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, ΔE), non-enzymatic browning (NEBI) and antioxidant activity (TEAC)) were also evaluated pre- and post-processing. Two PL (360μs, 3Hz) treatments were selected and the juice exposed to energy dosages of 4.03J/cm2 (‘low’ (L)) and 5.1J/cm2 (‘high’ (H)) corresponding to 51.5 and 65.4J/mL, respectively. The juice was also processed by TS (24kHz, 100μm) at 40°C for 2.9min (L) or 50°C for 5min (H), corresponding to 1456 and 2531J/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 4.9logCFU/mL (for TS (H) and PL (H) respectively), while most of the combined treatments achieved reductions in the vicinity of 6logCFU/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 (P<0.05). The energy level applied did not affect any of the measured quality attributes.

Inactivation of Escherichia coli and Listeria innocua by combinations of High Intensity Light Pulses (HILP), Ultrasound (US) and Pulsed Electric Fields (PEF) and sub-lethal concentrations of nisin (2.5mg/L) or lactic acid (500mg/L) was investigated in two different buffer systems (pH 4 for E. coli and pH 7 for L. innocua). Individually, HILP (3.3J/cm2), US (126s residence time, 500W, 40°C) and PEF (24kV/cm, 18Hz and 1μs of pulse width) did not induce a microbial reduction of greater than 2.7 or 3.6 log units, for L. innocua and E. coli, respectively. Combined treatment using HILP+PEF sufficiently inactivated E. coli without antimicrobial addition. The addition of either antimicrobial enhanced the effect of US+PEF for both E. coli and L. innocua. The addition of lactic acid enhanced the effect of HILP+US. For L. innocua the addition of nisin enhanced the effect of HILP+PEF. This confirms the potential of selected non-thermal technologies for microbial inactivation when combined with antimicrobials.

The combination of novel, non-thermal technologies for preservation purposes is a recent trend in food processing research. The objectives of the current study were (i) to optimise PEF or MTS treatment conditions which would achieve a maximum reduction of up to 3 log cycles of Listeria innocua in a milk based smoothie, when these technologies were applied individually, and (ii) to investigate possible additive or synergistic effects of the combined technologies. Microbiological analysis was performed by inoculating the smoothie with L. innocua and enumerating populations pre- and post-processing. All technologies applied within combinations significantly reduced L. innocua in the smoothie, when compared to untreated controls (p ≤ 0.0001). The sequence in which the MTS and PEF were applied was found to have a significant impact on the level of microbial reduction achieved (p ≤ 0.05). The sequence of MTS followed by PEF was the most effective in inactivating L. innocua achieving a mean reduction of 5.6 log cfu/ml, thereby exceeding the 5 log cycles minimum requirement specified by the United States Food and Drug Administration (US FDA). Significantly (p ≤ 0.05) lower reductions of 4.2 log cfu/ml were achieved when the PEF + MTS sequence combination was applied. The combination of MTS + PEF achieved inactivation comparable to thermally treated samples (p > 0.05). This study has shown the combination MTS + PEF is a promising hurdle preservation approach to control undesirable microorganisms in milk based smoothie beverages.

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/cm2 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/cm2 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/cm2 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.

The non-thermal technologies High Intensity Light Pulses (HILP) and Thermosonication (TS) were applied alone and in combination to study their effect on Escherichia coli inactivation in orange juice. Two different energy settings were chosen in the current study, 'Low' (L) and 'High' (H), being the combinations applied: HILP(L) (4.03 J/cm(2)), HILP(H) (5.1 J/cm(2)), TS(L) (2.8 min residence time at 40 °C) and TS(H) (5 min residence time at 50 °C). Both the individual technologies and their combinations (HILP&TS and TS&HILP) were studied. Results showed inactivation ranging from 1.10 (TS(H)) to 2.42 (HILP(H)) log cfu/ml for the hurdles when applied individually and from 2.5 (HILP(L)&TS(H)) to 3.93 (HILP(H)&TS(L)) log cfu/ml for the combined treatments. Similar reductions in E. coli populations were achieved in orange juice by all treatment combinations irrespective of the sequence in which they were applied.

