Bacterial community of winter salad during fermentation, and its antimicrobial properties

Abstract

The mixture of pickled vegetables with tomato juice, known as winter salad, is one of Iranian traditional fermented foods. The present work aimed to identify the predominant bacterial community in winter salad during fermentation, and to evaluate the antimicrobial activity of its cell-free supernatant (CFS) against Aspergillus niger IBRC-M 30095, Botrytis cinerea IBRC-M 30162, Aspergillus flavus IBRC-M 30092, Pseudomonas aeruginosa ATCC 9027, Salmonella typhi PTCC 1609, Bacillus cereus ATCC 11778, and Staphylococcus aureus ATCC 25923 using disc diffusion agar and microdilution assays. The fermentation dynamics of winter salad, changes in pH, acidity, salt, ash, protein, and fat contents, and bacterial composition were analysed during spontaneous fermentation. A total of 120 bacterial isolates were identified using 16S rDNA sequencing. Results showed that the following genera were dominant in the early stage of fermentation: Lactobacillus (Lb. brevis, Lb. japonicus, Lb. pentosus, Lb. senmaizukei, Lb. plantarum, Lb. acidifarinae, Lb. parabrevis, and Lb. alimentarius) (44%); Leuconostoc (Ln. mesenteroides and Ln. palmae) (13%); Pediococcus (Pc. pentosaceus, Pc. parvulus, Pc. cellicola, Pc. argentinicus, and Pc. stilesii) (7%); Acinetobacter (Ab. johnsonii) (4%); Enterobacter (E. soli) (10%); and unclassified isolates (22%). All isolates were identified successively during fermentation for 40 days; however, the species count changed throughout the fermentation. The CFS of winter salad showed inhibitory activity against all tested fungal species. Ps. aeruginosa and Sa. typhi were the most sensitive bacteria, while the minimum inhibitory percentage (MIP) and minimum bactericidal percentage (MBP) showed that St. aureus (MIPCFS-c 75; MBPCFS-c 75) and Ba. cereus (MIPCFS-c 50; MBPCFS-c 75) were the most resistant bacteria.