Optimizing critical high-intensity pulsed electric fields treatments for reducing pectolytic activity and viscosity changes in watermelon juice

A response surface methodology was used to determine the combined effect of high-intensity pulsed electric fields (HIPEF) variables such as frequency, pulse width and polarity on the inactivation of pectolytic enzymes involved in viscosity changes of juices. Pectin methylesterase (PME) and polygalacturonase (PG) activities as well as viscosity were determined in watermelon juices processed at pulse frequencies from 50 to 250 Hz and pulse widths ranging from 1.0 to 7.0 μs in monopolar or bipolar mode. Electric field strength and total treatment time were maintained constant in all treatments at 35 kV/cm and 1,000 μs. Second-order expressions were accurate enough to fit the experimental results. The great PME reduction contrasted with the low impact of HIPEF on the PG activity of watermelon juice within the range of assayed conditions. Minimal residual PME activity values (15%) were obtained by selecting pulse widths higher than 5.5 μs at 250 Hz in bipolar mode, whereas the lowest PG residual activities (60%) were achieved after applying 7.0-μs bipolar pulses at 250 Hz. Moreover, watermelon juice viscosity increased throughout the range of studied conditions. The highest viscosity observed in the juice after applying 7.0-μs bipolar pulses at 250 Hz was related to the lowest PME activities obtained in the product treated under those conditions. Hence, the HIPEF processing optimization through frequency, pulse width and polarity could contribute to assure enzymatic inactivation while keeping valuable attributes of juices.     

Unravelling process-induced pectin changes in the tomato cell wall: An integrated approach

The activity of the pectin-modifying enzymes pectin-methylesterase (PME) and polygalacturonase (PG) in tomato fruit was tailored by processing. Tomatoes were either not pretreated, high-temperature blanched (inactivation of both PME and PG), or high-pressure pretreated (selective inactivation of PG). Subsequently, two types of mechanical disruption, blending or high-pressure homogenisation, were applied to create tomato tissue particle suspensions with varying degrees of tissue disintegration. Process-induced pectin changes and their role in cell-cell adhesion were investigated through in situ pectin visualisation using anti-pectin antibodies. Microscopic results were supported with a (limited) physicochemical analysis of fractionated walls and isolated polymers. It was revealed that in intact tomato fruit pectin de-esterification is endogenously regulated by physical restriction of PME activity in the cell wall matrix. In disintegrated tomato tissue on the other hand, intensive de-esterification of pectin by the activity of PME occurred throughout the entire cell wall. PG was selectively inactivated (i.e. in high-pressure pretreated tomatoes), with de-esterification of pectin by PME, which resulted in a high level of Ca²⁺-cross-linked pectin and a strong intercellular adhesion. In non-pretreated tomato suspensions on the other hand, combined PME and PG activity presumably led to pectin depolymerisation and, hence, reduced intercellular adhesion. However, because of the high amount of Ca²⁺-cross-linked pectin in these samples, cell-cell adhesion was still stronger than in the high-temperature blanched tomatoes, in which the absence of PME activity during suspension preparation implied few Ca²⁺-cross-linked pectic polymers and extensive cell separation upon tissue disruption.     

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.     

Comparison of the application of high pressure and pulsed electric fields technologies on the selective inactivation of endogenous enzymes in tomato products

Application of novel technologies such as high pressure (HP) or pulsed electric fields (PEF) on the remaining activity of endogenous tomato pectinolytic enzymes such as Pectinmethylesterase (PME) and Polygalacturonase (PG), responsible for tomato products texture was studied. HP combined with temperature (200–800 MPa @ 55–75 °C), PEF (5.5–12.5 kV/cm, 0–12 ms treatment time) and thermally treated (55–75 °C) samples were studied. After thermal treatment, PG appeared to be more resistant than PME. Opposite behavior was observed for HP treated samples. For PME inactivation more intense P-T process conditions were necessary compared to PG. For PEF treatment, 98% inactivation was observed at 12.5 kV/cm and 6 ms for PME, and at 5.5 kV/cm and 11 ms for PG. PME appeared to be more HP and PEF resistant compared to PG. The results support the potential application of HP and PEF to selectively inactivate PG while partially retaining PME in tomato juices, aiming in improved tomato products' textural characteristics.Industrial relevanceThe aim of the tomato industry is to produce tomato products of desired textural and sensorial characteristics while increasing the yield by decreasing the evaporated water. This can be achieved by applying novel technologies such as high pressure (HP) processing or pulsed electric fields (PEF) that affect the remaining activity of the endogenous pectinolytic enzymes such as Pectinmethylesterase (PME) and Polygalacturonase (PG), responsible for the final texture leading to products with improved quality characteristics such as viscosity, color and consistency. However, HP treatment is a batch process and makes it difficult for the treatment of large quantities (production of small quantities of superior products could be the target of the application of HP technology), while PEF technology could be applied in line with the typical production flow of that kind of products before the cold break step.     

