Effect of Different Yeast and Lactobacillus plantarum Combined Fermentation on the Quality of Xinhui Citrus Ferment

In order to evaluate the effect of complex fermentation of different yeasts and Lactobacillus plantarum on the fermentation quality of Xinhui citrus, three kinds of yeasts and Lactobacillus plantarum were used as raw materials for compound fermentation of fresh fruit pulp of Xinhui citrus. The changes of yeast viable count, total sugar content, pH and total acidity in fermentation broth were tracked during the fermentation process, and the bioactive substances and antioxidant activities of Xinhui citrus fermentation liquor in different fermentation systems were compared. The results showed that all the three strains of yeast could grow normally in Xinhui citrus, but the growth rate of Saccharomyces cerevisiae (Sc) and Kluyveromyces marxianus (Km) in Xinhui citrus was higher than that of Kazachstania unispora (Ku). Fermentation could increase the contents of total flavonoids, polyphenols and γ-aminobutyric acid of Xinhui citrus fermentation liquor and its antioxidant activity in vitro, but it could partially degrade crude polysaccharides. The contents of crude polysaccharide and γ-aminobutyric acid were the highest in the yeast fermentation system, which could reach 4.37 g/kg and 82.85 mg/kg. The content of total flavonoids in the yeast fermentation system was the highest, which was 1.54 g/kg. In addition, the hydroxyl radical scavenging rate and total reducing power of K. marxianus fermentation broth were 82.48% and 1.09, respectively, which were significantly higher than those of other yeast fermentation(P<0.05). At the same time, the SOD activity, DPPH free radical scavenging capacity and ABTS⁺ free radical scavenging capacity were 161.62 U/mL, 0.293 mg/mL and 0.489 mg/mL, respectively, which were similar to other fermentation systems, indicating that the antioxidant activity of the Xinhui citrus ferment was higher under the fermentation conditions. Therefore, the combined fermentation of K. marxianus and L. plantarum was superior to the other two systems in terms of active substance content and antioxidant capacity.