Abstract
Protein quality parameters of wheat flour, as well as protein content, showed significant relationship with hardness, cohesiveness, springiness, adhesiveness, chewiness, and gumminess of the cooked noodles. A significant positive correlation (0.54) was observed between glutenins and hardness of noodles. Chewiness of the noodles increased with the protein content, sodium dodecyl sulfate sedimentation volume, dough development time, dough stability, and glutenins. Hardness, springiness, cohesiveness, gumminess, and chewiness of the noodles were negatively affected by gliadin to glutenin ratio. Multiple regression analysis depicted significant relationships of the various noodle quality parameters with wheat flour characteristics. The results revealed that the relative composition of the gliadins and glutenins had a considerable effect on the textural profile of noodles indicating their defining contribution on the noodle quality. The resulting information could be useful in predicting the noodle-quality potential of the varieties.
INTRODUCTION
In recent years cereal scientists have increased attention toward products such as noodles, steamed breads, and flat breads. Noodles have become an important part of the diet in many countries of Asia. The noodle consumption has grown considerably in the Western countries as well due to the increasing popularity of convenience foods among consumers. On the basis of color and formulation, Asian noodles can be divided into two general classes: white salted and yellow alkaline.[Citation1,Citation2] Chief factors contributing to improved quality of white salted noodles include high starch pasting peak viscosity, dough properties, soft grain texture, and high protein quality as measured by sodium dodecyl sulfate (SDS) sedimentation value.[Citation3] Texture is the key factor which influences white salted noodle quality.[Citation4] Previous studies have reported positive relationship of proteins[Citation5] and dough properties.[Citation6] Numerous studies have been carried out on the effect of wheat dough on the final product quality. Dough properties largely depend on the flour protein content, especially gluten protein. Khatkar and Schofield[Citation7] found significant correlation between gluten quality and bread quality. Zhang et al.[Citation8] reported that resilience, springiness, and cohesiveness values of noodles are chiefly governed by gluten. Noodles prepared from low protein wheat flour are more fragile than those prepared from flour with high protein content because of the formation of a weaker protein network.[Citation9] A few investigations on the effect of protein fractions on the noodle quality report that insoluble glutenin is directly related to the hardness, resilience, and optimum cooking time. SDS sedimentation volume based on a constant protein weight, proportion of salt-soluble protein, and high molecular weight glutenin subunit (HMW-GS) compositions score correlates with optimum water absorption of noodle dough and hardness of cooked white salted noodles.[Citation5] Additionally, Huang and Morrison[Citation10] showed that the existence of certain gliadin components was also related to the texture of noodles. This indicates that overall gluten composition can affect noodle texture. Despite the understanding of the impact of flour protein content on noodle texture, there is limited information regarding how the composition of gluten in different wheat varieties affects textural properties of the white salted noodles. Thus, the present study was aimed to understand the effect of the gluten protein composition and dough characteristics on the noodle quality of the wheat varieties.
MATERIALS AND METHODS
Wheat Samples
Samples of fifteen wheat varieties differing widely in their noodle making quality were selected for the study. These varieties were tempered to 15.5% moisture content for 24 h and milled in Chopin mill, yielding 65% flour. The wheat flours obtained were stored at 4°C for further analysis.
Analytical Methods
The moisture and protein content of the wheat flours were determined according to AACC approved methods 44-15A, 46-30.[Citation11] SDS sedimentation volume of flours was estimated according to the Axford et al.[Citation12] Damaged starch was evaluated by the Chopin SDmatic (Villeneuve la Garenne, France). Gluten was isolated from different selected wheat varieties by Perten Glutomatic (Model 2200, Newport Scientific Private Limited, Warriewood, Australia). Wet gluten, dry gluten, and gluten index was evaluated for the different wheat varieties. All analysis was carried out in triplicates, and expressed as mean value. Dough rheological parameters were evaluated by Chopin Mixolab (Villeneuve la Garenne, France) using Chopin S protocol. The different parameters obtained by the study were water absorption capacity of the flour (%), dough development time (DDT; min), stability (min), and softening (FU), respectively.
