Impact of temperature on lethality and energy efficiency of apple juice pasteurization by pulsed electric fields treatment

The applicability of pulsed electric fields as a non-thermal preservation process for liquid food decontamination has been shown in several studies. However, high costs of operation due to the occurrence of a high amount of dissipated electrical energy inhibited an industrial exploitation so far. In this study the focus was put on improving energy efficiency of this process for pasteurization of apple juice inoculated with Escherichia coli by investigating the relation between achieved reduction in survivor count and electric field strength and treatment temperature. An empirical mathematical model was derived to predict the required input of electrical energy for a given inactivation. Using synergistic effects of elevated treatment temperature of 35–65 °C on microbial inactivation the energy consumption could be reduced from above 100 to less than 40 kJ kg⁻¹ for a reduction of 6 log cycles and the need to preheat the juice before treatment provided a possibility to recover the dissipated electrical energy after treatment, leading to a drastic reduction in operation costs. To evaluate the thermal load of the product the pasteurization unit (PU) and the cook value, key benchmarks for the thermal load, were used to compare PEF and conventional heat treatment.     

Application of a multi-pass high-pressure homogenization treatment for the pasteurization of fruit juices

This work evaluates both the effects of a multiple-pass high-pressure homogenization treatment on the microbial inactivation of selected microbial strains (Saccharomyces cerevisiae, Lactobacillus delbrueckii, Escherichia coli) inoculated into commercial fruit juices (orange, red orange, pineapple) as well as the application of this non-thermal technology to the pasteurization of fresh juices (Annurca apple juice). The pressure level ranged from 50 to 250 MPa, the number of passes from 1 to 5 and the inlet temperature from 2 to 20 °C.Preliminary tests in distilled water showed that the efficiency of the multiple-pass treatment significantly depends on both the homogenizing pressure as well as the microbial species. The subsequent extension of the multiple-pass treatment to the inactivation of S. cerevisiae inoculated into three different fruit juices (orange, red-orange and pineapple juice) highlighted that the inactivation induced by the high pressure treatment did not depend on the properties of the tested juices and was not statistically different from inactivation in water (p value < 0.05). These findings were supported by the comparison of two different mathematical models used to fit the inactivation kinetics, whose fitting parameters were not significantly different for water and the fruit juices for any pressure level applied.Three homogenization passes at 150 MPa and 25 °C, which resulted to be optimal for yeast inactivation in fruit juices, were effective for the stabilization of the endogenous microbial load of fresh Annurca apple juice. The treated apple juice showed a minimum shelf-life of 28 days under refrigerated conditions, during which the natural qualities of the fresh juice were completely preserved.     

Inactivation Kinetics of Pectin Methylesterase,Polyphenol Oxidase,and Peroxidase in Cloudy Apple Juice under Microwave and Conventional Heating to Evaluate Non-Thermal Microwave Effects

Continuous-flow microwave pasteurization provides important advantages over conventional heat exchangers such as fast volumetric heating, lower tube surface temperature, and possible non-thermal effects that enhance enzymatic and bacterial inactivation. Conventional and microwave-assisted inactivation of pectin methylesterase (PME), polyphenol oxidase (PPO), and peroxidase (POD) in cloudy apple juice were investigated to evaluate non-thermal effects. Experiments were conducted to provide uniform heating with accurate temperature acquisition and similar temperature profiles for conventional and microwave treatments. A two-fraction first-order kinetic model was successfully fitted to the data in a procedure that took into account the whole time-temperature profile instead of assuming isothermal conditions. Predicted inactivation curves for pasteurization at 70 and 80 °C of the cloudy apple juice showed that PME has the highest thermal resistance (residual activity of 30% after 250 s at 80 °C) and that there was no evidence of non-thermal microwave effects on the inactivation of these enzymes.     

