Interactions of barley endosperm proteins with starch and their effects on functional properties

Abstract

Many factors can alter starch degradation rate, with interactions with proteins being one of the most important factors. Although barley protein content is currently a major parameter for predicting the quality of a barley genotype in brewing, the mechanisms underlying the effects of barley protein on grain utilization are poorly understood.This project aims to explore these mechanisms of these effects on starch utilization in both food and brewing industries to provide a better way for brewers and food producers to choose a suitable barley genotype for beer and food production. As part of this aim, mechanistic explanations of the observations will also be obtained.Protein content is currently an important parameter used to choose a suitable barley genotype, it is of value to find out if there are any relations among barley protein contents with other grain parameters, like, the grain size and starch properties. 30 different barley samples were used.Size-exclusion chromatography (SEC) and fluorophore-assisted carbohydrate electrophoresis (FACE) were used together to investigate starch molecular structure, while both amylose and amylopectin chain-length distributions (CLDs) being fitted with biosynthesis-based models to find statistically meaningful correlations.In order to understand the mechanism concerning how barley protein affects starch degradation, in vitro starch digestion measurements were carried out, using raw barley flour as substrate.Pepsin and porcine pancreatic α-amylase were used, and both logarithm of slopes and NLLSmethods used to fit the data, the latter being devised here for this purpose. Confocal microscopy was used to visualize the absorption of aamylase on barley protein.Another research goal is to investigate and understand how barley protein affects starch degradation during mashing (65 °C) as well as fermentable sugar productions (glucose, maltose, maltotriose). Ten barley samples with varied protein contents were used to do malting followed by mashing. For malting which is conducted based on industrial standards, both scanning XI