Fractionation of Gluten into Gliadins and Glutenins
The wheat flours were defatted according to MacRitchie.[Citation13] Flour (100 g) was extracted with 200 mL of chloroform at room temperature and then filtered through filter paper. The extraction was repeated twice for a total of three extractions. The defatted flour was allowed to dry at room temperature. Gluten was extracted from defatted flour samples by glutomatic and freeze dried. The freeze dried gluten samples were ground in a pestle and mortar. The resulting freeze dried gluten powder was dissolved in 200 ml of 70% ethanol. The mixture was stirred on a magnetic stirrer for 3 h at 25°C followed by centrifugation for 30 min at 1000 g at 4°C. Supernatant was collected and the pellet was again extracted with 70% ethanol. The supernatants were pooled and ethanol was removed from the gliadin extracts using rotary evaporator at 30°C. The gliadin and glutenin fractions, thus, obtained were freeze dried and powdered in pestle and mortar.
Noodle Making and Instrumental Texture Profile Analysis (TPA) of Cooked Noodles
Flour (100 g) was mixed with 35 ml of 6.25% sodium chloride in a mixer for 30 s at low speed (60 rpm) and then for 3 min at a medium speed (86 rpm). The dough was then passed through the rolls of dough sheeting machine at 3 mm gap. It was folded and passed through the rolls twice again. The dough sheet was rested for 1 h at ambient temperature (25°C) and then again rolled through the sheeting rolls three times at progressively smaller gap settings of 2.40 mm, 1.85 mm, and 1.30 mm, respectively. The sheet was then cut into noodle strands by machine. Noodles were put into plastic bags and stored at 4°C for 24 h until being cooked. Noodles (10 g) were cooked in 400 mL of boiling water for 5 min and subsequently rinsed in cold water to prevent the overcooking of the noodles. Cooked noodle texture characteristics such as hardness, adhesiveness, springiness, and cohesiveness were measured using TPA with a Texture Analyzer, TA-XT2i (Stable Micro Systems, Surrey, UK). The TPA was calculated from the areas of the force–time curves of two compressions using a flat-end cylindrical plunger (25-mm probe) descending to 70% of the original height of the noodles. Crosshead speeds of 4.0, 1.0, and 1.0 mm/s were used for pretest, test, and post test settings, respectively. Five observations were made using two cooked noodle strands (2 cm long) placed side by side each time.
Statistical Analysis
Statistical analysis of the experimental data was performed by SPSS 16.0 software (SPSS Inc., Chicago) using analysis of variance (ANOVA), Pearson's correlation coefficient and multiple linear regression. Best-fit linear regression model was determined using backward variable elimination.
Table 1 Flour quality characteristics
Table 2 Gluten composition and characterization
RESULTS AND DISCUSSION
Characteristics of Flour and Dough
The results of the flour quality analyses of fifteen wheat varieties are presented in . The moisture, protein, SDS sedimentation volume and the damaged starch content varied significantly. Moisture content ranged from 11.06 to 13.22%. The varieties HW 2004 displayed the lowest protein content (10.06%) while PBW 590 (14.17%) showed the highest protein content, respectively (). SDS sedimentation volume ranged from 26 mL in variety VL 892 and HI 8498 to 53 mL in NIAW 917. The lowest damaged starch content of 4.28% was found in variety VL 892 while variety HI 8498 had the highest damaged starch content of 9.06%. Gluten index ranged from 40.23 to 97.52% (). The variety CBW 38 had the highest (97.52%) gluten index followed by variety HI 977 (96.33%) while the variety WH 1025 (40.23%) had the least. The R/E ratio of gluten also varied significantly among the different varieties. Highest values were found in variety PBW 550 (1.45) while the variety MACS 1967 (0.26) had the lowest ratio. The varieties HI 977 and PBW 590 exhibited strong dough characteristics as evident from the higher DDT, higher dough stability and lower values for the degree of softening (DOS). The highest DDT was observed for variety HI 977 (4.5 min) followed by the variety PBW 590 (4.0 min) while the variety A-9-30-1 showed the lowest (). The water absorption capacity was highest for the variety HI 8498 (67.9%) while the variety VL 892 (50.4%) had the lowest. The optimum water requirement varies largely, depending on the type of flour.[Citation14] Though, water absorption capacity is largely influenced by the damaged starch but a weak positive correlation between water absorption capacity and damaged starch (r = 0.321) of flour was observed in the present study. The stability of the dough ranged between 1.5 and 8.5 min, while the DOS recorded the highest value of 140 FU for variety MACS 1967 while variety HI 977 (23 FU) reported the lowest indicating that it is a strong flour. DDT correlated positively with dough stability (r = 0.825) and negatively with DOS (r = –0.633). The flour's protein content was positively correlated with DDT (r = 0.585) and negatively with dough stability (r = –0.189). The dough test showed that the glutenin fraction, but not the gliadin fraction, was responsible for the strengthening effect on the wheat dough. The varieties with higher glutenin content had longer DDT, longer dough stability time, and low values of DOS. This could be explained on the basis of studies by MacRitchie,[Citation15] who found that the entanglement networks formed by the polypeptide molecules during mixing and the time required to mix the dough to peak is proportional to the size of the largest molecule present. Results of correlation analysis revealed negative correlations between the gliadin to glutenin ratio (Gli:Glu) and DDT (r = –0.423), dough stability (r = –0.617), and positive correlation with the DOS (r = 0.309). Similar results between the glutenin content and the dough strength had been reported previously by Primo-Martin et al.[Citation16]
