Influence of size distribution of proteins, thiol and disulfide content in whole wheat flour on rheological and chapati texture of Indian wheat varieties.

The influence of protein composition, as measured by size-exclusion high performance liquid chromatography (SE-HPLC), on rheological properties and chapati texture was investigated in the whole wheat flours of eight Indian wheat cultivars grown at a single location. Proteins were extracted using two-step procedure: extraction with buffer containing 0.5% SDS (SDS buffer), followed by sonication. The results showed that SDS buffer extracted 72-90% of the total flour protein in different varieties and 7-11% protein was extracted from the remaining residues by sonication. The proteins extracted were fractionated by SE-HPLC into large polymeric proteins (>130kDa), small polymeric proteins (80-130kDa) and monomeric proteins (10-80kDa). Total polymeric protein content in the flour protein showed a significant positive correlation with dough hardness (r=0.71, p<0.05) and positive correlation with chapati texture (r=0.58, p<0.05). Of the SDS extractable polymeric proteins, large polymeric protein in flour protein had significant positive correlation to dough hardness (r=0.89, p<0.05) and chapati cutting force, which reflects the chapati texture (r=0.70, p<0.05). Protein disulfide content showed positive correlation to dough hardness (r=0.66, p<0.05) and texture of chapati (r=0.58, p<0.05) while protein thiol content showed significant negative correlation to chapati texture (r=-0.77, p<0.05). Thus, the results indicate that high proportion of SDS extractable large polymeric protein in flour protein increases the toughness of chapati texture while flours having high thiol content decrease the toughness of chapati.