EFFECT OF GLIADINS ON QUALITY OF WHITE SALTED NOODLES

Transcription

1 CHAPTER 11 EFFECT OF GLIADINS ON QUALITY OF WHITE SALTED NOODLES 11.1 Abstract: The gliadin content of the wheat flours showed significant relationship with hardness, cohesiveness, springiness, adhesiveness, chewiness and gumminess of the cooked noodles. A positive correlation (0.380) was observed between gliadins and hardness of noodles. However, the hardness, springiness, cohesiveness, gumminess and chewiness of noodles were negatively affected by gliadin/glutenin ratio. Multiple regression analysis depicted significant relationships of the various noodle quality parameters with wheat flour characteristics. The results revealed that the composition of the gliadins had a considerable effect on the textural profile of noodles indicating their 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 towards products such as noodles, steamed breads and flat breads. Noodles have become an important part of the diet in many countries of Asia. The noodles 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 (Morris and Rose, 1996). 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 SDS sedimentation value (Wang et al., 2004). Texture is the key factor which influences white salted noodle quality (Epstein et al., 2002). Previous studies have reported positive relationship of proteins (Park et al., 2003) and dough properties (Crosbie et al., 1999). 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 (1997) found significant correlation between gluten quality and bread quality. Noodles prepared from low protein wheat flour are more fragile than those 126

2 prepared from flour with high protein content because of the formation of a weaker protein network. 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 HMW-GS compositions score correlates with optimum water absorption of noodle dough and hardness of cooked white salted noodles (Park et al., 2003). Additionally, Huang and Morrison (1988) 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. With respect to flour protein content, hardness of cooked noodles has been positively related to its increase (Park et al , Huang and Morrison, 1988). Despite our understanding of the impact of flour protein content on noodle texture, there is limited information regarding how the variable composition of gluten in different wheat genotypes affects texture. The literature does show some effects of the relationship between protein composition variability and effects on textural characteristics of noodles (Oh et al. 1985).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 Texture Profile Analysis of Cooked Noodles Texture is the key factor which influences white salted noodle quality (Epstein et al. 2002). Some common white salted noodles include Japanese Udon, and Chinese and Korean salt noodles. Although all these noodles are made only from flour, water and salt, the preferred textural attributes are type and regional specific. Noodle texture can be determined by means of sensory tests which involve a trained panel or it can be determined instrumentally. The physical structure of a noodle is made up of protein and starch, and these are the primary determinants of noodle texture. In addition, there is evidence that protein composition may be an important secondary determinant (Huang and Morrison 1988, Crosbie et al. 1999, Park et al. 2003). As protein content of flour increases, noodles generally become firmer (Park et al. 2003, Oh et al and Crosbie et al. 1999). The different TPA parameters of cooked noodles were calculated according to Epstein et al. (2002) (Table 9.1) TPA is a "two bite" test (Fig 11.1). There are two cycles of compression making up the first and second bite. The TPA parameters of the cooked noodles from different wheat varieties are presented in Table Hardness is the force required 127

3 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 fifteen 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. Table 11.1 Calculations of the TPA parameters (Epstein et al., 2002) Parameters Hardness Calculations The maximum force recorded in the first compression cycle Adhesiveness The work done after Fmax (Area 3) Cohesiveness Area2/Areal Springiness Length2/Length1 Chewiness Gumminess * Springiness 128

4 Figure 11.1 Texture Profile Analysis of cooked white salted noodle 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 0.11N.mm; however the values of adhesiveness did not vary much between the varieties. The springiness values ranged from 0.86 to Noodle cohesiveness refers to the strength of internal bonds that constitute its structure. In general, high values of springiness, cohesiveness and hardness are desirable (Hou, 2001). The cohesiveness values ranged from 0.49 for variety VL 892 to 0.63 for variety PBW 590. Table 11.2 Texture profile analysis of cooked noodles prepared from various wheat varieties Variety HD (N) AD (N.mm) SP (ratio) CO (ratio) GUM (N) CHEW(N.mm) CBW h -0.07a,b 0.92e 0.59e,f 7.61i 7.00i NIAW m -0.08b,c 0.98g 0.61g 8.46m 8.29n WH f -0.10d,e 0.86b 0.54c 6.77g 5.82f 129

