Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant‐Derived,Low‐Acid Foods,and Biomaterials

Cycle threshold (Ct) increase, quantifying plant‐derived DNA fragmentation, was evaluated for its utility as a time‐temperature integrator. This novel approach to monitoring thermal processing of fresh, plant‐based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time‐temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low‐acid product and simple linear regression, Ct value was highly correlated to time‐temperature treatment (R² = 0.87); the logarithmic reduction (log CFU/mL) of the spore‐forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R² = 0.87); and cumulative F‐value (min) in a canned retort process (R² = 0.88), all comparisons conducted at 121 °C. D₁₂₁ and z‐values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D₁₂₁ and z‐values for a 174‐bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof‐of‐concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low‐acid plant products.     

Effect of tumbling time and cooking temperature on quality attributes of cooked ham

This study evaluates effect of tumbling time and cooking temperature on cooking rate, cooking loss (CL), colour, water activity and water‐holding capacity of cooked restructured ham rolls. In experiment were investigated three tumbling times (2, 4 and 6 h) at constant temperature (+4 °C) and three cooking temperatures (76, 86 and 96 °C). It was observed that CL decreased (P < 0.01) from 5.41% to 3.22% with tumbling time (2 h vs. 6 h) but increased (P < 0.01) from 2.35% to 7.25% along with cooking temperature (76 °C vs. 96 °C). In contrast, pH value increased (P < 0.01) from 6.18 to 6.24 with tumbling time (2 h vs. 6 h) but decreased (P < 0.01) from 6.22 to 6.17 along with cooking temperature (76 °C vs. 96 °C). In addition, high temperature had higher efficiency for thermal lethality than low temperature (F₀ values were 19 and 92 min at 96 and 76 °C, respectively). Intermediate tumbling (4 h) and cooking (86 °C) could be preferential.     

Thermal inactivation of polyphenoloxidase and peroxidase in green coconut (Cocos nucifera) water

Coconut water is an isotonic beverage naturally obtained from the green coconut. After extracted and exposed to air, it is rapidly degraded by enzymes peroxidase (POD) and polyphenoloxidase (PPO). To study the effect of thermal processing on coconut water enzymatic activity, batch process was conducted at three different temperatures, and at eight holding times. The residual activity values suggest the presence of two isoenzymes with different thermal resistances, at least, and a two‐component first‐order model was considered to model the enzymatic inactivation parameters. The decimal reduction time at 86.9 ^°C (D_{86.9 °C}) determined were 6.0 s and 11.3 min for PPO heat labile and heat resistant fractions, respectively, with average z‐value = 5.6 °C (temperature difference required for tenfold change in D). For POD, D_{86.9 °C} = 8.6 s (z = 3.4 °C) for the heat labile fraction was obtained and D_{86.9 °C} = 26.3 min (z = 6.7 °C) for the heat resistant one.     

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

ABSTRACT: 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 °C to either 45 or 55 °C over 60 s and subsequently cooled to 10 °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 °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 °C, a higher reduction in E. coli numbers (1 compared with 1.7 log₁₀ 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 log₁₀ CFU/mL, P < 0.05). An increase in heating temperature from 45 to 55 °C during a combined heat/PEF hurdle approach induced a higher inactivation (5.1 compared with 6.9 log₁₀ CFU/mL, respectively {P < 0.05}) with the latter value comparable to the bacterial reduction of 6.3 log₁₀ CFU/mL (P≥ 0.05) achieved by thermal pasteurization (72 °C, 15 s). A reversed hurdle processing sequence did not affect bacterial inactivation (P≥ 0.05). No differences were observed (P≥ 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.     

