Antimicrobial effects of onion (Allium cepa L.) peel extracts produced via subcritical water extraction against Bacillus cereus strains as compared with ethanolic and hot water extraction

In this study, the antimicrobial effects of an onion peel extract prepared using subcritical water extraction (SWE) were assessed for possible development into new bio-functional materials. The extraction temperatures were controlled to 110 and 160°C. At 0.15, 0.3, 0.6, and 1.2 mg extract/mL of broth, the growth inhibition and bactericidal activity of SWE extracts against Bacillus cereus KCCM 40935 and KCCM 11341 were compared with those of ethanol and hot-water extracts. In the case of B. cereus KCCM 40935, it appeared that over 0.6 mg/mL of SWE (110°C) extract exerted a bactericidal effect, and 1.2 mg/mL of SWE (160°C) extract exerted a bacteriostatic effect during culturing, and also that B. cereus KCCM 11341 was more resistant than B. cereus KCCM 40935. Furthermore, our results demonstrated that the death time of 107 CFU/mL of B. cereus KCCM 40935 treated with SWE (110°C) extract at 1.2 mg/mL was 60 min at maximum in 0.8% NaCl. Additionally, the cells damaged by SWE extract were observed with a SEM. It was suggested that an extract of onion peels prepared via SWE (110°C) could be used as a functional biomaterial for the food or pharmaceutical industries.