F. Noci

Combined effect of temperature and pulsed electric fields on apple juice peroxidase and polyphenoloxidase inactivation.

Pulsed electric fields (PEF) were applied to freshly prepared apple juice using a laboratory scale continuous PEF system to study the feasibility of inactivating peroxidase (POD) and polyphenoloxidase (PPO). Square wave PEF using different combinations of electric field strength, pre-treatment temperature and treatment time were evaluated in this study and compared to conventional pasteurisation (72°C; 26s). Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed the highest level of decrease in the enzymatic activity of 71% and 68%, for PPO and POD, respectively, were obtained by using a combination of preheating to 50°C, and a PEF treatment time of 100μs at 40kV/cm. This level of inactivation was significantly higher (P<0.05) than that recorded in juice processed by conventional mild pasteurisation where the activity of PPO and POD decreased by 46% and 48%, respectively. The kinetic data for the inactivation of both enzymes could be described using a 1st-order model (P<0.001).

Effectiveness of High Intensity Light Pulses (HILP) treatments for the control of Escherichia coli and Listeria innocua in apple juice, orange juice and milk.

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.

Conjugated linoleic acid concentration in M. Longissimus dorsi from heifers offered sunflower oil-based concentrates and conserved forages.

Dietary inclusion of polyunsaturated fatty acid (PUFA)-rich plant oils is one approach to improving the fatty acid profile of ruminant meat and meat products from a human health perspective. Whole crop wheat silages represent a possible alternative forage to grass silage for beef production, however, they may adversely impact the fatty acid profile of ruminant muscle since grass silage is rich in C18:3n-3. The first objective of this experiment was to investigate the relationship between an increase in the dietary supply of C18:2n-6 from sunflower oil (SFO) and conjugated linoleic acid (CLA) concentration in the muscle tissue of beef cattle. The second objective was to investigate the effect of the basal forage type on the muscle fatty acid composition and its response to increasing inclusion of SFO. One hundred and five heifers were blocked according to initial bodyweight and assigned to one of seven silage treatments. The silage treatments were: (1) grass silage (GS), (2) whole crop wheat silage with 38% dry matter (DM) (W1), (3) GS and W1 at a ratio of 1:2 (DM basis) (W1GS) (4) GS and W1 at a ratio of 2:1 (DM basis) (GSW1), (5) whole crop wheat silage with 52% DM (W2), (6) GS and W2 at a ratio of 1:2 (DM basis) (W2GS), (7) GS and W2 at a ratio of 2:1 (DM basis) (GSW2). Within each silage treatment, 5 animals were assigned to one of three concentrate rations, differing in the content of SFO. The levels of inclusion of SFO in the concentrate were 0, 55, 110 g/kg concentrate. Inclusion of SFO in the diet led to an increase in the n-6:n-3 fatty acid ratio in muscle. In animals fed grass silage or mixed silages the n-6:n-3 ratio was lower in muscle compared with those fed whole crop wheat silages, with the exception of animals fed 55 g SFO/kg, for which feeding W1GS led to a higher ratio than W1. Other than the n-6:n-3 ratio there were no significant interactions between the effect of type of silage and the level of SFO on the concentration of fatty acids in intramuscular fat. Increasing the inclusion of SFO led to a linear increase in the CLAcis-9,trans-11 and PUFA concentration in intramuscular fat (P<0.001). This study confirmed the potential for modification, and improvement from a human health perspective, of the fatty acid composition of beef muscle by dietary manipulation.

PEF based hurdle strategy to control Pichia fermentans, Listeria innocua and Escherichia coli k12 in orange juice.

The combination of pulsed electric fields (PEF) and bacteriocins in a hurdle approach has been reported to enhance microbial inactivation. This study investigates the preservation of orange juice using PEF in combination with nisin (2.5 ppm), natamycin (10 ppm), benzoic acid (BA; 100 ppm), or lactic acid, (LA; 500 ppm). Pichia fermentans, a spoilage yeast frequently isolated from orange juice, Escherichia coli k12 or Listeria innocua were inoculated into sterile orange juice (OJ) with, and without, added preservatives. The antimicrobial activity over time was evaluated relative to an untreated control. The effect of PEF treatment (40 kV/cm, 100 micros; max temperature 56 degrees C) was assessed on its own, and in combination with each antimicrobial. The acidic environment of OJ inactivated E. coli k12 (1.5log reduction) and L. innocua (0.7log reduction) slightly but had no effect on P. fermentans. PEF caused a significant decrease (P<0.05) in the viability of P. fermentans, L. innocua and E. coli k12 achieving reductions of 4.8, 3.7 and 6.3log respectively. Nisin combined with PEF inactivated L. innocua and E. coli k12 in a synergistic manner resulting in a total reduction to 5.6 and 7.9log respectively. A similar synergy was shown between LA and PEF in the inactivation of L. innocua and P. fermentans (6.1 and 7.8log reduction), but not E. coli k12. The BA-PEF combination caused an additive inactivation of P. fermentans, whereas the natamycin-PEF combination against P. fermentans was not significantly different to the effect caused by PEF alone. This study shows that combining PEF with the chosen preservatives, at levels lower than those in current use, can provide greater than 5log reductions of E. coli k12, L. innocua and P. fermentans in OJ. These PEF-bio-preservative combination hurdles could provide the beverage industry with effective non-thermal alternatives to prevent microbial spoilage, and improve the safety of fruit juice.

