关键词: 全谷物糙米, 化学组成, 淀粉消化特征, α-葡萄糖苷酶抑制能力, 二肽基肽酶-Ⅳ抑制能力

Abstract:

【Objective】This study elucidated the starch digestion characteristics of different colored rice grains, and identified the differences in their hypoglycemic activities, such as α-glucosidase and dipeptidyl peptidase-IV inhibition capacity, during cooking and in vitro digestion. It would provide a basis for dietary optimization of whole rice grains diets and the development of functional rice products. 【Method】 An in vitro digestion method was employed to determine the starch digestion rates of polished and brown rice of non-pigmented, red, and black rice grains. Simultaneously, the differences was systematically analyzed and compared among these rice varieties based on their percent of bran part in brown rice, total starch, apparent amylose, total protein, protein fractions (albumin, globulin, prolamin and glutenin), and pasting properties of rice flour. Correlation analysis was conducted to explore the relationships among these indicators. The INFOGEST method was used to simulate the digestion of three colored rice grains cooked in a high-pressure rice cooker. The α-glucosidase and dipeptidyl peptidase-IV inhibitory capacities of bioactive constituents were measured in raw, cooked, and digested rice grains.【Result】 Brown rice exhibited a lower degree of starch digestion, and its starch digestion characteristics were related to its chemical composition. The final degree of starch digestion and the rapid digestion rate of rice starch were not directly correlated, but they showed a negative and positive correlation with the digestion coefficient, respectively (P<0.05). The starch digestion rate constant was significantly positively correlated with prolamin content. The rapid starch digestion rate was significantly positively correlated with percent of bran part in brown rice, total starch, and albumin content, while it was significantly negatively correlated with globulin and apparent amylose content. The final degree of starch digestion was significantly negatively correlated with percent of bran part in brown rice, albumin, and prolamin content (P<0.05). The digestion characteristics of starch also exhibited a certain correlation with its pasting properties. Rice with lower trough and final viscosity and higher breakdown value tended to have a higher rapid starch digestion rate. Colored rice varieties exhibited higher hypoglycemic activities, where red rice had higher α-glucosidase inhibitory capacity and black rice had higher dipeptidyl peptidase-IV inhibitory capacity. During cooking and in vitro digestion, the α-glucosidase inhibitory capacity of non-pigmented and red rice decreased first and then increased, while that of black rice remains basically unchanged. The DPP-IV inhibitory capacity of non-pigmented rice gradually increased during cooking and in vitro digestion, especially after digestion, while that of red and black rice exhibited initial decrease and then increase.【Conclusion】The starch digestion degree of brown rice is lower than that of polished rice. After cooking and digestion, the differences in α-glucosidase or dipeptidyl peptidase-IV inhibitory capacities among different colored rice grains were not significant. However, considering the synergistic effects of these two hypoglycemic activities, black rice grains showed certain advantages in reducing blood glucose levels.

Key words: brown rice, chemical composition, starch digestion characteristics, α-glucosidase inhibitory capacity, dipeptidyl peptidase- IV inhibitory capacity