Effects of dynamic low temperature during the grain filling stage on starch morphological structure, physicochemical properties, and eating quality of soft <i>japonica</i> rice
Yajie Hu, Luan Li, Jinyu Tian, Chengxin Zhang, Jie Wang, Enwei Yu, Zhipeng Xing, Bao-Wei GUO, Haiyan Wei, Zhong-Yang HUO, Hongcheng Zhang
Abstract
Abstract Background and objectives Temperature during the grain filling stage is the critical environmental factor affecting rice quality and starch physicochemical properties. Two soft japonica rice varieties were used to investigate starch morphological structure, gelatinization, and pasting properties, as well as the overall sensory quality of cooked rice under different ripening dynamic temperatures. Findings Compared to normal temperature (NT), dynamic low temperature (LT) during the grain filling stage increased amylose content and significantly influenced the crystalline structure of starch. These structural changes included the reduction in the relative crystallinity, IR ratio of 1,045/1,022 cm −1 , the lamellar peak intensity, and lamellar distance. With regard to pasting properties, LT increased the setback and decreased the peak, trough, final viscosities, and breakdown. However, LT reduced gelatinization temperature and enthalpy. For eating quality, the palatability of cooked rice under LT decreased, which was related to higher hardness as well as lower stickiness and gel consistency. Conclusions Low temperature during grain filling led to the deterioration of eating quality of cooked rice, and this deterioration could be attributed to high amylose content, low pasting viscosity, and reduced gel consistency. Significance and novelty The mean temperature at 22°C during the grain filling stage improved eating quality in soft japonica rice by enhancing pasting properties and gel consistency.