Abstract
Apples are naturally coated with a water-repelling hydrophobic wax layer, which may limit the antimicrobial efficacies of surface sanitizer solutions. Lauric arginate (LAE) is a cationic surfactant with antimicrobial efficacy against Listeria monocytogenes. In this study, we investigated the antimicrobial and the wettability effects of LAE in enhancing anti-L. monocytogenes efficacy of peracetic acid (PAA) and further verified the optimized treatment combinations in a pilot spray-bar brush bed system. Apples after 48 h of inoculation were treated with PAA surface sanitation in combination with different concentrations of LAE at 22 or 46°C. The effectiveness of PAA with LAE solutions in decontaminating L. monocytogenes significantly increased with the increased concentration of PAA (60–80 ppm) or LAE (0.01–0.05%) or the treatment temperature (from 22 to 46°C). A 30–120-sec wash by 80 ppm PAA with 0.01 and 0.05% LAE at 22°C reduced L. monocytogenes on apples by 2.10–2.25 and 2.48–2.58 log10 CFU/apple, respectively. Including LAE in the PAA solution decreased contact angles on apple surfaces. However, the increased wettability of the sanitizer solution may not be the main contributor to the enhanced antimicrobial efficacy of the PAA solution, given that the addition of Tween 80 or Tween 85 only slightly boosted the anti-L. monocytogenes efficacy of PAA solutions though both increased the wettability of the PAA solutions. The synergistic effects of PAA and LAE were further validated in a pilot spray-bar brush bed packing system, where a 30-sec spray wash with 80 ppm PAA and 0.05% LAE at 22 and 46°C caused 1.68 and 2.08 log reduction of Listeria on fresh apples, respectively. This study provides an improved PAA process/preventive strategy for ensuring microbial food safety of fresh apples that is applicable to commercial apple packing lines.
Highlights
Listeria monocytogenes can potentially transfer to fresh produce including apples during the postharvest handling, which results in deadly outbreaks (McCollum et al, 2013; Angelo et al, 2017)
peracetic acid (PAA) applied at 80 ppm, a concentration approved by the Food and Drug Administration (FDA) to wash fresh produce without further rinsing requirement (FDA, 2017a), is more efficient in decontaminating L. monocytogenes on fresh apples compared with 100 ppm chlorine-based sanitizers (Shen et al, 2019; Sheng et al, 2020a)
Adding Lauric arginate (LAE) as low as 0.001% significantly (P < 0.05) enhanced anti-Listeria efficacy of 80 ppm PAA, which resulted in an additional ∼ 1.48 log10 CFU/ml reduction of L. monocytogenes in water compared with that treated with 80 ppm PAA alone (Figure 1)
Summary
Listeria monocytogenes can potentially transfer to fresh produce including apples during the postharvest handling, which results in deadly outbreaks (McCollum et al, 2013; Angelo et al, 2017). Antimicrobial wash interventions including chlorine-based sanitizers (Du et al, 2002; Rodgers et al, 2004; Sheng et al, 2020a), organic acids such as lactic acid and citric acid (Park et al, 2011), and peracetic acid (PAA) (Rodgers et al, 2004; Shen et al, 2019) were used to decontaminate L. monocytogenes on fresh apples. Spray wash of 80 ppm PAA at the current industry practice (at ambient temperature for 30– 120 sec contact time) only resulted in about one log reduction of L. monocytogenes (Shen et al, 2020), indicating the need to boost the anti-Listeria efficacy of PAA
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