Effects of Freezing Rate and Storage Temperature on the Degree of Retrogradation, Texture and Microstructure of Cooked Rice

동결속도 및 저장온도가 취반된 쌀의 노화도, 조직감 및 미세구조에 미치는 영향

  • Choi, Sung-Gil (Department of Food Technology, Korea University) ;
  • Rhee, Chul (Department of Food Technology, Korea University)
  • 최성길 (고려대학교 식품공학과) ;
  • 이철 (고려대학교 식품공학과)
  • Published : 1995.10.31


Cooked rices were frozen at four different rates(3, 5, 7 and 12 hr) of maximum ice crystal formation zone and stored at $-20^{\circ}C\;and\;-70^{\circ}C$ for 3 months. Freezing rate, storage temperature and storage period all affected the degree of retrogradation of cooked rice. As the maximum ice crystal formation zone increased from 3 hrs to 12 hrs, the degree of retrogradation of cooked rice increased from 14.9% to 40.0%. Further retrogradation occurred during the freezing storage and cooked rice stored at $-20^{\circ}C$ retrograded faster than that held at $-70^{\circ}C$. The hardness and adhesiveness of frozen cooked rice thawed in $40^{\circ}C$ water were measured. Hardness of the frozen cooked rice was higher than that of non-frozen sample and was higher at lower freezing rate. However, the hardness of cooked rice decreased after 3 months of storage. On the other hand, the adhesiveness decreased during the freezing processing, and adhesiveness decreased more rapidly at a higher freezing rate. However, the adhesiveness of cooked rice increased after 3 months of the storage, and the level of decrease was higher at $-70^{\circ}C$ than at $-20^{\circ}C$. After 3 months of storage, ice crystal size of frozen cooked rice became larger by recrystalization than that of frozen sample prior to storage. Microstructure of cooked rice was damaged by ice crystal formation and its growth when observed by scanning electron microscope.