Determination of some functional properties and bioprotective potential of metabolites of native lactic acid bacteria isolates

In the relevant study, postbiotics were obtained from 10 native Lactic Acid Bacteria (LAB) and were analyzed for functional and antimicrobial properties. These species were from Lactobacillus (Lb. plantarum, Lb. paraplantarum, Lb. coryniformis, Lb. brevis, Lb. helveticus, and Lb. bulgaricus, Enterococcus (E. faecium and E. faecalis), Lactococcus (Lc. lactis), and Streptococcus (St. thermophilus) genera. The growth curve of all LAB was determined by measuring their optical densities. To obtain postbiotics, Lactobacillus species were anaerobically grown in MRS broth (37 ºC), and other LAB (enterococci, lactococci and streptococci) were grown aerobically (30 ºC) in M17 broth. Later, the bacterial pellet was separated by centrifugation, and postbiotics were taken to analyze for their functional properties such as antioxidant activity, antimicrobial activity, phenolic content, and organic acid content. These postbiotics were added to pasteurized milk (at 78 °C for 2 min) with and without E. coli (ATCC 25922) to check their bio-preservative effect during the shelf-life (1,5, and 10th days) of pasteurized milk. According to the obtained results, high antioxidant activity was shown by postbiotics of Lc. lactis, followed by that from E. faecalis while phenolic content was highest in postbiotics of Lb. plantarum and E. faecalis. In pasteurized samples of milk, although all postbiotics caused a decrease in E. coli (ATCC 25922) count, this decrease was significant in the presence of postbiotics from Lc. lactis, E. faecium, and Lb. helveticus which proved them to be having highest bio-preservatory activity. The TAMB count was reduced significantly by postbiotics of Lb. helveticus but was increased in samples containing postbiotics from Lb. plantarum and E. faecalis. While bio-preservative activity was shown by all postbiotics, considering the effect on pH, TA %, and rheology of pasteurized milk it was concluded that not all postbiotics were suitable for addition in pasteurized but could be evaluated for other dairy products as a bio-preservative