituted with banana flour to evaluate the color difference between the control and the and β-glucan by Choo and Aziz (2010). The mean scores for overall acceptability of pasta samples up sorghum-containing formulations. The E values of sorghumcontaining pastas increased significantly (P < 0.05) with the in- to 30% incorporation level of either RSF or WSF were greater creasing levels of RSF and WSF in both uncooked and cooked than 6.0 (Table 5D), satisfying the 1st preset acceptability criteforms. In addition RSF-containing pastas exhibited higher E rion, showing that on average, these pasta samples were rated more (P < 0.05) compared to the equivalent WSF-containing pastas in favorably than “like slightly” by the panel members. Pasta samuncooked form, indicative of the higher level of color compounds ples containing RSF or WSF at 40% incorporation level did not in RSF than in WSF. The E values were more than 12 for all achieve the targeted score of 6.0 and hence failed to meet the 1st sorghum-containing pastas in both uncooked and cooked forms, acceptability criterion. Vol. 79, Nr. 8, 2014 r Journal of Food Science S1565

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Table 3–Cooking quality characteristics of control and sorghum- Table 4–Color characteristics of control and sorghum-containcontaining pasta samples. ing pasta samples.

Effect of sorghum flour addition . . . Table 5–Mean score, mean difference, and 95% confidence inter- DWS with either RSF or WSF at all levels had no significant vals of difference in consumer rating of control and sorghum- effect on most of the instrumental quality attributes, except color containing pasta samples (n = 50)∗ .

and hardness which were affected negatively. Results on consumer

95% Confidence acceptability indicated that panelists assigned lower scores on color, interval of flavor, texture, and overall acceptability for all sorghum-containing difference Mean score

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(A) Color Control 7.56a 20% RSF 5.76c 30% RSF 5.50cd 40% RSF 5.08e 20% WSF 6.28b 30% WSF 5.42cde 40% WSF 5.34de (B) Flavor Control 7.32a 20% RSF 6.48b 30% RSF 6.26bc 40% RSF 5.42d 20% WSF 6.40b 30% WSF 5.98c 40% WSF 5.12d (C) Texture (in mouth) Control 7.28a 20% RSF 6.28b 30% RSF 6.10b 40% RSF 5.32c 20% WSF 6.22b 30% WSF 6.12b 40% WSF 5.36c (D) Overall acceptability Control 7.16a 20% RSF 6.50b 30% RSF 6.38b 40% RSF 5.26c 20% WSF 6.56b 30% WSF 6.34b 40% WSF 5.34c

pastas than the control pasta. However, pasta samples containing 20% incorporation level of either RSF or WSF fulfilled both Upper preset acceptability criteria indicating that this formulation may have market potential. Human dietary studies are now needed to ascertain if the lower in vitro starch digestibility of the red and −1.39 white sorghum-containing pastas than the control translates into a −1.65 health beneficial lower glycemic response in vivo.

Mean difference(sorghumcontaining − control)

Lower

−1.80 −2.06 −2.48 −1.28 −2.14 −2.22

−2.20 −2.46 −2.88 −1.68 −2.54 −2.62

−0.84 −1.60 −1.90 −0.92 −1.34 −2.20

−1.23 −1.45 −2.29 −1.31 −1.73 −2.59

−1.00 −1.18 −1.96 −1.06 −1.16 −1.92

−1.41 −1.59 −2.37 −1.47 −1.57 −2.33

−0.58 −0.76 −1.54 −0.64 −0.74 −1.50

−0.66 −0.78 −1.90 −0.60 −0.82 −1.82

−0.95 −1.04 −2.19 −0.89 −1.08 −2.11

−0.36 −0.48 −1.60 −0.30 −0.52 −1.52

−2.07 −0.87 −1.73 −1.81

This study was funded by Deakin Univ. and Curtin Univ. internal research grants. We are grateful to Curtin Univ. School of −0.44 Public Health for supplying semolina and sorghum flours. Author −0.66 I. Khan acknowledges the scholarships from Deakin Univ. and −1.50 KPK-Univ. of Agriculture, Peshawar, Pakistan. −0.52 −0.94 −1.80

Means in the same column for each section (A, B, C, or D) separately, with different letters are significantly different (P < 0.05, LSD test). RSF, red sorghum flour; WSF, white sorghum flour. ∗ Data collected on a 9-point hedonic scale (1 = dislike extremely; 9 = like extremely).

The lower 95% confidence interval of the mean difference in overall acceptability between the sorghum-containing minus the control pasta samples lay above minus 1 (−1.0) for the samples containing RSF or WSF at 20% incorporation level, but not for the samples containing RSF or WSF at 30% and 40% incorporation levels (Table 5D). Hence, pasta samples containing RSF or WSF at 20% incorporation level satisfied the 2nd preset acceptability criterion. This indicates enough confidence to predict that in the general population, pasta samples up to 20% incorporation level of either RSF or WSF would on average be rated no inferior than 1 rating category lower than the control pasta on the 9point hedonic scale used in the present study and hence have most promise from a commercial perspective.

Conclusion Sorghum flour has potential application as a health functional ingredient in pasta. The addition of both RSF and WSF at all levels significantly increased the dietary fiber content and reduced the RDS content compared to 100% DWS pasta. The results also suggest that addition of RSF is better able to reduce the starch digestibility of pasta than WSF. In addition, substitution of S1566 Journal of Food Science r Vol. 79, Nr. 8, 2014

Acknowledgments

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