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Relationship of gliadin and glutenin proteins with dough rheology, flour pasting and bread making performance of wheat varieties
LWT - Food Science and Technology 51 (2013) 211e217
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Relationship of gliadin and glutenin proteins with dough rheology, flour pasting and bread making performance of wheat varieties Sheweta Barak, Deepak Mudgil, B.S. Khatkar* Department of Food Technology, G.J. University of Science and Technology, Hisar 125001, Haryana, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 March 2012 Received in revised form 12 September 2012 Accepted 13 September 2012
Four wheat varieties were selected to study the contribution of gliadins and glutenins to the dough rheological parameters, pasting profile and bread quality. The results showed that gliadins, glutenins and Gli/Glu ratio had appreciable effects on the dough stability, dough development time, peak viscosity, breakdown viscosity, bread specific volume and crumb firmness. Glutenins observed a strong negative relation with peak viscosity, breakdown viscosity and pasting temperature while gliadins showed positive association with breakdown viscosity, setback and final viscosity. Gli/Glu ratio was negatively correlated with dough development time (r ¼ 0.988), dough stability (r ¼ 0.940), gluten index (r ¼ 0.975) and protein content (r ¼ 0.837). Protein (r ¼ 0.826), gluten index (r ¼ 0.557), gliadins (r ¼ 0.546) and glutenins (r ¼ 0.939) exhibited positive correlations with bread specific volume. However, higher Gli/Glu ratio was found to be adversely affecting the bread volume and crumb firmness suggesting the importance of a balance of both the gluten subfractions for enhanced bread quality. The results suggested that gliadins are equally important as glutenins in asserting the bread making performance of wheat varieties. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Gliadin Glutenin Bread Crumb firmness Specific volume
1. Introduction Wheat is the principal cereal crop used for bread making because of its baking properties which are attributed to the presence of gluten proteins. The type and quantity of the gluten proteins are important in determining the bread making properties of the wheat flour (Dupont & Altenbach, 2003; Gomez, Ferrero, Calvelo, Anon, & Puppo, 2011). The gluten plays a vital role in determining the appearance and crumb structure of cereal-based products (Demirkesen, Mert, Sumnu, & Sahin, 2010). Protein content alone is not a good loaf volume predictor (Dobraszczyk & Schofield, 2002). Hoseney (1994) and Wieser, Bushuk, and MacRitchie (2006) reported that the gluten complex consists of monomeric gliadin, which is responsible for dough-viscosity & extensibility, and polymeric glutenin, which is responsible for dough strength and elasticity (Gujral & Rosell, 2004; Khatkar, 2006; Wieser et al., 2006). Flour quality depends on a specific balance between gliadin and glutenin and for bread making, an appropriate balance between dough viscosity and elasticity/strength is required (Khatkar, Bell, & Schofield, 1995). Insufficiently elastic gluten leads to low bread loaf volume. Increased elasticity leads to higher loaf volume, but too * Corresponding author. Tel./fax: þ91 1662 263313. E-mail address: [email protected] (B.S. Khatkar). 0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2012.09.011
elastic gluten impedes the expansion of gas cells leading again to lower loaf volume. The high molecular weight glutenin subunits (HMW-GS) are considered as an important factor in determining the bread quality from a particular wheat variety. Payne, Nightingale, Krattiger, and Holt (1987) and Hoseney (1994) reported HMW-GS 5 being associated with good bread making quality and HMW-GS 2 being associated with poor bread making quality. Uthayakumaran et al. (2002) reported that HMW-GS pair 5 þ 10 makes a bigger contribution to dough properties when compared to HMW-GS pair 17 þ 18 and HMW-GS 1 makes the smallest contribution. Previous studies have suggested that gliadins may play an important role in determining the functional property of wheat flour (Barak, Mudgil, & Khatkar, 2012). The influence of gliadins on the bread quality has been debatable for decades. Several studies have demonstrated negative relationship between bread loaf volume and gliadins (Huebner & Bietz, 1986; Ohm et al., 2010; Uthayakumaran et al., 2001) while others reveal the positive effects of gliadins on loaf volume of bread (Khatkar, Fido, Tatham, & Schofield, 2002a, 2002b; Lan, Lan, Wei, Pu, & Zheng, 2009; Park, Bean, Chung, & Seib, 2006). Apart from gluten protein and its subfractions, bread properties are often influenced by other flour components (Dowell et al., 2008; Edwards et al., 2007; Perez Borla, Leonor Motta, Saiza, & Fritza, 2004) and rheological properties of the dough (Gras, Carpenter, & Andersen, 2000). Some researchers
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showed that the bread properties were appreciably affected by Zeleny sedimentation volume and falling number (Czubaszek et al., 2001). Research on determining relationships between the flour properties and the characteristics of the bread still remain a challenge for scientists. Most of the research has been focused on the glutenin proteins, especially the high molecular weight glutenin subunits (HMW-GS). Very little research has been reported on the relationship of flour gliadin content with respect to bread making properties. Thus it seems increasingly likely that, in order to understand the significance of the processes taking place in mixing and baking, it will be necessary to study both the gliadin and glutenin proteins rather than individual HMW-GS class. Thus, the objective of this study was to investigate the rheological and bread making characteristics of the wheat cultivars and the composition of their gluten proteins to find correlations between them. 2. Materials and methods Four wheat samples commonly cultivated in India (Gupta, Mohan, Ram, & Mishra, 2006, pp. 1e156; Shirpurkar, Sonawane, Wagh, & Patil, 2008) PBW 590, PBW 550, C-306 and HW 2004 differing in bread making performance were selected for the study. The samples were tempered at 15.5 g/100 g moisture for 24 h and milled to 65% extraction rate. The wheat flours were examined for the moisture, ash, protein content using standard AACC methods (2000). SDS Sedimentation values of flours were determined according to Axford, McDermott, and Redman (1979). Damaged starch was evaluated by the Chopin SDmatic. Gluten yield and gluten index were estimated by Perten Glutomatic. Gluten yield was expressed on dry basis. All the values reported are means of triplicate determinations. 2.1. Gluten extensibility test Measurements were performed with a TA.XT2i texture analyzer (Stable MicroSystems) using Kieffer dough/gluten extensibility rig with the test speed of 3.3 mm/s and data acquisition rate of 200 pps. The test mode of the instrument used was force in tension.
viscosity at test finish, corresponds to cool paste viscosity; breakdown: difference between peak and trough, indication of breakdown in viscosity of paste during 95 C holding period; and setback: difference between final viscosity and trough. All measurements were reported in Rapid Visco Units (RVU). 2.4. Fractionation of wheat proteins into gliadin and glutenin Wheat flours were defatted by successive extraction with chloroform according to MacRitchie (1987). Flour (100 g) was extracted with 200 ml of chloroform at room temperature and then filtered through filter paper. The extraction was repeated two more times for a total of three extractions. The defatted flour was left to stand at room temperature until dry. Gluten was extracted from defatted flour samples by glutomatic and freeze dried. The freeze dried gluten samples were ground in a pestle mortar. The resulting freeze dried gluten powder from each wheat variety was dissolved in 200 ml of 70% ethanol. The mixture was stirred on a magnetic stirrer for 3 h at 25 C. It was then centrifuged 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. 2.5. Bread making process For 30 g bread making method, the test baking formula was: flour (30 g, 14 g/100 g moisture basis), compressed yeast (1.59 g), salt (0.45 g), sugar (1.8 g), fat (0.9 g), malted barley flour (0.075 g), and ascorbic acid (100 mg/kg, flour basis). Yeast was added as a suspension. As soon as the dough was formed after mixing it was placed in a baking pan and proofed for 90 min at 30 C and 80 g/100 g relative humidity (RH). Doughs were molded after 52, 77 and 90 min in dough moulder. After the final molding, the doughs were placed in lightly greased pans and placed for final proofing for another 36 min at 30 C and 80% RH. Doughs were then baked for 13 min at 232 C. The loaves were removed from the pans and cooled at room temperature. Baking and firmness characteristics were tested 2 h after the loaves were removed from the oven.
