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Structural evolution of starch hydrolysates by luminal amylases

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Title: Structural evolution of starch hydrolysates by luminal amylases
Author: Nantanga, Komeine Kotokeni Mekondjo
Department: Department of Food Science
Program: Food Science
Advisor: Seetharaman, Koushik
Abstract: Digestion of starch in humans starts in the mouth and progresses to the small intestine. Structures from salivary and pancreatic amylases hydrolysis can impact subsequent steps of digestion at the mucosa of the small intestine. However, structures of the starch digestion products along the gut from the mouth to the small intestines – products that impact glucose homeostasis are not well understood. This thesis focuses on the luminal step of starch digestion, i.e. impact of salivary and pancreatic amylase on the structure of hydrolysis products obtained from cooked starches from different botanical sources. Normal corn (NCS), wheat (NWS) and potato (NPS) starches were cooked at 1:0.7 (T0.7) or 1:2 (T2) starch:water ratios. Cooked starches were subjected to salivary amylase at conditions mimicking oral digestion. The composition of the hydrolysates was characterised by gel-permeation chromatography. Extent of hydrolysis was lower at T0.7 compared to T2, but the amount of carbohydrates in different fractions and the molecular weight profiles within each treatment were not different between starches from different botanical sources. However, debranching of the hydrolysates revealed structural differences in extent of amylose hydrolysis and amount and profile of lower molecular weight fractions between different starches. Cooked starches were also subjected to salivary and pancreatic amylases hydrolysis. Extent of 20 min hydrolysis was lower at T0.7 compared to T2 for all the starches. Oligosaccharide composition of 120 min hydrolysates differed in amounts of DP 2, 3, 5, 6 and 7 between processing treatments and starches. NCS (T2) was treated with saliva from six participants at equal activity. Salivary amylase activities ranged from 470 x 103 to 118 x 103 U/mL among the participants. While saliva from participant 2 (high amylase activity) greatly reduced the high molecular weight fraction, saliva from participant 6 (low amylase activity) more extensively hydrolysed the starch to small molecular weight fractions of oligosaccharides. These results show that different starch hydrolysates are produced during oral digestion by saliva from different individuals and are also different based on cooking condition or botanical source of starch. Further research is therefore needed to understand how these hydrolysate structures, impact glucose homeostasis.
Date: 2012-12

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