5 WH b -0.11e 0.88c 0.51b 5.09b 4.47b HUW d -0.07a,b 0.86b 0.54c 6.11d 5.25d VL a -0.09c,d 0.84a 0.49a 4.81a 4.04a HI l -0.06a 0.94f 0.63h 8.54n 8.02m HW f -0.08b,c 0.90d 0.52b 6.52f 5.86g MACS i -0.09c,d 0.94f 0.58e 7.87j 7.39j DBW c -0.11e 0.88c 0.51b 5.76c 5.06c A g -0.10d,e 0.91d,e 0.56d 7.07h 6.43h PBW n -0.07a,b 0.98g 0.63h 8.78o 8.60o HI k -0.08b,c 0.94f 0.59e,f 8.09k 7.60l PBW j -0.06a 0.92e 0.60f,g 8.22l 7.56k C e -0.08b,c 0.88c 0.52b 6.47e 5.69e HD- hardness; AD- adhesiveness; SP- springiness; CO- cohesiveness; GUM- gumminess; CHEW-chewiness. Values are mean of three independent readings; Values followed by different letters are significantly different at P< 0.05 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 N while the values of chewiness ranged from 4.04 to 8.60 N.mm, respectively Dynamic Rheological Studies of Wheat Varieties for Noodle Making Wheat flour dough can be characterized as a viscoelastic material. The magnitude of the dynamic moduli G' and G" of the gluten is strongly affected by the composition of the dough and more importantly the composition of gliadin and glutenin proteins. Hou (2001) reported that higher values of springiness, cohesiveness and hardness are desirable textural parameters for white salted noodles while adhesiveness of cooked noodles is undesirable. Based on above, the wheat varieties NIAW 917, HI 977, PBW 550 and PBW 590 were found to be good varieties for noodle making while wheat varieties WH 1025, VL 892, HW 2004 and C 306 proved to be poor varieties for noodle making. The storage and loss modulus of gluten for the good noodle making wheat varieties are presented 130

6 Figure 11.2 Storage (G') and loss (G") modulus of gluten from good noodle making wheat varieties in Fig It was found that varieties NIAW 917, HI 977 (Fig. 5.2), PBW 550 and PBW 590 (Fig 11.2) had higher values for storage modulus (G') and lower values for the loss modulus (G"), i.e. the gluten from wheat varieties desirable for noodle making had more elastic than viscous character. Moreover, the gluten from wheat varieties WH 1025, VL 892 (Fig. 10.2), C 306 and HW 2004 (Fig. 5.2) had more viscous and less elastic character. The viscous character of these varieties was dominant at higher frequency. Also, the varieties found to be poor for noodle making were found to possess higher gliadin/glutenin ratio than good noodle making wheat varieties. The gliadin fraction of gluten is responsible for the viscous behavior while glutenin provides elasticity. As the content of gliadin in a wheat variety increased, its mechanical spectra also showed a more viscous behavior. Thus, it can be concluded that dynamic rheology can be explored as a useful tool for identifying the potential of wheat varieties for white salted noodle making 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 Table Protein content of the wheat varieties had 131

7 significant positive correlation with the hardness of cooked noodles (r = 0.607). Similar results have also been shown in many other studies (Park et al., 2003, Crosbie et al. 1999, Oh et al., 1985). 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 (1988) 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. (2007) 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 gliadin/glutenin ratio was negatively (r = ) 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. Table 11.3 Relationships between flour characteristics, gluten protein composition and cooked noodle parameters Parameters HD AD SP CO GUM CHEW Protein 0.607* * 0.700* 0.687** 0.690** SDSV * 0.535* 0.529* 0.535* DS 0.556* * DDT ** ** 0.601* 0.593* STA 0.529* ** 0.569* 0.769** 0.657** 0.656** GY