2.2. Rheological dough properties 2.6. Characterization of bread Dough rheological studies were conducted on wheat flour by Chopin Mixolab. The information obtained from the recorded curve of the Chopin S protocol included the percentage of water required for the dough to produce a torque of 1.1 0.07 Nm (water absorption, percent); the time to reach maximum torque at 30 C (dough development time, minutes); the elapsed time at which the torque produced is maintained at 1.1 Nm (stability, minutes); the difference between the maximum torque at 30 C and the ending torque after the holding time at 30 C (mechanical dough weakening, Farinograph units (FU)), respectively was used to evaluate the rheological parameters of different flours. 2.3. RVA analysis Paste viscosity properties of wheat flour samples were determined by RVA (Newport Scientific, Australia). Three RVA runs were conducted on each sample and the result were expressed as mean. The measured properties were pasting temperature: temperature of initial viscosity increase; peak viscosity: maximum viscosity recorded during heating and holding cycles, usually occurs soon after heating cycle reaches 95 C; peak time: time required to reach peak; trough: minimum viscosity after peak; final viscosity:
2.6.1. Specific volume The breads were weighed after cooling and their volume (cm3) was determined by rapeseed displacement method. The specific volume (cm3/g) was calculated as loaf volume/bread weight. 2.6.2. Crumb firmness Crumb hardness was measured in a Texture Analyzer TA-XT2i (Stable Microsystems, Surrey, UK) equipped with an aluminum 25 mm diameter cylindrical probe accordance with AACC method 74-09 (AACC 1995). Slices of 2 cm thickness were compressed to 50% of their original height at a crosshead speed of 1 mm/s. The resulting peak force of compression was reported as crumb firmness. Three replicates from three different sets of baking were analyzed and averaged. 2.7. Statistical analysis The experimental data collected was analyzed for significant differences with the help of analysis of variance (ANOVA) conducted using SPSS 16.0 software. The correlation matrix was obtained using SPSS 16.0.
S. Barak et al. / LWT - Food Science and Technology 51 (2013) 211e217
3. Result and discussion
Table 2 HMW-GS and protein characterization of different wheat varieties.
3.1. Flour characteristics analysis
HMW-GS
Glu-A1
Glu-B1
The flour characteristics are summarized in Table 1. The protein content of a wheat variety plays an important role in determining the end use quality. The functional properties of bread dough mainly depend on the proteins forming the gluten network. The SDS sedimentation value, protein content, damaged starch, gluten yield, gluten index and resistance to extensibility (R/E) varied significantly among the varieties. HW 2004 reported the highest SDS sedimentation value while PBW 590 had the highest protein content (14.17 g/100 g). The quantity and quality of gluten is an indicator of the baking quality. Gluten plays a crucial role in creating dough structure and baking bread. It affects the stability of the dough and bread volume by forming the skeleton of wheat dough that combines the remaining ingredients and additives to the dough. HW 2004 yielded lowest protein content and gluten yield (7.92 g/100 g) while highest gluten yield was shown by PBW 550 (10.07 g/100 g). The gluten index, which describes the quality of gluten, increased with the increase in glutenin as indicated by a positive correlation between them inferring that the presence of glutenin improves the gluten quality. The wheat variety HW 2004 displayed much higher damaged starch than other varieties owing to its higher kernel hardness. PBW 550 reported the highest R/E ratio (1.45) while the variety C 306 (0.43) had the lowest. This difference in R/E could be attributed to the decrease levels of glutenins in C 306. Higher glutenin levels make the dough more elastic thus giving dough its property of resistance to extension while higher gliadin content increases the extensibility of the dough. The correlation data also showed that glutenin content was highly positively correlated with R/E (r ¼ 0.751) while the contribution of gliadins were negligible (r ¼ 0.045). It was found that the percentage of glutenins and gliadins increased as the protein content of the wheat variety increased as evident from a positive correlation among the above parameters. However, the increase was more pronounced for glutenins as compared to the gliadins indicating that the glutenin content increase substantially with increase in protein content of wheat variety.
PBW 590 PBW 550 HW 2004 C 306
2* 2* N N
5 5 2 2
3.2. HMW-GS and protein characterization of wheat varieties The HMW-GS compositions of the four varieties are presented in Table 2. A number of studies have shown that the strength of dough is related to the amount and type of HMW glutenin subunit (Hoseney, 1994). Variations in both quantity and quality of glutenin strongly determine the variations in bread making performance (Veraverbeke & Delcour, 2002). Researches in the past have shown that glutenin subunits 1 and 5 þ 10 are superior to the allelic null and 2 þ 12 subunits, respectively (Payne, Holt, Jackson, & Law, 1984). It is evident that PBW 590 and PBW 550 had the same HMW-GS composition i.e. 2*, 5 þ 10, 7 þ 9 and a high Glu 1 score of 9 while the other two varieties HW 2004 and C306 had the Table 1 Flour quality characteristics. Variety
Moisture SDSV DS Protein GY GI R/E (g/100 g) (ml) (g/100 g) (g/100 g) (g/100 g) (g/100 g)
PBW 590 PBW 550 HW 2004 C 306
11.94b 13.05d 11.32a 12.76c
37c 34b 47d 30a
6.02b 5.82a 8.55d 6.14c
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14.17d 13.56e 10.06a 10.85b
10.03c 10.07d 7.92a 9.20b
78.90d 71.85c 56.80b 49.10a
1.02c 1.45d 0.53b 0.43a
SDSV e SDS sedimentation volume; DS e damaged starch; GY e gluten yield; GI e gluten index; R/E resistibility/extensibility of gluten. Values followed by different letters are significantly different at P < 0.05.
þ þ þ þ
10 10 12 12
Glu-D1
Glu1 score
Gli (g/100 g)
Glu (g/100 g)
Gli/Glu
7þ9 7þ9 20 20
9 9 4 4
4.57b 5.09c 4.20a 5.49d
5.53d 5.29c 3.99a 4.66b
0.82a 0.96b 1.05c 1.17d
Gli e gliadins; Glu e glutenins; Gli/Glu e gliadin to glutenin ratio. Values followed by different letters are significantly different at P < 0.05.
composition N, 2 þ 12, 20 and a low Glu 1 score of 4. The gliadin to glutenin ratio (Gli/Glu) varied widely among the varieties with C 306 exhibiting the highest ratio of 1.17. Though the Glu 1 scores of varieties PBW 590 and PBW 550 were similar, their Gli/Glu ratio varied significantly (0.82 and 0.96). Similar was the case with the varieties HW 2004 and C 306 which reported the Gli/Glu ratio 1.05 and 1.17, respectively. It can be concluded from the results that the varieties with lower Glu 1 score have higher gliadin content and vice versa. Moreover, from Tables 2 and 4 it can be deduced that flour from wheat varieties having HMW glutenin subunits 2*, 5 þ 10 and 7 þ 9 had higher dough development time and dough stability while flours with subunits N, 2 þ 12 and 20 resulted in doughs with lower stability values and higher dough weakening. This could be attributed to the fact that subunit 5 have the largest molecular weight and plays an important role in extending the polymer chains during glutenin synthesis (Huang & Khan, 1997a). Further, the subunit 5 and 2*, because of their larger molecular size contributes greater to the dough mixing properties than the other subunits (Huang & Khan, 1997b). Also it has been suggested that the positive effect of the subunits 5 þ 10 is largely due to the presence of an extra cysteine residue in the subunit 5 as compared to other subunits (Weiser, 2007). 3.3. Flour pasting characteristics The rapid visco analyzer indicates starch viscosity by measuring the resistance of flour and water slurry to the stirring action of a paddle. The highest point during the heating cycle is the peak viscosity. The RVA pasting profiles of the wheat varieties are presented in Table 3. The variety PBW 590 reported the highest peak viscosity of 232.75 RVU whereas; the highest final viscosity of 237.58 RVU was reported by C 306. Pasting temperatures of flours from the different wheat varieties ranged from 66.85 (HW 2004) to 68.75 (PBW 590). Pasting temperature indicates the minimum temperature required to cook as well as the temperature at which the viscosity increases during the heating process. The flours with higher protein content took more time to reach peak viscosity as evident from higher peak time. Moreover, the peak viscosity observed a strong negative correlation with protein. The peak viscosity indicates the maximum swelling of the starch granules which could be adversely affected by the presence of higher protein which competes for the water along with the starch granules. Peak viscosity and breakdown viscosity showed strong negative correlation (r ¼ 0.979, r ¼ 0.700) with the pasting temperature while Table 3 RVA pasting properties of flours. Variety
PV (RVU) BKD (RVU)
Trough (RVU)
PBW 590 PBW 550 HW 2004 C 306
194.92a 213.58b 232.75d 217.42c
135.67d 98.50b 234.17c 123.58a 91.00a 214.58a 126.67c 102.42c 229.08b 125.00b 112.58d 237.58d
68.08a 78.83b 92.25c 97.58d
Setback FV (RVU) (RVU)
Peak time Pasting (min) temp ( C) 6.13b 6.13b 6.13b 5.87a
68.75d 67.60b 66.85a 67.80c
PV e peak viscosity; BKD e breakdown; FV e final viscosity; Pasting Temp e pasting temperature. Values followed by different letters are significantly different at P < 0.05.
