Development of novel Meju starter culture using plant extracts with reduced Bacillus cereus counts and enhanced functional properties

We developed a novel type of Meju starter culture using single and combined extracts of Allium sativum (garlic clove), Nelumbo nucifera (lotus leaves), and Ginkgo biloba (ginkgo leaves) to improve the quality and functionality of Meju-based fermented products. Meju samples fermented with plant extracts (10 mg/ml) showed phenolic contents of 11.4–31.6 mg/g (gallic acid equivalents). Samples of extracts (garlic clove, lotus leaves, ginkgo leaves and their combination) fermented with Meju strongly inhibited tyrosinase, α-glucosidase, and elastase activities by 36.43–64.34%, 45.08–48.02%, and 4.52–10.90%, respectively. Specifically, ginkgo leaves extract added to fermented Meju samples at different concentrations (1% and 10%) strongly inhibited tyrosinase, α-glucosidase, and elastase activities and exhibited a potent antibacterial effect against Bacillus cereus with a significant reduction in bacterial counts compared with the effects observed for garlic clove and lotus leaf added to Meju samples. Scanning electron microscopy revealed severe morphological alterations of the B. cereus cell wall in response to ginkgo leaf extracts. Gas chromatographic mass spectroscopic analysis of plant extract-supplemented Meju samples and control Meju samples identified 113 bioactive compounds representing 98.44–99.98% total extract. The proposed approach may be useful for the development of various fermented functional foods at traditional and commercial levels.