Comparative study on color,viscosity and related enzymes of tomato juice treated by high-intensity pulsed electric fields or heat

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,500 μs using bipolar 4-μs pulses at 100 Hz) on color parameters and viscosity, as well as peroxidase (POD), pectin methylesterase (PME) and polygalacturonase (PG), were evaluated during 77 days of storage at 4 °C and compared to thermal treatments at 90 °C for 1 min or 30 s for unprocessed tomato juice. HIPEF-treated tomato juice showed higher values of lightness than the thermally processed and the untreated juice throughout storage time (P < 0.05). Viscosity of HIPEF-treated tomato juice was also greater than both thermally treated and untreated for the first 35 days of storage. POD of HIPEF-treated tomato juice was inactivated by 97% whereas in the case of the thermally treated, 90 and 79% inactivation was achieved after 1 min and 30 s, respectively. The highest PME inactivation in tomato juice was obtained by PEF (82%) and heat treatment at 90 °C for 1 min (96%). PG of PEF-treated tomato juice was inactivated by 12% whereas thermal treatments at 90 °C for 1 min or 30 s achieved 44 and 22%, respectively. Despite the low rates of PG inactivation obtained, the pattern followed in the residual activity along the storage time was similar in the tomato juice treated by HIPEF than the thermally processed.     

Changes in quality attributes throughout storage of strawberry juice processed by high-intensity pulsed electric fields or heat treatments

The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV/cm for 1700 μs applying 4-μs pulses at 100 Hz in bipolar mode) on color, viscosity and PME and PG activities in strawberry juice were studied and compared to those of heat treatments (90 °C for 60 s or 30 s) through 63 days of storage. L^∗ and viscosity values of the HIPEF-processed juices were higher than those found in the thermally treated. In addition, HIPEF-treated juice exhibited lower 5-(hydroxymethyl)-2-furfural (HMF) concentration and browning index than heat-treated juices throughout storage. On the other hand, HIPEF-treated juice maintained low residual pectin methylesterase (PME) activity (13.1%) for 63 days, whereas in the case of the thermally treated, 22.2 and 48.8% was retained after 60 s and 30 s, respectively. Strawberry juice treated by HIPEF achieved lower residual polygalacturonase (PG) activity (73.3%) than those of heat-processed at 90 °C for 60 s (76.2%) or 30 s (96.8%). Thus, HIPEF could be a feasible alternative to thermal processing to minimize browning and viscosity loss in strawberry juice during storage.     

Immobilisation of pectinases into PVA gel for fruit juice application

In this study, for the first time, the use of polyvinyl alcohol gel in the form of LentiKats^® to immobilise pectinase was investigated and its application in fruit juice clarification was evaluated. Six pectolytic enzymes were tested for their polygalacturonase (PG) and pectin lyase (PL) activities. Panzyme YieldMASH and Panzyme Smash XXL exhibited maximum PG and PL activity, respectively (P < 0.05), in free and immobilised forms. The immobilised enzymes revealed a good adaptability to an acidic solution like fruit juice. Moreover, the immobilised Panzyme YieldMASH and Panzyme Smash XXL retained about 60% and 74% residual activity, respectively, in the second cycle and more than 30% during the third cycle. After that, both immobilised enzymes retained about 20% of their initial activity after repeating eight times without a significant decrease in the observed activity. The best result in terms of turbidity reduction was obtained in apple juice with immobilised Panzyme YieldMASH (about 80%), and the same % of turbidity reduction was successfully retained in the two following uses.     

