The role of amylopectin linear chain length and branch density on susceptibility to amylolytic enzymes
Abstract
The topic of carbohydrates and health is increasingly important in the minds of consumers, particularly in the area of glycemic index and slowly digesting starches. Starch, from the nutritional point of view, is categorized into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Evidence has shown that human glycemic response is highly correlated with the amount of RDS in food products, while SDS and RS are associated with benefits resulting from slow release of glucose and insulin. Thus, starch digestion properties have been implicated in the health problems of diabetes, obesity and cardiovascular disease. The relationship between molecular fine structure of cooked maize starch and its rapid or slow digestion property were investigated. Specifically, this study tested the hypothesis that amylopectins with high proportion of short α-1, 6 branch chains have a slow digestion rate and corresponding glucose yield. Single and double mutant isolated maize starches prepared by cooking a dilute suspension and processing quickly to minimize retrogradation. Suspensions were digested with porcine α-amylase for 4 h and aliquots were taken at different time intervals. Based on chromatographic analysis of the debranched samples, starch samples were classified into 2 categories: samples with high proportion of long B chains (i.e. branched) but low proportion of short chains (i.e.unbranched), and samples with low proportion of long B chains but high proportion of short chains and branching density. Digestion profiles of the samples showed that samples with high proportion of short chains had a slower digestion rate as opposed to those with high proportion of long chains. Debranched profiles of α-amylase hydrolysates revealed that the initial attack on amylopectin occurred at the external chains and independently at longer internal chain segments between branches. Digestion of the α-amylase hydrolysates with glucoamylase (fungal amyloglucosidase) further showed an inverse relationship between glucose production and the proportion of short chains and branch density. Consequently, genetic starch mutants of maize have a good potential to provide raw starch materials with unique nutritional qualities.
Degree
Ph.D.
Advisors
Hamaker, Purdue University.
Subject Area
Food science
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