Effect of high pressure processing on the quality of acidified Granny Smith apple purée product

The aim of the present study was the evaluation of the physicochemical, nutritional and microbial quality of acidified Granny Smith (GS) apple purée processed on industrial-scale high pressure system during 3 weeks of refrigerated storage (5 °C ± 1 °C). Two commercially feasible pressure treatments (400 and 600 MPa/5 min/20 °C) and a mild conventional pasteurization at 75 °C/10 min, with pasteurization values of P_70°C^7.5 = 8.15 min, were conducted and their effect on total vitamin C (total Vit C), ascorbic acid (AA) and total phenolic content (TPP), and on instrumental quality parameters (color, viscosity, soluble solids, titratable acidity and pH) were comparatively studied. Inactivation of indigenous microorganisms (total aerobic mesophilic and psychrotrophic counts and moulds and yeasts) of the apple product was also studied and monitored during storage. Total Vit C and AA contents were unaffected by the 400 MPa and the mild pasteurization treatment. TPP content was not changed during processing at 400 MPa, but was affected by the 600 MPa and also slightly by the pasteurization treatment. Experimental data on the loss of total Vit C during storage were described with a first-order reaction kinetic and times of half loss between 9.3 to 10.3 days could be estimated for the three studied processes. Storage provoked loss of TPP content and color deterioration of pressurized GS puree samples, which was attributed to enzymatic browning reactions. Microbial counts were reduced by the different preservation techniques below the detection limit (50 cfu g^?1) and storage revealed no further growth.Industrial relevanceThis is one of the first studies applying commercial industrial-scale high pressure equipment for the pasteurization of an acidified apple purée product. The pressures of 400 and 600 MPa with 5 min holding time at ambient temperature render economically feasible processes with high throughput and productivity. In the European Union the most important fruits in terms of production are apples. Apple purée is a largely consumed preserve in many households and beside apple juice or cider is one of the most important apple products in the market. In contrast to traditional apple purée preparation, high pressure processing or mild thermal treatments could imply new opportunities for the apple processing industry in developing more fresh-like, value-added apple products with reasonable shelf life.     

Heat resistance of Byssochlamys nivea, Byssochlamys fulva and Neosartorya fischeri isolated from canned tomato paste

Cultures of heat resistant molds (20) were isolated from spoiled canned tomato paste in order to estimate the pasteurization efficiency applied to commercially canned products. Ascospores of nine strains grown on malt extract agar for 30 days at 30°C, survived heating at 85°C for 20 min when initial numbers were near 10⁵/mL. Of these heat resistant strains were identified: two Byssochlamys nivea, three Byssochlamys fulva and four Neosartorya fischeri strains. Ascospores of all cultures were more heat resistant in tomato juice than in phosphate buffer. Thermal death rate curves were nonlogarithmic but approached logarithmic death rates at higher temperatures. The thermal destruction time for 1 log₁₀ at 90°C was 1.5 min for a Byssochlamys nivea strain, 8.1 min for a Byssochlamys fulva strain and 4.4 to 6.6 min for Neosartorya fischeri strains.     

High hydrostatic pressure treatment and storage of carrot and tomato juices: Antioxidant activity and microbial safety

The application of high hydrostatic pressure (HHP) (250 MPa, 35 °C for 15 min) and thermal treatment (80 °C for 1 min) reduced the microbial load of carrot and tomato juices to undetectable levels. Different combinations of HHP did not cause a significant change in the ascorbic acid content of either juice (P > 0.05). Both heat treatments (60 °C for 5–15 min and 80 °C for 1 min) resulted in a significant loss (P < 0.05) in the free‐radical scavenging activity as compared to untreated samples. HHP‐treated juices showed a small loss of antioxidants (below 10%) during storage. The ascorbic acid content of pressurized tomato and carrot juices remained over 70 and 45% after 30 days of storage, respectively. However, heat treatment caused a rapid decrease to 16–20%. Colour changes were minor (ΔE = 10) for pressurised juices but for heat‐pasteurised samples it was more intense and higher as a result of insufficient antioxidant activity. HHP treatment (250 MPa, 35 °C for 15 min) led to a better product with regard to anti‐radical scavenging capacity, ascorbic acid content and sensory properties (colour, pH) of the tomato and carrot juices compared to conventional pasteurisation. Therefore, HHP can be recommended not only for industrial production but also for safe storage of fresh juices, such as tomato and carrot, even at elevated storage temperatures (25 °C). Copyright © 2007 Society of Chemical Industry     

