Sorghum endosperm components responsible for promoting protein polymerization through sulfhydryl-disulfide interchange
Abstract
Cooked sorghum flour has been shown to have poor digestibility compared to other cereals. It is thought that a three-dimensional web-like protein structure, developed through sulfhydryl-disulfide interchange, contains gelatinized starch granules, which limits digestive enzyme action. The overall goal of this project was to determine the factors responsible for promoting protein web-like structures and polymerization through sulfhydryl-disulfide interchange reactions in cooked sorghum flour. Maize flour was used as a model for identifying protein structures through light microscopy. After treatments with water, potassium bromate and a phenolic extract from sorghum flour, different varieties of maize flours showed a range of web-like protein structures, owing to pre-existing protein characteristics including protein content and matrix structure. For protein polymerization quantification, gel electrophoresis was used with chicken egg albumin as a model protein. Potassium bromate, sorghum flour, and sorghum phenolic extracts led to increased protein polymerization due to disulfide bonds, confirmed by a decrease in molecular weight after the addition of β-mercaptoethanol. Sorghum phenolic extracts adjusted to a low pH increased polymerization, while the sorghum extract adjusted to a high pH resulted in protein monomers. Total phenolic content of sorghum phenolic extract and maize phenolic extract were similar, but sorghum had twice the antioxidant capacity. HPLC-MS showed that the maize phenolic extract contained large amounts of phenolic acids, with little reactivity. The sorghum phenolic extract was high in anthocyanin derivatives which have greater ability to transfer electrons. These results suggest that the anthocyanin derivatives in the sorghum phenolic extract act as antioxidants which reduce the disulfide bond and subsequently act as oxidizers to facilitate new disulfide bond formation with new or pre-existing free sulfhydryl groups. The cascade of the sulfhydryl-disulfide interchange reaction promotes protein polymerization and results in extensive web-like protein structures that contain gelatinized starch granules.
Degree
M.S.
Advisors
Ferruzzi, Purdue University.
Subject Area
Agricultural chemicals
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