Evaluation of hybrid pressure-driven and osmotically-driven membrane process for non-thermal production of apple juice concentrate

This study investigates the potential of hybrid membrane processes including microfiltration (MF), ultrafiltration (UF) and forward osmosis (FO) for non-thermal concentration of apple juice. The process performance and characteristics (physicochemical properties, nutritional and aroma components and microbiological quality) of apple juice were studied. The clarity of apple juice was significantly promoted as pore size of membrane reduced. MF and UF can also ensure microbiological safety in pre-treated apple juice. According to its efficiency of filtration as well as performance of simultaneous clarification and cold-sterilization, 0.22 μm MF membrane was identified as the optimal membrane for the pre-treatment. The pre-treated apple juice can be concentrated up to 65°Brix by subsequent single stage FO. FO retained nutritional and volatile compounds of apple juice while significant reductions were found in the juice concentrated by vacuum evaporation. Hybrid MF-FO can be a promising non-thermal technology to produce apple juice concentrate with high quality.     

Effects of bubble and reactor shape on cold plasma yeast inactivation

Cold plasma is a promising non-thermal technology for inactivating pathogenic and spoilage microorganisms in food by generating various reactive species that damage and inactivate the microorganisms. In this study, a mathematical model was established using COMSOL software to quantitatively describe the process of yeast inactivation by cold plasma under different treatment conditions. The study investigated the effects of discharge voltage, bubble size, and reactor shape on the efficiency of yeast inactivation in apple juice. The results revealed that the discharge voltage significantly influenced yeast inactivation, with a 0.4-fold voltage increase leading to a 53% reduction in inactivation time, achieving a 4-log reduction within 12 min at 21 kV. However, bubble size and reactor shape had no significant impact on the inactivation. The developed model can help to predict the cold plasma inactivation yeast in apple juice, facilitating the design and optimization of plasma-based microbial inactivation in liquid food processing.     

膜技术在苹果汁加工中的应用

应用平板式超滤技术对苹果浊汁进行了过滤澄清和除菌。研究了巴式杀菌酶解或未酶解的苹果浊汁、未巴式杀菌未酶解的苹果浊汁、温度对膜通量的影响,超滤组件形式、操作参数对3种不同预处理料液的滤液质量的影响及反渗透系统的浓缩效果。结果表明:平板式超滤膜通量能满足工业需求且大于管式超滤膜,操作温度宜为50℃,当加水倍数0.09倍时,可使浓缩倍数达到20倍。苹果汁超滤液的透光率在97%以上、色值在50%以上、浊度指标小于0.3,pH值、总酸、糖度、氨基态氮等却未发生明显的变化。苹果汁超滤液质量指标和耐热细菌检查结果比较表明,平板式超滤可代替对苹果汁巴式杀菌及酶解。反渗透系统对苹果汁超滤液进行浓缩,浓缩倍数为2～2.3倍,糖截留率为100%。     

流体食品的非热冷杀菌新技术的研究

本研究介绍了一种新型的非热等离子杀菌技术,研究表明这种非热等离子能杀灭流体食品如饮用水、苹果汁、橘子汁中像沙门氏菌那样的病原体。通过本试验条件的处理,杀菌效力可以达到5个对数。具体叙述了非热等离子在各种处理量和作用时间下的杀菌效力以及原料特性对处理效果的影响,同时也比较了非热等离子与其它不同处理方式的VC减少情况。     

Effect of high hydrostatic pressure on Cryptosporidium parvum infectivity

The incidence of foodborne disease outbreaks caused by contaminated low-pH fruit juices is increasing. With recent mandatory pasteurization of apple juice and the industry's concerns of food safety, fruit juice processors are showing more interest in alternative nonthermal technologies that can kill >99.99% of microbial pathogens present in foods. The association of the coccidian protozoan, Cryptosporidium, with diarrheal disease outbreaks from contaminated tap water and fruit juice raises a safety concern in the food and beverage industries. The objective of this study was to evaluate the effects of high hydrostatic pressure (HHP) on C. parvum oocysts. Oocysts were suspended in apple and orange juice and HHP treated at 5.5 x 10(8) Pa (80,000 psi) for 0, 30, 45, 60, 90, and 120 s. Oocyst viability was assessed by excystation using bile salts and trypsin while the cell culture foci detection method was used to assess infectivity. Results indicated that HHP inactivated C. parvum oocysts by at least 3.4 log10 after 30 s of treatment. No infectivity was detected in samples exposed to > or =60 s of HHP and >99.995% inactivation was observed. This study demonstrated that HHP efficiently rendered the oocysts nonviable and noninfectious after treatment at 5.5 x 10(8) Pa.     