Optimisation of High Hydrostatic Pressure Processing of Pêra Rio Orange Juice

The influence of high hydrostatic pressure (HHP) on Pêra Rio orange juice was investigated using response surface methodology. A central composite design was used to evaluate the effects of three processing conditions (independent variables), namely pressure (100–600 MPa), temperature (30–60 °C) and time (30–360 s), on the native microflora and pectin methylesterase (PME) activity of orange juice. Analysis of variance showed that second-order polynomial models fitted well with the experimental data for PME residual activity (R ²?=?0.9586, p?<?0.001) and aerobic microorganism count (R ²?=?0.9879, p?<?0.001). The optimum HHP processing conditions to produce orange juice with PME residual activity of less than 20 % and low microorganism count (<2 log cycles CFU/mL) were 550 to 600 MPa, 55 to 60 °C and 330 to 360 s.     

Evaluation of processing qualities of tomato juice induced by thermal and pressure processing

Effects of processing conditions including hot-break processing (92 °C for 2 min), cold-break processing (60 °C for 2 min) and hydrostatic pressure treatments (100-500 MPa) at different temperatures (4, 25 and 50 °C) for 10 min on quality aspects of tomato juice were investigated. Both hot- and cold-break processing induced significant changes in color, viscosity and radical-scavenging capacity of tomato juice compared with control (fresh tomato juice); moreover, hot-break processing induced a specific range of reduction of pectin methylesterase (PME) and polygalacturonase (PG) activities. Pressure treatments at and below 200 MPa at 4 and 25 °C maintained the color, extractable total carotenoids and lycopene, and radical-scavenging capacity; further, those at 500 MPa at 4 and 25 °C improved all the quality attributes the most except inactivation of PME in this study. The residual activity of PME showed the lowest after treating by 200 MPa at 25 °C; however, the PME activity was enhanced by treatments at 300-500 MPa and various temperatures. The residual activity of PG decreased gradually to 72% with pressure elevated from 100 to 400 MPa at 4 and 25 °C, further, that declined quickly to 10% after 500 MPa treatments. This research clearly shows that it is possible to selectively produce good tomato juice products by high pressure processing at ambient temperature.     

Thermal and high-pressure stability of purified polygalacturonase and pectinmethylesterase from four different tomato processing varieties

Polygalacturonase (PG) and pectinmethylesterase (PME) were extracted and purified from four tomato varieties (Galeón, Malpica, Perfectpeel and Soto) used in the processing industry. The processing stability (thermal and high pressure) of PG and PME from the four varieties was analyzed, and they all showed the same behavior. PG was present in two isoforms, PG1 (inactivated at 90 °C, 5 min) and PG2 (inactivated at 65 °C, 5 min). In contrast, PG1s and PG2s showed the same pressure stability, both can be inactivated at room temperature in the pressure range of 300–500 MPa. On the other hand, purified PMEs could be thermally inactivated (5 min, 70 °C) but 50% of its activity remained after high-pressure treatment (850 MPa, 15 min, 25 °C). High pressure processing can thus be used for selective inactivation of PG in tomato processing (while keeping PME intact). This fact could open prospectives for improving texture/rheology of processed tomato based products; however further research in the texture/rheology area is needed.     

Evaluation of microbial inactivation and physicochemical properties of pressurized tomato juice during refrigerated storage

Effects of high pressure processing (300-500 MPa/25 °C/10 min) on microbial inactivation and processing qualities of tomato juices during refrigerated storage at 4 °C for 28 days were investigated to compare with those of conventionally thermal processing. Conventionally, thermal processing almost inactivated all the microorganisms and pectolytic enzymes and produced microbially and consistency stable tomato juices; however, they also reduced the color, extractable carotenoids and lycopene and vitamin C compared with fresh juice. During storage, all the pressure processing could improve the extractable carotenoids and lycopene contents compared with fresh juice, and they also retained more vitamin C contents than thermal processing. Although 300- and 400-MPa processing could retain a/b values of tomato juices as fresh juice during storage for 21 and 28 days, 500-MPa processing could improve the color of juices even after storage. Syneresis occurred in the 300- and 400-MPa processing juices by storing for 7 and 14 days; however, viscosity stable juice was produced by 500-MPa processing. Moreover, 400- and 500-MPa processing significantly inactivated microorganisms and the juices were microbially stable during storage. This study demonstrated that 500-MPa processing would be an alternative for conventionally thermal processing for tomato juice with improvement of some processing quality attributes.     

