Purpose: This study develops an efficient sanitization strategy by using multiple sanitizer “hurdles” [chlorine (Cl2), aqueous chlorine dioxide (ClO2), and lactic acid] at practical industrial treatment times in combination with freezing against foodborne pathogens on blueberries.
Methods: Wild blueberries were inoculated with bacterial cocktail (two strains for each pathogen – Listeria monocytogenes or Salmonella Typhimurium) by a dipping method. To investigate synergistic effect of chemical sanitizers, a conveyer belt equipped with double spraying system was developed to spray 150 ml of multiple chemical sanitizers [chlorine 100 ppm (Cl2) + lactic acid (2%), aqueous chlorine dioxide 10 ppm (ClO2) + lactic acid (2%), and chlorine 200 ppm (Cl2) + aqueous chlorine dioxide 15 ppm (ClO2)] on 25 g of blueberries and later berries were exposed 10 sec, 1 min, and 3 min industrial treatment times. Bacterial enumeration was conducted before and after freezing (at -17°C for 1 week).
Results: The efficacy of multiple sanitizer “hurdle” when combined with freezing increased significantly in inactivating foodborne pathogens. The double spraying treatment of chlorine and lactic acid in combination with freezing resulted in 6.8 log CFU/g (detection limit <1 log CFU/g) reduction of L. monocytogenes at 3 min contact time. Other double spraying combinations like chlorine dioxide + chlorine and chlorine dioxide + lactic acid with freezing resulted in > 6 log CFU/g reduction of L. monocytogenes at 3 min contact. Salmonella Typhimurium was reduced to 7.1 log CFU/g (detection limit < 1 log CFU/g) with double spraying chemical treatments such as chlorine + lactic acid and chlorine + chlorine dioxide, in combination with freezing.
Significance: This approach of multiple sanitizer “hurdles” together with quick freezing process is worth to be considered by frozen fruit industries.