2011 Annual Report
MECHANISM AND IN VITRO TEST METHOD OF DIGESTION OF GRANULAR STARCHES WITH DIFFERENT AMYLOSE CONTENTS: The rate and extent of granular starch digestion are related to its nutritional properties. Slowly digestible starch (SDS) and enzyme resistant starch (RS) are desirable. Type 2 resistant starch is a granular starch that, in portion or whole, escapes the small intestine undigested. To determine the rapidly digestible starch, the addition of amyloglucosidase is used to convert hydrolyzates from a-amylase digestion to glucose. Four maize starches differing in amylose content: waxy maize (0% amylose), normal maize (~ 26% amylose) and two high amylose starches (~ 50% and ~ 70% amylose) were examined. Without amyloglucosidase addition, the outcome of the expected slowly digestible starch fraction was 20% lower, while the resistant starch increased with increasing amylose content. In the method without a-amylase addition, less resistant starch was produced than without amyloglucosidase added, except in maize at 70% amylose content. The molecular weight distributions of the digestive residues were compared with gel permeation chromatography (GPC). Scanning electron microscopy (SEM) revealed the digestive patterns of pinholes with a-amylase and burrowing with amyloglucosidase as well as the degree of digestion between samples. To understand roles of amyloglucoisdase and a-amylase in the in vitro test, multiple analytical techniques were used, showing that amyloglucosidase has a significant impact on SDS and RS content of granular maize starches.
MEASUREMENT OF SORGHUM PHYTATE CONTENT: Phytate decreases sorghum protein digestibility through the formation of pepsin resistant protein-phytate complexes. Addition of the phytate degrading enzyme phytase to animal diets results in a significant increase in protein utilization especially in poultry. In order to determine the distribution and content of phytate in sorghum a subset of the KSU sorghum diversity panel was used. A representative sample set of 46 sorghum lines composed of 28 non-tannin and 18 tannin containing samples were examined. Phytate contents ranged from 0.55 to 9.28 mg/g with an average of 5.45 mg/g. No significant difference was observed between non-tannin samples which averaged 5.05 mg/g and tannin samples that averaged 5.88 mg/g.
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