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Table 4 Dough rheological characteristics.
Table 6 Correlation between RVA properties and flour characteristics.
Variety
WAC (%)
DDT (min)
STA (min)
DW (FU)
PBW 590 PBW 550 HW 2004 C 306
56.8b 57.9c 60.2d 56.5a
4.0d 3.0c 2.0b 1.5a
6.5c 4.5b 1.5a 1.5a
45a 71b 116c 122d
Protein DS SDSV GY DDT STA DW GLI GLU GLI/GLU
WAC e water absorption capacity; DDT e dough development time; STA e dough stability; DW e dough weakening. Values followed by different letters are significantly different at P < 0.05.
trough viscosity observed a positive correlation (r ¼ 0.735). Breakdown indicates the stability of the paste during cooking with lower breakdown viscosity inferring better resistance to shear thinning of flour pastes. Flours with lower protein content showed higher breakdown viscosity. Setback is the recovery of the viscosity during cooling of the heated flour suspension. It was observed that the setback viscosity was higher for flours with lower protein content. Highest setback viscosity was reported by C 306 (112.58 RVU) while PBW 550 showed the lowest setback viscosity (91 RVU). Final viscosity is dependent on the starch content, amylose, amylopectin, amylose/amylopectin ratio (Tester & Morrison, 1990). Final viscosity of the flours increases due to the aggregation of the amylose molecules (Miles, Morris, Orford & Ring, 1985). Final viscosity was found to be, though not significantly, but inversely related with protein and glutenin content of the flour while it was positively related with the gliadin content and gliadin to glutenin ratio. The peak viscosity increased with increase in the damaged starch content. A possible explanation is that damaged starch absorbs much more water than undamaged starch granules. Thus, higher damaged starch content absorbed more water and swell upon heating thereby increasing the viscosity of the flour paste. 3.4. Dough rheological characteristics The rheological properties of dough are critical in food manufacturing. The results of dough rheological characteristics are depicted in Table 4. As expected, the highest dough stability was shown by PBW 590 followed by PBW 550 as they had a high Glu 1 score of 9, higher protein contents and lower Gli/Glu ratios, respectively (Table 2). PBW 590 reported the highest dough development time while C 306 reported the lowest value for the parameter. The dough stability decreased markedly from 6.5 min (PBW 590) to 1.5 min (HW 2004 and C 306) suggesting a low tolerance of flour to mixing. The observed weakening of the dough could be due to combined effect of higher level of gliadins, presence of weaker HMW glutenin subunits and lower gluten content of the
Peak h
BKD
Trough
Setback
Final h
Peak time
Pasting temp
0.883 0.772 0.487 0.862 0.811 0.892 0.853 0.178 0.931 0.721
0.925 0.449 0.010 0.705 0.999** 0.987* 0.994** 0.289 0.826 0.982*
0.486 0.104 0.177 0.264 0.723 0.681 0.654 0.461 0.444 0.739
0.686 0.193 0.188 0.466 0.706 0.659 0.715 0.313 0.512 0.726
0.347 0.115 0.073 0.271 0.237 0.218 0.283 0.030 0.215 0.247
0.434 0.255 0.643 0.070 0.676 0.544 0.606 0.766 0.200 0.768
0.768 0.743 0.523 0.784 0.702 0.792 0.739 0.226 0.851 0.608
DS e damaged starch; SDSV e SDS sedimentation volume; GY e gluten yield; DDT e dough development time; STA e dough stability; DW e dough weakening. GLI e gliadins; GLU e glutenins; GLI/GLU e gliadin to glutenin ratio; **Correlation is significant at 0.01 level, *Correlation is significant at 0.05 level.
flour of the latter varieties. Both the varieties (HW 2004 and C 306) with high gliadin to glutenin ratio and low Glu 1 score of 4 also showed high dough weakening. The study also revealed that varieties with similar HMW-GS composition but different Gli/Glu ratio (PBW 590 and PBW 550) also differed in their dough rheological properties. PBW 590 came out to be stronger flour as compared to PBW 550. This could be due to the higher percentage of gliadins in PBW 550 as compared to the percentage of glutenin. This observation was in concordance with the studies of MacRitchie (1987) and Khatkar et al. (2002a) who found that addition of increased levels of gliadin rich fraction to base flour shortened the mixing time and stability of dough. Similar results were also sought in this study, where gliadin content exhibited a negative correlation (r ¼ 0.139) with dough stability (Table 5) while glutenin content showed a strong positive correlation (r ¼ 0.903). The DDT and dough stability increased with the protein content of the wheat varieties. DDT and dough stability showed a significant negative correlation (r ¼ 0.989 and r ¼ 0.997) with dough weakening. It was observed that the quality of the gluten in terms of gluten index was also significantly positively associated with dough stability while dough weakening was negatively affected by higher gluten index values. The results were in agreement with other authors (Collar, Bollain, & Rosell, 2007) who reported a similar correlation in their study. Also, it was observed that flours with higher R/E ratio had higher dough development time and dough stability. Peak viscosity was found to be negatively correlated (Table 6) with DDT and dough stability (r ¼ 0.811, r ¼ 0.892) while dough weakening observed a positive correlation with peak viscosity. The above data further strengthened the negative association of protein with peak viscosity i.e. the stronger flours with higher protein content, dough development
Table 5 Correlation among gluten protein subfractions and flour characteristics.
PRO DS SDSV GY GI R/E DDT STA DW GLI GLU GLI/GLU
PRO
DS
SDSV
GY
GI
R/E
DDT
STA
DW
GLI
GLU
GLI/GLU
1 0.742 0.366 0.918 0.919 0.845 0.908 0.965* 0.961* 0.088 0.969* 0.837
1 0.896 0.946 0.418 0.549 0.419 0.582 0.542 0.724 0.875 0.272
1 0.703 0.029 0.201 0.021 0.169 0.116 0.946 0.571 0.177
1 0.689 0.751 0.677 0.800 0.777 0.474 0.979* 0.557
1 0.819 0.986* 0.966* 0.984* 0.307 0.800 0.975*
1 0.721 0.747 0.781 0.045 0.751 0.680
1 0.982* 0.989* 0.322 0.806 0.988*
1 0.997** 0.139 0.903 0.940
1 0.184 0.881 0.955*
1 0.300 0.466
1 0.704
1
PRO e protein; DS e damaged starch; SDSV e SDS sedimentation volume; GY e gluten yield; GI e gluten index; R/E resistibility/extensibility of gluten; DDT e dough development time; STA e dough stability; DW e dough weakening GLI e gliadins; GLU e glutenins; GLI/GLU e gliadin to glutenin ratio. **Correlation is significant at 0.01 level, *Correlation is significant at 0.05 level.
S. Barak et al. / LWT - Food Science and Technology 51 (2013) 211e217 Table 7 Bread quality analysis. Wheat variety
CF (g)
SV (cm3/g)
PBW 590 PBW 550 HW 2004 C 306
169.95a 318.05c 442.10d 213.45b
3.31d 2.97c 1.68a 2.86b
CF e crumb firmness; SV e specific volume. Values followed by different letters are significantly different at P < 0.05.
time and dough stability showed lower peak viscosities. Further, the pasting temperature increased with increasing values for DDT and dough stability values indicating that stronger flours with higher protein content have higher pasting temperatures. 3.5. Bread quality The quality of bread was assessed through bread specific volume and crumb firmness measurements (Table 7). The specific volume of the breads ranged from 1.68 to 3.31. A decrease in bread specific volume was observed on moving from PBW 590, PBW 550 and C 306 to HW 2004 (Fig. 1). A significant decrease in bread specific volume can be explained as the lower ability of gluten network to enclose the carbon dioxide produced during fermentation. The bread firmness values also varied significantly among the varieties. The crumb firmness of PBW 550 was significantly higher (318.05 g) than that obtained for PBW 590 (169.95 g). The higher Glu 1 score of PBW 550 was not reflected in a higher specific volume. The significant lower firmness of PBW 590, thus softer texture, than PBW 550 probably could be due to higher quantity of HMW-GS in the former variety leading to better loaf volume and thus lower crumb firmness. Other reasons may be the higher protein content, better gluten quality and lower Gli/Glu ratio. It is noteworthy that both the wheat varieties PBW 550 and PBW 590 possessing the same HMW-GS composition varied significantly in their bread quality. Thus, the subunit 2* and 5 þ 10 subunits had good contribution to the bread quality of wheat, therefore these may be introgressed into the genetic background of wheat varieties to improve their bread making quality. The specific volume of HW 2004 was appreciably lower than C 306 due to its poor gluten yield (7.92 g/100 g) and low gluten quality measured in terms of gluten index (56.80%). 3.6. Correlation among bread quality, protein composition, gluten subfractions, pasting properties and dough properties of flour All the studied factors as well as the interaction among them exerted a very significant effect on the dough rheological properties of the samples and bread quality (Table 8). The effect of protein
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Table 8 Correlation among gluten protein subfractions, flour properties, pasting properties and bread quality.
