the effect of bug damage on physicochemical, electrophoretic and quality factors of wheat gluten

one of the most important forms of preharvest damage to wheat is caused by sunn pests. the insects insert their mouth parts into the immature grain and while injecting their saliva suck the milky juices. flour from damaged wheat results in low baking performance due to the bug proteolytic enzymes’ injected which cause the breakdown of gluten structure in the dough. in the present study three wheat varieties named alvand, mahdavi and roshan with different levels of bug damage were studied. the effect of bug damage on physicochmical properties showed reduced thousand kernel weight, protein and ash contents. gluten and gluten index decreased significantly upon bug damage. among the factors the degree of gluten hydrolysis, total reducing substances and sulfhydryl groups content were increased upon bug damage in all the three varieties examined but disulfide groups content was reduced. monitoring of the wheat flour protein by sds-page indicated that some of the bands related to hmw-gs at the top of electropherogram were disappeared and the intensity of some other were decreased. in roshan and alvand varieties, the intensity of bands with similar mobility to gliadins was decreased. incubation of bug-damaged samples resulted in further degradation of electropherogram bands of high molecular weights and development of bands with lower molecular weights that is due to the hydrolyzing effect of bug protease.