Characterization of Bacteriocin-like Inhibitory Substances from Lactic Acid Bacteria Isolated during Spontaneous Fermentation of Shimeji Mushrooms (Hypsizygus sp.)

Abstract

Background: Spontaneous is an effective method to enhance the bioactivity and stability of foods through the action of Lactic Acid Bacteria (LAB), the dominant microbes in this fermentation which generate antimicrobial metabolites, while also serving as a form of biological preservation. Hypsizygus sp., an edible mushroom valued for its high nutritional value, is highly perisable and benefits from biological preservation strategies. This study investigated LAB isolated from spontaneous fermentation of Hypsizygus sp. and characterized their bacteriocin-like inhibitory activity.

Methods: Spontaneous fermentation was performed on Hypsizygus sp. using 2% NaCl, 1% sucrose, 3% chili pepper, and 2% garlic then incubated for 6 days at 27±1 °C. LAB were isolated on days 0, 2^nd, 4^th, and 6^th using de Man, Rogosa, and Sharpe agar (MRSA) medium, and characterized through colony and cell morphology, catalase activity, carbohydrate fermentation, and tolerance to salt and temperature.  Bacteriocin-like inhibitory substances activity and stability were evaluated for antibacterial activity and stability across temperature, pH, and proteolytic enzyme treatment. Statistical analysis used two-way ANOVA followed by Sidak’s post-hoc test (p<0.05).

Results: Four isolates exhibited promising traits, with ISL-2A and ISL-4G—identified as belonging to the genus Lactobacillus—demonstrating the highest antibacterial activity against Staphylococcus aureus and Escherichia coli. The bacteriocin-like inhibitory substances produced were stable across a pH range of 3.0–7.0 and temperatures up to 80 °C, but were inactivated by proteolytic enzyme.

Conclusion: These findings underscore the potential of LABs derived from fermented Hypsizygus sp. as natural antimicrobials and biopreservatives for food.