Survival of some food-borne pathogenic microorganisms in ozonated tropical fruits juices treated with chitosan

Abstract

Enteric pathogens in non-pasteurized fruit juices can cause gastroenteritis. The ability of chitosan to inactivate food-borne pathogens in tropical fruit juices was investigated. Challenge studies was conducted with Salmonella typhimurium, Escherichia coli 0157:H7, Listeria monocytogenes and Staphylococcus aureus. Tropical fruit juices employed were orange, pineapple, watermelon and a mix of the three. Fruit juices samples (100ml) were dispensed into 150ml conical flasks. Chitosan powder was added directly to the juice to give a final concentration of 1000μg/ml, 1500μg/ml and 2000μg/ml respectively. For challenge testing, 0.1ml of 24h old broth cultures of the microorganisms were inoculated into the flasks at a level of ≤ 6.69Log₁₀CFU/ml. The juices were then stored at 28^oC and 4^oC for 7-14 days and 20 days respectively. Chitosan concentration of 2000μg/ml was effective in killing Escherichia coli 0157:H7 in all fruit juices in 36 h irrespective of temperature of storage. Salmonella only survived up to 24h in pineapple and mixed fruit juices treated with ≥1500μg/ml chitosan. A greater killing occurred for Listeria monocytogenes with the application of concentration of 1500-2000μg/ml chitosan. At these concentrations Listeria monocytogenes counts were reduced from an initial challenge inoculum of 5.82log₁₀CFU/ml to zero count in 12h to 24h in all fruit juices. The addition of 1500μg/ml or 2000μg/ml chitosan to the juices reduced Staphylococcus counts to zero in 18h in watermelon and orange juices. The ≥5log reduction of these pathogens by chitosan demonstrates its potential preservative power for unpasteurised fruit juices.