Inactivation of pectinmethylesterase in fresh orange juice by cold atmospheric plasma technology: A kinetic study

Preservation of fruit juices requires the inactivation of natural endogenous enzymes, such as pectinmethylesterase (PME). Within this work, cold atmospheric plasma (CAP), and in particular a dielectric barrier plasma jet fed with helium gas, was demonstrated to effectively inactivate PME of freshly squeezed orange juice in short treatment times (2–30 min). By a combination of temperature measurements and a multidimensional heat transfer model, the temperature profile of the whole sample during plasma treatment was extracted. It was found that the thermal phenomena were not a driving factor for PME inactivation. Plasma treatment of orange juices resulted in inactivation of 55–80% of PME with <5.0% of PME inactivation caused by the temperature increase from 20 to 90 °C. The Weibull distribution model compared to the first-order fractional, the sigmoidal logistic and the Hulsheger's kinetic models was found to better describe mathematically (R² > 0.99; A_f = 1.002–1.052) the effect of CAP processing on residual PME activity. Multi-parameter equation fits allowed the prediction of residual PME activity as a function of the applied voltage, helium flow, and treatment time. Generally, higher voltages and lower helium flows applied led to higher PME inactivation rates in fresh orange juice.     

Changes in pectin methylesterification and accumulation of methanol during production of diced tomatoes

The degree of methylesterification (DM) of the pectins in tomatoes affects the firmness of diced products and the consistency of juices. We examined the changes in DM that occur during commercial production of diced tomatoes packed in tomato juice. Ripe processing tomatoes contained low amounts of free methanol (<20 μg g fresh weight⁻¹) and had a high degree of pectin methylesterification (60%). During production of diced tomatoes, the level of free methanol increased while the degree of pectin methylesterification decreased. Diced tomatoes canned in tomato juice contained about 200 μg methanol g fresh weight⁻¹, and had a DM of about 35% in the dice and less than 25% in the juice. Similar results were obtained for aseptically processed bulk packed tomatoes. Low-temperature blanching of canned diced tomatoes caused additional pectin de-esterification in the diced tomatoes and improved firmness. Heating of the diced tomatoes prior to mixing with topping juice, first to temperatures that maximally activate PME then to temperatures that inactivate PME and other enzymes, is proposed as a way to both improve dice firmness and preserve the consistency of the topping juice.     

Processing of clear and turbid grape juice by a continuous flow UV system

The inactivation of inoculated (S. cerevisiae) and spoilage microorganisms, i.e. yeasts and lactic acid bacteria (LAB), in clear and turbid grape juice was investigated using a pilot scale UV system. The biodosimetry method was used for UV dose prediction in a continuous flow UV reactor. Weibull model was applied for fitting the inactivation data. The flow rates (774, 820 ml/min) in this system were very close to the ones used in fruit juice processing. S. cerevisiae in clear juice was reduced by 3.39 ± 0.04 at 65.50 mJ/cm² of UV dose. 1.54 ± 0.04 and 1.64 ± 0.03 log CFU/ml reductions were obtained for spoilage yeasts and LAB in turbid juice at UV dose of 78.56 and 67.97 mJ/cm², respectively. The soluble solids (°Brix) and pH of grape juice samples were not affected by UV-C treatment (p > 0.05). Although the color parameters slightly were changed after irradiation, the color of PCGJ and FSTGJ did not show visual difference compared to the untreated samples.Industrial relevanceUV light has a potential to reduce the levels of microbial contamination in liquid foods. Although grape juice has many beneficial health effects, it has a fairly short shelf life. Therefore, pasteurization is required. But the thermal pasteurization has some undesired effects on the juice quality. Consumer demands for high quality fruit juice with fresh-like characteristics have markedly expanded in recent years. In the current study, the microbial inactivation efficiency of a pilot scale UV system for non-thermal treatment of clear and turbid grape juice was evaluated under conservative conditions. Most of the physicochemical properties of grape juice samples were not significantly affected from UV-C treatment (p > 0.05). This would be a major advantage in the processing of nutritious juice products.     