Improved Ultrafiltration for Color Reduction and Stabilization of Apple Juice

Polyphenols that are responsible for haze-formation and browning during storage of clear apple juice and concentrates could be selectively removed by an ultrafiltration process using membranes of polyether sulfone and polyvinylpyrrolidone. Results were compared with those from commercial UF membranes made out of regenerated cellulose acetate. The effects of laccase treatment on removal of polyphenols and color in apple juice were also investigated. Custom membranes were effective to reduce the amount of polyphenols. A remarkable desired color removal of apple juice could also be achieved using these membranes. Resulting products were stable in color and clarity at 50°C up to 6 wk. Laccase treatment increased the percentage removal of polyphenols from apple juices. However, laccase treated samples were more susceptible to coloration and haze-formation during storage.     

Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system

The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO₂) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO₂ system at a CO₂ concentration range of 0-12% (g CO₂/100 g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO₂ significantly (P < 0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5 log reduction with 8% CO₂ at 42 °C. The response surface model indicated that both CO₂ concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO₂ concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO₂ processing at 42 °C. Structural damage in cell membranes after SCCO₂ processing was observed by SEM. Refrigeration (4 °C) after SCCO₂ processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO₂ processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.     

Changes in Apple Juice Flavor Compounds During Processing

Apple juice flavor fractions were collected at several stages during a commercial process. Replicated experiments were designed to collect samples from untreated pulp, from enzyme treated pulp, after pectinase treatment, after microfiltration (MF), and after pasteurization. Additional juice heating experiments were carried out. Six apple juice flavor compounds were identified based on to retention times and reported studies. The flavor profile changed at the different stages of the production line. Temperatures used (～57.2°C) for enzyme activation and MF tended to increase flavor compounds in apple juice except iso-butyl acetate. The higher temperatures used (～85°C) for pasteurization decreased all flavor compounds except propyl butyrate which increased. Results indicate apple juice may contain heat activated precursors of identified flavor compounds.     

Inactivation of E. coli K12 in apple juice by high voltage pulsed electric field

Pulsed Electric Field (PEF) technology is an emerging non-thermal food preservation technique that has mainly been applied to improve the shelf life of such foods as bread, milk, orange juice, apple juice and liquid eggs. It involves the application of pulses of high voltage to liquid or semi-solid materials, placed between two electrodes at ambient, sub-ambient, or slightly above ambient temperature. The voltage is typically in the range 20–80 kV/cm, and may be applied in the form of exponentially decaying, square wave, oscillatory, or in some cases, bipolar (instant-charge-reversal) pulses. In the present work, the effect number of pulses on the inactivation of E. coli K12 in apple juice was studied at two different voltages, namely 20 and 40 kV/cm and the number of pulses was varied from 0 to 100. The results indicate that the regulatory requirement of 5-log reduction in microbial count for food safety purposes could only be achieved with 40 kV/cm applied voltage and 100 pulses. The experiments were carried out at 20 °C and the maximum temperature rise was 2 °C.     

Inactivation of in Apple Juice by Radio Frequency Electric Fields

ABSTRACT: Heat pasteurization may detrimentally affect the quality of fruit and vegetable juices; hence, nonthermal pasteurization methods are actively being developed. Radio frequency electric fields processing has recently been shown to inactivate yeast in water at near-ambient temperatures. The objective of this study was to extend the radio frequency electric fields (RFEF) technique to inactivate bacteria in apple juice. A converged-field treatment chamber was developed that enabled high-intensity RFEF to be applied to apple juice using a 4-kW power supply. Finite element analyses indicated that uniform fields were generated in the treatment chamber. Escherichia coli K12 in apple juice was exposed for 0.17 ms to electric field strengths of up to 26 kV/cm peak over a frequency range of 15 to 70 kHz. The population of E. coli was reduced by 1.8 log following exposure to an 18 kV/cm field at an outlet temperature of 50 °C. Raising the temperature increased inactivation. Intensifying the electric field up to 16 kV/cm increased inactivation; however, above this intensity, inactivation remained constant. Radio frequencies of 15 and 20 kHz inactivated E. coli better than frequencies of 30 to 70 kHz. Inactivation was independent of the initial microbial concentration between 4.3 and 6.2 log colony-forming units (CFU)/mL. Applying 3 treatment stages at 50 °C increased inactivation to 3 log. The electric energy for the RFEF process was 300 J/mL. The results of the present study provide the 1st evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.     