8 GI * R/E Gliadins Glutenins 0.541* * 0.590* 0.585* 0.588* Gli/Glu * HD- hardness; AD- adhesiveness; SP- springiness; CO- cohesiveness; GUM-gumminess; CHEW-chewiness; SDSV- SDS sedimentation volume; DS- damaged starch; DDT- dough development time; STA- dough stability; GY- gluten yield; GI- gluten index; R/E- resistibility/ extensibility of gluten; Gli:Glu- gliadin/glutenin ratio. ** Correlation is significant at 0.01 level, * correlation is significant at 0.05 level. The dough development time 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 Table 8.4 represents multiple linear regression results between the cooked noodle characteristics and wheat flour quality parameters. Table 11.4 Prediction of textural quality of noodles using wheat flour and gluten quality parameters Cooked noodle parameters Selected parameters R 2 Hardness DS, PRO, GY, GI, GLI, GLU, GLI/GLU Adhesiveness GLI, R/E, SDSV,DDT, GLI/GLU,GY,GLU Springiness DS, PRO Cohesiveness DS, SDSV, PRO, GY, GI, GLI/GLU Gumminess GLI, GLU, GLI/GLU, DS, R/E, SDSV, GI,GY,PRO DS- damaged starch; PRO- protein; GY- gluten yield; GI- gluten index; GLI- gliadin; GLU- glutenin; GLI/GLUgliadin/glutenin ratio; SDSV- SDS sedimentation volume; R/E-resistance to extensibility of gluten Chewiness GLI, DS, R/E, GLI/GLU, GI, PRO, GY, GLU 0.851

9 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 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. Gliadins, gliadin/glutenin 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. 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. In this study we were 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 and mixing 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. 134

10 SUMMARY AND FUTURE RECOMMENDATIONS Wheat is among the three main cereal crops produced in the world, the other two being rice and maize. The wheat production of India was estimated to be million tonnes in crop year (July-June) as against million tonnes in The importance of wheat is attributed to the gluten storage proteins conferring unique viscoelastic properties to dough. Upon removal of the gluten proteins from the flour, the property of forming viscoelastic dough is lost. Studies have revealed that storage proteins can be divided into two major classes- gliadins which determine viscosity and dough extensibility and glutenins that regulate strength and elasticity. It is the unique combination of these two properties that determines the functional properties of dough, ultimately determining the end-use quality. Glutenins are polymeric proteins which are further divided into high and low molecular weight glutenin subunits, whereas gliadins are heterogeneous mixtures of single chained polypeptides which are soluble in 70% aqueous alcohol. Gliadins have been described as heterogeneous mixtures of single chained polypeptides soluble in 70% aqueous alcohol. They account for about half the gluten proteins and have been divided into 4 groups- α- (fastest mobility), β-, γ-, and ω-gliadins (slowest mobility) based on their electrophoretic mobility in A-PAGE at low ph The molecular weight range of gliadins is 30,000 to 75,000 Da. The genes coding the gliadin proteins are located on the short arms of group 1 and 6 chromosomes. They are tightly linked genes located at three homologous loci of the group 1 chromosome- Gli-A1, Gli-B1, and Gli-D1 and group 6 chromosomes- Gli-A2, Gli- B2, and Gli-D2 loci. Most γ- and ω - gliadins are encoded by Gli-1 genes and all the α-/β- and some of the γ-gliadins are encoded by the Gli-2 genes There is a tight linkage between the ω- and γ- gliadins encoded at the Gli 1 locus and LMW glutenin subunits. Gliadin behaves mainly as a viscous liquid when hydrated and confers extensibility, allowing the dough to rise during fermentation, whereas glutenin provides elasticity and strength, preventing the dough from being over-extended and collapsing during fermentation. The balance between gliadins and glutenins is responsible for important rheological properties such as viscosity and elasticity. Due to extensive polymorphism, gliadins have been widely used for cultivar identification in hexaploid and 135

