Antimicrobial properties of microencapsulated cell free supernatant of streptococcus thermophilus in combination with thyme extract on fish spoilage bacteria and food-borne pathogens

In this study, the antibacterial properties of the combination of microencapsulated Streptococcus thermophilus cell free supernatant and thyme extract on fish spoilage and pathogenic bacteria were investigated. The combined S. thermophilus supernatant with the microencapsulated ethanolic thyme extract had a particle size of 1.11-11.39 µm. A total of 11 compounds were determined in the cell free supernatant of S. thermophilus, acetic acid (39.64%), methyl-d3 1-dideuterio-2-propenyl ether (10.87%), and 7-octen-2-ol, 2-methyl-6-methylene ( 10.46%) were the main components. Thyme extract contained 7 components, the main component being carvacrol with 67.96% and 1,2,3-propanetriol with 25.77%. Significant differences (p<0.05) were observed in the inhibition zones of the extracts on bacteria. The highest inhibition effect was observed in raw thyme extract (p<0.05). The inhibitory effect of thyme extract on fish spoilage bacteria varied between 25.00 mm (P. damselae) and 41.67 mm (V. vulnificus). Microencapsulated S. thermophilus extracts showed lower inhibition zone against bacteria compared to their crude extracts (p<0.05). As a results, it was found that microencapsule forms of S. thermophilus extract prepared especially in combination with 2% thyme extract, generally showed a higher antimicrobial effect on bacteria.