Effect on Orange Juice of Batch Pasteurization in an Improved Pilot-Scale Microwave Oven

ABSTRACT:  The effects on orange juice batch pasteurization in an improved pilot-scale microwave (MW) oven was evaluated by monitoring pectin methyl-esterase (PME) activity, color, carotenoid compounds and vitamin C content. Trials were performed on stirred orange juice heated at different temperatures (60, 70, 75, and 85 °C) during batch process. MW pilot plant allowed real-time temperature control of samples using proportional integrative derivative (PID) techniques based on the infrared thermography temperature read-out. The inactivation of heat sensitive fraction of PME, that verifies orange juice pasteurization, showed a  z -value of 22.1 °C. Carotenoid content, responsible for sensorial and nutritional quality in fresh juices, decreased by about 13% after MW pasteurization at 70 °C for 1 min. Total of 7 carotenoid compounds were quantified during MW heating: zeaxanthin and β-carotene content decreased by about 26%, while no differences ( P  < 0.05) were found for β-cryptoxanthin in the same trial. A slight decrease in vitamin C content was monitored after MW heating. Results showed that MW heating with a fine temperature control could result in promising stabilization treatments.     

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.     

EFFECT OF DIFFERENT PASTEURIZATION CONDITIONS ON ENZYME INACTIVATION OF ORANGE JUICE IN PILOT-SCALE EXPERIMENTS1

The orange juice pasteurization is associated with enzymatic degradation (primarily pectin-methylesterase) of soluble pectin. Time-temperature curves were established to study different pasteurization conditions on enzyme inactivation, for fresh single-strength orange juice from Florida, containing natural PME enzyme. The orange juice was heated in a DeLaval, model P5-VRB plate heat exchanger with heating and cooling sections, and a 0.0101 m³ volume holding tube. The temperature in the heat exchanger was controlled by means of a pneumatic proportional controller. The residence time in the holding tube of the heat exchanger was monitored by adjusting the flow rate of the positive feed pump. The calculated holding times to obtain 90% reduction of enzyme activity ranged from 33.27 s at 80C to 17.85 s at 90C.     

Evaluation of Phosphatase Inactivation Kinetics in Milk Under Continuous Flow Microwave and Conventional Heating Conditions

Raw milk was subjected to conventional isothermal water bath heating, continuous flow microwave heating and continuous flow thermal holding in the pasteurization temperature range (60–75°C), and then immediately cooled in an ice-water bath. The associated alkaline phosphatase (ALP) residual activities were evaluated. Based on the gathered time-temperature profiles, the come-up time (CUT) and come-down time (CDT) contributions to enzyme inactivation were assessed and adjusted prior to first order rate kinetic data handling. The time-corrected D-values of ALP varied from 1250 s at 60°C to 1.7 s at 75°C with a z-value of 5.2°C under conventional batch heating conditions, 128 s at 65°C to 13.5 s at 70°C, with a z-value of 5.2°C under continuous-flow thermal holding condition, 17.6 s at 65°C to 1.7 s at 70°C with a z-value of 4.9°C under continuous-flow microwave heating condition. D values associated ALP inactivation under microwave heating were therefore an order of magnitude lower than under conventional thermal heating. The results thus emphasize that ALP inactivation occurred much faster under microwave heating condition than under conventional heating thereby confirming the existence of enhanced thermal effects from microwave. Because of the enhanced effects, MW pasteurization would reduce the severity of the treatment and hence potentially offer pasteurized milk of higher quality.     

A review of pectin methylesterase inactivation in citrus juice during pasteurization

BackgroundPectin, naturally found in citrus, plays a key role in the quality of the obtained juices. Pectin methylesterase enzyme (PME) influences the cloud stability, viscosity, color, mouth feeling and flavor of the juices by de-esterification of pectin. Iinactivation of PME is introduced as a pasteurization index in citrus juices, due to its higher thermal resistance than the spoilage microorganisms.Scope and approachInactivation of PME using different thermal (conventional, microwave and ohmic heating) and non-thermal (pulsed electric field, high pressure processing and high pressure carbon dioxide) processes is important in juice production. The aim of this study was to review the effect of these processing methods on the PME inactivation in different citrus juices.Key finding and conclusionUsing non-thermal methods in combination with moderate thermal methods can be more effective in PME inactivation with minimum loss in citrus juice quality.     

