Study On Physicochemical And Volatile Characteristics Present In Different Layer Of Rice,and In Vitro Fermentation Characteristics For Polyphenolic

Polished rice is obtained by milling the rice grain from out layer to the inside after husking,and the different milling degree can influence the functional properties and edible quality of rice.In general,the higher milling degree provides a better cooking quality.However,an excessive milling can cause a loss of nutrients and characteristic flavors.In addition,compared with white rice,the pigmented rice is rich in various phenolic acids,anthocyanins and flavonoids,which have attracted more attention for the consumers.But previous studies have shown that about 90% of the phenolic compounds need to reach the colon,where can be transformed and utilized by the gut microbiotas.Therefore,in this study,five kinds of rice were used as raw materials,and they were milled into three layers to explore the physicochemical properties and volatile characteristics present in different grain layer of rice.At the same time,three kinds of pigmented rice were used as raw materials to extract the phenolic compounds,and explored the interaction between phenolic compounds and gut microbiotas,the aim of this study is provide a theoretical basis for the processing and utilization of rice from physicochemical properties,flavor and nutrition.The main results are as follows:(1)The non-starchy components in rice are mainly concentrated in the outer layer of rice,and the starch granules in the third layer presented the smallest particle size and the largest crystallinity;Gelatinization property shown that the first layer shown a lower peak viscosity and higher gelatinization temperature;Rheological properties shown the G’ and G’’ of the starch paste increased gradually from the surface to the center of rice grains,showing higher viscoelasticity;The digestion property showed that the second layer had the highest digestibility,while the third layer had slower digestion.(2)The types and contents of volatile components gradually decreased from the outward to the inward in the rice grains,and the 2-Acetyl-1-pyrroline was only detected in shan lan xiang and hei se dao gu;1-octen-3-ol,2-pentylfuran and 2-acetyl-1-Pyrroline had an important contribution to the flavor for the cooked rice;the result analyzed by Principal component analysis shown that 6-methyl-5-heptanone-2-one,2-pentylfuran,1-octen-3-ol could be used to distinguish the flavors of different grains.(3)Protocatechuic acid,chlorogenic acid,caffeic acid and p-coumaric acid were the major metabolites after gut microbiota fermentation;Phenolic compounds could modulate the structure of gut microbiota,the ratio of Firmicutes and Bacteroidetes and the abundance of Proteobacteria were increased significantly,The results at genus level showed that phenolic compounds could promote an increase of Prevotella,Megamonas and Bifidobacteriu,while the Bacteroides and Escherichia-Shigella were inhibited;In addition,the presence of phenolic compounds promoted the synthesis of short-chain fatty acids by gut microbiotas.(4)Correlation analysis of phenolic compounds and gut microbiota indicated that ferulic acid and syringic acid were positively correlated with Lactobacillus,Megamonas were positively correlated with catechin and caffeic acid,the Escherichia-Shigella and Citrobacter were significantly negatively correlated with chlorogenic acid.