| Zha-chili is a special fermented food popular in Hunan,Sichuan,Chongqing and other regions.It uses fresh pepper as the main raw material and fermented with starchy raw materials,spices,salt and so on in different proportions.Zha-chili is widely used,suitable for spicy and sour,and has a unique taste,which is deeply loved by consumers.Zha-chili is a local specialty food,its industrial production is restricted by the fermentation process,resulting in the lack of flavor and unstable quality of the product.At present,most of the research on Zha-chili focuses on process optimization and flavor analysis,but there are no reports about improving the quality of Zha-chili by fragrant yeast and studying the nutrient substances in Zha-chili by simulating digestion in vitro.Therefore,in this study,at first the aroma-producing yeast was selected from the naturally fermented Zha-chili,and optimize the production process of Zha-chili by combining the Lactobacillus plantarum XZ3 which screened from the natural fermented Zha-chili by the experimental team in the early stage.Then comparing with the natural fermented and inoculated XZ3 fermented Zha-chili,the effect of mixed fermentation with fragrant yeast on the quality of Zha-chili was studied.At last,with the help of the domestic fourth-generation dynamic human stomach(DHS-IV),comparing the changes in nutrients,active ingredients and antioxidant properties of Zha-chili with three fermentation methods,and provide a theoretical reference for choosing Zha-chili that is more beneficial to human digestion and absorption.The main findings are as follows:(1)Research on the selection of aroma-producing yeast and the optimization of the technology of Zha-chili.Yeasts were isolated and purified from naturally fermented Zha-chili,and the suspected aroma-producing yeasts were selected based on the morphological characteristics of the colonies and the ability to produce esters,then tested for tolerance.The results showed that the top 5 yeasts with ester yield were Y50,Y11,Y19,Y26,Y21,among which Y11,Y19,Y50 were acid and salt tolerant and more suitable for fermentation.The control group(natural fermentation)had similar odor profiles to the inoculation group Y11,Y19,Y50,and Y50 had a higher overall response value.After linear discriminant analysis(LDA),the 4 groups of Zha-chilis were distributed in different areas,and the odor characteristics were different.Compared with the control group,the total ester content of Y11,Y19,and Y50 in the inoculation group increased by 36.7%,16.9%,and 164.2% respectively by GC-MS analysis,which was consistent with the order of total ester content measured by chemical methods,namely Y50>Y11>Y19> Control group.Aroma-producing yeast Y50 had the strongest ester-producing ability,obvious aroma characteristics and the highest comprehensive score of principal component analysis.It had been identified that aroma-producing yeast Y50 was Pichia kudriavzevii by 26 S r DNA.The optimal process conditions for compounding it with XZ3 were: XZ3: fragrant yeast Y50=1:1,the amount of mixed bacteria added was 2.5%,the amount of salt added was 4%,and the fermentation time was 6 days.The fuzzy comprehensive sensory score of Zha-chili was 8.45.It was bright yellow,sour and spicy,and had the unique sourness and aroma of Zha-chili.(2)The effect of fragrant yeast on the quality of Zha-chili.Comparing the differences in physical and chemical indicators,active ingredients and flavor substances among the naturally fermented Z0,the Z1 fermented with XZ3 and the Z2 fermented with XZ3 and aroma yeast Y50.The results showed that the p H value,total acid,nitrite,carotene,and total phenol contents of the 3 kinds of Zha-chilis were relatively close,but the content of reducing sugar was significantly different,and the content of Z2 was the lowest.The content of total flavonoids in Z2 and Z1 had no significant difference,but it was significantly higher than Z0(p<0.5).Eight kinds of polyphenols were detected in Z2,with the content of 819.82±3.68mg/kg,and the most detected species and the highest content.The organic acid content of Z2 was 25.456±0.316g/kg,which was57.8% and 32.2% higher than Z0 and Z1,respectively.Among them,the content of tartaric acid,formic acid,acetic acid,citric acid and succinic acid was higher.Compared with Z0 and Z1,the content of sweet amino acid of Z2 increased,and the ratio of bitter amino acid decreased.Compared with Z1,the content of total amino acids,essential amino acids and umami-flavored amino acids in Z2 increased.90,67 and 72 kinds of volatile flavor substances were detected in the 3 kinds of Zha-chilis,respectively.There were the most types of volatile substances in Z0,but the highest content of volatile substances in Z2,which was 10101.11±99.04 μg/kg and 33.3% and 16.1% higher than Z0 and Z1,respectively.Among them,esters,alcohols,aldehydes,and acids had increased,which was increased by 75%,358%,106%,and 23% respectively than that of Z0,and increased by 102%,59%,68% and 51% respectively compared with Z1.The content of ketones in Z2 was lower than Z1 but higher than Z0.Only 4 phenolic substances were detected in the 3 kinds of Zha-chilis.Although the types and contents of olefins in Z2 was lowest,it contained characteristic aroma components(+)-limonene and β-caryophyllene.(3)Study on the in vitro digestion characteristics of 3 kinds of Zha-chilis.The 3kinds of Zha-chilis were subjected to in vitro dynamic simulation digestion,and the digestion solution and digestion residue were collected at 30 min,60 min,90 min and120 min respectively.Determine the relevant indicators to study the digestive characteristics of Zha-chili.The results showed that the dynamic changes of the p H of the 3 kinds of Zha-chilis were consistent with the digestion trend of the human body.The average particle size of Z2 was the smallest in each digestion stage,and the digestibility was the highest.More than 70% of the starch in the 3 kinds of Zha-chilis was digested within 30 minutes,and the starch digestibility of Z1 and Z2 were higher than that of Z0.In each digestion stage,the protein digestibility of Z2 was the highest,and capsaicin was more released into the digestive juice.There was no significant difference in the total phenol content of Z0 and Z2(p>0.05),and the total phenol content of Z1 was the lowest in each digestion stage.The content of flavonoids in the 3kinds of Zha-chilis showed an overall downward trend,and the content of flavonoids in in Z0 decreased the most.The content of polyphenols in the digestive juice of the 3kinds of Zha-chilis decreased,and the types increased.Among them,the content of polyphenols in the digestive solution of Z2 was the highest.The scavenging ability of hydroxyl radicals in 3 kinds of Zha-chilis increased first and then decreased.Among them,Z0 had the strongest scavenging ability of hydroxyl radicals.The scavenging ability of ABTS free radicals of the 3 kinds of Zha-chili fluctuated in the range of83.2±0.1%～88.3±0.2%,which was basically stable.There was no significant difference in the reducing force of the digestive juices of Z0 and Z2,but they were significantly stronger than Z1.Conclusion: A strain of fragrant yeast Y50 was sieved from the naturally fermented Zha-chili,and it was identified as Pichia kudriavzevii.The best process with Lactobacillus plantarum XZ3 was: XZ3: fragrant yeast Y50=1:1,the amount of mixed bacteria was 2.5%,the amount of salt was 4%,and the fermentation time was 6 days.The comparison with natural fermentation and inoculated Lactobacillus plantarum fermentation showed that adding aroma yeast Y50 fermentation could improve the overall flavor quality of Zha-chili.The test in vitro simulated digestion showed that the Z2 with aroma-producing yeast Y50 had a higher degree of digestion,and showed certain differences in the digestion of protein,starch,capsaicin,and polyphenol components. |
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