11 tetraploid wheats. The gliadin composition is characteristic of the wheat variety. Differences in the gliadin/glutenin ratio among wheat cultivars are considered an important source of intercultivar variation in physical properties and bread making quality. An inverse relationship exists between the gliadin/glutenin ratio and the elasticity of gluten. Doughs that are too elastic and inextensible give poorer bread making performance than doughs that have an appropriate balance of extensibility and elasticity. Cysteine residues of gliadins mainly form intramolecular disulfide bonds, although α gliadins with odd numbers of cysteine residues have also been reported. Addition of gliadins decreases the mixing tolerance of the dough in the order ω1- > γ- > α- > β- gliadins. Few gliadin alleles and components, such as Gli-B1b, Gli-B2c and Gli-A2b, in bread wheat cultivars, γ-45 in pasta, γ gliadins in cookies, lower gliadin content for chapatti and alteration in Gli 2 loci in tortillas have been reported to improve the product quality. Much of wheat research to date has been focused on the study of glutenins and its importance in the end use quality of wheat has been well established. Although, research has been carried out gliadin proteins as well, but a better understanding of its fundamental properties and how it affects the end quality of the product still needs to be explained. Though, studies on the significance of gliadins on the wheat product quality have been carried out in various parts of the globe. But no single conclusion has been drawn even after numerous studies. Some researchers suggest that gliadin affects the loaf volume of bread whereas others regard glutenin as the sole determinant of the bread quality. Further studies are needed in order to elucidate the precise role of gliadins in dough strength and product quality. Thus, the present research was designed to achieve the following objectives- 1. To study the compositional variation of gluten proteins in wheat varieties. 2. To carry out biochemical characterization of gliadins of diverse wheat varieties. 3. To investigate the relative importance of gliadins to end use qualities of wheat varieties. The investigation entitled Biochemical Characterization of Gliadins of Indian Wheat Varieties was carried out to understand the intervarietal differences in gliadin composition, the electrophoretic banding patterns of gliadins and their role in dough properties and end product quality. Fifteen commonly cultivated Indian wheat varieties were selected for the study including CBW 38, NIAW 917, WH 1021, WH 1025, HUW 234, VL 892, HI 977, MACS 1967, A , 136

12 DBW 16, HW 2004, PBW 590, PBW 550, HI 8498 and C 306. Flours from different wheat varieties was analyzed for physicochemical properties such as moisture, protein, fat, ash, falling number, damaged starch, SDS sedimentation volume, solvent retention capacities (SRC) and alkaline water retention capacity (AWRC). The gluten from each variety was extracted and analyzed for wet and dry gluten, gluten index, resistance to extensibility and gluten baking volume. The gluten subfractions- gliadins and glutenins were extracted from freeze dried gluten powder and compositional variation of gluten proteins in different wheat varieties was studied. The gluten quality and quantity, gliadin and gliadin/glutenin ratio varied widely among the selected wheat varieties. Gluten with higher gluten index, resistance to extensibility and gluten baking volume was present in wheat varieties HI 977, DBW 16, CBW 38, PBW 550 and PBW 590. Gluten quality mainly depends on the relative proportions of glutenin and gliadin and determines end use quality in wheat. The gliadin content of the wheat varieties ranged from 4.16% to 6.33 %. The gliadin/glutenin ratio ranged from 0.77 to Wheat varieties C 306, A and HW 2004 showed gliadin/ glutenin ratio greater than 1 while wheat varieties such as NIAW 917, HI 977, PBW 590 and CBW 38 observed a lower gliadin/glutenin ratio ( ). The gliadins observed a negative correlation with dough stability and positive correlation with dough softening implying that increased percentage of gliadins in the dough decrease the strength of dough. The resistance to extensibility also decreased with the increase in gliadin content of the wheat variety. The dynamic rheological studies were conducted on the gluten extracted from different wheat varieties. An inverse relationship was found between the gliadin/glutenin ratio and storage modulus (G'). The loss modulus (G") was dominant at higher frequency for wheat varieties with higher gliadin content and low Glu 1 score. On the other hand, the storage modulus (G') of the wheat varieties with stronger gluten, higher glutenin and lower gliadin content such as CBW 38 and NIAW 917, was greater than the loss modulus (G") throughout the frequency range. This indicated that the weak glutens underwent substantial structural change from solid-like behavior to liquid-like behavior at higher frequencies while the stronger glutens maintained their elastic characters to a greater extent. The biochemical characterization of gliadins was carried out by Acid PAGE and the influence of the banding patterns of gliadins on product quality was studied. The patterns within each gliadin group of α-, β-, γ- and ω-gliadins were identified by their relative mobility. Each wheat variety 137

