| Summary: | 碩士 === 國立屏東科技大學 === 食品科學系所 === 96 === The purpose of this study was to evaluate the antimicrobial activity of fruit extracts from cranberry (Vaccinium macrocarpon), unripe guava (Psidium guajava L.) and lemon (Citrus limon (Linn.) Burm.f.) against twelve foodborne microorganisms. The antimicrobial activities were examined by agar diffusion method. Results revealed that water extract of cranberry by ultrasonic extraction, the ethanol extracts of unripe guava at 50℃ and the ethanol extract of lemon by steeping showed higher antimicrobial activities respectively. 5% extracts of fruits in this study showed strong inhibitory effects against Penicillium italicum with inhibition ability than 78%. Extracts of cranberry and lemon showed stronger inhibitory effects against Aspergillus niger with inhibition ability over than 83%. The antimicrobial activities of all extracts didn’t decrease after heat treatment at 121℃ were for 20 min. Antimicrobial activities of cranberry and lemon extracts were affected by pH. Metal ions addition to extracts showed different influence on antimicrobial activities. Addition of citric acid and chitosan enhanced the antimicrobial
ability of lemon extract and all extracts respectively. The minimal inhibitory concentrations of these extracts against the 8 bacterial strains varied from 4 to 20 mg/ml. The antimicrobial mechanism of fruit extracts is bacteriostatic. Storage temperature (4-5, 37 and 60℃) didn’t affect the antimicrobial activities of all extracts. Comparing with potassium sorbate, the antimicrobial activites of 0.2% fruit extracts were better than potassium sorbate, especially against the Vibrio parahaemolyticus that expressing 40% higher activity. 5% lemon preservative inhibited the survival rate more than 90% of Listeria monocytogenes, Staphylococcus aureus, Pseudomonas aeruginosa and V. parahaemolyticus. In food model, examining the influence on total counts of chinese cabbage treated with 10% lemon preservative and commercial preservative for 5 days, the total counts were 8.5×108 CFU/mL and 4.65×102 CFU/mL respectively. Isolation and purification of antibacterial compounds of lemon extract were carried out by Sephadex G-25. Molecular weight of antibacterial compound was about 1104.23 Da. After purification, the antimicrobial component assayed by HPLC and compared with standard might be hesperidin. Different dosages (0.3125 0.625, 1.25, 2.5, 5 and 10 mg/plate) of lemon extract showed no toxicity and mutagenicity to Salmonella typhimurium TA97 and TA100. The antimutagenicity of lemon extracts is dose dependent. At the concentrations of 10 mg/plate, lemon extract reduced 55.56% of mutagenicity. Different dosages (250-1500 μg/mL) of lemon extract were used to treat rat normal liver cell (Clone 9) for 72 hr, the results showed that lemon extract didn’t reduce survival rate of Clone 9 cell line. In cytotoxicity assay, after 72hr treatment, 1500 μg/mL lemon extract displayed inhibitory effect on the growth of the human hepatoma cell lines Hep G2 resulting in the reduced survival rate of Hep G2 to 35.71%.
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