Assessment of the thermal treatment of orange juice during continuous microwave and conventional heating

The effect of continuous-flow microwave heat treatment of orange juice was evaluated by using parameters of quality (pectin methylesterase (PME) inactivation and ascorbic acid, free amino acids, carbohydrates and hydroxymethyl furfural (HMF) contents, as well as degree of browning). Results were compared with those obtained using a conventional tubular heat exchanger having the same heating and cooling phases. The continuous microwave process proved to be an effective system for PME inactivation without the inclusion of a holding phase. In general, no differences were found between the two systems used in the majority of the indicators studied, except that a slight decrease was observed in the most reactive amino acids in the case of conventionally heated orange juice. This fact could be due to overheating of the juice at the tubular heat exchanger. © 1998 Society of Chemical Industry     

Inactivation of Pectin Methyl Esterase in Orange Juice by Pulsed Electric Fields

ABSTRACT: Pulsed electric fields (PEF) treatments were applied to nonpasteurized orange juice using a bench top PEF system to study effects of PEF on the activity of pectin methyl esterase (PME). Effects of electric strength on PME activity at a constant water bath temperature were studied using electric field strengths up to 35 kV/cm at 30 °C. Increase of electric field strength caused a significant inactivation of PME with increase in orange juice temperature ( p < 0.05). A thermal inactivation study showed that heating of orange juice at the same temperature as orange juice during PEF treatment was not effective as PEF treatment in inactivating PME. Effects of electric field strength at different water bath temperatures were studied using electric field strengths up to 25 kV/cm and water bath temperatures of 10–50 °C. Higher electric field strengths at higher water bath temperature were the more effective to inactivate PME. A combination of PEF treatment at 25 kV/cm and a water bath temperature of 50 °C caused 90% inactivation of PME.     

Enhanced destruction of spoilage microorganisms in apple juice during continuous flow microwave heating

Destruction kinetics of two selected spoilage microorganisms, Saccharomyces cerevisiae and Lactobacillus plantarum in apple juice were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a water bath. Inoculated apple juice was heated in a microwave oven (700 W, 2450 MHz) under continuous-flow conditions to selected exit temperatures (52.5–65°C). Aliquots of inoculated juice were also subjected to batch thermal treatments (50–80°C) in a well-stirred water bath. Time-temperature profiles obtained both during heating and cooling of test samples were used to correct both come-up and come-down times. The time-corrected D-values under microwave heating were 4.8, 2.1 and 1.1 s at 52.5, 55 and 57.5°C, respectively, for S. cerevisiae and 14, 3.8 and 0.79 s at 57.5, 60 and 62.5°C, respectively, for L. plantarum with corresponding z-values of 7 and 4.5°C. D-values under batch thermal heating were 58, 25, 10 and 1.9 s at 50, 55, 60 and 70°C, respectively, for S. cerevisiae and 52, 22, 8.4 and 1.2 s at 55, 60, 70 and 80°C, respectively, for L. plantarum with corresponding z-values of 13.4 and 15.9°C. Microbial destruction thus occurred much faster under microwave heating than under thermal heating suggesting some contributory enhanced effects to be associated with microwave heating.     

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.     

Orange Juices and Concentrates Stabilization by a Proteic Inhibitor of Pectin Methylesterase

A proteic inhibitor of pectin methylesterase (PME), recently discovered in kiwi, was used to stabilize cloud of orange juice concentrate with “Cut-back,” 42° Brix. To concentrated and pasteurized orange juice were added increasing amounts of fresh juice (12° Brix) with PME 0.8 U/mL at the fresh to pasteurized ratios 6.6 to 38%. The PME inhibitor (65% pure), from kiwi, was added at 50 mg/L. After 8 mo at 5°C samples were compared with controls containing the same amount of fresh juice with PME inhibited by pasteurization. Pasteurized samples were not different from those treated with PME inhibitor. Conversely, where PME was not inhibited, cloud stability decreased with increasing amounts of fresh juice. Use of kiwi PME inhibitor in fruit juice production has potential advantages.     