Variation in Gluten Protein Composition
The proportions of gluten subfractions from different wheat varieties are presented in . Gliadin fraction ranged from 4.16 to 6.33%, the highest for variety HI 8498 while the variety CBW 38 had the lowest. Glutenin proportion also varied significantly among the varieties with HI 8498 (6.69%) showing the highest content and the variety HW 2004 (3.99%) showing the lowest value of this subfraction. The Gli:Glu ranged from 0.78 to 1.17, respectively. The variety C 306 had the highest Gli:Glu ratio of 1.17, followed by the variety HW 2004 (1.05) while the variety NIAW 917 (0.78) showed the least ratio. A positive correlation was observed between gliadins and glutenins (r = 0.707). Significant differences in the gluten protein subfractions in the different wheat varieties could be attributed to varietal differences. The gluten protein subfractions increased with the protein content of the flour, though the increase was less pronounced for gliadin as evident from the strong and significant correlation between glutenin and protein (r = 0.742) () indicating that with the increase in protein content of the wheat variety, the percentage of glutenins also increase. Gomez et al.[Citation17] reported that the ratio of glutenin to gliadin in wheat flour influence the dough rheology via changes in gluten matrix. Similarly in the present study, it was found that the Gli:Glu ratio was strongly negatively correlated with the R/E ratio of gluten (r = –0.568) and dough stability (r = –0.505). It is widely accepted that gliadins confer viscous properties and extensibility while glutenin imparts elasticity.[Citation18] Therefore, as the glutenin percentage in the wheat varieties increased, its elastic properties also increased. As a result the extensibility of the gluten decreased and its resistance to extension increased. Similar results were also observed by Khatkar et al.[Citation19] who found a strong inverse relationship between Gli:Glu ratio and elasticity of gluten. The decrease in elasticity could also be attributed to the plasticising effect of gliadin and the interference of gliadin with the glutenin-glutenin interactions.[Citation7] These results were in agreement with the results reported by Weiser and Kieffer[Citation20] who found the maximum resistance of gluten to be highly positively correlated with the quantity of glutenin. Glutenin showed higher correlation with the DDT (r = 0.415) and dough stability (r = 0.455) as compared to gliadin, which are important indicators of dough strength and dough's tolerance to mixing.
Table 3 Correlation among various wheat flour parameters and gluten composition
Table 4 TPA of cooked noodles prepared from various wheat varieties
Table 5 Relationships between flour characteristics, gluten protein composition, and cooked noodle parameters
Instrumental Texture Profile Analysis of Cooked Noodles
Instrumental TPA parameters of cooked noodles prepared from different wheat flours are summarized in . Hardness is the force required to attain a particular deformation while gumminess and chewiness are the energy requirements to disintegrate or masticate the noodle for easy swallowing. Hardness values of cooked white salted noodles were highest for variety PBW 590, followed by NIAW 917, and HI 977 which also reported higher protein content, whereas the varieties with lower protein content produced noodles of lower hardness. Significant differences were observed for the adhesiveness and springiness of cooked noodles prepared from 15 different wheat varieties. Springiness expresses noodle tendency to return to an undeformed state or shape after a biting force is removed or after biting down (compressing), respectively. The degree of stickiness measured as adhesiveness in the TPA profile is very important parameter for Asian noodle products. Stickiness of noodles is considered undesirable. Noodle stickiness is described as the work necessary to separate the testing probe from the surface of noodle strips. In the TPA curve, cooked noodle adhesiveness is represented as the area of the negative peak. Adhesiveness values of the cooked noodles ranged from 0.06 to 0.11; however, the values of adhesiveness did not vary much between the varieties. The springiness values ranged from 0.86 to 0.98. Noodle cohesiveness refers to the strength of internal bonds that constitute its structure. In general, high values of springiness, cohesiveness, and hardness are desirable.[Citation21] The cohesiveness values ranged from 0.49 for variety VL 892 to 0.63 for variety PBW 590. Gumminess is a product of hardness and cohesiveness; and chewiness is a product of gumminess and springiness. Thus the values of gumminess and chewiness increased with the increase in hardness, cohesiveness, and springiness values. The range of gumminess was 4.18 to 8.78 while the values of chewiness ranged from 4.04 to 8.60, respectively.