Protein RE Gluten yield Gluten index Dough development time Stability Dough weakening Gliadin Glutenin Gliadin/glutenin ratio Peak viscosity Breakdown Trough Setback Final viscosity Peak time Pasting temperature
Bread firmness
Specific volume
0.576 0.116 0.732 0.307 0.405 0.542 0.473 0.521 0.737 0.287 0.862 0.409 0.516 0.198 0.453 0.398 0.931
0.826 0.523 0.954* 0.557 0.592 0.733 0.687 0.546 0.939 0.459 0.916 0.612 0.377 0.200 0.026 0.146 0.898
*Correlation is significant at 0.05 level.
content of the flour on the loaf volume of bread has been well documented in literature. The protein content of the flour observed a strong positive correlation (r ¼ 0.826) with the specific volume of the bread. Most of the factors depicting the protein quality were found to be positively correlated with the specific volume of the bread. Gluten yield showed a significantly strong correlation with the specific volume (r ¼ 0.954) of bread. R/E showed slight negative correlation (r ¼ 0.116) with bread firmness indicating that a balance of elasticity and extensibility of dough is important to produce bread of lower firmness and higher loaf volume. On the other hand, gluten index observed a negative correlation with bread firmness indicating the role of strong gluten on lowering the firmness of bread. Gliadins and glutenins observed negative correlation with crumb firmness, however glutenins showed a higher negative correlation (r ¼ 0.737) with bread crumb firmness implying that higher glutenin content results in softer bread. The glutenins observed a strong positive correlation with the specific volume of bread. Lundh and MacRitchie (1989) also found that varieties differing in their glutenin content differed in their bread making performance with higher glutenins yielding excellent bread making quality. The effect of gliadins on the bread loaf volume has been debatable since decades. Park et al. (2006) reported that percentage of gliadins based on flour and protein content of wheat varieties exhibited positive correlation (r ¼ 0.730) with bread loaf volume. Similarly, Khatkar et al. (2002a) also reported that addition of total gliadins and its subgroups (a-, b-, gand u-gliadins) to the dough significantly improved its bread making performance. In the present study, a similar positive
Fig. 1. Bread prepared from different wheat varieties.
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relationship was found between the percentage of gliadins in wheat variety and its specific volume. Gliadins exhibited a positive correlation (r ¼ 0.546) with the specific volume of bread. Many researchers have reported difference in gliadin to glutenin ratio as an important criterion in determining bread making quality of a wheat variety (Kasarda, 1994). Khatkar and Schofield (2002) reported that gluten-water doughs from poor quality wheat varieties exhibited lower elasticity and greater viscosity as compared to those from good quality wheat varieties. Overall, the Gli/Glu ratio was positively associated with bread firmness and negatively with the specific volume implying that the balance of gliadins and glutenins is important in judging the suitability of a wheat variety for bread making. In our attempt to study the effect of RVA flour pasting properties on the bread quality, it was found that flours with higher peak viscosity degraded the quality of bread. This could be attributed to the fact that flours with higher protein content inhibit the swelling of the starch granules, thus lowering the peak viscosity. Breakdown was also found to be negatively associated with the specific volume of the bread. Moreover, flours with higher trough viscosity gave breads with a softer texture and higher loaf volume. Final viscosity was found to be negatively associated with crumb firmness and positively with the specific volume of bread. The dough properties such as DDT and dough stability exhibited a negative relationship with the bread firmness (r ¼ 0.405 and r ¼ 0.542, respectively) and positive correlation with specific volume (r ¼ 0.592 and r ¼ 0.733). Thus, strong flours with higher DDT and dough stability prove to produce bread of superior quality. On the other hand, flours with higher dough weakening produce bread of inferior quality. Thus, the information above can be of assistance to breeders to select for acceptable rheological and baking characteristics for bread making. Huang, Yun, Quail, and Moss (1996) reported that the dough development time, dough stability, had significant positive correlation with specific volume of Chinese steamed bread. 4. Conclusion The study allowed us to understand the effects of various flour components on bread quality. The gliadins and glutenins provided useful predictions of technological quality of the wheat varieties investigated. Also, in the literature, there was no study on investigating the effect of dough pasting properties on the bread making potential of the wheat varieties and the contribution of gliadins and glutenins to the flour pasting properties. Breeders are interested in parameters that are highly heritable and reproducible and that these parameters should provide information about dough mixing properties. Being important breeding objectives, doughmixing properties, the factors affecting these properties and the information they provide in improving the bread making quality have been discussed in this paper. These parameters can be identified as selection criteria to assist wheat breeders in selecting acceptable rheological and baking criteria for bread making. The gluten subfractions had substantial effect on the dough rheological properties and RVA pasting profile of the wheat varieties. Baking tests showed that gliadins and glutenins had positive effect on the bread specific volume, however, the effect of glutenins was more pronounced. The Gli/Glu ratio was positively associated with the bread crumb firmness. The bread crumb firmness reduced with the increase in pasting properties of the flours. Dough that had longer dough development time and dough stability performed well in the bread baking test. The subunit 2* and 5 þ 10 subunits contributed significantly to the improved bread quality of wheat. Thus, it was found that gliadins and glutenins contributed significantly to the dough & flour pasting properties and bread quality.
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St. Paul, Minnesota, USA: American Association of Cereal Chemists, Inc. Huang, D. Y., & Khan, K. (1997a). Characterization and quantitation of native glutenin aggregates by multi-stacking sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) procedures. Cereal Chemistry, 74, 229e234. Huang, D. Y., & Khan, K. (1997b). Quantitative determination of high molecular weight glutenin subunits of hard red spring wheat by SDS-PAGE. Ii. Quantitative effects of individual subunits on breadmaking quality characteristics. Cereal Chemistry, 74, 786e790. Huang, S., Yun, S. H., Quail, K., & Moss, R. (1996). Establishment of flour quality guidelines for northern style Chinese steamed bread. Journal of Cereal Science, 24, 179e185. Huebner, F. R., & Bietz, J. A. (1986). Assessment of the potential breadmaking quality of hard wheats by reversed-phase high performance liquid chromatography of gliadins. Journal of Cereal Science, 4, 379e388. Kasarda, D. D. (1994). Glutenin structure in relation to wheat quality. In Y. Pomeranz (Ed.), Wheat is unique (pp. 73e106). St. Paul, Manhatten: AACC. Khatkar, B. S. (2006). Effects of high Mr glutenin subunits on dynamic rheological properties and bread making qualities of wheat gluten. Journal of Food Science and Technology, 43, 382e387. Khatkar, B. S., Bell, A. E., & Schofield, J. D. (1995). The dynamic rheological properties of glutens and gluten subfractions from wheats of good and poor bread-making quality. Journal of Cereal Science, 22, 29e44. Khatkar, B. S., Fido, R. J., Tatham, A. S., & Schofield, J. D. (2002a). Functional properties of wheat gliadins: 1. Effects on mixing characteristics and bread making quality. Journal of Cereal Science, 35, 299e306. Khatkar, B. S., Fido, R. J., Tatham, A. S., & Schofield, J. D. (2002b). Functional properties of wheat gliadins: 2. Effects on dynamic rheological properties of wheat gluten. Journal of Cereal Science, 35, 307e313. Khatkar, B. S., & Schofield, J. D. (2002). Dynamic rheology of wheat flour dough. I. Non-linear viscoelastic behaviour. Journal of the Science of Food and Agriculture, 82, 827e829. Lan, W. X., Lan, X. J., Wei, Y. M., Pu, Z. E., & Zheng, Y. L. (2009). Quality evaluation of gliadins from Zhengmai 9023 a99E18 in wheat. Journal of Plant Sciences, 4, 1e9. Lundh, G., & MacRitchie, F. (1989). Size exclusion HPLC characterisation of gluten protein fractions varying in bread making potential. Journal of Cereal Science, 10, 247e253.
