Quantitative proteomics analysis of bacteriocin-like substance producing Lactococcus spp. in simulated vegetable and fruit media.

Lactic acid bacteria (LAB) and their metabolites such as bacteriocins have gained considerable interest in terms of their bio-preservative properties to improve food safety and quality. In this study, a quantitative proteomic investigation employing stable isotope labeling by peptide demethylation was carried out to investigate changes in intracellular proteins of bacteriocin-like substance (BLS) producing Lactococcus spp. 7.17 grown in vegetable or fruit juice culture media at 10 °C for 0, 3 or 7 days. In total, 1053 proteins in vegetable medium and 1113 in fruit medium were identified and quantified. Proteins that changed more than two- fold were identified as increased or decreased ones and grouped into four clusters. Those increased proteins were involved in the events of low temperature and ROS stress responses, DNA processing, transcription and translation, central carbon metabolism, fatty acid and phospholipid metabolism, amino acid and cell wall biosynthesis. Key proteins in relation to BLS producing property were also identified suggesting that at least one bacteriocin IIa production system exists in Lactococcus spp. 7.17. These findings provide insights into protein changes of L. lactis at low temperature and lay foundations for further investigations on BLS producing LAB using targeted quantitative proteomic approaches. SIGNIFICANCE OF THE RESEARCH: The inhibitory effects of Lactococcus spp. 7.17 on Listeria innocua in fruit and vegetable juice culture media were confirmed. Using a quantitative proteomic approach employing stable isotope labeling by peptide demethylation, 99 or 113 significantly changed proteins of Lactococcus spp. 7.17 grown in vegetable or fruit juice medium were determined, respectively. The significant change in protein abundance suggested an adaptive mechanism of Lactococcus spp. to culture condition at low temperatures. This research provides insights on protein changes of Lactococcus spp. which has potential application in fresh and fresh-cut fruit and vegetables at low temperature.