Comparison in glass transition and enthalpy relaxation between native and gelatinized rice starches

Hyun Jung Chung, Eun Jung Lee, Seung Taik Lim

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Abstract

Native and gelatinized rice starches were compared in their glass transition and enthalpy relaxation at various water contents using a differential scanning calorimetry (DSC). In a low moisture content range (8-18%), the glass transition temperature (T g) of native starch was higher (up to 20°C) than that of gelatinized starch, and the difference became greater as the moisture content decreased. Heat capacity change (ΔC(p)) at T g became substantially higher by gelatinization. Plasticizing effect of water on the glass transition in the low moisture content range followed the Couchman-Karasz equation. The glass transition temperature (T g′) of native starch with sufficient moisture (40 or 60%) also appeared higher (-6.8 or -6.0°C) than that of gelatinized starch (-10.0 or -7.7°C), but ice-melting occurred in broader temperature range with smaller ΔH when the starch was gelatinized. Upon extended storage up to 14 days at 4°C, the gelatinized starch showed increased T g′ but decreased ice-melting enthalpy due to the water incorporation in recrystallization of starch. Enthalpy relaxation appeared only when the moisture was <20% regardless of gelatinization. The relaxation peak increased in magnitude as the moisture content increased, and appeared as 'T g overshoot' at a moisture content above 12% due to superimposed glass transition, whereas at a moisture content below 12%, it located in a temperature range far below glass transition, showing a 'sub-T g endotherm'.

Original languageEnglish
Pages (from-to)287-298
Number of pages12
JournalCarbohydrate Polymers
Volume48
Issue number3
DOIs
Publication statusPublished - 2002 May 15

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Keywords

  • Enthalpy relaxation
  • Glass transition
  • Rice starch

ASJC Scopus subject areas

  • Food Science
  • Biochemistry

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