S. Barak et al. / LWT - Food Science and Technology 51 (2013) 211e217 MacRitchie, F. (1987). Evaluation of contributions from wheat protein fractions to dough mixing and breadmaking. Journal of Cereal Science, 6, 259e268. Miles, M. J., Morris, V. J., Orford, P. D., & Ring, S. G. (1985). The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydrate Research, 135, 271e281. Ohm, J., Hareland, G., Simsek, S., Seabourn, B., Maghirang, E., & Dowell, F. (2010). Molecular weight distribution of proteins in hard red spring wheat: relationship to quality parameters and intrasample uniformity. Cereal Chemistry, 87, 553e560. Park, S. H., Bean, S. R., Chung, O. K., & Seib, P. A. (2006). Levels of protein and protein composition in hard winter wheat flours and the relationship to breadmaking. Cereal Chemistry, 83, 418e423. Payne, P. I., Holt, L. M., Jackson, E. A., & Law, C. N. (1984). Wheat storage proteins: their genetics and their potential for manipulation by plant breeding. Philosophical Transactions of Royal Society B, 304, 359e371. Payne, P. I., Nightingale, M. A., Krattiger, A. F., & Holt, L. M. (1987). The relationship between HMW glutenin subunit composition and bread making quality of British grown wheat varieties. Journal of the Science of Food and Agriculture, 40, 51e65. Perez Borla, O. P., Leonor Motta, E., Saiza, A., & Fritza, R. (2004). Quality parameters and baking performance of commercial gluten flours. LWT e Food Science and Technology, 37, 723e729.
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Shirpurkar, G. N., Sonawane, P. D., Wagh, M. P., & Patil, D. T. (2008). Performance of wheat genotypes under restricted irrigation conditions. Agricultural Science Digest, 28, 57e58. Tester, R. F., & Morrison, W. R. (1990). Swelling and amylosization of cereal starches. I. Effects of amylopectin, amylose and lipids. Cereal Chemistry, 67, 551e557. Uthayakumaran, S., Beasley, H. L., Stoddard, F. L., Keentok, M., Phan-Thien, N., Tanner, R. I., et al. (2002). Synergistic and additive effects of three HMW glutenin subunit loci. I. Effects on wheat dough rheology. Cereal Chemistry, 79, 294e300. Uthayakumaran, S., Tomoskozi, S., Tatham, A. S., Savage, A. W. J., Gianibelli, M. C., Stoddard, F. L., et al. (2001). Effects of gliadin fractions on functional properties of wheat dough depending on molecular size and hydrophobicity. Cereal Chemistry, 78, 138e141. Veraverbeke, W. S., & Delcour, J. A. (2002). Wheat protein composition and properties of wheat glutenin in relation to breadmaking functionality. Critical Reviews in Food Science and Nutrition, 42, 179e208. Weiser, H. (2007). Chemistry of glutenin proteins. Food Microbiology, 24, 115e119. Wieser, H., Bushuk, W., & MacRitchie, F. (2006). The polymeric glutenins. In C. W. Wrigley, F. Bekes, & W. Bushuk (Eds.), Gliadin and glutenin. The unique balance of wheat quality (pp. 213e240). St. Paul, Minnesota, USA: American Association of Cereal Chemists, Inc.
Contents lists available at SciVerse ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Relationship of gliadin and glutenin proteins with dough rheology, flour pasting and bread making performance of wheat varieties Sheweta Barak, Deepak Mudgil, B.S. Khatkar* Department of Food Technology, G.J. University of Science and Technology, Hisar 125001, Haryana, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 March 2012 Received in revised form 12 September 2012 Accepted 13 September 2012
Four wheat varieties were selected to study the contribution of gliadins and glutenins to the dough rheological parameters, pasting profile and bread quality. The results showed that gliadins, glutenins and Gli/Glu ratio had appreciable effects on the dough stability, dough development time, peak viscosity, breakdown viscosity, bread specific volume and crumb firmness. Glutenins observed a strong negative relation with peak viscosity, breakdown viscosity and pasting temperature while gliadins showed positive association with breakdown viscosity, setback and final viscosity. Gli/Glu ratio was negatively correlated with dough development time (r ¼ 0.988), dough stability (r ¼ 0.940), gluten index (r ¼ 0.975) and protein content (r ¼ 0.837). Protein (r ¼ 0.826), gluten index (r ¼ 0.557), gliadins (r ¼ 0.546) and glutenins (r ¼ 0.939) exhibited positive correlations with bread specific volume. However, higher Gli/Glu ratio was found to be adversely affecting the bread volume and crumb firmness suggesting the importance of a balance of both the gluten subfractions for enhanced bread quality. The results suggested that gliadins are equally important as glutenins in asserting the bread making performance of wheat varieties. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Gliadin Glutenin Bread Crumb firmness Specific volume
1. Introduction Wheat is the principal cereal crop used for bread making because of its baking properties which are attributed to the presence of gluten proteins. The type and quantity of the gluten proteins are important in determining the bread making properties of the wheat flour (Dupont & Altenbach, 2003; Gomez, Ferrero, Calvelo, Anon, & Puppo, 2011). The gluten plays a vital role in determining the appearance and crumb structure of cereal-based products (Demirkesen, Mert, Sumnu, & Sahin, 2010). Protein content alone is not a good loaf volume predictor (Dobraszczyk & Schofield, 2002). Hoseney (1994) and Wieser, Bushuk, and MacRitchie (2006) reported that the gluten complex consists of monomeric gliadin, which is responsible for dough-viscosity & extensibility, and polymeric glutenin, which is responsible for dough strength and elasticity (Gujral & Rosell, 2004; Khatkar, 2006; Wieser et al., 2006). Flour quality depends on a specific balance between gliadin and glutenin and for bread making, an appropriate balance between dough viscosity and elasticity/strength is required (Khatkar, Bell, & Schofield, 1995). Insufficiently elastic gluten leads to low bread loaf volume. Increased elasticity leads to higher loaf volume, but too * Corresponding author. Tel./fax: þ91 1662 263313. E-mail address: [email protected] (B.S. Khatkar). 0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2012.09.011
elastic gluten impedes the expansion of gas cells leading again to lower loaf volume. The high molecular weight glutenin subunits (HMW-GS) are considered as an important factor in determining the bread quality from a particular wheat variety. Payne, Nightingale, Krattiger, and Holt (1987) and Hoseney (1994) reported HMW-GS 5 being associated with good bread making quality and HMW-GS 2 being associated with poor bread making quality. Uthayakumaran et al. (2002) reported that HMW-GS pair 5 þ 10 makes a bigger contribution to dough properties when compared to HMW-GS pair 17 þ 18 and HMW-GS 1 makes the smallest contribution. Previous studies have suggested that gliadins may play an important role in determining the functional property of wheat flour (Barak, Mudgil, & Khatkar, 2012). The influence of gliadins on the bread quality has been debatable for decades. Several studies have demonstrated negative relationship between bread loaf volume and gliadins (Huebner & Bietz, 1986; Ohm et al., 2010; Uthayakumaran et al., 2001) while others reveal the positive effects of gliadins on loaf volume of bread (Khatkar, Fido, Tatham, & Schofield, 2002a, 2002b; Lan, Lan, Wei, Pu, & Zheng, 2009; Park, Bean, Chung, & Seib, 2006). Apart from gluten protein and its subfractions, bread properties are often influenced by other flour components (Dowell et al., 2008; Edwards et al., 2007; Perez Borla, Leonor Motta, Saiza, & Fritza, 2004) and rheological properties of the dough (Gras, Carpenter, & Andersen, 2000). Some researchers
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showed that the bread properties were appreciably affected by Zeleny sedimentation volume and falling number (Czubaszek et al., 2001). Research on determining relationships between the flour properties and the characteristics of the bread still remain a challenge for scientists. Most of the research has been focused on the glutenin proteins, especially the high molecular weight glutenin subunits (HMW-GS). Very little research has been reported on the relationship of flour gliadin content with respect to bread making properties. Thus it seems increasingly likely that, in order to understand the significance of the processes taking place in mixing and baking, it will be necessary to study both the gliadin and glutenin proteins rather than individual HMW-GS class. Thus, the objective of this study was to investigate the rheological and bread making characteristics of the wheat cultivars and the composition of their gluten proteins to find correlations between them. 2. Materials and methods Four wheat samples commonly cultivated in India (Gupta, Mohan, Ram, & Mishra, 2006, pp. 1e156; Shirpurkar, Sonawane, Wagh, & Patil, 2008) PBW 590, PBW 550, C-306 and HW 2004 differing in bread making performance were selected for the study. The samples were tempered at 15.5 g/100 g moisture for 24 h and milled to 65% extraction rate. The wheat flours were examined for the moisture, ash, protein content using standard AACC methods (2000). SDS Sedimentation values of flours were determined according to Axford, McDermott, and Redman (1979). Damaged starch was evaluated by the Chopin SDmatic. Gluten yield and gluten index were estimated by Perten Glutomatic. Gluten yield was expressed on dry basis. All the values reported are means of triplicate determinations. 2.1. Gluten extensibility test Measurements were performed with a TA.XT2i texture analyzer (Stable MicroSystems) using Kieffer dough/gluten extensibility rig with the test speed of 3.3 mm/s and data acquisition rate of 200 pps. The test mode of the instrument used was force in tension.