Inactivation of pectin methylesterase and stabilization of opalescence in orange juice by dynamic high pressure

The effect of dynamic high pressure homogenization (DHP) alone or in combination with pre-warming on pectin methylesterase (PME) activity and opalescence stability of orange juice was studied. DHP without heating reduced PME activity by 20%. Warming the juice (50 °C, 10 min) prior to homogenization significantly increased the effectiveness of DHP. PME inactivation was further increased by adjusting the pH downward prior to treatment. Accelerated shelf-life study at 30 °C revealed that opalescence stability can be increased by several days by DHP treatment, even in the presence of active PME. These results suggest that the opalescence stability of orange juice treated by DHP does not depend entirely on PME activity but also on particle size reduction and structural changes to pectin resulting from the treatment. The freshness attributes of orange juice treated by warming was improved by DHP treatment.     

Inactivation of pectin Methylesterase and Lactobacillus Plantarum by ohmic heating in pomelo juice

The use of ohmic heating (OH) to inactivate damaging elements in pomelo juice was evaluated. The work investigated the effect of frequencies (50–20 000 Hz) on pectin methylesterase (PME) and Lactobacillus plantarum (L. plantarum) in pomelo juice at 30 V cm⁻¹ of electric field strength. The results show that frequency does not affect PME inactivation (P > 0.05) but affects bacterial reduction and has the most efficiency at 60 Hz, followed by 50 Hz, and in the frequency range at or higher than 500 Hz (P < 0.05). Additionally, the inactivation kinetics of PME and L. plantarum and the impact of nonthermal factors were given. The nonthermal element has contributed to the inactivation enhancement of L. plantarum and PME to reduce the necessary treatment temperature and time. The major spoilage bacteria and enzyme destruction in pomelo juice occurred faster under OH than under conventional heating (CH) suggesting that OH can be effectively used to pasteurise pomelo juice.     

Chilled orange juices stabilized by centrifugation and differential heat treatments applied to low pulp and pulpy fractions

Thermal treatments of citrus juices to inactivate microorganisms and pectinmethylesterase (PME) must be as soft as possible to preserve fresh taste. PME, a cell wall enzyme associated with pulp, is more heat resistant than spoilage microorganisms. This paper analyzes fresh taste and storage stability of orange juices in which the pulp receives a heat treatment more intense than the rest of the juice. The products compared where: A) low pulp juice treated at 60 °C–15 s; B) aseptic blend of A and the corresponding pulpy fraction treated at 85 °C–15 s; C) non aseptic blend of non-treated low pulp fraction and the corresponding pulpy fraction treated at 85 °C–15 s. Product C was finally treated at 60 °C–15 s and packed under aseptic conditions. PME activity in A, B and C was around 10% of that in the original juice (1.30 nkat/ml).After 12 months at 3 °C, juices B and C retained the original fresh taste with minimal losses of color and cloudiness. Juice A maintained fresh taste but its color and cloud were not satisfactory.

Industrial Relevance

The procedures proposed in this paper can be applied to produce chilled orange juices without losses in fresh taste having in addition, higher stability than commercial juices. Other advantages when compared to non thermal emergent technologies are that can be carried out by regular equipments used in citrus industries with an important energy saving. These procedures imply energy savings of 22% to 38% when compared to thermal requirements of juice pasteurization at 85 °C.     

Novel,non-thermal hydrodynamic cavitation of orange juice: Effects on physical properties and stability of bioactive compounds

Effect of hydrodynamic cavitation (HC) at pressure 3–15 bar and treatment time5–25 min on physical and chemical qualities of orange juice was investigated. Processing parameters were optimized on the basis of retention of vitamin C and antioxidant activity; inactivation of pectin methyl esterases (PME) and peroxidase (POD) enzyme and stability of pH, °Brix, viscosity, titratable acidity and total color difference. HC of orange juice at 5 bar 15 min and 13 bar 10 min resulted into maximal overall desirability at 0.52 and 0.40 respectively. No significant change in °Brix, pH, titratable acidity for fresh and cavitated orange juice was observed. Only 21% and 13% of reduction in PME and POD respectively was recorded. A 94% and 91% of antioxidant activity and vitamin C retention was noted in both optimized samples. This study demonstrated that HC can produce orange juice more economically with better physical properties and nutritional value.Industrial relevanceThe demand for more natural, preservative free with highest nutritional bioactive containing juices has created a need of non-thermal processing. Hydrodynamic cavitation (HC) processing is novel, emerging and under explored technology for fruit juices. HC due to the formation of cavities and shock waves causes enzyme and microbial inactivation at low temperature while retaining natural bioactives with fresh-like organoleptic characteristics. It is believed worldwide that non thermal technologies like HC will be among the most cost effective, scalable and impactful liquid food processing technologies in the coming decades especially for commercial products.     

