Products of Lactobacillus delbrueckii subsp. bulgaricus strain F17 and Leuconostoc lactis strain H52 are biopreservatives for improving postharvest quality of 'Red Globe' grapes

Authors: FANG, XIANG - Lanzhou University; DUAN, QINCHUN - Lanzhou University; WANG, ZHUO - Lanzhou University; LI, FUYUN - Lanzhou University; DU, JIANXIONG - Lanzhou University; KE, WENCAN - Lanzhou University; LIU, DIRU - Lanzhou University; Beier, Ross; GUO, XUSHENG - Lanzhou University; ZHANG, YING - Lanzhou University

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2020
Publication Date: 4/30/2020
Publication URL: https://handle.nal.usda.gov/10113/7033678
Citation: Fang, X., Duan, Q., Wang, Z., Li, F., Du, J., Ke, W., Liu, D., Beier, R.C., Guo, X., Zhang, Y. 2020. Products of Lactobacillus delbrueckii subsp. bulgaricus strain F17 and Leuconostoc lactis strain H52 are biopreservatives for improving postharvest quality of 'Red Globe' grapes. Microorganisms. 8(5):656. https://doi.org/10.3390/microorganisms8050656.
DOI: https://doi.org/10.3390/microorganisms8050656

Interpretive Summary: As consumer awareness of food contaminants and human health has increased, consumers are more informed of food safety issues and critical of the use of chemical food preservatives. Currently, the quality of postharvest table grapes is controlled primarily by gaseous sulfur dioxide fumigation. However, the levels of sulfur dioxide are difficult to control, and the residues can be harmful to humans as well as impart a sulfurous flavor to the grapes. In this study, we investigated the Lactobacillus delbrueckii susp. bulgaricus strain F17 isolated from traditional fermented yak milk obtained from Qinghai-Tibetan Plateau, China as a potential biopreservative to improve the postharvest quality of “Red Globe” table grapes. Strain F17 was cultured, and then the bacteria were removed from the culture resulting in a supernatant that contained all the secondary metabolites of the bulgaricus strain. The primary metabolites are produced by bacteria to play a role in the growth of the bacteria, but the secondary metabolites are small molecular weight compounds produced by the bacteria which are used to regulate or suppress other organisms. The supernatant of strain F17 significantly reduced grape berry weight loss, decay rate, aerobic bacteria growth, delayed maturity and senescence of the grapes, and strain F17 was more effective and resulted in better sensory evaluations compared to another strain of bacteria and the control. Based on the data collected in this study and the sensory organoleptic qualities as determined by a panel of tasters, the secondary metabolites from strain F17 had the best potential as a biopreservative to improve the postharvest quality of “Red Globe” table grapes.

Technical Abstract: The effects of secondary metabolites of Lactobacillus delbrueckii subsp. bulgaricus strain F17 and Leuconostoc lactics strain H52 on “Red globe” table grapes were investigated for enhancement of shelf-life and improvement of quality characteristics of grapes during postharvest storage. Strains F17 and H52 were isolated from traditional fermented yak milk obtained in the Qinghai-Tibetan Plateau, and their supernatants were used to improve preservation of table grapes. Samples from untreated and treated grapes stored at 25 °C for 0, 5, 10, 15, and 20 d were analyzed for physicochemical, biochemical, and microbiological properties (weight loss, decay rate, pH, total soluble solids content, titratable acidity (TA), total phenols, sensory evaluation, and microbial growth). Although results demonstrated supernatants from both strains F17 and H52 significantly reduced weight loss, decay rate, aerobic mesophilic bacteria and coliform bacteria counts, delayed maturity and senescence of table grapes, and reduce TA and total phenols, strain F17 was more effective and resulted in better sensory evaluations. For yeast and mold, the supernatant from strain F17 had a significant inhibitory effect by day 5, but the colony counts on day 5 to 20 were only slightly less than that of the control group. The supernatant from strain H52 had a significant inhibitory effect on yeast and mold over the whole storage period. In addition, the results of the Pearson correlation analysis suggested that weight loss, decay rate, total soluble solids content and microorganism were highly correlated with sensory evaluation data and quality of postharvest grapes when treated with strain F17 secondary metabolites. Based on this data and sensory organoleptic qualities, secondary metabolites from strain F17 had the best potential as a biopreservative to improve the postharvest quality of “Red Globe” table grapes.