viscosity at test finish, corresponds to cool paste viscosity; breakdown: difference between peak and trough, indication of breakdown in viscosity of paste during 95 C holding period; and setback: difference between final viscosity and trough. All measurements were reported in Rapid Visco Units (RVU). 2.4. Fractionation of wheat proteins into gliadin and glutenin Wheat flours were defatted by successive extraction with chloroform according to MacRitchie (1987). Flour (100 g) was extracted with 200 ml of chloroform at room temperature and then filtered through filter paper. The extraction was repeated two more times for a total of three extractions. The defatted flour was left to stand at room temperature until dry. Gluten was extracted from defatted flour samples by glutomatic and freeze dried. The freeze dried gluten samples were ground in a pestle mortar. The resulting freeze dried gluten powder from each wheat variety was dissolved in 200 ml of 70% ethanol. The mixture was stirred on a magnetic stirrer for 3 h at 25 C. It was then centrifuged 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. 2.5. Bread making process For 30 g bread making method, the test baking formula was: flour (30 g, 14 g/100 g moisture basis), compressed yeast (1.59 g), salt (0.45 g), sugar (1.8 g), fat (0.9 g), malted barley flour (0.075 g), and ascorbic acid (100 mg/kg, flour basis). Yeast was added as a suspension. As soon as the dough was formed after mixing it was placed in a baking pan and proofed for 90 min at 30 C and 80 g/100 g relative humidity (RH). Doughs were molded after 52, 77 and 90 min in dough moulder. After the final molding, the doughs were placed in lightly greased pans and placed for final proofing for another 36 min at 30 C and 80% RH. Doughs were then baked for 13 min at 232 C. The loaves were removed from the pans and cooled at room temperature. Baking and firmness characteristics were tested 2 h after the loaves were removed from the oven.
2.2. Rheological dough properties 2.6. Characterization of bread Dough rheological studies were conducted on wheat flour by Chopin Mixolab. The information obtained from the recorded curve of the Chopin S protocol included the percentage of water required for the dough to produce a torque of 1.1 0.07 Nm (water absorption, percent); the time to reach maximum torque at 30 C (dough development time, minutes); the elapsed time at which the torque produced is maintained at 1.1 Nm (stability, minutes); the difference between the maximum torque at 30 C and the ending torque after the holding time at 30 C (mechanical dough weakening, Farinograph units (FU)), respectively was used to evaluate the rheological parameters of different flours. 2.3. RVA analysis Paste viscosity properties of wheat flour samples were determined by RVA (Newport Scientific, Australia). Three RVA runs were conducted on each sample and the result were expressed as mean. The measured properties were pasting temperature: temperature of initial viscosity increase; peak viscosity: maximum viscosity recorded during heating and holding cycles, usually occurs soon after heating cycle reaches 95 C; peak time: time required to reach peak; trough: minimum viscosity after peak; final viscosity:
2.6.1. Specific volume The breads were weighed after cooling and their volume (cm3) was determined by rapeseed displacement method. The specific volume (cm3/g) was calculated as loaf volume/bread weight. 2.6.2. Crumb firmness Crumb hardness was measured in a Texture Analyzer TA-XT2i (Stable Microsystems, Surrey, UK) equipped with an aluminum 25 mm diameter cylindrical probe accordance with AACC method 74-09 (AACC 1995). Slices of 2 cm thickness were compressed to 50% of their original height at a crosshead speed of 1 mm/s. The resulting peak force of compression was reported as crumb firmness. Three replicates from three different sets of baking were analyzed and averaged. 2.7. Statistical analysis The experimental data collected was analyzed for significant differences with the help of analysis of variance (ANOVA) conducted using SPSS 16.0 software. The correlation matrix was obtained using SPSS 16.0.
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3. Result and discussion
Table 2 HMW-GS and protein characterization of different wheat varieties.
3.1. Flour characteristics analysis
HMW-GS
Glu-A1
Glu-B1
The flour characteristics are summarized in Table 1. The protein content of a wheat variety plays an important role in determining the end use quality. The functional properties of bread dough mainly depend on the proteins forming the gluten network. The SDS sedimentation value, protein content, damaged starch, gluten yield, gluten index and resistance to extensibility (R/E) varied significantly among the varieties. HW 2004 reported the highest SDS sedimentation value while PBW 590 had the highest protein content (14.17 g/100 g). The quantity and quality of gluten is an indicator of the baking quality. Gluten plays a crucial role in creating dough structure and baking bread. It affects the stability of the dough and bread volume by forming the skeleton of wheat dough that combines the remaining ingredients and additives to the dough. HW 2004 yielded lowest protein content and gluten yield (7.92 g/100 g) while highest gluten yield was shown by PBW 550 (10.07 g/100 g). The gluten index, which describes the quality of gluten, increased with the increase in glutenin as indicated by a positive correlation between them inferring that the presence of glutenin improves the gluten quality. The wheat variety HW 2004 displayed much higher damaged starch than other varieties owing to its higher kernel hardness. PBW 550 reported the highest R/E ratio (1.45) while the variety C 306 (0.43) had the lowest. This difference in R/E could be attributed to the decrease levels of glutenins in C 306. Higher glutenin levels make the dough more elastic thus giving dough its property of resistance to extension while higher gliadin content increases the extensibility of the dough. The correlation data also showed that glutenin content was highly positively correlated with R/E (r ¼ 0.751) while the contribution of gliadins were negligible (r ¼ 0.045). It was found that the percentage of glutenins and gliadins increased as the protein content of the wheat variety increased as evident from a positive correlation among the above parameters. However, the increase was more pronounced for glutenins as compared to the gliadins indicating that the glutenin content increase substantially with increase in protein content of wheat variety.
PBW 590 PBW 550 HW 2004 C 306
2* 2* N N
5 5 2 2
3.2. HMW-GS and protein characterization of wheat varieties The HMW-GS compositions of the four varieties are presented in Table 2. A number of studies have shown that the strength of dough is related to the amount and type of HMW glutenin subunit (Hoseney, 1994). Variations in both quantity and quality of glutenin strongly determine the variations in bread making performance (Veraverbeke & Delcour, 2002). Researches in the past have shown that glutenin subunits 1 and 5 þ 10 are superior to the allelic null and 2 þ 12 subunits, respectively (Payne, Holt, Jackson, & Law, 1984). It is evident that PBW 590 and PBW 550 had the same HMW-GS composition i.e. 2*, 5 þ 10, 7 þ 9 and a high Glu 1 score of 9 while the other two varieties HW 2004 and C306 had the Table 1 Flour quality characteristics. Variety
Moisture SDSV DS Protein GY GI R/E (g/100 g) (ml) (g/100 g) (g/100 g) (g/100 g) (g/100 g)
PBW 590 PBW 550 HW 2004 C 306
11.94b 13.05d 11.32a 12.76c
37c 34b 47d 30a
6.02b 5.82a 8.55d 6.14c
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14.17d 13.56e 10.06a 10.85b
10.03c 10.07d 7.92a 9.20b
78.90d 71.85c 56.80b 49.10a
1.02c 1.45d 0.53b 0.43a
SDSV e SDS sedimentation volume; DS e damaged starch; GY e gluten yield; GI e gluten index; R/E resistibility/extensibility of gluten. Values followed by different letters are significantly different at P < 0.05.
