Evaluation of molecular weight distribution of unreduced wheat gluten proteins associated with noodle quality

Effect of Sitophilus zeamais (Coleoptera: Curculionidae) Infestation on the Protein Physicochemical and Structural Properties of Wheat Grain

Boring pests such as Sitophilus zeamais (S. zeamais) are major threats in grain storage. However, how these pests affect the proteins of stored grains remains largely unknown. Here we aimed to investigate the effect of S. zeamais infestation on wheat protein during postharvest storage. In this study, wheat grain infested by S. zeamais was sampled at egg (4 d), larval (20 d), pupal (35 d), and adult stages (45 d), respectively. The protein's physicochemical and structural properties and the edible quality of whole wheat noodle were analyzed. The results showed that S. zeamais infestation significantly decreased the quality of wheat protein by altering its constitution and structure properties. Especially, compared with the control, the content of wet and dry gluten, gluten index, sodium dodecyl sulfate sedimentation volume, sulfhydryl groups, and disulfide bonds in insect-infested wheat decreased by 19.40, 5.42, 18.40, 8.12, 29.13, and 14.30%, respectively, during the storage period of one life cycle of S. zeamais. Additionally, the proportions of wheat protein fractions (albumin [1.16-fold], globulin [0.96-fold], gliadin [1.16-fold], and glutenin [0.95-fold]) and secondary structures (α-helix [0.91-fold], β-fold [0.96-fold], β-turn [1.06-fold], and random coil [1.05-fold]) of protein changed significantly, and the gluten network structure was broken in S. zeamais-infested wheat. Furthermore, the color of whole wheat noodle became darker, cooking loss rate increased, and textural properties (hardness, adhesiveness, springiness, cohesiveness, chewiness, and resilience) decreased as well. The results in the present study provided new insights for analyzing the quality deterioration mechanism and further quality improvement of boring pests-infested wheat grain.

Extraction and purification of low molecular weight glutenin subunits using size exclusion chromatography

Crude glutenin of commercial Indian wheat varieties was fractionated into high molecular weight glutenin subunits (HMW-GS) and low molecular weight glutenin subunits (LMW-GS) by employing size-exclusion chromatography (SEC). The SEC profile of glutenins obtained with different buffers were discriminated effectively with respect to the quality of the proteins eluted in each peak. The most efficient separation of LMW-GS was achieved using 3 M urea (pH 5.5) buffer under unreduced conditions. The chromatogram was segregated predominantly into three peaks with varied molecular weights as determined by SDS-PAGE. Peak I corresponded to a mixture of HMW-GS and LMW-GS (M_w 100-30 kDa). Peak II enclosed LMW-GS specifically with molecular weights in the range of 45-35 kDa. Lastly, a mixture of proteins associated with LMW-GS (M_w < 35 kDa) were eluted in peak III. SEC proved to be a valuable tool in purifying LMW-GS in a functionally active state.

Quantification and varietal variation of low molecular weight glutenin subunits (LMW-GS) using size exclusion chromatography

Crude glutenin of four commercial wheat varieties viz. C 306, HI 977, HW 2004 and PBW 550 of diverse origin and breadmaking quality were fractionated by size-exclusion chromatography into three fractions of decreasing molecular weights. The relative quantity of peak II, containing LMW-GS specifically, varied considerably among the varieties as reflected from their discrete SEC profiles. The area % of peak II, containing protein of interest, was maximal for C 306 (22.08%) followed by PBW 550 (15.86%). The least proportion of LMW-GS were recovered from variety HW 2004 (9.68%). As the concentration of the sample extract injected to the column increased, the resolution of the peak declined in association with the slight shifting of retention time to the higher values. The best results were obtained for variety C 306 at 100 mg protein concentration with 3 M urea buffer. Consequently, the optimized conditions for purification of LMW-GS in appreciable amounts using SEC were established.

Fractionation of unreduced gluten proteins on SEC and their relationship with cookie quality characteristics

The size distribution assessment of unreduced wheat gluten proteins of commercial Indian wheat varieties was examined using Size-Exclusion Fast Protein Liquid Chromatography. Elution profiles were fractionated into five peaks, with the molecular weights of eluting peaks as 130-30, 55-20, 28-10 and <10 kDa (IV and V), respectively. Peak I (glutenins) and II (gliadins) exhibited contrary results with AWRC (r = 0.928** and r = -0.831**), R/E ratio (r = 0.745** and r = -0.869**), gluten index (r = 0.959** and r = -0.994**), gliadin/glutenin ratio (r = -0.952** and r = 0.948**), dough development time (r = 0.830** and r = -0.930**), dough stability (r = 0.901** and r = -0.979**) and dough weakening (r = -0.969** and r = 0.986**). Significant statistical correlation was also observed for peak I and II with cookie hardness (r = 0.948** and r = -0.924**) and cookie spread (r = -0.837** and r = -0.743**) respectively. Peak III, IV and V occupied a minor fraction of whole and did not exhibit a statistically significant correlation with any of the quality parameters.