Composition of the glutenin macropolymer: effects of flour quality and nonamylolytic enzyme addition

Abstract

The effects of the non-amylolytic enzymes pentosanase (PP), glucose oxidase (GLZ) and laccase (LAC), singly and in binary and ternary combinations, and wheat flour—a pure cultivar F0, and low- grade F1 and high-grade F2 commercial blends—on the electro- phoretic pattern of the glutenin macropolymer (GMP) were investigated by sodium dodecyl sulphate polyacry- lamide gel electrophoresis (SDS-PAGE). GMP profiles of high (HMW), medium (MMW) and low (LMW) molecular weight glutenin subunits (GS) were correlated with dough and GMP characteristics and with bread quality and keepability. The total relative percentages of separated HMW, MMW and LMW-GS of GMP in control and enzyme-supple- mented samples were: 33-37, 11-16 and 46-54% (F0), 47-74, 0 and 26-57% (F1) and 30-47, 15-18 and 32- 38% (F2), respectively. HMW-GS/LMW-GS ratios, a quality index of glutenin, were found to range from 0.63 to 0.80 for all flour GMP. Enzyme addition induced moderate effects in pure wheat cultivar F0. Combinations of PP and GLZ (PPGLZ) allowed glutenin repolymeriza- tion after resting, leading to an increase of the bands of 104-107 and 88-90 kDa in GMP by SDS-PAGE. Analogously, PP plus LAC (PPLAC) and LAC alone increased the amount of the subunit of 81-82 kDa. Subunits of LMW increased with PPLAC and LAC, the subunit of 37-38 kDa having a higher percentage in GMP probably due to the presence of a-, b- and g-gliadins besides the LMW-GS. Only the subunit of 81-82 kDa was positively associated with the dynamic rheological moduli G 0 and G* and the subunit of 88-90 kDa correlated with a lower delta angle and, consequently, with a more elastic gel. After fermentation, the total percentage of subunits of HMW, MMW and LMW changed mainly in low-grade flour F1 (36-37, 17-19 and 14-19%) compared with high-grade flour F2 (32-37, 14-17 and 47-51%). The subunit of HMW with MW of 120-125 kDa (F1) and 93- 95 kDa (F2) was positively correlated with the specific volume of breads and negatively with firmness of fresh and stored bread. Subunits of MMW negatively influ- enced the quality of fresh and stored bread of F1. The ratio HMW/LMW was positively correlated with bread firmness during staling in breads prepared with F2.