Isolation and Identification of Spoilage Fungi in the Fermentation Broth of Sanhua Plum, Evaluation of the Potency of Related Antibacterial Agents and Optimization of Fermentation Technology

In order to explore the causes of abnormal fermentation of Sanhua plum fruit by inoculating lactic acid bacteria and improve the fermentation process, the spoilage fungi were isolated and purified from the abnormal fermentation broth with white bacterial membrane on the surface, through morphological observation and ITS sequence identification, three dominant spoilage fungi were obtained, namely Candida stellimalicola, Pichia kudriavzevii and Pichia occidentalis; the Oxford cup method was used to evaluate antibacterial activity of sorbic acid, natamycin and dimethyldicarbonate, it was found that the three kinds of antibacterial agents had obvious inhibition zones on three strains of spoilage fungi, dimethyldicarbonate had slight inhibition on Lactobacillus casei used in fermentation, the diameter of inhibition zone was 10.45±0.11mm, which indicated that the three antimicrobial agents could be used to inhibit the growth and reproduction of spoilage fungi without affecting the normal fermentation; the combined bacteriostatic effect of antibacterial agents was determined by chessboard dilution method, natamycin on Pichia kudriavzevii was 0.50; the combined inhibitory effect of sorbic acid and dimethyldicarbonate on Candida stellimalicola and Pichia occidentalis was 0.50 and 0.38, respectively, all of them showed synergistic antibacterial effect; the fermentation process was optimized by response surface methodology; the results showed that 0.040% sorbic acid, 0.010% natamycin and 0.015% dimethyldicarbonate were added to the fermentation broth according to the fruit weight, fermentation time was 30 days at room temperature, the number of viable yeast in the fermentation broth was 3.212 lg CFU/mL, which was far lower than the number of viable yeast and mold in the fermentation broth of the old process, there was no white film on the surface of the fermentation broth. The new process was simple, effective and stable, the problems of softening and peculiar smell caused by abnormal fermentation were solved.