13 comprised of different gliadin bands. Thirteen different bands were observed in ω- zone, eight different bands in the γ- zone and twelve bands in the β- and α- zone. Wheat variety WH 1025 reported the highest number of bands in omega zone followed by HI 977 indicating appreciable genetic variability in these varieties for omega gliadin zone. The gliadin band with mobility 0.62 was related with poor gluten quality while the band with mobility 0.69 was associated with stronger gluten. The band with mobility 0.62 was found to be negatively associated with gluten index, R/E, dough stability and positively with dough softening values while the band with mobility 0.69 was found to be positively related with the gluten index, R/E values, dough stability and negatively associated with the dough softening values. The gliadin banding pattern was found to be a reliable parameter for judging the bread making potential of the wheat varieties. It was found that the wheat varieties having band with mobility 0.69 showed higher specific loaf volume while the band with mobility 0.62 was negatively associated with bread quality. However, the gliadin bands showed weak relationship with cookie and white salted noodle quality. Further, the influence of gliadins on the lowering of thermal stability of gluten was studied by Thermo gravimetric analysis (TGA) and the glass transition behavior of the control and gluten obtained from dough with gliadins at 5 and 10% levels. The TGA profile indicated lowering of the thermal stability of gluten upon the addition of gliadins. The values of glass transition temperature (Tg) of control gluten and gluten extracted from dough with gliadins at 5 and 10 % levels also shifted to lower temperature i.e. 66 C, 63 C and 59 C inferring decrease in thermal stability of the gluten. Scanning electron microscopy revealed development of a weaker and open structure with the increase in gliadin levels due to the dilution of gluten. The gliadins also showed significant effects on the rheological properties of flour and dough. The direct addition of gliadins to the flour at increasing levels of 2%, 4%, 6%, 8% and 10% was studied. The addition of gliadins resulted in decreased the peak dough consistency, dough development time, dough stability and increased softening of the dough. The pasting characteristics varied with the varying concentrations of gliadins. The peak, final, breakdown and setback viscosities decreased upon the addition of gliadins. The higher gliadins percentage resulted in dough with greater adhesiveness. The recovery of the gluten increased by up to 98.79% upon addition of 10% gliadins while the gluten quality measured in terms of gluten index was decreased. 138

14 The contribution of gliadins to different products was investigated. The results showed that gliadins had appreciable effects on the bread specific volume and crumb firmness. Gliadins showed negative relationship with bread specific volume (r = ) and positive association with crumb firmness. The gliadins observed a positive association with spread ratio of cookies. Moreover, a positive association of gliadins with the adhesiveness of noodles was found while the cohesiveness values increased with increase in gliadin content. In the present study, an association of the gliadin bands with the bread quality was found. Likewise it is suggested that in future, association of the banding pattern of gliadins with other products such as chapatti, peta bread and other products can be studied and particular bands can be identified which have positive influence on the quality of these products. Moreover the thermal stability and influence of the gliadin subgroups i.e. α-, β-, γ- and ω-gliadins on the development of gluten microstructure can be studied and vital information regarding the influence of gliadins on dough and product characteristics can be obtained. Further quantification of the different gliadin subgroups in the Indian wheat varieties and their association with product characteristics can be carried out. 139