Chitosan inactivates spoilage yeasts but enhances survival of Escherichia coli O157:H7 in apple juice

Abstract

To develop new measures for controlling both spoilage and pathogenic micro-organisms in unpasteurized apple juice using chitosan.Micro-organisms were isolated and identified from apple juice treated or untreated with chitosan using enrichment, selective media, microscopy, substrate assimilation patterns and ribosomal DNA profiling. Chitosan (0.05-0.1%) delayed spoilage by yeasts at 25 degrees C for up to 12 days but the effect was species specific: Kloeckera apiculata and Metschnikowia pulcherrima were inactivated but Saccharomyces cerevisiae and Pichia spp. multiplied slowly. In challenge experiments at 25 degrees C, total yeast counts were 3-5 log CFU ml(-1) lower in chitosan-treated juices than in the controls for 4 days but the survival of Escherichia coli O157:H7 was extended from 1 to 2 days; at 4 degrees C, chitosan reduced the yeast counts by 2-3 log CFU ml(-1) for up to 10 days but survival of the pathogen was prolonged from 3 to 5 days. The survival of Salmonella enterica serovar Typhimurium was unaffected by chitosan at either temperature.The addition of chitosan to apple juice delayed spoilage by yeasts but enhanced the survival of E. coli O157:H7.The results suggest that the use of chitosan in the treatment of fruit juices may potentially lead to an increased risk of food poisoning from E. coli O157:H7.