Comparing the impact of high pressure,pulsed electric field and thermal pasteurization on quality attributes of cloudy apple juice using targeted and untargeted analyses

The impact of low-oxygen spiral-filter press technology combined with thermal pasteurization (TP), pulsed electric field (PEF) and high pressure processing (HPP) on cloudy apple juice quality was investigated immediately after the treatments and after 3 weeks of storage at 4 °C. Based on equivalent levels of microbial safety and desired shelf-life, low and high processing intensities were selected: TP (72 °C/15 s; 85 °C/30 s), PEF (12.5 kV/cm, 76.4 kJ/L; 12.3 kV/cm, 132.5 kJ/L), and HPP (400 MPa/3 min; 600 MPa/3 min). High intensity thermal treatment resulted in a bright, yellowish color which was maintained during storage. PPO and POD activities were largely reduced by high intensity PEF and TP yet showed high resistance to HPP. The highest vitamin C content was provided by fresh juice followed by PEF-treated juices. Due to oxidative degradation reactions, vitamin C of all treated samples significantly decreased during storage. Immediately after processing, high cloud stability values were obtained in all samples; however, cloud stability decreased during storage particularly for HPP juices with high residual PME. No significant changes were observed in pH, titratable acidity, organic acid and sugar content which also corresponded to sweet and sour taste. Results from untargeted volatile profiles showed that esters increased after PEF and were better retained after HPP. Contrary to TP treatment where ester degradation reactions occurred together with the formation of off-flavors. Most of the volatiles decreased during storage which could be linked to oxidation and ester hydrolysis reactions.Industrial relevanceBeing one of the most popular fruit juices consumed worldwide, cloudy apple juice can still undergo quality changes such as color degradation, cloud loss (fast sedimentation) and flavor changes during processing and storage. This study evaluates the potential of low-oxygen spiral-filter press in combination with different preservation technologies to obtain a maximal quality of cloudy apple juice. Results showed that high intensity thermal pasteurization can effectively inactivate quality-degrading enzymes, therefore it is useful to obtain an optimal cloudy apple juice product in terms of color and cloud stability. Although HPP has minimal impact on aroma of the juice, shelf-life of the juice may be limited due to incomplete enzyme inactivation. In the case of PEF treatment, thermal effects may contribute to maintain apple juice quality.     

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) (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.     

Control of Lactobacillus plantarum and Escherichia coli by pulsed electric fields in MRS Broth,Nutrient Broth and orange–carrot juice

Pulsed electric fields (PEF) are an emerging non-thermal treatment valid for liquid foods. This novel technology offers a relevant alternative to traditional thermal methods avoiding thermal damage to the product (loss of flavour and nutritional value). The aim of this work was to evaluate the influence of PEF treatment conditions, inoculum size (initial cell concentration) and substrate conditions after PEF treatment on the inactivation and potential growth of Lactobacillus plantarum and Escherichia coli in orange–carrot juice. Although a maximum inactivation of 1.3 and 2.6 log reductions were achieved for L. plantarum and E. coli, respectively, after PEF treatment, it was effective inducing sub-lethal injury. An increase in the lag-phase duration was evidenced under refrigeration conditions. When sub-lethal damage could be repaired, the subsequent growth rate was not affected. An increased inhibitory effect of PEF, low temperature and low inoculum size on the delay in lag phase was observed.     

新型热和非热加工对非浓缩还原苹果汁品质影响的研究现状

非浓缩还原(not from concentrate,NFC)苹果汁作为市面上新兴起的果汁,最大程度保留了苹果的风味和营养成分,但存在易褐变、分层等问题。热处理是最常用的加工技术,但它对果汁的营养和感官品质有不利影响,相反,非热处理技术是一种合适的加工保鲜技术,对产品质量的负面影响较小。然而,关于使用非热处理技术来加工NFC苹果汁的文献是有限的。因此,该文对新型热和非热加工NFC苹果汁技术进行了综述,系统介绍了其原理和应用,以期为NFC苹果汁生产加工提供参考。     

