Efficacy of low concentration acidic electrolysed water and levulinic acid combination on fresh organic lettuce (Lactuca sativa Var. Crispa L.) and its antimicrobial mechanism

• Published in: Food control Vol. 101; pp. 241 - 250
• Main Authors: Zhao, Lin, Zhao, Mitchie Yiqi, Phey, Chin Ping, Yang, Hongshun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2019
• Subjects: Atomic force microscopy; Bacterium; Electrolyzed water; Epifluorescence microscopy; Escherichia coli; Listeria; Mechanism; Microbial safety; Modeling; Nanostructure; Organic acid; Organic produce; Physicochemical property; Protein; Sanitization; SDS-PAGE; Atomic force microscopy; Organic produce; Organic acid; Escherichia coli; Nanostructure; Sanitization; Epifluorescence microscopy; Modeling; Protein; Mechanism; SDS-PAGE; Bacterium; Listeria; Physicochemical property; Microbial safety; Electrolyzed water
• ISSN: 0956-7135; 1873-7129
• DOI: 10.1016/j.foodcont.2019.02.039

The sanitising effect of low concentration acidic electrolysed water (AEW, free available chlorine (FAC): 4 mg/L) combined with levulinic acid (LA, 3% v/v) on fresh organic lettuce during 7-day storage was evaluated. The combined sanitising method showed additional bactericidal efficacy against naturally existing microbiota, while LA alone and combined with AEW could reduce survival population of Escherichia coli ATCC 25922 and Listeria innocua Seeliger ATCC 33090 inoculated on lettuce surface effectively, with 3.5–4.0 log CFU/g reduction for both during storage. Moreover, the modified Gompertz model provided a good fitness to the sanitising results during storage, with highest R2 in AEW group for E. coli (0.99) and in combination group for L. innocua (1.00), respectively. In addition, the physicochemical properties of organic lettuce treated by each sanitising treatment were not changed significantly during storage. Epifluorescence microscopy and atomic force microscopy (AFM) revealed that the cell permeability and morphology of E. coli and L. innocua were changed after sanitising treatments, with damaged cell membrane and disordered cellular structure in different degrees. Besides, the size of cells became smaller after combined sanitising treatment, with 2.12 and 1.24 μm2 for E. coli and L. innocua, respectively, indicating some cytoplasm leakage. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed the number and intensities of the protein bands of E. coli were reduced, while those of L. innocua remained similar after sanitising treatments. The results suggest that low concentration AEW combined with LA is a potential effective approach to sanitise organic produce. •Low concentration acidic electrolysed water was combined with levulinic acid.•Combination treatment showed broad spectrum bactericidal effect on organic lettuce.•Cell membrane permeability and morphologies were damaged by combination treatment.•Whole cell protein profiles were changed under combination treatment.•Combination treatment is promising for sanitisation in organic produce industry.