Effect of combined high pressure–temperature treatments on color and nutritional quality attributes of pineapple (Ananas comosus L.) puree

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The present work investigates the impact of pressure (P; 300-600 MPa) and holding time (t; 5-20 min) on the quality attributes and microbial stability of jackfruit shreds. The results revealed that the P and t had significantly affected physico-chemcial and bioactive composition of the jackfruit shreds. Higher levels of P and t increased the firmness of the shreds. Better colour retention and lower colour deviation were observed after processing at 450 and 600 MPa for 20 and 23 min, respectively. The ascorbic acid content in jackfruit shreds increased from 15.42-16.32 mg/100 g and the total flavonoid content in high pressure processed sample increased maximum of about 31% after HPP processing. All the response variables fitted well with the polynomial model of degree two by multilinear regression analysis. High pressure processing at 600 MPa/8 min rendered jackfruit shreds with optimal quality and improved microbial stability with a desirability value of 0.832.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-06022-z.

Effect of continuous microwave processing on enzymes and quality attributes of bael beverage

Bael (Aegle marmelos) beverage was pasteurized using continuous-microwave (MW) and traditional thermal processing and the activity of native enzymes, pulp-hydrolyzing enzymes, bioactive, physicochemical, and sensory properties were analyzed. First-order and linear biphasic models fitted well (R2 ≥ 0.90) for enzyme inactivation and bioactive alteration kinetics, respectively. For the most resistant enzyme, polyphenoloxidase (PPO), the inactivation target of ≥ 90 % was achieved at 90 °C TMW (final temperature under MW) and 95 °C for 5 min (conventional thermal). MW treatment displayed faster enzyme inactivation and better retention of TPC and AOC. MW treatment at 90 °C TMW showed 5.3 min D-value, 90% total carotenoid content, 3.42 crisp sensory score (out of 5), and no or minor change in physicochemical attributes. Thermal and MW treatment caused the loss of 14 and 10 bioactive compounds, respectively. The secondary and tertiary structural modifications of PPO enzyme-protein revealed MW's lethality primarily due to its thermal effects.

Pulsed light treatment of whole white button mushroom (Agaricus bisporus): Kinetics and mechanism of microbial inactivation and storage study

The whole white button mushrooms (WWBMs) are highly perishable due to susceptibility to microbial spoilage. This study explored the potential of pulsed light (PL) treatment for decontamination and shelf-life extension of WWBM. WWBM surface was inoculated with Escherichia coli, Listeria monocytogenes, and Aspergillus niger spores (8.1, 8.0, and 8.05 log10 CFU/g, respectively) and tested for inactivation against various PL intensities (fluence 0.13-0.75 J/cm2). The kinetics and mechanism of microbial inactivation were explored, and shelf life was determined at 4, 20, and 37°C. Microbial inactivation increased with increasing PL intensity. PL-induced microbial inactivation was well explained by Weibull model with shape parameters (β-value) for E. coli, L. monocytogenes, A. niger, aerobic mesophiles, and yeast and mold as 0.87, 0.92, 0.91, 0.89, and 0.94, respectively. PL-treatment at 0.75 J/cm2 resulted in >5-log cycle reduction in all inoculated and natural microorganisms. Exposure to PL led to collapse of cellular structure, ruptured cell wall, and leakage of cellular material in all microorganisms and spores along with alterations in nucleic acid and lipid bands. At 4°C, maximum shelf life of 5 days was achieved when WWBM was exposed at 0.75 J/cm2. The WWBM retained 83.3% phenolics, 83.9% antioxidant capacity, and 77.4% vitamin D2 at 4°C while reducing the polyphenol oxidase and peroxidase activity by 89% and 79%. The degradation rate for quality parameters increased with storage temperature. The activation energy of the browning index affirmed it as the most sensitive quality attribute during storage. The study concluded the potential of PL treatment to prolong the shelf life of WWBM.