Liposomes as vehicles for vitamins E and C: An alternative to fortify orange juice and offer vitamin C protection after heat treatment

Soy phosphatidylcholine-based liposomes were studied as vitamin transporters to be incorporated in orange juice, which is later subjected to pasteurization. These systems allowed the incorporation of vitamins E and C. Stearic acid and calcium stearate were incorporated into liposomes as an alternative to lipid bilayer stabilizers. Calcium ions and essential fatty acids are contained in calcium stearate and soy phosphatidylcholine, respectively, conferring extra nutritional value. Liposomes prepared by the dehydration–rehydration method were tested in a food model system to avoid interference caused by orange juice components. The oxidative stability was analyzed by the thiobarbituric acid method before and after the pasteurization process. Size was analyzed by light scattering also before and after pasteurization, and shape was analyzed by transmission electron microscopy. Percentage encapsulation efficiency (EE%) of vitamins C and E was determined by a centrifugation process. Also, EE% of vitamin C was measured against dialysis for 72 h.Liposomes had a protective effect on antioxidant activity of vitamins before and after pasteurization; even considering that vitamin C is thermolabile. Besides, EE% by centrifugation showed a high encapsulation of vitamins E and C. And the results of dialysis of vitamin C, demonstrated that it was retained by all the systems. Formulations that included stearic acid were the most efficient encapsulating with a 38%.The results showed a relationship between oxidative stability and aggregation, along with changes in size and morphology: peroxidation increases with aggregation. Addition of stearic acid favors oxidative stability and EE% due to a bilayer stabilizing effect.It is important to note that the combination of liposomal formulations and vitamins with orange juice did not change its organoleptic characteristics, and showed microbiological stability after pasteurization and storage at 4 °C for 37 days.     

Storage quality of pineapple juice non-thermally pasteurized and clarified by microfiltration

Microfiltration (MF) is classified as a non-thermal process for the fruit juice industry. It could provide a better preservation of the phytochemical property and flavor of the juice. This work aimed to study the stability of phytochemical properties including vitamin C, total phenolic content, antioxidant capacity (2-Diphenly-1-picrylhydrazyl: DPPH, free radical scavenging capacity and Oxygen Radical Absorbance Capacity: ORAC assays), microbial and chemical–physical (color, browning index, pH and total soluble solid) properties of MF-clarified pineapple juice during storage at various temperatures (i.e. 4, 27, and 37 °C). The juices were clarified by microfiltration using hollow fiber module. The results showed that most of the phytochemical properties and soluble components were retained in the juice after microfiltration. No microbial growth was detected after 6 months of storage. The storage time and temperature did not affect total soluble solids and pH (P > 0.05). The color (L^*) of clarified juice stored at 4 °C was lighter than the juices stored at higher temperature levels (P < 0.05). The phytochemical properties and total phenol content of the juice significantly decreased as storage time and temperature increased (P < 0.05). Vitamin C content was the attribute that affected storage time and temperature most as indicated by reaction rate constant and activated energy. Storage of non-thermally pasteurized and clarified pineapple juice at 4 °C was the most suitable since it allowed the best quality preservation.     

Application of biosensors in early detection of contamination with lactic acid bacteria during apple juice and concentrate production

The aim of Collective Research Project QUALI-JUICE (COLL-CT-2005, Co Nr 012461) was to introduce the biosensors in control of microbiologically pure apple juice production. Three commercial lactate biosensors were used and compared with enzyme kits assays. Parallel the microbiological analysis of the production process at one juice producing enterprise was done. The results of lactic acid assay with biosensors were in good correlation with those obtained by enzyme kits. The main benefit of biosensor use was shortening of measurement time as compared with assay by enzyme kit and possibility to measure at line. The concentration of l-lactic acid in apple pulp could be correlated with the number of lactic acid bacteria. Pasteurization process was eliminating lactic acid bacteria and the concentration of lactic acid was at this stage not exceeding 0.1 g L⁻¹. The final product (apple concentrate) contained in some cases very high amounts of lactic acid indicating secondary microbiological contamination after pasteurization step. Parallel microbiological analysis of production process and lactate assay indicated that the critical point during production was prolonged vacuum filtration after pasteurization.