| Summary: | 博士 === 國立臺灣海洋大學 === 食品科學系 === 94 === The Pediococcus pentosaceus ACCEL bacteriocin was purified to electrophoretical homogeneity by cells-adsorption-desorption and Superose 12TM Fast Performance Liquid Chromatography (FPLC). The purified bacteriocin, with a Mw of 17.5 kDa and N-terminal sequence of -KYYGNGVTXGKHSXXVDXG-, was belonged to Class IIa and designated as pediocin ACCEL. It was inactivated by various proteases and stable at pH 2.0-6.0, <100�aC. More than 80% activity was left even after 15 min heating at 121�aC, pH 2.0–4.0. G (+) food-borne pathogens were inhibited by this bacteriocin, but G (−) was not. According to storage stability study, the purified pediocin ACCEL was stable at pH < 6.0 and low temperature. No significant change in bactericidal activity was observed after freeze-drying and subsequent 1-month storage at room temperature. In order to study the antimicrobial mechanism of pediocin ACCEL, effects of pediocin ACCEL and nisin on carboxyfluorescein diacetate (cFDA) stained Listeria monocytogenes BCRC 14845 was carried out. Decrease of fluorescence intensity in stained cells and increase in efflux were observed with the increase in bacteriocin concentrations up to 12.5 �慊/mL. No further decreases in fluorescence intensity and cell numbers was obtained when the concentration of bacteriocins was over 12.5 �慊/mL. The leakage of efflux was further confirmed by the release of intracellular ultraviolet-absorbing substances. Comparing the leaking time of fluorescence, the intensity of cFDA in nisin-treated cells within 1 min incubation was almost comparable to that in pediocin ACCEL-treated samples after 40 min incubation. Considering the leakage of cFDA, UV-absorbing substances, changes in cell numbers during incubation of cFDA stained cells, and restoration ability, nisin and pediocin ACCEL seemed to reveal inhihibiton effect on L. monocytogenes were mainly resulted from the pores formation on the cell membrane. They revealed both bacteriostatic and bactericidic effects.
To compare the biopreservative effectiveness of pediocin ACCEL with nisin, fresh fish fillets were immersed in different concentrations of pediocin ACCEL, nisin or their combination and stored at 4�aC and 0�aC, respectively. The Aerobic Plate Counts (APC) of those with bacteriocins was <102 CFU/g after 2 days storage at 0�aC, except that with 1,500 IU/mL of pediocin ACCEL. The APC of samples with nisin was >102 CFU/g after 2 d storage at 4oC, while that with pediocin ACCEL occurred after 1 d storage. Pediocin ACCEL and nisin could suppress L. monocytogenes during 2 and 1 wk storage at 4�aC, respectively. It seemed to be better than nisin in the inhibition of L. monocytogenes during 2 wks storage at 4�aC.
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