| Apple is the most produced and consumed fruit in China, and is one of the most popular fruit to produce fresh-cut fruits and vegetables. Since the peel is removed, fresh-cut apple is sensitive to foodborne pathogens. Salmonella is the most common pathogen associated with fresh-cut fruits and vegetables. Ultraviolet (UV) and lactic acid bacteria (LAB) were selected to investigate their antibacterial capability against Salmonella and mould and yeast on fresh-cut apple, their influence on the quality of fresh cut apple (soluble solids content, titratable acid content, color, firmness, polyphenol oxidase activity and sensory) was also detected. Baranyi model was applied to fit the growth of microorganisms on fresh cut apple. The main contents of this study were:1. Baranyi model were used to monitor the growth of the Salmonella and mould and yeast at 4,10,15 and 25 ℃ in 168 h. The results showed that:the models fitted well with the growth of the tested microorganisms as the coefficient of determination were relatively high, and the root mean square error were relatively low and the fitted models reached the significant level of P<0.01.2. This study used 0.48,0.96,2.88,4.80,9.60 kJ/m2 UV irradiation to detect the germicidal efficiency against Salmonella and mould and yeast on the surface of fresh cut apple. The results showed that at the UV irradiation of 0.96 kJ/m2, Salmonella population reduction and mould and yeast reduction were 2.38±0.16 and 1.03±0.11 log(CFU/g), respectively. However, higher irradiation dose did not cause more reduction or only caused only a slightly more reduction. For the quality of fresh cut apple, no significant quality deterioration was observed between treated or untreated with different UV irradiation during storage time at 10 ℃ . Thus, the double sides UV irradiation device was very promising to apply on the safety control of fresh cut apple.3. This study was to isolate lactic acid bacteria (LAB) from pao cai with outstanding inhibitory activity against Salmonella inoculated on fresh cut apple, using modeling method. Four kinds of pao cai were selected. A total of 122 isolates exhibited typical LAB characteristics:Gram-positive and catalase negative, among which 104 (85.24%) colonies showed antibacterial capability against Salmonella by well diffusion assay. Four colonies showing maximum antibacterial radius against Salmonella were selected to co-inoculate with Salmonella on fresh cut apple and stored at 10 ℃ , further identified as three strains of Lactobacillus plantarum and one strain of Lactobacillus brevis by 16s rRNA gene sequences analysis. The Baranyi model was employed to analyze the growth of the microorganisms on apple wedges. RD1, exhibited best inhibitory activity (Salmonella were greatly inhibited when co-inoculated with RD1 at 10℃ in the 168 h). The LAB RD1 is a promising agent to be applied on the preservation of fresh cut apple.4.3.57±0.28,4.36±0.31,5.59±0.10 log(CFU/g) LAB were co-inoculated with Salmonella on fresh-cut apple to detect the minimum concentration to be applied on fresh-cut apple. Their influence on the quality of fresh-cut apple was also detected. The results showed that at low concentration of 3.57 log(CFU/g), LAB could have a good antibacterial ability, Salmonella could not growth when co-inoculated with LAB at this concentration. And LAB could inhibit the growth of mould and yeast on fresh-cut apple. Tested concentration of LAB did not cause any deteriorate of soluble solids content, titratable acid content, color, firmness and polyphenol oxidase activity of fresh-cut apple, however, after 2 d storage, the sensory score of fresh-cut apple inoculated with LAB was lower than that not inoculated with LAB.5. UV irradiation and subsequently inoculating with LAB was applied to compare the disinfection ability with chlorine method. In the test group, apple wedges inoculated with Salmonella were placed in the center of test tray to be irradiated by UV for 0.96 kJ/m2, and subsequently inoculated with 3.89±0.33 log(CFU/g) LAB. In the control group, apple wedges were submerged in 200 mg/L chlorine solution for 3 min. The treated apples were stored at 10 ℃ for 8 d. The results showed that after UV and LAB treatment, Salmonella and mould and yeast dropped by 2.67±0.13 and 0.96±0.23 log(CFU/g), but in the control group, Salmonella and mould and yeast only reduced by 1.25±0.38 and 0.40±0.12 log(CFU/g). During storage, Salmonella did not grow in test group, but grown in control group. The results of sensory test showed that just after treatment, the scores in control group were significant lower (P＜0.05) than that in test group. The chlorine-like scent was contributed to the low score in control group. However, after 2 d storage, panelists gave a lower score to test group because of abnormal sour taste.No physiological and biochemical quality differences were found between test and control group. |
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