þ þ þ þ
10 10 12 12
Glu-D1
Glu1 score
Gli (g/100 g)
Glu (g/100 g)
Gli/Glu
7þ9 7þ9 20 20
9 9 4 4
4.57b 5.09c 4.20a 5.49d
5.53d 5.29c 3.99a 4.66b
0.82a 0.96b 1.05c 1.17d
Gli e gliadins; Glu e glutenins; Gli/Glu e gliadin to glutenin ratio. Values followed by different letters are significantly different at P < 0.05.
composition N, 2 þ 12, 20 and a low Glu 1 score of 4. The gliadin to glutenin ratio (Gli/Glu) varied widely among the varieties with C 306 exhibiting the highest ratio of 1.17. Though the Glu 1 scores of varieties PBW 590 and PBW 550 were similar, their Gli/Glu ratio varied significantly (0.82 and 0.96). Similar was the case with the varieties HW 2004 and C 306 which reported the Gli/Glu ratio 1.05 and 1.17, respectively. It can be concluded from the results that the varieties with lower Glu 1 score have higher gliadin content and vice versa. Moreover, from Tables 2 and 4 it can be deduced that flour from wheat varieties having HMW glutenin subunits 2*, 5 þ 10 and 7 þ 9 had higher dough development time and dough stability while flours with subunits N, 2 þ 12 and 20 resulted in doughs with lower stability values and higher dough weakening. This could be attributed to the fact that subunit 5 have the largest molecular weight and plays an important role in extending the polymer chains during glutenin synthesis (Huang & Khan, 1997a). Further, the subunit 5 and 2*, because of their larger molecular size contributes greater to the dough mixing properties than the other subunits (Huang & Khan, 1997b). Also it has been suggested that the positive effect of the subunits 5 þ 10 is largely due to the presence of an extra cysteine residue in the subunit 5 as compared to other subunits (Weiser, 2007). 3.3. Flour pasting characteristics The rapid visco analyzer indicates starch viscosity by measuring the resistance of flour and water slurry to the stirring action of a paddle. The highest point during the heating cycle is the peak viscosity. The RVA pasting profiles of the wheat varieties are presented in Table 3. The variety PBW 590 reported the highest peak viscosity of 232.75 RVU whereas; the highest final viscosity of 237.58 RVU was reported by C 306. Pasting temperatures of flours from the different wheat varieties ranged from 66.85 (HW 2004) to 68.75 (PBW 590). Pasting temperature indicates the minimum temperature required to cook as well as the temperature at which the viscosity increases during the heating process. The flours with higher protein content took more time to reach peak viscosity as evident from higher peak time. Moreover, the peak viscosity observed a strong negative correlation with protein. The peak viscosity indicates the maximum swelling of the starch granules which could be adversely affected by the presence of higher protein which competes for the water along with the starch granules. Peak viscosity and breakdown viscosity showed strong negative correlation (r ¼ 0.979, r ¼ 0.700) with the pasting temperature while Table 3 RVA pasting properties of flours. Variety
PV (RVU) BKD (RVU)
Trough (RVU)
PBW 590 PBW 550 HW 2004 C 306
194.92a 213.58b 232.75d 217.42c
135.67d 98.50b 234.17c 123.58a 91.00a 214.58a 126.67c 102.42c 229.08b 125.00b 112.58d 237.58d
68.08a 78.83b 92.25c 97.58d
Setback FV (RVU) (RVU)
Peak time Pasting (min) temp ( C) 6.13b 6.13b 6.13b 5.87a
68.75d 67.60b 66.85a 67.80c
PV e peak viscosity; BKD e breakdown; FV e final viscosity; Pasting Temp e pasting temperature. Values followed by different letters are significantly different at P < 0.05.
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Table 4 Dough rheological characteristics.
Table 6 Correlation between RVA properties and flour characteristics.
Variety
WAC (%)
DDT (min)
STA (min)
DW (FU)
PBW 590 PBW 550 HW 2004 C 306
56.8b 57.9c 60.2d 56.5a
4.0d 3.0c 2.0b 1.5a
6.5c 4.5b 1.5a 1.5a
45a 71b 116c 122d
Protein DS SDSV GY DDT STA DW GLI GLU GLI/GLU
WAC e water absorption capacity; DDT e dough development time; STA e dough stability; DW e dough weakening. Values followed by different letters are significantly different at P < 0.05.
trough viscosity observed a positive correlation (r ¼ 0.735). Breakdown indicates the stability of the paste during cooking with lower breakdown viscosity inferring better resistance to shear thinning of flour pastes. Flours with lower protein content showed higher breakdown viscosity. Setback is the recovery of the viscosity during cooling of the heated flour suspension. It was observed that the setback viscosity was higher for flours with lower protein content. Highest setback viscosity was reported by C 306 (112.58 RVU) while PBW 550 showed the lowest setback viscosity (91 RVU). Final viscosity is dependent on the starch content, amylose, amylopectin, amylose/amylopectin ratio (Tester & Morrison, 1990). Final viscosity of the flours increases due to the aggregation of the amylose molecules (Miles, Morris, Orford & Ring, 1985). Final viscosity was found to be, though not significantly, but inversely related with protein and glutenin content of the flour while it was positively related with the gliadin content and gliadin to glutenin ratio. The peak viscosity increased with increase in the damaged starch content. A possible explanation is that damaged starch absorbs much more water than undamaged starch granules. Thus, higher damaged starch content absorbed more water and swell upon heating thereby increasing the viscosity of the flour paste. 3.4. Dough rheological characteristics The rheological properties of dough are critical in food manufacturing. The results of dough rheological characteristics are depicted in Table 4. As expected, the highest dough stability was shown by PBW 590 followed by PBW 550 as they had a high Glu 1 score of 9, higher protein contents and lower Gli/Glu ratios, respectively (Table 2). PBW 590 reported the highest dough development time while C 306 reported the lowest value for the parameter. The dough stability decreased markedly from 6.5 min (PBW 590) to 1.5 min (HW 2004 and C 306) suggesting a low tolerance of flour to mixing. The observed weakening of the dough could be due to combined effect of higher level of gliadins, presence of weaker HMW glutenin subunits and lower gluten content of the
Peak h
BKD
Trough
Setback
Final h
Peak time
Pasting temp
0.883 0.772 0.487 0.862 0.811 0.892 0.853 0.178 0.931 0.721
0.925 0.449 0.010 0.705 0.999** 0.987* 0.994** 0.289 0.826 0.982*
0.486 0.104 0.177 0.264 0.723 0.681 0.654 0.461 0.444 0.739
0.686 0.193 0.188 0.466 0.706 0.659 0.715 0.313 0.512 0.726
0.347 0.115 0.073 0.271 0.237 0.218 0.283 0.030 0.215 0.247
0.434 0.255 0.643 0.070 0.676 0.544 0.606 0.766 0.200 0.768
0.768 0.743 0.523 0.784 0.702 0.792 0.739 0.226 0.851 0.608
DS e damaged starch; SDSV e SDS sedimentation volume; GY e gluten yield; DDT e dough development time; STA e dough stability; DW e dough weakening. GLI e gliadins; GLU e glutenins; GLI/GLU e gliadin to glutenin ratio; **Correlation is significant at 0.01 level, *Correlation is significant at 0.05 level.
flour of the latter varieties. Both the varieties (HW 2004 and C 306) with high gliadin to glutenin ratio and low Glu 1 score of 4 also showed high dough weakening. The study also revealed that varieties with similar HMW-GS composition but different Gli/Glu ratio (PBW 590 and PBW 550) also differed in their dough rheological properties. PBW 590 came out to be stronger flour as compared to PBW 550. This could be due to the higher percentage of gliadins in PBW 550 as compared to the percentage of glutenin. This observation was in concordance with the studies of MacRitchie (1987) and Khatkar et al. (2002a) who found that addition of increased levels of gliadin rich fraction to base flour shortened the mixing time and stability of dough. Similar results were also sought in this study, where gliadin content exhibited a negative correlation (r ¼ 0.139) with dough stability (Table 5) while glutenin content showed a strong positive correlation (r ¼ 0.903). The DDT and dough stability increased with the protein content of the wheat varieties. DDT and dough stability showed a significant negative correlation (r ¼ 0.989 and r ¼ 0.997) with dough weakening. It was observed that the quality of the gluten in terms of gluten index was also significantly positively associated with dough stability while dough weakening was negatively affected by higher gluten index values. The results were in agreement with other authors (Collar, Bollain, & Rosell, 2007) who reported a similar correlation in their study. Also, it was observed that flours with higher R/E ratio had higher dough development time and dough stability. Peak viscosity was found to be negatively correlated (Table 6) with DDT and dough stability (r ¼ 0.811, r ¼ 0.892) while dough weakening observed a positive correlation with peak viscosity. The above data further strengthened the negative association of protein with peak viscosity i.e. the stronger flours with higher protein content, dough development
Table 5 Correlation among gluten protein subfractions and flour characteristics.