Exploring the impact of high pressure processing on the characteristics of processed fruit and vegetable products: a comprehensive review

Consumers are increasingly interested in additive-free products with a fresh taste, leading to a growing trend in high pressure processing (HPP) as an alternative to thermal processing. This review explores the impact of HPP on the properties of juices, smoothies, and purees, as well as its practical applications in the food industry. Research findings have explained that HPP is a most promising technology in comparison to thermal processing, in two ways i.e., for ensuring microbial safety and maximum retention of micro and macro nutrients and functional components. HPP preserves natural color and eliminates the need for artificial coloring. The review also emphasizes its potential for enhancing flavor in the beverage industry. The review also discusses how HPP indirectly affects plant enzymes that cause off-flavors and suggests potential hurdle approaches for enzyme inactivation based on research investigations. Scientific studies regarding the improved quality insights on commercially operated high pressure mechanisms concerning nutrient retention have paved the way for upscaling and boosted the market demand for HPP equipment. In future research, the clear focus should be on scientific parameters and sensory attributes related to consumer acceptability and perception for better clarity of the HPP effect on juice and smoothies/purees.

Geothermal food dehydrator system, operation and sensory analysis, and dehydrated pineapple quality

Food dehydration is a preservation technique that guarantees its supply. Food like vegetables and fruits are traditionally dehydrated with natural gas or solar energy, however, this work demonstrates the feasibility of doing it with energy from a geothermal power plant in Nayarit, Mexico. Different species of pineapple (Miel, Cayenne, and Esmeralda) were dehydrated at different temperatures from 64 to 80°C and the safety of the product was subsequently verified, for these aerobic mesophiles (<230 ufc/g), total coliforms (<0.3 s.m.), molds and yeasts (<120 v.e.), and salmonella spp (Absent in 25 g), and results were obtained within the proposed specifications, which were generated taking as reference the national and international guidance standards. A sensory evaluation, a modified Flash Profile (mFP), was carried out with a group of judges trained in descriptive methodology, since a better consensus of responses was obtained, thus demonstrating the usability of mFP for food dehydration. The studies of pineapple allowed the evaluation of production with the DGA 200 technology, and the microbiological standards, as well as sensory and physicochemical parameters, were considering just to verify that product is suitable for human consumption. The technology is a system that takes advantage of the heat of the earth, with which it is possible to work 7 days a week or the entire pineapple season. Physicochemical changes caused by its dehydration with respect to the content of vitamin C, carbohydrates, and dietary fiber in the three species of dehydrated pineapple were measured. In the fresh samples, an average concentration of vitamin C 9 mg/100 g, carbohydrates 11.6 g sugar/100 g, and dietary fiber 0.96% were measured. The dehydrated samples presented an average value of vitamin C of 95 mg/100 g, carbohydrates 72.6 g sugar/100 g, and dietary fiber 8.6%, these results were similar to Mühlbauer and Müller, 2020, Drying atlas, drying kinetics and quality of agricultural products, Elsevier.

The influence of non-thermal technologies on color pigments of food materials: An updated review

The color of any food is influenced by several factors, such as food attributes (presence of pigments, maturity, and variety), processing methods, packaging, and storage conditions. Thus, measuring the color profile of food can be used to control the quality of food and examine the changes in chemical composition. With the advent of non-thermal processing techniques and their growing significance in the industry, there is a demand to understand the effects of these technologies on various quality attributes, including color. This paper reviews the effects of novel, non-thermal processing technologies on the color attributes of processed food and the implications on consumer acceptability. The recent developments in this context and a discussion on color systems and various color measurement techniques are also included. The novel non-thermal techniques, including high-pressure processing, pulsed electric field, ultrasonication, and irradiation which employ low processing temperatures for a short period, have been found effective. Since food products are processed at ambient temperature by subjecting them to non-thermal treatment for a very short time, there is no possibility of damage to heat-sensitive nutrient components in the food, any deterioration in the texture of the food, and any toxic compounds in the food due to heat. These techniques not only yield higher nutritional quality but are also observed to maintain better color attributes. However, suppose foods are exposed to prolonged exposure or processed at a higher intensity. In that case, these non-thermal technologies can cause undesirable changes in food, such as oxidation of lipids and loss of color and flavor. Developing equipment for batch food processing using non-thermal technology, understanding the appropriate mechanisms, developing processing standards using non-thermal processes, and clarifying consumer myths and misconceptions about these technologies will help promote non-thermal technologies in the food industry.

