Key Laboratory of Special Food Supervision Technology for State Market Regulation, School of Food and Health, Beijing Technology and Business University (BTBU), 11 Fucheng Road, Beijing 100048, China.
College of Chemistry and Materials Engineering, Beijing Technology and Business University (BTBU), 11 Fucheng Road, Beijing 100048, China.
Food Res Int. 2023 Jan;163:112254. doi: 10.1016/j.foodres.2022.112254. Epub 2022 Nov 30.
Brown rice (BR) is a promising source for convenience rice that are mostly stored frozen. However, freezing and thawing may cause deterioration in rice texture quality. To investigate how rice texture is influenced by freeze-thaw cycles, BR, the pretreated BR with partially ruptured bran layer (UER) and white rice (WR) were cooked and treated with repeated freeze-thaw cycles, with their textural properties, variations in moisture distribution and starch structure being measured. Results showed that the repeated freeze-thaw treatment induced a progressive reduction in hardness and stickiness of all cooked rice. The reduced hardness of rice could be explained by the enlarged pore size of starch inside rice under scanning electron microscopy. Moisture migration in WR was the fastest responding to multiply freeze-thaw cycles, followed by UER, while water mobility in BR was slowest. Moreover, WR, BR and UER resulted in a similar extent of amylopectin retrogradation and chains length distribution after repeated freeze-thaw cycles. It indicated similar and minor effect of starch variations on determining the texture of different rice samples against freeze-thawing. Water mobility tended to be a main factor leading to the textural difference of fully gelatinized rice samples. This study focused on the relationship between water distribution and starch retrogradation, providing a better understanding on influences of multiple freeze-thawing on textural quality of cooked rice maintaining different extents of surface layer.
糙米（BR）是一种很有前途的方便米饭原料，通常储存于冷冻状态。然而，冷冻和解冻可能会导致米饭质地变差。为了研究冻融循环对大米质地的影响，我们将糙米（BR）、部分破裂糠层预处理的糙米（UER）和白米（WR）进行烹饪并进行重复冻融循环处理，测量其质地特性、水分分布和淀粉结构的变化。结果表明，重复的冻融处理会导致所有蒸煮米饭的硬度和粘性逐渐降低。米饭硬度的降低可以通过扫描电子显微镜下大米内部淀粉的孔径增大来解释。WR 中的水分迁移对多次冻融循环的响应最快，其次是 UER，而 BR 中的水分迁移最慢。此外，WR、BR 和 UER 在经过多次冻融循环后，支链淀粉的回生程度和链长分布相似。这表明淀粉变化对不同大米样品抗冻融性决定质地的影响相似且较小。水分迁移往往是导致完全胶凝米饭样品质地差异的主要因素。本研究关注水分分布和淀粉回生之间的关系，为更好地理解多次冻融对保持不同程度表面层的蒸煮米饭质地品质的影响提供了依据。
