Combined effect of selected non-thermal technologies on Escherichia coli and Pichia fermentans inactivation in an apple and cranberry juice blend and on product shelf life

The combination of novel, non-thermal technologies for preservation purposes is a recent trend in food processing research. In the present study, non-thermal hurdles such as ultraviolet light (UV) (5.3J/cm ²), high intensity light pulses (HILP) (3.3J/cm ²), pulsed electric fields (PEF) (34kV/cm, 18Hz, 93μs) or manothermosonication (MTS) (4bar, 43°C, 750W, 20kHz) were examined. The objective was to establish the potential of these technologies, applied individually or in paired sequences, to inactivate Escherichia coli and Pichia fermentans inoculated in a fresh blend of apple and cranberry juice. The shelf-life evaluation of selected non-thermally treated samples was conducted over 35days and compared to pasteurised samples and untreated juices. All treatments applied individually significantly reduced (1.8-6.0logcfu/ml) microbial counts compared to the untreated sample (p<0.01). Furthermore, UV treatment produced significantly greater inactivation (p<0.05) for E. coli compared to P. fermentans. Combinations of non-thermal hurdles consisting of UV or HILP followed by either PEF or MTS resulted in comparable reductions for both microorganisms (p≥0.05) to those observed in thermally pasteurised samples (approx. 6logcfu/ml). Thermally pasteurised samples had a shelf life exceeding 35days, while that of UV+PEF and HILP+PEF-treated samples was 14 and 21days, respectively. These results indicate that combinations of these non-thermal technologies could successfully reduce levels of E. coli and P. fermentans in apple and cranberry juice, although optimisation is required in order to further extend shelf life.