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) (5.3 J/cm2), high intensity light pulses (HILP) (3.3 J/cm2), pulsed electric fields (PEF) (34 kV/cm, 18 Hz, 93 μs) or manothermosonication (MTS) (4 bar, 43 °C, 750 W, 20 kHz) 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 35 days and compared to pasteurised samples and untreated juices. All treatments applied individually significantly reduced (1.8–6.0 log cfu/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. 6 log cfu/ml). Thermally pasteurised samples had a shelf life exceeding 35 days, while that of UV + PEF and HILP + PEF-treated samples was 14 and 21 days, 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.

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.

High Intensity Light Pulses (HILP) represent an emerging processing technology which uses short (100-400 μs) light pulses (200-1100 nm) for product decontamination. In this study, model and real foods of differing transparencies (maximum recovery diluent (MRD), apple and orange juices and milk) were exposed to HILP in a batch system for 0, 2, 4 or 8 s at a frequency of 3 Hz. After treatment, inactivation of Escherichia coli or Listeria innocua was evaluated in pre-inoculated samples. Sensory and other quality attributes (colour, pH, Brix, titratable acidity, non-enzymatic browning, total phenols and antioxidant capacity (TEAC)) were assessed in apple juice. Microbial kill decreased with decreasing transparency of the medium. In apple juice (the most transparent beverage) E. coli decreased by 2.65 and 4.5 after exposure times of 2 or 4 s, respectively. No cell recovery was observed after 48 h storage at 4°C. No significant differences were observed in quality parameters, excepting TEAC and flavour score, where 8 s exposure caused a significant decrease (p<0.05). Based on these results, HILP with short exposure times could represent a potential alternative to thermal processing to eliminate undesirable microorganisms, while maintaining product quality, in transparent fruit juices.

Treatments involving pulsed electric fields (PEF) in combination with high intensity light pulses (HILP) were applied to reconstituted apple juice in a continuous system using a 2 x 4 factorial design, with sequence and energy levels as main factors. Two PEF field strengths (24 kV/cm or 34 kV/cm) were selected (treatment time 89 mu s each) corresponding to "high" (H) and a "low" (L) energy inputs (261.9 and 130.5 J/ml, respectively). Juice was also pumped through a HILP system (pulse length 360 mu s, frequency 3 Hz) and exposed to energy dosages of 5.1 J/cm(2) (H) or 4.0 J/cm(2) (L) corresponding to 65.4 and 51.5 J/ml, respectively. Microbiological analysis was performed by inoculating juice with Escherichia coli 1(12 and counting microbial populations pre- and post-processing. Selected physical and chemical quality attributes were compared with those of unprocessed controls. A sensory evaluation was conducted using 31 untrained panellists and the products compared to thermally processed juice (94 degrees C for 26 s). With the exception of HILP (H) and PEF (L), all combinations achieved the minimum microbial reduction of 5 log units required by the FDA. The results obtained for PEF (L) followed by either HILP (Lot H) suggest a synergistic effect on microbial inactivation. In general, the quality attributes were not affected by the chosen treatments and sensory evaluation revealed that the HILP(L)/PEF(L) combination was the most acceptable of the selected non-thermal treatments.Industrial Relevance: Heat remains the dominant microbial/enzyme inactivation technique though its impact on food quality is often at odds with increased consumer demand for minimally processed (MP) products. The reduction in intrinsic preservation in MP products raises new safety and stability risks and a major trend is the combination of inhibitory techniques to effectively preserve without the extreme use of a single technique (i.e. hurdle technology). PEF and HILP are emerging nonthermal/mild-heat technologies which have antimicrobial capabilities when applied alone or in combination with other physicochemical hurdles. Only a limited amount of work has focused on combinations of emerging technologies. As consumers have less reservations about physical (vs. chemical) preservation treatments, the objective of this paper is to assess if novel combinations of these emerging physical hurdles achieves the twin goals of food safety and quality in apple juice. This will involve assessing whether these combinations are effective vs. selected microorganisms un-/mildly heated products. In addition the nutritional/sensory quality of these MP products will be compared to untreated products. (C) 2011 Elsevier Ltd. All rights reserved.