Abstract:

This study determined the minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) of plant derived active substances, and screened a synergistic combination of phloretin (Ph) and lauraldehyde (La) against the spores of Alicyclobacillus acidoterrestris by measuring the fractional inhibitory concentration index (FICI). The MIC of phloretin is 0.1 mg/mL, and MBC is more than 6.4 mg/mL; The MIC of lauraldehyde is 0.4 mg/mL, and MBC is more than 6.4 mg/mL; The FICI of the combined effect of the two substances is 0.5. The 8PL (2 MIC_Ph+2 MIC_La) synergistic combination showed the best spores killing effect in the synergistic combinations, and in the culture medium, the number of spores decreased by 6.1 log CFU/mL after 2 days of treatment in the 8PL synergistic combination; Inoculating 4 log CFU/mL of Alicyclobacillus acidoterrestris spores in apple juice, the 8PL synergistic combination treatment can reduce the spores to 0 CFU/mL after 1 day and maintain the effect for at least 14 days; For apple juice samples with an inoculation concentration of 6 log CFU/mL, the 8PL synergistic combination treatment required more than 3 days to reduce spores to 0 CFU/mL, but after 14 days, 2.2 log CFU/mL spores were detected again. As the concentration of synergistic combination increases, the spore absorbance significantly decreases and the fluorescence spectrum increases; By scanning electron microscopy, irregular wrinkles on the surface of the spores disappeared, and the surface gradually became smooth with an increase in the degree of depression and fragmentation. By transmission electron microscopy, it was observed that the spore membrane cracking; The leakage concentration of nucleic acids and proteins was gradually increasing. The above results indicate that the synergistic combination will cause certain damage to structures such as spore membranes. In addition, the release of pyridine dicarboxylic acid (DPA) also significantly increased, greatly reducing the stress resistance of spores. In summary, the synergistic combination of phloretin and lauraldehyde has a good killing effect on Alicyclobacillus acidoterrestris spores, and it is an effective strategy for fruit juice antibacterial and preservative properties.

Key words: Alicyclobacillus acidoterrestris, spores, juice, phloretin; lauraldehyde, food control technology