Immobilized Peroxidase: A Potential Bioindicator for Evaluation of Thermal Processes

The heat-stable fraction of covalently immobilized peroxidase on/in porous glass beads in an environment of dodecane was studied as a bioindicator for evaluation of thermal processes under conditions of pasteurization. The verified bioindicator had a z value of 10.1°C and a Dref (at 70°C) of 22 min. At processing temperatures of 70°C and 80°C, the lethalities (F)_bio as read from the bioindicator agreed very well with the target Ft^10.0 values calculated from the time temperature data according to the general method.     

Properties of polyphenol oxidase in mango (Mangifera indica) kernel

Polyphenol oxidase (PPO) activity of filtered extract of ground mango kernel suspension (400 g litre⁻¹) was studied spectrophotometrically at 420 nm using catechol as substrate. The enzyme was most active at pH 6·0 and 25°C. Activity was reduced by 50% at pH values of 5·0 and 7·1, and also at temperatures of 14°C and 30°C. The calculated activation energy and the Michaelis constant (K_m) were 21·4 kcal mol⁻¹ °C⁻¹ and 24·6 mM , respectively. The V_max value was 2·14 units g⁻¹ mango kernel. The time to heat inactivate PPO decreased rapidly to < 10 min with increasing temperature of ⩾ 70°C at 50% activity. © 1998 SCI.     

Reductionin Listeria monocytogenes,Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

Increased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P < 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.     

Optimization and evaluation of heat-shock condition for spore enumeration being used in thermal-process verification: Differential responses of spores and vegetative cells of Clostridium sporogenes to heat shock

To evaluate a heat-shock condition for the enumeration of Clostridium sporogenes spores, a surrogate for C. botulinum spores, we examined the heat tolerance of C. sporogenes spores and vegetative cells exposed to a heat shock at 90°C. From the D values of the spores determined in the temperature range of 113–121°C, z value (±SD) and D_90°C value were estimated to be 10.16±0.90°C and 1,071.52 min, respectively, and the inactivation rates were predicted to be only approximately 2% at 90°C for up to 10 min. Meanwhile, the viable count of spores was significantly higher when activated under a heat-shock condition of 90°C for over 9 min than those activated for shorter time periods. The heat tolerance of vegetative cells was extremely low, showing a D_90°C value (±SD) of 0.21±0.01 min. Finally, 3 different heat-shock conditions were compared: 70°C for 30 min, 80°C for 20 min, and 90°C for 10 min, and the experimental comparative data showed no significant differences in viable spore counts. Consequently, these results support that the heat-shock treatment at 90°C for 10 min is suitable to activate spores and to inactivate vegetative cells of C. sporogenes.     

Extraordinary Heat Resistance of Talaromyces flavus and Neosartorya fischeri Ascospores in Fruit Products

Ascospores of three strains each of Talaromyces flavus, Neosartorya fischeri and Byssochlamys fulva/nivea were analyzed for resistance to thermal inactivation in five fruit-based (blueberry, cherry, peach, raspberry and strawberry) products. D_91°C values for two strains of T. flavus ranged from 2.9–5.4 min; D_88°C values ranged from 7.1–22.3 min. Ascospores of N. fischeri were somewhat less heat resistant; D_91°C values were < 2.0 min and D_88°C were 4.2–16.2 min. Ascospores of Byssochlamys spp. were considerably less heat resistant. The type of fruit product did not appear to substantially influence rates of thermal inactivation. No heat-resistant ascospores of T. flavus or N. fischeri, i.e., ascospores capable of surviving 15 min at 75°C, were formed on fruit products stored at 10°C for 137 days. However, T. flavus and N. fischeri formed ascospores on cherry substrate stored at 25°C within 65 and 137 days, respectively, that survived 15 min at 88°C.     