Correlations Between Wheat Flour Characteristics, Gluten Protein Composition, and TPA Parameters of Cooked Noodles
The correlations between wheat flour characteristics, gluten protein composition and TPA parameters of cooked noodles are listed in . Protein content of the wheat varieties had significant positive correlation with the hardness of cooked noodles (r = 0.607). Similar results have also been shown in many other studies.[Citation5,Citation6,Citation22] Thus, noodles prepared from low protein wheat flour were more fragile than those made from flour with high protein content because of the formation of a weaker protein network. Thus, with increase in the protein content of the varieties the noodle quality characteristics such as hardness, gumminess, and chewiness improved. SDS sedimentation volumes also correlated positively (r = 0.509) with the cooked noodle hardness. Huang and Morrison[Citation10] also reported that higher SDS sedimentation volumes are positively related to the cooked noodle firmness. Adhesiveness was negatively correlated with most of the flour quality parameters. Springiness was found to be positively correlated with the protein, SDS sedimentation volumes, damaged starch content and hardness, respectively. Glutenins were found to be significantly positively correlated with the noodle hardness (r = 0.541) and cohesiveness (r = 0.590). These results were in agreement with the results of Zhong et al.,[Citation23] who reported that the noodle hardness is significantly affected by the soluble and insoluble glutenin content of the wheat flour. Gliadins were though not significantly, but slightly positively correlated to the hardness of cooked noodles. Moreover, it was found that Gli:Glu ratio was negatively (r = –0.309) correlated with the hardness of the noodles. Thus, it can be concluded that not only the protein content is important in asserting the hardness of noodles, but the protein quality and composition is equally important in judging the suitability of a particular variety for its noodle making quality. The DDT and dough stability were found to be positively associated with hardness, springiness, and cohesiveness; whereas with adhesiveness, they were negatively correlated. The gluten yield was not strongly associated with any of the TPA parameters. The effects of protein content on the cooked noodle texture could be explained as a result of competition between starch and protein for water absorption, and the inhibition of starch granular hydration due to the protection provided by the gluten network.
Regression Analysis
represents multiple linear regression results between the cooked noodle characteristics and wheat flour quality parameters. A high regression (R > 0.541) indicated a good fit of data in the prediction of noodle quality and suggested that the protein quantity and quality, rheological parameters and gluten content and quality considerably affect the textural parameters of the noodles. Thus, these factors should be considered in the evaluation and selection of the wheat varieties for white salted noodle making.
Table 6 Prediction of textural quality of noodles using wheat flour and gluten quality parameters
CONCLUSION
The present study showed that significant differences in the white salted noodle quality results from both protein content and protein quality. Protein was positively associated with most of the textural parameters of noodles such as hardness, cohesiveness, springiness, and negatively associated with the adhesiveness of the cooked noodles. Gli:Glu ratio and glutenins had a considerable effect on the TPA parameters of cooked noodles indicating that the relative amount of these two fractions of gluten is very important in predicting the textural parameters of white salted noodles. Damaged starch also substantially affected the cooked noodle characteristics. Previous studies which have been conducted on the influence of proteins on the quality parameters of cooked white salted noodles have shown that gluten proteins are mainly responsible for the differences in the noodle making quality of the wheat varieties. This study was able to deduce the relationships between gluten protein fractions on the different quality parameters of the noodles and also predict the textural characteristics of the cooked white salted noodles. Thus, the study clearly demonstrated that protein content, gluten protein quality, and rheological characteristics are important contributors to the noodle making potential of the wheat varieties. Thus, it is important to establish the protein quality standards for identifying the potential noodle making wheat varieties.
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