PRO DS SDSV GY GI R/E DDT STA DW GLI GLU GLI/GLU
PRO
DS
SDSV
GY
GI
R/E
DDT
STA
DW
GLI
GLU
GLI/GLU
1 0.742 0.366 0.918 0.919 0.845 0.908 0.965* 0.961* 0.088 0.969* 0.837
1 0.896 0.946 0.418 0.549 0.419 0.582 0.542 0.724 0.875 0.272
1 0.703 0.029 0.201 0.021 0.169 0.116 0.946 0.571 0.177
1 0.689 0.751 0.677 0.800 0.777 0.474 0.979* 0.557
1 0.819 0.986* 0.966* 0.984* 0.307 0.800 0.975*
1 0.721 0.747 0.781 0.045 0.751 0.680
1 0.982* 0.989* 0.322 0.806 0.988*
1 0.997** 0.139 0.903 0.940
1 0.184 0.881 0.955*
1 0.300 0.466
1 0.704
1
PRO e protein; DS e damaged starch; SDSV e SDS sedimentation volume; GY e gluten yield; GI e gluten index; R/E resistibility/extensibility of gluten; DDT e dough development time; STA e dough stability; DW e dough weakening GLI e gliadins; GLU e glutenins; GLI/GLU e gliadin to glutenin ratio. **Correlation is significant at 0.01 level, *Correlation is significant at 0.05 level.
S. Barak et al. / LWT - Food Science and Technology 51 (2013) 211e217 Table 7 Bread quality analysis. Wheat variety
CF (g)
SV (cm3/g)
PBW 590 PBW 550 HW 2004 C 306
169.95a 318.05c 442.10d 213.45b
3.31d 2.97c 1.68a 2.86b
CF e crumb firmness; SV e specific volume. Values followed by different letters are significantly different at P < 0.05.
time and dough stability showed lower peak viscosities. Further, the pasting temperature increased with increasing values for DDT and dough stability values indicating that stronger flours with higher protein content have higher pasting temperatures. 3.5. Bread quality The quality of bread was assessed through bread specific volume and crumb firmness measurements (Table 7). The specific volume of the breads ranged from 1.68 to 3.31. A decrease in bread specific volume was observed on moving from PBW 590, PBW 550 and C 306 to HW 2004 (Fig. 1). A significant decrease in bread specific volume can be explained as the lower ability of gluten network to enclose the carbon dioxide produced during fermentation. The bread firmness values also varied significantly among the varieties. The crumb firmness of PBW 550 was significantly higher (318.05 g) than that obtained for PBW 590 (169.95 g). The higher Glu 1 score of PBW 550 was not reflected in a higher specific volume. The significant lower firmness of PBW 590, thus softer texture, than PBW 550 probably could be due to higher quantity of HMW-GS in the former variety leading to better loaf volume and thus lower crumb firmness. Other reasons may be the higher protein content, better gluten quality and lower Gli/Glu ratio. It is noteworthy that both the wheat varieties PBW 550 and PBW 590 possessing the same HMW-GS composition varied significantly in their bread quality. Thus, the subunit 2* and 5 þ 10 subunits had good contribution to the bread quality of wheat, therefore these may be introgressed into the genetic background of wheat varieties to improve their bread making quality. The specific volume of HW 2004 was appreciably lower than C 306 due to its poor gluten yield (7.92 g/100 g) and low gluten quality measured in terms of gluten index (56.80%). 3.6. Correlation among bread quality, protein composition, gluten subfractions, pasting properties and dough properties of flour All the studied factors as well as the interaction among them exerted a very significant effect on the dough rheological properties of the samples and bread quality (Table 8). The effect of protein
215
Table 8 Correlation among gluten protein subfractions, flour properties, pasting properties and bread quality.
Protein RE Gluten yield Gluten index Dough development time Stability Dough weakening Gliadin Glutenin Gliadin/glutenin ratio Peak viscosity Breakdown Trough Setback Final viscosity Peak time Pasting temperature
Bread firmness
Specific volume
0.576 0.116 0.732 0.307 0.405 0.542 0.473 0.521 0.737 0.287 0.862 0.409 0.516 0.198 0.453 0.398 0.931
0.826 0.523 0.954* 0.557 0.592 0.733 0.687 0.546 0.939 0.459 0.916 0.612 0.377 0.200 0.026 0.146 0.898
*Correlation is significant at 0.05 level.
content of the flour on the loaf volume of bread has been well documented in literature. The protein content of the flour observed a strong positive correlation (r ¼ 0.826) with the specific volume of the bread. Most of the factors depicting the protein quality were found to be positively correlated with the specific volume of the bread. Gluten yield showed a significantly strong correlation with the specific volume (r ¼ 0.954) of bread. R/E showed slight negative correlation (r ¼ 0.116) with bread firmness indicating that a balance of elasticity and extensibility of dough is important to produce bread of lower firmness and higher loaf volume. On the other hand, gluten index observed a negative correlation with bread firmness indicating the role of strong gluten on lowering the firmness of bread. Gliadins and glutenins observed negative correlation with crumb firmness, however glutenins showed a higher negative correlation (r ¼ 0.737) with bread crumb firmness implying that higher glutenin content results in softer bread. The glutenins observed a strong positive correlation with the specific volume of bread. Lundh and MacRitchie (1989) also found that varieties differing in their glutenin content differed in their bread making performance with higher glutenins yielding excellent bread making quality. The effect of gliadins on the bread loaf volume has been debatable since decades. Park et al. (2006) reported that percentage of gliadins based on flour and protein content of wheat varieties exhibited positive correlation (r ¼ 0.730) with bread loaf volume. Similarly, Khatkar et al. (2002a) also reported that addition of total gliadins and its subgroups (a-, b-, gand u-gliadins) to the dough significantly improved its bread making performance. In the present study, a similar positive
Fig. 1. Bread prepared from different wheat varieties.
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S. Barak et al. / LWT - Food Science and Technology 51 (2013) 211e217
relationship was found between the percentage of gliadins in wheat variety and its specific volume. Gliadins exhibited a positive correlation (r ¼ 0.546) with the specific volume of bread. Many researchers have reported difference in gliadin to glutenin ratio as an important criterion in determining bread making quality of a wheat variety (Kasarda, 1994). Khatkar and Schofield (2002) reported that gluten-water doughs from poor quality wheat varieties exhibited lower elasticity and greater viscosity as compared to those from good quality wheat varieties. Overall, the Gli/Glu ratio was positively associated with bread firmness and negatively with the specific volume implying that the balance of gliadins and glutenins is important in judging the suitability of a wheat variety for bread making. In our attempt to study the effect of RVA flour pasting properties on the bread quality, it was found that flours with higher peak viscosity degraded the quality of bread. This could be attributed to the fact that flours with higher protein content inhibit the swelling of the starch granules, thus lowering the peak viscosity. Breakdown was also found to be negatively associated with the specific volume of the bread. Moreover, flours with higher trough viscosity gave breads with a softer texture and higher loaf volume. Final viscosity was found to be negatively associated with crumb firmness and positively with the specific volume of bread. The dough properties such as DDT and dough stability exhibited a negative relationship with the bread firmness (r ¼ 0.405 and r ¼ 0.542, respectively) and positive correlation with specific volume (r ¼ 0.592 and r ¼ 0.733). Thus, strong flours with higher DDT and dough stability prove to produce bread of superior quality. On the other hand, flours with higher dough weakening produce bread of inferior quality. Thus, the information above can be of assistance to breeders to select for acceptable rheological and baking characteristics for bread making. Huang, Yun, Quail, and Moss (1996) reported that the dough development time, dough stability, had significant positive correlation with specific volume of Chinese steamed bread. 4. Conclusion The study allowed us to understand the effects of various flour components on bread quality. The gliadins and glutenins provided useful predictions of technological quality of the wheat varieties investigated. Also, in the literature, there was no study on investigating the effect of dough pasting properties on the bread making potential of the wheat varieties and the contribution of gliadins and glutenins to the flour pasting properties. Breeders are interested in parameters that are highly heritable and reproducible and that these parameters should provide information about dough mixing properties. Being important breeding objectives, doughmixing properties, the factors affecting these properties and the information they provide in improving the bread making quality have been discussed in this paper. These parameters can be identified as selection criteria to assist wheat breeders in selecting acceptable rheological and baking criteria for bread making. The gluten subfractions had substantial effect on the dough rheological properties and RVA pasting profile of the wheat varieties. Baking tests showed that gliadins and glutenins had positive effect on the bread specific volume, however, the effect of glutenins was more pronounced. The Gli/Glu ratio was positively associated with the bread crumb firmness. The bread crumb firmness reduced with the increase in pasting properties of the flours. Dough that had longer dough development time and dough stability performed well in the bread baking test. The subunit 2* and 5 þ 10 subunits contributed significantly to the improved bread quality of wheat. Thus, it was found that gliadins and glutenins contributed significantly to the dough & flour pasting properties and bread quality.
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