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Citrus fruit (Citrus unshiu) peels were extracted with hot water and then acid-hydrolyzed using hydrochloric acid. Antimicrobial activities of acid-hydrolyzed Citrus unshiu peel extract were evaluated against pathogenic bacteria, including Bacillus cereus, Staphylococcus aureus, and Listeria monocytogenes. Antilisterial effect was also determined by adding extracts at 1, 2, and 4% to whole, low-fat, and skim milk. The cell numbers of B. cereus, Staph. aureus, and L. monocytogenes cultures treated with acid-hydrolyzed extract for 12h at 35°C were reduced from about 8log cfu/mL to <1log cfu/mL. Bacillus cereus was more sensitive to acid-hydrolyzed Citrus unshiu peel extract than were the other bacteria. The addition of 4% acid-hydrolyzed Citrus unshiu extracts to all types of milk inhibited the growth of L. monocytogenes within 1d of storage at 4°C. The results indicated that Citrus unshiu peel extracts, after acid hydrolysis, effectively inhibited the growth of pathogenic bacteria. These findings indicate that acid hydrolysis of Citrus unshiu peel facilitates its use as a natural antimicrobial agent for food products.

Antibacterial activities of ginseng extracts produced from ginseng by-products, stems and leaves, using subcritical water extraction (SWE) at 110, 165 and 190°C, were evaluated and compared with those of ginseng extracts prepared by hot water and ethanol extraction. The ginseng stems-leaves extract produced by SWE at 190°C contained the greatest concentration of phenolics (98.4 mg GAE g À1 of extract). All ginseng extracts inhibited the growth of Bacillus cereus, Salmonella enteritidis, Escherichia coli O157:H7 and Listeria monocytogenes. Among four strains, B. cereus was more sensitive to the ginseng extract by SWE at 190°C than other bacteria. Cell membranes of bacteria were disrupted by the addition of SWE ginseng extract, observed by transmission electron microscopy (TEM), with the release of cellular contents. These findings provided evidence about the potential utilisation of ginseng stems and leaves by using an environmental friendly extraction process, SWE, to produce ginseng extract for the inhibition of bacteria growth. a Values are mean AE SD. Values followed by different letters within a column are significantly different (P < 0.05). b Total phenolic content was expressed as milligrams of gallic acid equivalent (GAE) per gram of extract (dry weight). c Total flavonoid content was expressed as milligrams of kaempferol equivalent (KE) per gram of extract (dry weight). d The diameter of inhibition zone (DIZ) of control without ginseng extract for each strain was 8.0 mm.