Optimisation of immersion vacuum cooling operation and quality of Irish cooked sausages by using response surface methodology

The effects of initial water temperature (X₁, 20–72 °C), pressure reduction rate (X₂, 60–90 mbar/min), agitation speed (X₃, 300–600 rpm) as well as condensing temperature (X₄, ?10 ?2 °C) during immersion vacuum cooling (IVC) of Irish cooked sausages were evaluated and optimised by response surface methodology for the first time. The cooling loss, colour, texture and moisture content of the sausages were estimated. The significant polynomial regression models on cooling time (P < 0.001) and hardness (P < 0.05) were established. Results showed that the condensing temperature affected the cooling time of IVC sausage significantly (P < 0.001), while hardness was significantly influenced by initial water temperature and condensing temperature. Three optimum operational modules were determined and validated. The cooling times in all modules were compliant within US Department of Agriculture (USDA). Module 3 (X₁: 4.51 °C, X₂: 72.88 mbar/min, X₃: 459.09 rpm, X₄: ?8 °C) was the most practical option for achieving the required high cooling rate with high‐quality properties.     

Seasonality of the Thermal Kinetics of Color Changes in Whole Spinach (Spinacia Oleracea) Leaves Under Pasteurization Conditions

Color changes in whole spinach (Spinacia oleracea) leaves at pasteurization temperatures (65 to 90°C) indicate that the parameter of “greenness” (-a_t/b_t) increased during a short initial period of heating, followed by a loss that was more pronounced at higher temperatures. Seasonality was evident in kinetic models for color changes possibly due to seasonal difference in chemical composition influencing color degradation kinetics. The mechanism for loss of greenness at lower temperatures was attributed to enzymatic activity while cell collapse, cell compaction, and oxidative changes were probably more important at higher temperatures. Lower temperatures resulted in a higher retention of green color of spinach leaves during the thermal pasteurization process and the kinetic models presented in this work could be used for optimizing pasteurization processes.     

Effects of High‐Hydrostatic Pressure on Inactivation of Human Norovirus and Physical and Sensory Characteristics of Oysters

The purpose of the study was to determine the effect of high‐hydrostatic pressure (HHP) on inactivation of human norovirus (HuNoV) in oysters and to evaluate organoleptic characteristics of oysters treated at pressure levels required for HuNoV inactivation. Genogroup I.1 (GI.1) or Genogroup II.4 (GII.4) HuNoV was inoculated into oysters and treated at 300 to 600 MPa at 25 and 0 °C for 2 min. After HHP, viral particles were extracted by porcine gastric mucin‐conjugated magnetic beads (PGM‐MBs) and viral RNA was quantified by real‐time RT‐PCR. Lower initial temperature (0 °C) significantly enhanced HHP inactivation of HuNoV compared to ambient temperature (25 °C; P < 0.05). HHP at 350 and 500 MPa at 0 °C could achieve more than 4 log₁₀ reduction of GII.4 and GI.1 HuNoV in oysters, respectively. HHP treatments did not significantly change color or texture of oyster tissue. A 1‐ to 5‐scale hedonic sensory evaluation on appearance, aroma, color, and overall acceptability showed that pressure‐treated oysters received significantly higher quality scores than the untreated control (P < 0.05). Elevated pressure levels at 450 and 500 MPa did not significantly affect scores compared to 300 MPa at 0 °C, indicating increasing pressure level did not affect sensory acceptability of oysters. Oysters treated at 0 °C had slightly lower acceptability than the group treated at room temperature on day 1 (P < 0.05), but after 1 wk storage, no significant difference in sensory attributes and consumer desirability was observed (P > 0.05).     

