Study on the correlation between metabolites and antioxidant activity during natural fermentation of fig enzyme
Edible plant enzymes are made from one or more fresh vegetables, fruits, mushrooms, and other raw materials, which are fermented for a long time by various beneficial bacteria. They contain rich functional components with high nutritional value, such as enzymes, organic matter, probiotics, and secondary metabolites. Not only does it give enzymes a unique flavor and taste, but it can also provide various health benefits to the human body, such as whitening, anti-aging, and enhancing immunity. Fruit enzymes have gradually become a research hotspot due to their good biological activity. For example, the SOD enzyme activity of fermented mulberry enzymes (24122.2U/mL) can be increased by 123% compared to mulberry juice (10818.7U/mL); Zhao et al. demonstrated through studying the effect of maturity on the quality of Norifruit enzyme that Norifruit enzyme has potential whitening and obesity prevention effects; Siroli et al. demonstrated that inoculating Lactobacillus plantarum strains CIT3 and V7B3 onto apples and lettuce, respectively, can improve the safety and shelf life of the products.

Fig belongs to the mulberry family fruit genus and is known as the “fruit of life”. It contains more than 18 types of amino acids, including 8 essential amino acids for the human body, as well as essential nutrients such as vitamins and carbohydrates. It has the effects of lowering blood pressure, moisturizing the intestines, and promoting bowel movements. Fig trees are rich in nutrients, but their skin is easily contaminated by microorganisms, making transportation and storage difficult after harvesting. Therefore, on-site fermentation is a better treatment method. At present, there is relatively little in-depth research on figs in the field of functional foods, mainly used for fresh or processed dried fruits, fruit pulp, preserved fruits, etc., which have problems such as relatively low product development value and added value. From the perspective of nutrition and health benefits, figs are an excellent plant resource for developing edible enzymes. In recent years, enzyme products have become mainstream in the international market, but domestic enzymes are still in the early stages of research and lack independent intellectual property rights. Fig enzymes are rarely reported. Processing figs into fig enzymes with high nutritional value is beneficial for the transformation, upgrading, and high-value utilization of the fig industry.

This article takes figs as the research object, prepares fig enzymes by natural fermentation method, and explores the changes in physical and chemical indicators (pH, total acid, organic acid), active substances (total flavonoids, total phenols), antioxidant activity (DPPP free radicals, hydroxyl free radicals, superoxide free radical scavenging ability and reducing power) during the fermentation process, in order to obtain the optimal fermentation time, standardize the traditional fermentation process by standardized means, and provide scientific research support for the natural fermentation of fig enzymes.

At present, there are few reports on the research of fig enzyme. The results of this study show that during the fermentation process, the pH value continues to decrease, and the total flavonoids show a fluctuating upward trend. The total acid, total phenol, DPPH free radicals, hydroxyl free radicals, superoxide free radical scavenging ability, and reducing ability all show a trend of first increasing and then decreasing. However, the DPPH free radical and hydroxyl free radical scavenging ability show irregular changes in the later stage of fermentation, so prolonging the fermentation time is not conducive to improving antioxidant capacity. Fig enzymes are rich in organic acids, including common lactic acid, citric acid, malic acid, and succinic acid, as well as a large amount of glucuronic acid and pantothenic acid. Correlation analysis shows that citric acid, malic acid, fumaric acid, and pantothenic acid in fig enzymes play an important role in their antioxidant activity. The comprehensive evaluation index analysis results show that the comprehensive score is highest on the 60th day of fermentation, and there is a significant downward trend after 80 days of fermentation. This can be used as a basis for the end of fig enzyme pre fermentation. The changes in metabolites and antioxidant activity in fig enzyme are the result of microbial extinction and adaptation. Therefore, it is necessary to study the changes in microbial flora during the natural fermentation process of fig enzyme, in order to implement more precise regulation of the fermentation process of fig enzyme, guide actual production, and obtain higher quality enzyme products.