Study On The Mechanism Of Change And Antioxidant Activity Of Phenolic Acids And Peptides In Rice Wine Brewing Process

Rice wine,a popular family wine,has the advantages of low cost,easy fermentation and good taste.Studies have shown that under the action of microorganisms and other enzymes,large molecules such as protein,starch and fat in glutinous rice are converted into small molecules such as monosaccharides,peptides,phenolic acids and amino acids,and a small amount of harmful substances,for example,ethyl carbamate,are also produced.Current research on rice wine has focused on its volatile flavor components,and research on nutrients has mostly focused on small molecule compounds.This project investigated the metabolic changes of the nutrient phenolic acid and the harmful substance ethyl carbamate during the fermentation process and their connection with sensory characteristics,in addition to the antioxidant peptides in rice wine.1.Metabolic changes of rice wine compounds during fermentationThe metabolism of phenols during the fermentation of rice wine was analyzed by HPLC,and it was found that the content of most phenolic compounds increased and then decreased throughout the fermentation process,and reached a maximum at the72 nd hour.Protocatechuic acid was the lowest and catechin was the highest among the phenolic compounds.The sensory evaluation of the rice wine showed that the fermented rice wine was pleasant in taste at the 48 th hour and 72 nd hour.The correlation evaluation and the combination with the available literature revealed that chlorogenic acid,gallic acid and catechins contribute to the astringency of rice wine in rice wine.In addition,GC and UV analysis revealed that the concentration of the harmful substance ethyl carbamate during the fermentation of rice wine decreased and then increased with the advancement of fermentation,with the lowest value of 0.21μg/m L.The concentrations of citrulline,urea and ethanol increased significantly as fermentation progressed,while the concentration of arginine showed a significant decrease.In addition,the correlation analysis showed that urea,citrulline and ethanol showed positive correlation with ethyl carbamate,and the correlation was stronger for citrulline than for urea.Arginine was negatively correlated with ethyl carbamate.It was shown that urea,citrulline and alcohol are important precursors of ethyl carbamate in the fermentation and brewing process of rice wine,where the reaction of citrulline with alcohol plays a crucial role.And arginine will be involved in the synthesis of ethyl carbamate through conversion to urea and citrulline.2.Phenolic chemical metabolism changes brought on by the in vitro digestion of rice wineThe mouth cavity,stomach,and small intestine were all involved in the in vitro digestive process.The metabolism of phenolic compounds during in vitro digestion was evaluated in terms of total phenolic content,the content of each phenolic compound and antioxidant activity.The findings demonstrated that following oral digestion,total phenolic content,phenolic compound content,and antioxidant activity did not change significantly.However,following gastric and intestinal digestion,total phenolic content,phenolic compound content,and antioxidant activity all decreased.The bioaccessibility of most of the phenolic compounds in rice wine was found to be around 70% in the stomach and between 50-70% in the small intestine.3.Preparation of antioxidant peptides by enzymatic protein digestionAlkaline protease was used as the hydrolyzing enzyme and the peptide content and DPPH radical scavenging rate as the detection index.The optimal mating conditions for the production of antioxidant peptides were ultimately obtained by optimizing the enzymatic system p H,temperature,enzyme addition and feed-liquid ratio: system p H 10.5,temperature 45°C,enzyme addition 5000U/g,feed-liquid ratio20 mg/m L.The enzymatic digests were isolated and purified using Sephadex G-15,followed by LC-MS/MS for peptide sequence determination.The peptide sequences were screened by BIOPEP,Pep Draw and molecular docking to obtain three antioxidant peptides: ALPHAIL(Aln-Leu-Pro-His-Aln-IIe-Leu,733.89 Da),EWAPGAH(Glu-Trp-Ala-Pro-Gln-Ala-His,766.80 Da)FDDLYFDR(Phe-Asp-Asp-Leu-Yyr-Phe-Asp-Arg,1090.13 Da).By using solid-phase synthesis,the antioxidant activity of the synthesized peptides was also evaluated.The results revealed that these three peptides exhibited good antioxidant activity,with DPPH radical scavenging rates in the range of 60% and ABTS radical scavenging rates in the range of 78–88%.In order to investigate whether these three antioxidant peptides have other potential biological activities,molecular docking of angiotensin-converting enzyme(ACE)was performed on these three peptides.The molecular docking results showed that ALPHAIL(Aln-Leu-Pro-His-Aln-IIe-Leu,733.89Da)had good docking results with t ACE,and it was speculated that it might have ACE inhibitory activity,and the specific activity needs to be further investigated.This study analyzes rice wine in terms of water-soluble flavor substances,nutrients,and harmful substances,and provides some theoretical basis for the safe production and functional discovery of rice wine.