Effect of thermosonication on quality improvement of tomato juice

Inactivation of pectinmethylesterase (PME) and polygalacturonase (PG) is required to minimize quality loss in tomato products. Tomato juice was subjected to thermosonication (TS) (24 kHz), at amplitudes of 25, 50 and 75 μm at 60, 65 and 70 °C or heat only treatments. The TS treatment at 60 °C, 65 °C and 70 °C for 41.8, 11.7 and 4.3 min exposure, respectively reduced PME activity by 90%. The heat only treatment at 60 °C, 65 °C and 70 °C for 90.1, 23.5 and 3.5 min, respectively inactivated PME by 90%. TS treatments with 25–75 μm amplitude had no significant impact on the inactivation efficiency between 60 and 70 °C. After TS the average particle size decreased noticeably (< 30 μm) and viscosity increased 2–4 fold, compared to the heat treated or untreated juice (180 μm)_. These results suggest that TS at 60 and 65 °C could be useful to obtain tomato juice with a low residual PME activity and high viscosity.Industrial relevanceThe processed tomato industry is constantly in search for potential alternative processes to conventional “cold break” and “hot break” treatments that could inactivate the pectic enzymes of importance. The findings of this study would help the industry to inactivate pectinmethylesterase (PME) enzyme at a lower temperature range and also achieve a higher viscosity due to the mechanical effects of thermosonication. Low temperature treatment would enable the retention of fresh-like properties of tomato juice. Based on the findings of this study, thermosonication could be considered as a potential alternative to conventional “cold break” and “hot break” treatments of tomato juice.     

Thermal Inactivation Kinetics of Tulane Virus in Cell‐Culture Medium and Spinach

Human noroviruses (HNoVs) cause significant gastrointestinal disease outbreaks worldwide. Tulane virus (TV) is a cultivable HNoV surrogate widely used to determine control measures against HNoVs. The objective of this study was to determine the heat inactivation kinetics (D‐ and z‐values) of TV in cell‐culture media and on spiked homogenized spinach using the first‐order and Weibull models. TV in cell‐culture media at approximately 7 log PFU/mL (PFU—plaque forming unit) in 2‐mL glass vials was heated at 52, 54, and 56 °C for up to 10 min in a circulating water bath. Survivors were enumerated using confluent host LLC‐MK2 cells in six‐well plates by plaque assay. Data from three replicate treatments assayed in duplicate were analyzed statistically. D‐values by the first‐order model for TV in cell‐culture media at 52, 54, and 56 °C were 4.59 ± 0.05, 2.91 ± 0.05, and 1.74 ± 0.07 min, respectively, with a z‐value of 9.09 ± 0.01 °C (R² = 0.997). The Weibull model showed t_d = 1 values of 2.53 ± 0.08, 1.99 ± 0.10, and 0.57 ± 0.64 min, respectively, at the same temperatures. The D‐values for TV in spinach were 7.94 ± 0.21, 4.09 ± 0.04, and 1.43 ± 0.02 min and the z‐value was 10.74 ± 0.01 °C (R² = 0.98) by the first‐order model and 4.89 ± 0.02, 3.21 ± 0.45, and 0.25 ± 0.38 min for the Weibull model at 50, 54, and 58 °C, respectively. In comparison to previously reported results for the cultivable HNoV surrogate, murine norovirus ‐1, TV in cell‐culture media and spiked on spinach homogenates showed lower D‐ and z‐values. TV may not be an ideal HNoV surrogate for heat inactivation studies in cell‐culture media or homogenized spinach in vacuum bags.     

