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Keywords:

  • apple juice;
  • chitosan;
  • Escherichia coli O157:H7;
  • Salmonella Typhimurium;
  • yeast

Abstract

Aims:  To develop new measures for controlling both spoilage and pathogenic micro-organisms in unpasteurized apple juice using chitosan.

Methods and Results:  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°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°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°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.

Conclusions:  The addition of chitosan to apple juice delayed spoilage by yeasts but enhanced the survival of E. coli O157:H7.

Significance and Impact of the Study:  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.