TY - JOUR
T1 - Physical aging of glassy normal and waxy rice starches
T2 - Effect of aging temperature on glass transition and enthalpy relaxation
AU - Chung, Hyun Jung
AU - Lim, Seung Taik
N1 - Funding Information:
This research was financially supported by Korea Research Foundation (KRF-2001-041-G00062).
Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2003/8/1
Y1 - 2003/8/1
N2 - Effect of physical aging at different temperatures (Ta) on the amorphous transitions of normal and waxy rice starches has been investigated using differential scanning calorimetry (DSC). Glass transition temperature (Tg) increased, but ΔCp at the Tg decreased, as the difference (Tg - Ta) between Tg and Ta increased, because the molecular mobility was reduced as the aging temperature was farther from Tg. The extent of relaxation was analyzed by determining the limiting relaxation enthalpy (ΔH∞) at various aging temperatures. The ΔH∞ versus Tg - Ta revealed the two different roles by kinetic and thermodynamic controls for the relaxation. When Tg - Ta was low (0 ∼ 30°C), ΔH∞ increased with Tg - Ta, whereas when Tg - Ta was high (above 30°C), it decreased with Tg - Ta. At a constant Tg - Ta, the residual moisture raised ΔH∞ due to plasticization effect. The effect of aging temperature on the relaxation temperature range was opposite to that on ΔH∞, and the peak range became narrower as the moisture content increased. The ΔH∞ and peak temperature range were different between normal and waxy rice starches. The normal rice starch had a higher ΔH∞ and a narrower peak temperature range than did waxy rice starch.
AB - Effect of physical aging at different temperatures (Ta) on the amorphous transitions of normal and waxy rice starches has been investigated using differential scanning calorimetry (DSC). Glass transition temperature (Tg) increased, but ΔCp at the Tg decreased, as the difference (Tg - Ta) between Tg and Ta increased, because the molecular mobility was reduced as the aging temperature was farther from Tg. The extent of relaxation was analyzed by determining the limiting relaxation enthalpy (ΔH∞) at various aging temperatures. The ΔH∞ versus Tg - Ta revealed the two different roles by kinetic and thermodynamic controls for the relaxation. When Tg - Ta was low (0 ∼ 30°C), ΔH∞ increased with Tg - Ta, whereas when Tg - Ta was high (above 30°C), it decreased with Tg - Ta. At a constant Tg - Ta, the residual moisture raised ΔH∞ due to plasticization effect. The effect of aging temperature on the relaxation temperature range was opposite to that on ΔH∞, and the peak range became narrower as the moisture content increased. The ΔH∞ and peak temperature range were different between normal and waxy rice starches. The normal rice starch had a higher ΔH∞ and a narrower peak temperature range than did waxy rice starch.
KW - Enthalpy relaxation
KW - Glass transition
KW - Physical aging
KW - Rice starch
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U2 - 10.1016/S0144-8617(03)00077-8
DO - 10.1016/S0144-8617(03)00077-8
M3 - Article
AN - SCOPUS:0037411903
SN - 0144-8617
VL - 53
SP - 205
EP - 211
JO - Carbohydrate Polymers
JF - Carbohydrate Polymers
IS - 2
ER -