Storage temperature effects on survival of Escherichia coli and Escherichia coli O157:H7 in fresh orange juice [Citrus sinensis (L.) Osbeck]

Orange juice is the predominant juice manufactured by the beverage processing industry worldwide. However, this product is not free from microbiological spoilage problems, especially unpasteurized single-strength juice. This challenge study was undertaken to assess the effects of storage temperature on survival of Escherichia coli ATCC 25922 and Escherichia coli O157:H7 ATCC 35150 in fresh Sanguinello, Tarocco and Moro orange juice [Citrus sinensis (L.) Osbeck] varieties. Standard (ascorbic acid) and sensory (anthocyanins)-influencing quality parameters of these orange juice cultivars were monitored in order to detect the limiting quality factor. Microbial and nutrient analyses were conducted every week. The initial concentration (ca. 5x108 cfu ml-1) of E. coli gradually decreased by about 3 log10 in 4 weeks in all varieties compared to the control samples. Escherichia coli O157:H7 cells were reduced in Sanguinello juice with the same trend as E. coli whereas the former decreased by about 5 log10 and 6 log10 in Moro and Tarocco juices respectively. Both strains seem to use ascorbic acid for the their survival, they significantly (P > 0.001) reduced the ascorbic acid concentrations in all orange juice varieties with respect to variety controls. The strains significantly also decreased the anthocyanins content in Sanguinello (P > 0.05) and Moro (P > 0.001) juices but not in the Tarocco juice. The reduction of the bacterial number of each strain was highly correlated (r > 0.99) to ascorbic acid and anthocyanin degradation levels. Despite its physical and chemical properties and critical conditions it is subjected to during storage, the fresh orange juice can be considered a food suitable for the survival of E. coli and E. coli O157:H7. Moreover, the ascorbic acid could be held as a good control marker to monitor microbiological quality and safety of orange juice.