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.     

Kinetic study of high pressure microbial and enzyme inactivation and selection of pasteurisation conditions for Valencia Orange Juice

Keeping quality of fresh orange juice is highly dependent on pectinolytic enzyme activity and the growth of spoilage microorganisms. The inactivation kinetics of indigenous pectin methylesterase (PME) and of the two more pressure resistant species of spoilage lactic acid bacteria (LAB) Lactobacillus plantarum and L. brevis in freshly squeezed Valencia orange juice under high hydrostatic pressure (100–500 MPa) combined with moderate temperature (20–40 °C) was investigated. PME inactivation followed first order kinetics with a residual PME activity (15%) at all pressure–temperature combinations used. The values of activation energy and activation volume were estimated at each pressure and at each temperature, respectively. Values of 90 kJ/mol and ?30 mL/mol at reference pressure of 300 MPa and reference temperature of 35 °C were estimated respectively. The corresponding z_T and z_P values of LAB inactivation were also estimated at all conditions tested. Values of 19.5 °C and 95 MPa at reference pressure of 300 MPa and reference temperature of 30 °C were estimated respectively for L. plantarum, while the corresponding values for L. brevis were 40 °C and 82 MPa, respectively, at the same reference conditions. Pressure and temperature were found to act synergistically both for PME and LAB inactivation. The PME and LAB inactivation rate constants were expressed as functions of the temperature and pressure process conditions. These functions allow the determination of the pressure/temperature conditions that achieve the target enzyme and microbial inactivation at a selected processing time. The process conditions of 350 MPa at 35 °C for 2 min are proposed as effective for Valencia orange juice cold pasteurisation.     

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.     

High Pressure and Temperature Effects on Enzyme Inactivation in Strawberry and Orange Products

High hydrostatic pressure treatment (50-400 MPa) combined with heat treatment (20–60°C) effects on peroxidase (POD), polyphenoloxidase (PPO) and pectin methylesterase (PME) activities of fruit-derived products were studied. Assays were carried out on fresh orange juice and strawberry puree. Pressurization/depressurization treatments caused a significant loss of strawberry PPO (60%) up to 250 MPa and POD activity (25%) up to 230 MPa, while some activation was observed for treatments carried out in 250–400 MPa range for both enzymes. Optimal inactivation of POD was using 230 Mpa and 43°C in strawberry puree. Combinations of high pressure and temperature effectively reduced POD activity in orange juice (50%) to 35°C. The effects of high pressure and temperature on PME activity in orange juice were very similar to those for POD.     

Comparing equivalent thermal, high pressure and pulsed electric field processes for mild pasteurization of orange juice: Part II: Impact on specific chemical and biochemical quality parameters

The impact of thermal, high pressure (HP) and pulsed electric field (PEF) processing for mild pasteurization of orange juice was compared on a fair basis, using processing conditions leading to an equivalent degree of microbial inactivation. Examining the effect on specific chemical and biochemical quality parameters directly after treatment and during storage at 4 °C revealed only significant differences in residual enzyme activities. For pectin methylesterase inactivation, none of the treatments was able to cause a complete inactivation, although heat and HP pasteurization were the most effective in limiting the residual activity. Peroxidase was completely inactivated by heat pasteurization and was much less susceptible to HP and PEF. All other quality parameters investigated, including the sugar profile, the organic acid profile, bitter compounds, vitamin C (ascorbic acid and dehydroascorbic acid), the carotenoid profile, furfural and 5-hydroxymethylfurfural, experienced no significantly different impact from the three pasteurization techniques.

Industrial relevance

HP and PEF processing have received important attention during the last years for application as alternatives to traditional thermal pasteurization. For the further implementation of HP and PEF treatment in the food industry, legal approval of such processes is required. Accordingly, an in-depth characterization of products treated by these novel technologies is indispensable. This paper addresses orange juice as a relevant model food product to compare the impact of HP and PEF processing with that of a conventional thermal pasteurization process and to search for significant differences in specific known nutrients, undesired substances and other quality-related aspects of orange juice.