Review on Furan as a Food Processing Contaminant: Identifying Research Progress and Technical Challenges for Future Research

A wide range of food processing contaminants (FPCs) are usually formed while thermal processing of food products. Furan is a highly volatile compound among FPCs and could be formed in a variety of thermally processed foods. Therefore, identification of possible reasons of furan occurrence in different thermally processed foods, identification of the most consequential sources of furan exposure, factors impacting its formation, and its detection by specific analytical approaches are necessary to indicate gaps and challenges for future research findings. Furthermore, controlling furan formation in processed foods on a factory scale is also challenging, and research advancements are still ongoing in this context. Meanwhile, understanding adverse effects of furan on human health on a molecular level is necessary to gain insights into human risk assessment.

Effect of citric acid/ pomelo essential oil nanoemulsion combined with high hydrostatic pressure on the quality of banana puree

In this work, the influence of citric acid & pomelo essential oil nanoemulsion (CA&PEN) assisted with HHP on microbial counts, oxidative enzyme activity and related quality of banana puree were examined. The total aerobic bacteria (TAB) counts of all groups decreased to 1.2 ∼ 2.52 lg CFU/g from 3.97 lg CFU/g, except the CA&PEN group, which was still below the detection level. CA&PEN combined with HHP (500 or 600 MPa, 5 min) succeeded in keeping TAB counts of banana puree below the detection limit for 3 months of cold storage. During 90 days of cold storage, the color, total phenolics, DPPH and ABTS antioxidant capacities were better conserved in acidified groups than non-acidified groups. In conclusion, CA&PEN assisted with HHP can be utilized to promote the inhibition of enzymatic browning and maintain the quality of banana puree, due to its reduced oxidative enzyme activity, low pH, strong antioxidant capacity and excellent color retention.

Nonthermal pasteurization of pineapple juice: A review on the potential of achieving microbial safety and enzymatic stability

Pineapple juice is preferred by consumers for its unique aroma and flavor that come from a set of amino acids, amines, phenolic compounds, and furanone. The juice is susceptible to spoilage, and a common practice is to pasteurize it at 70-95°C for 0.5-5 min. However, the characteristic flavors and phytochemicals are negatively influenced by the intense time-temperature treatment. To retain the thermosensitive compounds in the juice, some nonthermal technologies such as high-pressure processing, pulsed electric field, pulsed light, ultrasound, and ultraviolet treatments have been explored. These techniques ensured microbial safety (5-log reduction in E. coli, S. Typhimurium, or S. cerevisiae) while preserving a maximum ascorbic acid (84-99%) in the juice. The shelf life of these nonthermally treated juice varied between 14 days (UV treated at 7.5 mJ/cm² ) and 6 months (clarified through microfiltration). Moreover, the inactivation of spoilage enzyme in the juice required a higher intensity. The present review discusses the potential of several nonthermal techniques employed for the pasteurization of pineapple juice. The pasteurization ability of the combined hurdle between mild thermal and nonthermal processing is also presented. The review also summarizes the target for pasteurization, the plan to design a nonthermal processing intensity, and the consumer perspective toward nonthermally treated pineapple juice. The techniques are compared on the common ground like safety, stability, and quality of the juice. This will help readers to select an appropriate nonthermal technology for pineapple juice production and design the intensity required to satisfy the manufacturers, retailers, and consumers.

Design consideration and modelling studies of ultrasound and ultraviolet combined approach for shelf-life enhancement of pine apple juice

Although both ultraviolet (UV) radiation and ultrasound (US) treatment have their capabilities in microbial inactivation, applying any one method alone may require a high dose for complete inactivation, which may affect the sensory and nutritional properties of pineapple juice. Hence, this study was intended to analyse and optimise the effect of combined US and UV treatments on microbial inactivation without affecting the selected quality parameters of pineapple juice. US treatment (33 kHz) was done at three different time intervals, viz. 10 min, 20 min and 30 min., after which, juice samples were subjected to UV treatment for 10 min at three UV dosage levels, viz. 1 J/cm2, 1.3 J/cm2, and 1.6 J/cm2. The samples were evaluated for total colour difference, pH, total soluble solids (TSS), titrable acidity (TA), and ascorbic acid content; total bacterial count and total yeast count; and the standardization of process parameters was done using Response Surface Methodology and Artificial Neural Network. The results showed that the individual, as well as combined treatments, did not significantly impact the physicochemical properties while retaining the quality characteristics. It was observed that combined treatment resulted in 5 log cycle reduction in bacterial and yeast populations while the individual treatment failed. From the optimization studies, it was found that combined US and UV treatments with 22.95 min and1.577 J/cm2 ensured a microbiologically safe product while retaining organoleptic quality close to that of fresh juice.