Combination of high-frequency ultrasound with propyl gallate for enhancing inactivation of bacteria in water and apple juice

This study evaluated a combination of high-frequency ultrasound (HFU, 1 MHz, 1.6 W/cm²).and a food-grade antioxidant, propyl gallate (PG, 10 mM), to enhance inactivation rates of Listeria innocua and Escherichia coli O157:H7 in water and clarified apple juice. Treatment times ranged from 5 to 20 min. The study also assessed the potential mechanisms of synergistic interactions based on an evaluation of changes in bacterial permeability, morphology, and intracellular oxidative stress. Within 15 min of treatment time, HFU + PG significantly (reduced by 5.5 log CFU/mL, P < 0.05) decreased the bacterial load of both L. innocua and E. coli O157:H7 from an initial inoculum of 6.5 log CFU/mL in both water and clarified apple juice. Overall, L. innocua demonstrated significantly higher resistance to inactivation than E. coli O157:H7 using a combination of HFU + PG. The synergistic antimicrobial activity of HFU+ PG resulted in enhanced membrane damage and oxidative stress induction in bacteria compared to the individual treatments of HFU or PG alone.Industrial relevanceThis study evaluates the synergistic combination of high frequency ultrasound and the food grade antioxidant propyl gallate for non-thermal processing of liquids. The results illustrate significant (>5 log CFU) and rapid inactivation (∼15 min) of inoculated model Gram positive and Gram negative bacteria in apple juice using a synergistic combination of propyl gallate and high frequency ultrasound. The synergistic interactions result in enhanced membrane damage and oxidative stress induction in bacteria. These results illustrate potential of the synergistic non-thermal thermal processing method for processing liquid beverages. Further studies are required for evaluating the scale up and optimization of the novel processing technology and enhancement in quality attributes of beverages.     

Thermosonication: a potential technique that influences the quality of grapefruit juice

Thermosonication (TS) is an emerging nonthermal processing technique used for the liquid food preservation and is employed to improve the quality and acceptability of grapefruit juice. In this study, fresh grapefruit juice samples were subjected to TS treatment in an ultrasonic cleaner with different processing variables, including temperature (20, 30, 40, 50 and 60 °C), frequency (28 kHz), power (70%, 420 W) and processing time (30 and 60 min) for bioactive compounds, inactivation of enzymes pectin methylesterase (PME), peroxidase (POD) and polyphenolase (PPO) and micro‐organisms (total plate count, yeasts and moulds). The micro‐organism activity was completely inactivated in the treatment (60 °C for 60 min). The TS treatment at 60 °C for 60 min exposure reduced PME, PPO and POD activity by 91%, 90% and 89%, respectively. Results indicate that the advantages of TS for grapefruit juice processing at low temperature could enhance the inactivation of enzymes and micro‐organisms and it can be used as a potential technique to obtain better results as compared to alone .     

Enhanced inactivation of pectin methyl esterase in orange juice using modified supercritical carbon dioxide treatment

The aim of the study is to quantify the effect of ethanol addition and exposure surface on the inactivation of pectin methyl esterase (PME), a juice clarifying enzyme, in orange juice using supercritical carbon dioxide (SC‐CO₂). Addition of ethanol to the SC‐CO₂ at 2% (v/v) caused greater inactivation than SC‐CO₂ alone, with a maximum reduction of PME activity of 97% at 30 MPa and 40 °C for 60 min. As the surface area to volume ratio was increased, the rate of inactivation of PME increased. Analysis of first‐order reaction kinetic data revealed that D values were greatly influenced by ethanol addition and agitation. With the addition of 2% ethanol, the D value reduced by half, that is, 56 min from 109 min. With impeller agitation of the sample at 1100 ± 100 rpm, the D value for PME was further reduced to 43 and 30 min without and with ethanol, respectively. The activity of PME treated with SC‐CO₂ remained unchanged after 14 days of storage at 4 °C. Treatment did not significantly change pH or colour, but did significantly increase the cloud values of the juice, resulting in a cloud stabilised juice with similar qualities to fresh juice.     

