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Title:Investigation of the phase transitions of pregelatinized waxy maize starch at low moisture contents
Author(s):Wicklund, Rachel A
Director of Research:Schmidt, Shelly J
Doctoral Committee Chair(s):Bohn, Dawn
Doctoral Committee Member(s):Engeseth, Nicki; Lee, Youngsoo
Department / Program:Food Science & Human Nutrition
Discipline:Food Science & Human Nutrition
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):pregelatinized starch
Abstract:A sub-Tg endotherm has been identified in many cereal-based, low moisture food systems, including several commercial varieties of crackers. Given the similarity of this endotherm to the retrogradation endotherm of amylopectin under higher moisture conditions, the presence of this endotherm may indicate structural changes in amylopectin occurring at low moisture contents that could lead to textural changes in the corresponding food system. Pregelatinized waxy maize starch was studied by MDSC as a function of moisture content and storage temperature. A sub-Tg endotherm was observed between 45-65°C in the non-reversing signal for pregelatinized waxy maize starch stored between 0 and 72% RH and over a storage temperature range from 5 to 35°C. The enthalpy of this transition was independent of storage temperature, but exhibited an exponential relationship with increasing moisture content. FTIR-ATR and 13C CP/MAS NMR identified the fundamental structural cause of the endotherm as the reorganization of amylopectin into double helices following gelatinization, but without the aggregation of the double helices into crystalline arrays that can occur during the full retrogradation process. The reorganization into double helices, and hence the development of the sub-Tg endotherm, was observed to increase with time according to Avrami kinetics, which is often used to describe crystallization processes. The Avrami exponent, n, was estimated at 0.24 and was found to be independent of starch moisture content. The Avrami rate constant, K, was exponentially correlated with starch moisture content similar to the enthalpy of the sub-Tg endotherm. In a model wheat-flour based cracker system the development of the sub-Tg endotherm, due to reformation of amylopectin double helical structure, was also found to follow Avrami kinetics and was correlated with a decrease in the hardness and an increase in the toughness of the crackers. This work confirms that staling and associated textural changes in low moisture starch-based food systems, such as crackers, is a result of reformation of amylopectin double helices without crystallization or aggregation of those helices that develops in high moisture starch-based food systems, such as bread.
Issue Date:2016-03-29
Rights Information:Copyright 2016 Rachel Wicklund
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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