Osmo-air drying of banana slices: multivariate analysis, process optimization and product quality characterization

In the present work, osmotic dehydration (OD) was applied as a pretreatment to hot air drying of banana slices and the effect of OD parameters on mass transfer characteristics, color profile was analysed. Principal component analysis (PCA) of OD process revealed that solid gain, weight reduction, water loss and total soluble solids were positively correlated with each other but were found to be negatively correlated with moisture content (MC) of sample. Response surface methodology was used for optimizing the OD of banana slices and and the optimum conditions were 61.26°Brix sucrose concentration at 50 °C for 6 h, resulting in moisture reduction from 75 to 49.78%. PCA-biplot of osmo-air drying (OAD) process showed the association among response parameters, which further revealed a positive correlation of MC with bioactive components. Additionally, OAD samples were also studied for microstructure and Fourier Transform Infra-red analysis. Addition of calcium lactate to sucrose solution resulted in preserving the firmness and bioactive components during osmosis, in addition to fortifying the sample with calcium. The present study provides new possibilities for food industries in preserving the ripe banana and developing calcium fortified functional food products.

High Pressure Processing vs. Thermal Pasteurization of Whole Concord Grape Puree: Effect on Nutritional Value, Quality Parameters and Refrigerated Shelf Life

High-pressure processing (HPP) is utilized for food preservation as it can ensure product safety at low temperatures, meeting consumers’ demand for fresh-like and minimally processed products. The purpose of this study was to determine the effects of HPP (600 MPa, 3 min, 5 °C) and pasteurization by heat treatment (HT, 63 °C, 3 min) on the production of a novel whole Concord grape puree product (with skin and seeds, no waste), and the shelf-life of the puree under refrigerated storage (4 °C). Microbial load, physicochemical properties, phenolic content and antioxidant activity, composition and sensorial attributes of puree samples were evaluated. HPP- and HT-treated purees were microbiologically stable for at least 4 months under refrigeration, with less microbial growth and longer shelf life for HPP samples. HPP and HT samples had similar levels of phenolic contents and antioxidant activities throughout the 4-month refrigerated storage period, even though HPP retained >75% PPO and POD enzyme activities while those of HT were less than 25%. Inclusion of seeds in the puree product significantly increased the fiber, protein, total fatty acid, and linoleic acid contents. Sensory results showed that HPP-treated puree retained more fresh-like grape attributes, had better consistency, and showed significantly higher ratings in consumer overall liking, product ranking, and purchase intent than the HT puree (p < 0.05).

Functional and Quality Characteristics of Ginger, Pineapple, and Turmeric Juice Mix as Influenced by Blend Variations

In this current work, the functional and quality characteristics of ginger, pineapple, and turmeric juice mix as influenced by blend variations were investigated. Specifically, the blends had constant ginger amounts, decreased pineapple, and increased turmeric proportionally. Additionally, the functional properties involved physicochemical (pH, soluble solids (SS), total titratable acidity (TA) and viscosity), proximate (moisture, protein, fat and ash), minerals (Ca, and Mg) and vitamin C and β-carotene analyses, whereas quality properties involved microbiological and sensory analyses. The results showed that as quantities of pineapple and turmeric respectively decreased and increased, there was significant increases in Ca, Mg, vitamin C, and β-carotene contents (p < 0.05). Across the blends, the degree of significant differences (p < 0.05) in the protein, fat, and ash seemed more compared to those of moisture contents. Despite the increases in pH and viscosity, and decreases in SS and TA, the increases in turmeric potentially reinforced by ginger most likely decreased the bacterial/fungi counts, as well as inhibition zones. Increasing and decreasing the respective amounts of turmeric and pineapple might not necessarily make the blends more acceptable, given the decreases in appearance, taste, aroma, and mouthfeel scores.