Inactivation of Escherichia coli in a Tropical Fruit Smoothie by a Combination of Heat and Pulsed Electric Fields

Moderate heat in combination with pulsed electric fields (PEF) was investigated as a potential alternative to thermal pasteurization of a tropical fruit smoothie based on pineapple, banana, and coconut milk, inoculated with Escherichia coli K12. The smoothie was heated from 25 degrees C to either 45 or 55 degrees C over 60 s and subsequently cooled to 10 degrees C. PEF was applied at electric field strengths of 24 and 34 kV/cm with specific energy inputs of 350, 500, and 650 kJ/L. Both processing technologies were combined using heat (45 or 55 degrees C) and the most effective set of PEF conditions. Bacterial inactivation was estimated on standard and NaCl-supplemented tryptone soy agar (TSA) to enumerate sublethally injured cells. By increasing the temperature from 45 to 55 degrees C, a higher reduction in E. coli numbers (1 compared with 1.7 log(10) colony forming units {CFU} per milliliter, P < 0.05) was achieved. Similarly, as the field strength was increased during stand-alone PEF treatment from 24 to 34 kV/cm, a greater number of E. coli cells were inactivated (2.8 compared with 4.2 log(10) CFU/mL, P < 0.05). An increase in heating temperature from 45 to 55 degrees C during a combined heat/PEF hurdle approach induced a higher inactivation (5.1 compared with 6.9 log(10) CFU/mL, respectively [P < 0.05]) with the latter value comparable to the bacterial reduction of 6.3 log(10) CFU/mL (P> or = 0.05) achieved by thermal pasteurization (72 degrees C, 15 s). A reversed hurdle processing sequence did not affect bacterial inactivation (P> or = 0.05). No differences were observed (P> or = 0.05) between the bacterial counts estimated on nonselective and selective TSA, suggesting that sublethal cell injury did not occur during single PEF treatments or combined heat/PEF treatments.

Antimicrobial effect and shelf‐life extension by combined thermal and pulsed electric field treatment of milk

Aims:  The impact of a combined hurdle treatment of heat and pulsed electric fields (PEF) was studied on native microbiota used for the inoculation of low‐fat ultra‐high temperature (UHT) milk and whole raw milk. Microbiological shelf‐life of the latter following hurdle treatment or thermal pasteurization was also investigated.

Lipid and colour stability of M. longissimus muscle from lambs fed camelina or linseed as oil or seeds

Colour and lipid stability of M. longissimus dorsi (LD) from sheep fed diets containing different lipid sources (Megalac (MG), camelina oil (CO), linseed oil (LO), NaOH-treated camelina seed (CS), NaOH-treated linseed (LS) or CO treated with ethanolamine (CA)) were examined. After 100 days on-feed, samples of LD were collected, fatty acid profile determined and colour and lipid oxidation (2-thiobarbituric acid reactive substances; TBARS) measured during retail display in high oxygen packaging. The LS ration was most effective in increasing the 18:3n-3 and conjugated linoleic acid (CLA) concentration in muscle. Within camelina, CA resulted in the highest 18:3n-3 and lowest CLA concentration in muscle. There was no difference in colour stability. Oil (seed) supplementation increased TBARS compared to MG in the early part of display while linseed-based rations tended to cause higher TBARS than camelina-based rations. Higher muscle 18:3n-3 concentration was associated with higher oxidation during early retail display but this was not reflected in a loss of colour stability.

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) (5.3 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) (4bar, 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.

Effect of Pulsed Electric Field treatments at various stages during conditioning on quality attributes of beef longissimus thoracis et lumborum muscle

Beef longissimus thoracis et lumborum (LTL) muscle was used to evaluate the effect of PEF treatments (1.4 kV/cm, 10 Hz, 20 μs, 300 and 600 pulses) on meat quality attributes (weight loss, colour, cook loss and texture) and its evolution at various stages during ageing (2, 10, 18 and 26 days post-mortem). The length of meat ageing before and after PEF application exerted no influence on weight loss, colour and cook loss. Results also demonstrated that PEF treatments applied at different times post-mortem (2, 10, 18 and 26 days) showed a tendency towards reducing toughness of beef samples but that the application of PEF did not affect the tenderization process provided by ageing itself. 60% of the sensory panellists scored PEF treated samples as tender (≥6.0 points out of 9.0) whereas only 27.5% did so for untreated samples.

An assessment of the impact of pulsed electric fields processing factors on oxidation, color, texture, and sensory attributes of turkey breast meat.

Pulsed electric fields (PEF) is a novel nonthermal technology that has the potential to cause physical disruption to muscle tissue which in turn could alter the sensorial aspects of meat in both a positive (e.g., enhanced tenderization) and a negative way (e.g., off-flavor development). If there is a risk of off-flavor development it should be identified prior to embarking on an extensive investigation on PEF in meat tenderization and turkey meat was chosen for this purpose as it is particularly prone to oxidation. The objective of this study was to investigate the effect of various PEF treatments on the quality attributes of turkey breast meat. Turkey breast meat obtained 1 d postslaughter was treated in a batch PEF chamber with increasing electric field strength up to 3 kV/cm and analyzed for lipid oxidation by thiobarbituric acid reactive substances assay (TBARS) with up to 5 d storage at 4°C in aerobic conditions. In a separate experiment, turkey breast meat samples were exposed to PEF under various combinations of pulse number, frequency, and voltage. Following PEF treatments weight loss, cook loss, lipid oxidation, texture, and color were assessed by instrumental methods. A sensory analysis was also performed to determine consumer acceptability for color, texture, and odor of the samples. Lipid oxidation in all PEF-treated samples progressed at the same rate with storage as the untreated samples and was not found to be significantly different to the control. Under the conditions examined PEF treatments did not induce differences in instrumentally measured weight loss, cook loss, lipid oxidation, texture, and color (raw and cooked) either on fresh or frozen samples. However, the sensory evaluation suggested that panelists could detect slight differences between the PEF-treated samples and the controls in terms of texture and odor.