Inactivation activity and mechanism of natural antimicrobial agents against Alicyclobacillus spp. in apple juice

Alicyclobacillus spp. are one of the major harmful microorganisms that can cause fruit juice spoilage. In this study, the inactivation activity and mechanism of phenyllactic acid (PLA) and glycerol monolaurate (GML) against Alicyclobacillus spp. were evaluated, and their effects on fruit juice quality were also investigated. The results displayed that the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of GML were 0.01-0.02 mg/mL and 0.04-0.60 mg/mL, while those of PLA were in the range of 0.25-0.50 mg/mL and 0.5-16.0 mg/mL, respectively. All of these antibacterial agents disrupted the permeability of cell membranes, destroyed the morphology of bacteria, and led to the leakage of cell contents. GML could stimulate bacteria to release a large number of reactive oxygen species, causing some oxidative damage and destroying bacteria. Treatment with L-PLA could reduce the level of adenosine triphosphate (APT) in cells by inactivating ATP synthase. In addition, the MBC of GML and L-PLA in apple juice were 0.02-0.6 and 0.25-16 mg/mL, respectively, which mainly depended on the strain difference. The treatment of L-PLA and GML had no significant adverse effect on the quality of apple juice, except that GML had some effect on color and organic acids, and L-PLA increased the total acid content. Sensory evaluation revealed that these treatments did not affect the organoleptic properties of apple juice. This study provides preliminary theoretical and data support for the application of GML and L-PLA to control Alicyclobacillus spp. contamination in apple juice.