Formulation of a mixed fruit beverage using fuzzy logic optimization of sensory data and designing its batch thermal pasteurization process

The study aims to formulate a mixed fruit beverage through sensory analysis, and the composition was optimized using a fuzzy logic algorithm. The fuzzy optimization algorithm was developed using a modified Takagi and Sugeno's approach, polynomial mixture modeling, and nonlinear solver engine. The optimized blend consisted of amla juice, pineapple juice, and coconut water in 14.3, 63.0, and 22.7%, respectively. Further, the batch thermal treatment was carried out within 50 to 95 °C for an isothermal holding time of 1 s to 10 min, and pasteurization condition for the beverage was estimated from kinetic modeling. The concept of thermal pulse inactivation due to non-isothermal heat-up-time and cool-down-time has been introduced within the process time calculation. From the kinetic study, polyphenoloxidase enzyme appeared to be the most resistant entity towards inactivation among all the natural microbiota and quality deteriorating enzymes. Pasteurization in terms of achieving a 5D reduction of both aerobic mesophilic and yeast-mold counts was attained over a range of 80 to 95 °C for 10.2 + 1.4 to 3.1 + 2.0 min (1.4 and 2.0 min = heat-up-time + cool-down-time), respectively. The 90% inactivation of both polyphenoloxidase and peroxidase enzymes was obtained over a range of 90 to 95 °C for 12.8 + 1.7 to 8.4 + 2.0 min, respectively. While obtaining both the microbial and enzyme stability at the isothermal condition of 95 °C for 8.4 min, the corresponding retention in ascorbic acid, total phenolics, and antioxidant capacity were observed as 49.7, 63.0, and 61.4%, respectively. PRACTICAL APPLICATION: In this work, the formulation of a fruit blend was optimized through an intelligent optimization technique (fuzzy algorithm) applied to the sensory data set. The approach for calculating thermal processing time or pasteurization condition provides a new dimension with better precision. The thermal treatment condition of 95 °C for 10 min can be used for this mixed beverage to achieve both microbial stability (5-log reduction) and enzyme stability (90% reduction). The presented study can be used as a reference for other similar beverages to achieve a complete process design from basic formulation optimization to thermal (batch-type) processing conditions.

Mitigation of relative humidity (RH) on phytochemicals and functional groups of dried pineapple (Ananas comosus) slices

As part of finding a mechanism to ameliorate the decomposition of phytochemicals and antioxidant in drying processing, this research was conducted. To achieve this, pineapple slices was dried using relative humidity (RH) dryer at varied temperature (60–80 °C) combined with RH (10–30%) conditions. The results revealed that higher RH retained with significantly difference (p <0.05) the phytochemical and antioxidant concentrations and preserved the color and functional groups of dried pineapple under varying drying temperatures. The result also shows that concentrations of these compounds may differ as a result of disparities in the chemical composition which may be worsening by drying conditions such as higher temperature and lower RH. In effect, RH could savage the intensity of losses of these compounds and could therefore play a critical role in drying technology. Practical application: The loss of phytochemicals including polyphenols and antioxidant remains one of the challenging phenomena in drying technology. This research finds ameliorative option for mitigating against the loss of polyphenols and antioxidant by exploring the use of relative humidity (RH). The result shows that RH could savage the intensity of loss of these compounds and could therefore play a critical role in drying technology.

Effect of Pulsed Light Treatment on Natural Microbiota, Enzyme Activity, and Phytochemical Composition of Pineapple (Ananas comosus [L.] Merr.) juice

The effect of pulsed light (PL) on numerous important quality characteristics of pineapple juice was studied and compared with untreated and thermally pasteurised samples. The laboratory scale PL batch system used was operated with each three different voltages (1.8, 2.1, and 2.4 kV) and numbers of pulses (47, 94, and 187). Treatments with 2.4 kV and either 94 or 187 pulses (757/1479 J·cm−2) resulted in a 5-log reduction in aerobic mesophiles and the yeast and mould counts. Peroxidase was more resistant to PL than polyphenol oxidase, whereas the bromelain activity was completely retained in all PL-treated juices. Colour and antioxidant capacity were minimally affected, while vitamin C, genuine pineapple furanones, and phenolic compounds declined. In contrast, thermal pasteurisation was more detrimental to colour, antioxidant capacity, and vitamin C content, but resulted in a superior inactivation of microorganisms and enzymes and retention of phenolic compounds. Principal component analysis (PCA) permitted the differentiation of fresh, thermally pasteurised, and all PL-treated juices. PCA on the basis of the individual juice constituents additionally arranged the latter juices according to the number of pulses and voltage levels applied, particularly promoted by the oxidation of ascorbic to dehydroascorbic acid. In conclusion, PL treatment represents a promising new alternative to conventional thermal preservation techniques, whereby the inactivation of deteriorative enzymes may be further optimised.

