Bacterial inactivation in fruit juices using a continuous flow Pulsed Light (PL) system

In this work, the susceptibility to pulsed light (PL) treatments of both a Gram-positive (L. innocua 11288) and a Gram-negative (E. coli DH5-α) bacteria inoculated in apple (pH=3.49, absorption coefficient 13.9 cm−1) and orange juices (pH=3.78, absorption coefficient 52.4 cm−1) was investigated in a range of energy dosages from 1.8 to 5.5 J/cm2. A laboratory scale continuous flow PL system was set up for the experiments, using a xenon flash-lamp emitting high intensity light in the range of 100–1100 nm. The flashes lasted 360 μs at a constant frequency of 3 Hz. The results highlighted how the lethal effect of pulsed light depended on the energy dose supplied, the absorption properties of liquid food as well as the bacterial strain examined. The higher the quantity of the energy delivered to the juice stream, the greater the inactivation level. However, the absorbance of the inoculated juice strongly influenced the dose deliver and, therefore, the efficiency of the PL treatment. Among the bacteria tested, E. coli cells showed a greater susceptibility to the PL treatment than L. innocua cells in both apple and orange juices. Following treatment at 4 J/cm2, microbial reductions in apple and orange juices were, respectively, 4.00 and 2.90 Log-cycles for E. coli and 2.98 and 0.93 Log-cycles for L. innocua. Sublethally injured cells were also detected for both bacterial strains, thus confirming that membrane damage is an important event in bacterial inactivation by PL

The Effect of Ultraviolet Light on Microbial Inactivation and Quality Attributes of Apple Juice

Non-thermal technologies such as UV irradiation can offer advantages for minimal processing of transparent beverages. In this study, reconstituted apple juice was exposed to UV light in a continuous laboratory scale system at energy dosages ranging from 2. 66 to 53. 10 J/cm 2 by changing the exposure time. Treated juices were then evaluated for microbial inactivation and selected physical and chemical attributes. Product quality was further assessed by sensory evaluation using a 30-member consumer panel. Microbiological analysis was performed by inoculating apple juice with Escherichia coli K12 and Listeria innocua and microbial numbers were counted pre- and post-processing. UV energy levels did not affect pH, °Brix, or total phenols content, but decreased non-enzymatic browning (p < 0.01) and antioxidant capacity (p < 0.05) compared to unprocessed juice. A colour-lightening effect was noted with increasing energy dose. All UV treatments applied (2.66 J/cm 2 and above) resulted in a reduction below the detection level (<1 log cfu/ml) for both E. coli and L. innocua in apple juice. Sensory evaluation showed that samples treated with energy dosages up to 10.62 J/cm 2 were comparable to the control in terms of acceptability, though higher dosages produced adverse effects in terms of flavour and colour. Based on these results, UV treatment with low energy dosages could represent a valid alternative to thermal processing to eliminate pathogenic microorganisms while maintaining quality in reconstituted apple juice.Department of Agriculture, Food and the MarineAccess provided by IReL consortiumNon-Commissioned Food Institutional Research Measur

Effects on Escherichia coli inactivation and quality attributes in apple juice treated by combinations of pulsed light and thermosonication

Pulsed light (PL) and Thermosonication (TS) were applied alone or in combination using a continuous system to study their effect on Escherichia coli inactivation in apple juice. Selected quality attributes (pH, °Brix, colour (L, a, b, ÄE), non-enzymatic browning (NEBI) and antioxidant activity (TEAC)) were also evaluated pre- and post-processing. Two PL (360 ìs, 3 Hz) treatments were selected and the juice exposed to energy dosages of 4.03 J/cm2 (‘low’ (L)) and 5.1 J/cm2 (‘high’ (H)) corresponding to 51.5 and 65.4 J/mL, respectively. The juice was also processed by TS (24 kHz, 100 ìm) at 40 °C for 2.9 min (L) or 50 °C for 5 min (H), corresponding to 1456 and 2531 J/ml energy inputs, respectively. The effect of the resulting four energy levels and sequence (PL+TS and TS+PL) was studied. When the technologies were applied individually the maximum reduction achieved was 2.7 and 4.9 log CFU/mL (for TS (H) and PL (H) respectively), while most of the combined treatments achieved reductions in the vicinity of 6 log CFU/mL, showing an additive effect for both technologies when acting in combination, regardless of the sequence applied. All treatments significantly changed the colour of apple juice and the sequence in which the technologies were applied affected colour significantly (Pb0.05). The energy level applied did not affect any of the measured quality attributes