The Comparative Heat Stability of Bovine β-Lactoglobulin in Buffer and Complex Media

The heat stability of β-lactoglobulin (β-lg) is usually described with reference to a concentration-dependent pseudo-rate constant k. Kinetic and thermodynamic parameters for the irreversible denaturation of β-lg, in a whey protein mixture dissolved in Tris-HCl buffer, were examined over a wide temperature range 75–120°C and for degrees of denaturation [(C_o-C_t)/C_o] up to about 90%. The first-order kinetic model best described β-lg denaturation over the temperature range 75–85°C, whereas the second-order model applies in the range 90–120°C. A comparison between β-lg thermostability in buffer and literature data pertaining to more complex heating media (whey and milk), over the range 75–120°C, was carried out on the basis of changes in activation free energy (ΔG^#), which itself takes into account changes in both activation enthalpy (ΔH^#) and activation entropy (ΔS^#). It was found that the thermal stability of β-lg in different media, and irrespective of the kinetic model assumed in the present study, can be ranked: buffer ≪ whey>milk for the temperature range 75–85°C. On the contrary, at the higher temperature range, 90–120°C, the ranking is buffer<whey<milk, when using the second-order model to describe the present data. For such comparisons to be valid the initial concentration of β-lg in various studies, as well as the reaction order applied, should be taken into consideration. © 1997 SCI.     

Impact of high‐pressure and traditional thermal processing of tomato purée on carotenoids,vitamin C and antioxidant activity

Bioactive compounds (carotenoids and vitamin C) and 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH^?) scavenging activity [50% depletion of initial DPPH^? radical (EC₅₀) and antiradical efficiency (AE)], in aqueous (AQ) and organic (OR) fractions, were measured in tomato purée subjected to high‐pressure (HP) (400 MPa/25 °C/15 min), low pasteurisation (LPT) (70 °C/30 s), high pasteurisation (HPT) (90 °C/1 min), freezing (F) (?38 °C/15 min), and HPT plus F (HPT + F). In addition, physical and physicochemical parameters were evaluated. CIELab uniform colour space parameters (lightness, L*; green‐red tonality, a*; and blue‐yellow tonality, b*) were significantly higher both in the untreated and in the HP tomato purée than in the rest of the samples. Individual and total carotenoids, and provitamin A carotenoids, were significantly higher in HP tomato purée than in the untreated and other treated tomato purées. Ascorbic acid and total vitamin C were significantly lower in HP, LPT, HPT, and HPT + F tomato purées than in the untreated and F purées. In the AQ fractions, we found an inverse significant correlation between both ascorbic acid and total vitamin C and EC_50AQ; and a positive significant correlation with AE_AQ. In the OR fractions, a significant correlation was found between EC_50OR and AE_OR parameters and lycopene and total carotenoids. Total scavenging activity (AQ + OR fractions) in HP tomato purée was similar to that in LPT, HPT, and HPT + F purées. Copyright © 2005 Society of Chemical Industry     

Comparative study on shelf life of orange juice processed by high intensity pulsed electric fields or heat treatment

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,000 μs; bipolar 4-μs pulses at 200 Hz) on the microbial shelf life and quality-related parameters of orange juice were investigated during storage at 4 and 22 °C and compared to traditional heat pasteurization (90 °C for 1 min) and an unprocessed juice. HIPEF treatment ensured the microbiological stability of orange juice stored for 56 days under refrigeration but spoilage by naturally occurring microorganisms was detected within 30 days of storage at 22 °C. Pectin methyl esterase (PME) of HIPEF-treated orange juice was inactivated by 81.6% whereas heat pasteurization achieved a 100% inactivation. Peroxidase (POD) was destroyed more efficiently with HIPEF processing (100%) than with the thermal treatment (96%). HIPEF-treated orange juice retained better color than heat-pasteurized juice throughout storage but no differences (p<0.05) were found between treatments in pH, acidity and °Brix. Vitamin C retention was outstandingly higher in orange juice processed by HIPEF fitting recommended daily intake standards throughout 56 days storage at 4 °C, whereas heat-processed juice exhibited a poor vitamin C retention beyond 14 days storage (25.2–42.8%). The antioxidant capacity of both treated and untreated orange juice decreased slightly during storage. Heat treatments resulted in lower free-radical scavenging values but no differences (p<0.05) were found between HIPEF-processed and unprocessed orange juice.