Screening of an Antagonistic Endophytic Bacterium against Colletotrichum capsici and Its Fresh-keeping Effects on Postharvest Capsicum
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Abstract:
An antagonistic endophytic bacterium strain (P5) against Colletotrichum capsici was isolated from capsicum fruits, and identified as Bacillus subtilis based on observations of bacterial cell and colony morphologies, physiological and biochemical measurements, and 16S rDNA sequence analysis. The physical and chemical properties of the crude fermentation extract were determined with Colletotrichum capsici as the indicative bacterium. In addition, the fresh-keeping effects of the crude fermentation extract of P5 on postharvest capsicum were studied by measuring the weight loss rate, rate of decay, titratable acidity, and the contents of vitamin C, total carbohydrates, and chlorophyll, along with other quality indices of capsicum. The results indicated that the crude fermentation extract had good thermal stability, and the antibacterial activity was stable, showing no changes in an environment with a pH value <8.0 and a temperature range from 40~100 ℃. The antibacterial activity decreased to 85% of that of the control group after treatment at 121 ℃ for 30 min. No changes in the antibacterial activity were observed from pH 2.0 to pH 12.0 under room temperature, showing good stability to pH fluctuations. The crude fermentation extract was stable to ultraviolet (UV) light and could maintain 89.87% of the initial activities under UV irradiation for 12 h. The crude fermentation extract treatment group exhibited better fresh-keeping effect on postharvest capsicum compared with the sterile water treatment group, and the fermentation extract could effectively reduce the weight loss rate and rate of decay. The treatment inhibited the reductions in titratable acidity and the contents of vitamin C, total carbohydrates, and chlorophyll, showing an apparent fresh-keeping effect on capsicum.