A review on furan: Formation, analysis, occurrence, carcinogenicity, genotoxicity and reduction methods

Furan (C₄H₄O) is a volatile, heterocyclic and carcinogenic heterocyclic chemical compound occurring in a wide range of thermally processed foods. Several studies have been conducted to analyze the formation conditions, triggering furan formation via model systems. Furan can be encountered via various pathways including thermal degradation, oxidation of polyunsaturated fatty acids, thermal rearrangement of carbohydrates in the presence of amino acids, thermal degradation of certain amino acids. Furan has been proven to cause cancer in experimental animal models and classified as a possible human carcinogen by International agency for research on cancer based on sufficient evidences. Thus, different strategies should be developed to reduce furan contents in commercially available food stuffs while food processing. This review summarizes some current evidences of furan formation from different precursors, analytical methods for its detection, and its toxicity that might lead to carcinogenicity and genotoxicity with human risk assessment. In addition, furan occurrence in different thermally processed foods entailed by several recent studies as well as furan mitigation strategies during food processing have also been illustrated in this review.

Kinetic modeling of high-pressure induced inactivation of polyphenol oxidase in sugarcane juice (Saccharum officinarum)

BACKGROUND

Polyphenol oxidase (PPO) is the main enzyme in sugarcane juice associated with rapid browning and degradation of organoleptic properties. High-pressure processing (HPP) (300-600 MPa) of sugarcane juice in combination with moderate temperatures (30-60 °C) for different processing times (10-25 min) has shown promising results in minimizing PPO activity while preserving the juice's freshness.

RESULTS

A maximum PPO inactivation of 98% was achieved at 600 MPa/60 °C/25 min, while the corresponding value for thermal treatment at 0.1 MPa/60 °C was only 66%. The nonlinearity in the inactivation data was well described by the Weibull distribution model with a high adjusted R² and reduced χ² values at all levels of pressure and temperature. The PPO inactivation data were fitted at shape parameter, β = 1 (log linear) and β ≠ 1. A refitted Weibull model was used to predict kinetic parameters such as the inactivation rate constants (k), activation energy (E_a ) and activation volume (V_a ), which govern PPO inactivation in HPP-treated sugarcane juice. A secondary kinetic model was formulated to predict the k values as a function of pressure (P) and temperature (T), incorporating E_a and V_a .

CONCLUSIONS

Combined high-pressure and temperature processing has been considered a reliable alternative to conventional heat treatment for inhibiting PPO activity in sugarcane juice. While the isothermal inactivation of PPO followed first-order kinetics, inclusion of high pressure resulted in a strong deviation from log linear kinetics. Identification of suitable kinetic models describing these inactivation processes is expected to aid product development and process control of high-pressure processed sugarcane juice. © 2018 Society of Chemical Industry.

Effect of low thermal pasteurization in combination with carvacrol on color, antioxidant capacity, phenolic and vitamin C contents of fruit juices

Mild thermal treatment in combination with natural antimicrobials has been described as an alternative to conventional pasteurization to ensure fruit juices safety. However, to the best of our knowledge, no study has been undertaken to evaluate what could be its effect on their color and nutritional value. This study therefore aimed at assessing how a low thermal pasteurization in combination with carvacrol could affect these parameters, with orange, pineapple, and watermelon juices as selected fruit juices. The experimental design used had levels ranging from 50 to 90°C, 0 to 60 μl/L, and 0 to 40 min for temperature, concentration of carvacrol supplemented, and treatment length, respectively. The only supplementation of fruit juices with carvacrol did not affect their color. In comparison with high thermal pasteurization (>70°C), a combined treatment at mild temperatures (50-70°C) better preserved their color, antioxidant capacity (AOC), and vitamin C content, and increased their total phenolic content (TPC). Globally, carvacrol supplementation had a positive impact on the TPC of thermally treated juices and increased the AOC of treated watermelon juice, which was the lowest of the three fruit juices. Mild heat treatment in combination with natural antimicrobials like carvacrol is therefore an alternative to limit the negative effects of conventional pasteurization on fruit juices quality.