Color and viscosity of watermelon juice treated by high-intensity pulsed electric fields or heat

The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV/cm for 1727 μs applying 4-μs pulses at 188 Hz in bipolar mode) on color, viscosity and related enzymes in watermelon juice were evaluated during 56 days of storage and compared to thermal treatments (90 °C for 60 s or 30 s). HIPEF-treated juice maintained brighter red color than thermally treated juices along the storage time. In addition, the application of HIPEF as well as heat at 90 °C for 60 s led to juices with higher viscosity than those untreated for 56 days of storage. On the other hand, peroxidase (POD) was inactivated more efficiently after HIPEF processing than after applying heat treatments. However, the thermally processed juice at 90 °C for 60 s kept the lowest residual POD activity values beyond day 7 of storage. Differences in lipoxygenase (LOX) activity among treatments were not appreciated at day 0. However, storage time had a strong reducing influence on the enzyme activity of heat-treated samples. A substantial loss of pectin methylesterase (PME) activity (more than 50%) was observed in all the treated juices, whereas a slight reduction in polygalacturonase (PG) activity was only achieved after the HIPEF treatment. The use of HIPEF technology could be an alternative to thermal treatments and could contribute to better maintain valuable attributes of watermelon juice.Industrial RelevanceHIPEF processing is a feasible alternative to thermal treatments to obtain watermelon juice, achieving optimal inactivation of deleterious microorganisms and quality-related enzymes. HIPEF-treated watermelon juices exhibit better physical properties such as color or viscosity than thermally treated juices throughout storage. Thus, HIPEF technology can help processors to obtain juices that keep their fresh characteristics, thus being better accepted by consumers.     

Ultraviolet treatment of orange juice

Ultraviolet (UV) with a wavelength of 254 nm tends to inactivate most types of microorganisms. Most juices are opaque to UV due to the high-suspended solids in them and hence the conventional UV treatment, usually used for water treatment, cannot be used for treating juices. In order to make the process efficient, a thin film reactor was designed and constructed from glass with the juice flowing along the inner surface of a vertical glass tube as a thin film. The decimal reduction doses required for the reconstitute orange juices (OJ; 10.5° Brix) were 87±7 and 119±17 mJ/cm² for the standard aerobic plate count (APC) and yeast and moulds, respectively. The shelf life of fresh squeezed orange juice was extended to 5 days with a limited exposure of UV (73.8 mJ/cm²). The effect of UV on the concentration of Vitamin C was investigated using both HPLC and titration methods of measurements. The degradation of Vitamin C was 17% under high UV exposure of 100 mJ/cm², which was similar to that usually found in thermal sterilization. Enzyme pectin methylesterase (PME) activity, which is the major cause of cloud loss of juices, was also measured. In contrast to the heat treatment, UV processing does not inactivate enzyme pectin methylesterase. The energy required for UV treatment of orange juice (2.0 kW h/m³) was much smaller than that required in thermal treatment (82 kW h/m³). The color and pH of the juice were not significantly influenced by the treatment.

Industrial relevance

This paper is of interest since it suggest—despite the low UV transmittance in orange juices—the use of a thin film UV reactor. The data suggest that shelf life extension from 2 to more than 5 days could be achieved with less energy requirements than for thermal processing. However, it seems unlikely that such thin film reactors could provide a real alternative to current conventional or new (e.g. high pressure pulsed electric field) processing.     

Comparative study on cloudy apple juice qualities from apple slices treated by high pressure carbon dioxide and mild heat

Qualities of cloudy apple juices from apple slices treated by high pressure carbon dioxide (HPCD) and mild heat (MH) were evaluated. Temperatures were from 25 to 65 °C, time 20 min, and pressure 20 MPa. Polyphenol oxidase (PPO) was completely inactivated by HPCD and its minimal residual activity (RA) by MH at 65 °C was 38.6%. RA of pectin methylesterase (PME) with HPCD was significantly lower than MH and its minimum was 18%. L value of cloudy apple juice from HPCD-treated apple slices was significantly greater than that from MH-treated apple slices, however, b value, browning degree (BD) and turbidity were lower. And no differences in a value, total soluble solids, pH and conductivity were observed. After 7-day storage at 4 °C, HPCD caused no BD alteration but a significant turbidity loss. MH increased BD at 55 and 65 °C, and led to turbidity loss from 35 to 65 °C. The turbidity was not well related to RA of PME.Industrial relevanceCloudy apple juice is one of the popular fruit juices, and it requires strict processing treatment conditions to protect its quality, especially to prevent enzymatic browning and cloud loss. HPCD is one promising novel non-thermal technique and is likely to replace or partially substitute thermal processes. This study analyzed the effect of HPCD as a pretreatment means on qualities of cloudy apple juice, including inactivating enzymes which are crucial to quality control. Available data provided in this study will benefit the fruit juice industry.