Efficacy of Peroxyacetic Acid and Aqueous Chlorine Dioxide Treatments to Reduce Salmonella and E. coli O157:H7 on Frozen Berries and Mangoes

Introduction: Minimally processed fruit products, such as frozen fruit blends intended for raw consumption, pose a potential risk to consumers.  Proposed Food Safety Modernization Act (FSMA) regulations mandate implementation of preventive approaches to reduce microbiological food safety hazards in these products.  The primary option to control microbiological hazards is to employ sanitizers; however, limited data is available on their efficacy against foodborne pathogens under industry-relevant conditions. 

Purpose:  Evaluate efficacy of peroxyacetic acid and aqueous chlorine dioxide to reduce Salmonella and E. coli O157:H7 on frozen berries and mangoes.

Methods:  Frozen fruit pieces (berries or mangoes) were spot-inoculated with a five-strain cocktail of Salmonella spp. or E. coli O157:H7 to achieve 5 - 6 log CFU/g.  Inoculated fruit was and held at -20°C for 24 - 48 h prior to treatment with sanitizer. Peroxyacetic acid (Tsunami 200, 40 - 80 ppm) and chlorine dioxide treatments (Selectrocide, 5 ppm) were performed by agitating frozen fruit in a thermostatically-controlled circulating water bath (10°C - 30°C) for industry-relevant timeframes (15 - 60 seconds). Immediately following treatment, fruit samples were neutralized by diluting and gently rinsing in buffered peptone water (BPW; 1:2). Rinses were serially diluted with BPW and plated on tryptic soy agar and Hektoen Enteric Agar and incubated (37°C, 24 - 48 hours) prior to enumeration. 

Results:  Physical agitation and rinsing associated with all treatments resulted in significant reduction of both pathogens compared to inoculated, unwashed fruit (P < 0.05). Mean log reductions of 1.16 ± 0.46 to 1.61 ± 0.52 achieved by peroxyacetic acid treatments (40 and 80  ppm; 25°C) were significantly greater (P < 0.05) than treatments without sanitizer (0.78 ± 0.37). Chlorine dioxide (5 ppm) was not significantly more effective than water to reduce Salmonella spp. or E. coli O157:H7 on frozen fruits. 

Significance:  Peroxyacetic acid rinses (40 and 80 ppm) significantly reduce survival of foodborne pathogens on frozen berries and mangoes compared with water only.