甘油水溶液提取米糠多酚绿色工艺优化及多酚种类鉴定.

During rice-milling process, rice bran is produced as one kind of byproduct with high contents of polyphenols. Although there is a huge amount of rice bran in China, most of it is used to feed animals. Therefore, it is inevitable to fully explore the additional value of rice bran for the economic benefit of rice processing industry. Rice bran can be used for extraction of polyphenols. Conventional solvents are methanol, acetone and ethanol, which exhibit some disadvantages. To overcome these disadvantages, we need to find a suitable solvent to replace conventional solvents. Glycerol is one kind of colorless, odorless, viscous liquid, which is sweet-tasting and non-toxic. It is widely applied in the food and pharmaceutical industry. Glycerol might be a potential alternative for green extraction of polyphenols from rice bran. Thus, in our research, a green extraction process of polyphenols from rice bran using glycerol was studied. Four individual factors including extraction temperature, volume fraction of glycerol, liquid-to-solid ratio and extraction time were chosen, and single-factor experiments combined with response surface methodology (RSM) were applied for optimization of the extraction process. The relationship between extraction efficiency of glycerol and its viscosity, the physical property, was analyzed and a UPLC-Triple-TOF/MS method was also conducted for identification of polyphenols. Results showed the order of independent factors affecting the yield of polyphenols was as follows: extraction temperature> volume fraction of glycerol>liquid-to-solid ratio. The ANOVA analysis revealed that independent factors (extraction temperature, volume fraction of glycerol and liquid-to-solid ratio), interaction effect (extraction temperature and volume fraction of glycerol) and their quadratic terms significantly influenced the yield of polyphenols (P<0.05). The optimum conditions were extraction temperature at 67 °C, volume fraction of glycerol at 19 %, liquid-to-solid ratio at 33 mL/g and extraction time fixed at 80 min. Under the optimal conditions, the maximum yield of polyphenols was 700.35 mg/100 g. There is a significantly negative correlation between extraction efficiency of glycerol and its viscosity. During extraction processes, the viscosity of glycerol changed as extraction conditions changed. As the viscosity increased there was a significant decrease in yield of polyphenols, with significant negative correlation coefficient value of -0.878 9 (P<0.01). Under the optimal conditions, there were thirteen phenolic compounds identified in the glycerol extract according to UPLC-Triple-TOF/MS analysis. The quantification of all the six phenolic acids was conducted by UPLC. The contents of phenolic acids were as follows: 4-hydroxybenzoic acid (48.53 μg/g), vanillic acid (69.64 μg/g), syringic acid (33.63 μg/g), 4-coumaric acid (361.18 μg/g), ferulic acid (392.17 μg/g), and salicylic acid (34.67 μg/g), which significantly enhanced the value of rice bran. [ABSTRACT FROM AUTHOR]