Novel thermal and non-thermal processing of watermelon juice

Trends in Food Science & Technology 93 (2019) 234–243

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Novel thermal and non-thermal processing of watermelon juice ∗

T

Chiranjit Bhattacharjee , V.K. Saxena, Suman Dutta Department of Chemical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, 826004, India

A R T I C LE I N FO

A B S T R A C T

Keywords: Watermelon juice Non-thermal processing Microorganisms PEF Lycopene

Background: Watermelon juice has gained a lot of consumer interest in recent years due to its richness in phytochemical lycopene and its high antioxidant activity. The water activity of this juice is very high and it has a low acid content. Therefore the microbial activity in watermelon juice is comparatively high than most juices. Due to high percentage of spoilage microorganisms, it is quite difficult to store it for longer times without processing. Heat treatment has been used a pasteurization technique but it has a negative effect on its nutritional and sensory properties as bioactives are sensitive to high temperature processing. So the need arises for nonthermal processes to treat watermelon juice. Scope and approach: In recent years non-thermal or novel thermal processes have been successfully tested in research laboratories for processing of watermelon juice. These processes include pulsed electric field (PEF), ultraviolet irradiation (UV), sonication, ohmic heating (OH), high pressure processing (HHP), high pressure carbon dioxide (HPCD), nano fluid thermal processing (NFT) and membrane technology. The effects of these processes on micorobial activity and physicochemical properties of watermelon juice have been reported in this study. Key findings and conclusions: Non-thermal processes have been quite successfully analyzed for processing watermelon juice. They showed positive results in reducing the microbial spoilage of the juice and at the same time have retained a high portion of nutritional compounds. Among the non-thermal processes, PEF is the most widely used for watermelon juice processing and also showed most acceptable results.

1. Introduction The degradation of fruit juices is mainly caused by chemical, microbial and enzymatic reactions. Polyphenol oxidase (PPO) and pectin methylesterase (PME) are the primary enzymes responsible for juice deterioration. They react with dissolved oxygen and thereby causing browning of the juice and off color. Maillard reaction is another factor which generates non-enzymatic browning in juices. In this reaction, intermediate is formed by the coming together of carbonyl group of reducing sugars and amino group of amino acid. Further the intermediate reacts to form brown colored pigments producing unpleasant changes in juice color (Bharate & Bharate, 2014). This microbial growth also leads to unwanted flavor and odor, high turbidity and gas production. Therefore it becomes inevitable to control the growth of these spoilage microorganisms so as to minimize the juice spoilage (Odumeru, 2012). In earlier days foodborne disease outbreaks were never associated with fruit juices primarily beacause of their low pH values (pH ≤ 4). Due to limited progress in scientific research at that time, the growth and survival of pathogens under such acidic pH was thought to be ∗

almost impossible. But since 1980s, with the increase of research in food science, acidic fruit juices were found to be responsible for many foodborne disease outbreaks. In recent times, with the progress in food science and increasing health consciousness of the consumers, search for exotic and seasonal fruits such as watermelon and berries have brought a challenging role for food technologists. Although these exotic fruits provide a high amount of nutritional bioactive compounds to the consumers, but they also are most susceptible to the growth and survival of food borne pathogens. Since these fruits have a very high amount of antioxidants which are vulnerable to high temperature, researchers have to maintain a fine balance between stability of these bioactives and inactivation of unwanted pathogens. Watermelon is a highly nutritious and perishable juice. It has become popular recently among the consumer due to its unique refreshing flavor and various health benefits (Edwards et al., 2003; Giovannucci, 2002). As it has a pH close to neutral value and a high amount of water activity makes it an ideal medium for the growth of microorganisms. These microorganisms make it hard to store the juice for a longer period. Therefore it is very hard to find commercial watermelon juice products in the market. It is often mixed with other high acidic juices to

Corresponding author. E-mail address: [email protected] (C. Bhattacharjee).

https://doi.org/10.1016/j.tifs.2019.09.015 Received 3 April 2019; Received in revised form 14 August 2019; Accepted 14 September 2019 Available online 16 September 2019 0924-2244/ © 2019 Elsevier Ltd. All rights reserved.

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3. Non-thermal technologies

produce beverages. For longer storage, watermelon juice has to be processed to minimize the water activity and to inactivate the spoilage microorganisms and enzymes. The growing interest in fresh fruit juices have made researchers innovate and develop non-thermal fruit juice processing methods which can preserve the nutritional compounds for longer times. Until recently fruit juices were processed by thermal pasteurization techniques to increase shelf life. However research has shown that thermal treatment of fruit juices degrades their color, flavor and nutrients because of protein denaturation and also effects the vitamins and volatile sensory components. Non-thermal processes have been successful in extending the shelf life of fruit juices while simultaneously preserving organoleptic and nutritional compounds. These non-thermal methods are also energy efficient and are able to retain higher nutritional quality than conventional thermal techniques. Non-thermal techniques are termed so because of their ability to achieve microbial inactivation without the use of heat. They eliminated the adverse effect of heat on the bioactive compounds of fruit juices. Non-thermal and novel thermal processes provide a suitable alternative to thermal processing as they help in maintaining original juice like features in processed juices. The non-thermal and novel thermal processes which are mainly used for watermelon juice processing are as follows. (1) (2) (3) (4) (5) (6) (7) (8)

3.1. Pulsed electric field processing Pulsed electric field (PEF) is one of the promising non-thermal technologies for fruit juice processing. It constitutes a suitable substitute for thermal methods for inactivating enzymes and pathogenic microorganisms simultaneously retaining sensorial and nutritional components of fruit juices (Cortés, Esteve, & Frígola, 2008; Cserhalmi, Sass-Kiss, Tóth-Markus, & Lechner, 2006; Esteve, Barba, Palop, & Frígola, 2009). The process generates some amount of heat during its application but its maximum temperature (40 °C) is way below thermal processing temperatures. Fruit juices are placed between two electrodes and are applied pulses with a high voltage (usually 50 kV/cm) for short periods of time (μs to ms) (Puértolas & Barba, 2016; Señorans, Ibáñez, & Cifuentes, 2003). Its principle is a combination of electroporation and electropermeabilization (Teissie, Golzio, & Rols, 2005; Wouters, Alvarez, & Raso, 2001). Exposure of an electric field to the membrane of a microorganism leads to instabilities altering the cell wall and formation of pores in the cell membrane takes place (electroporation). Due to this electroporation, cellular structure destabilizes and consequently increase in permeability occurs (electropermeabilization). This enhanced permeability leads to destruction of the cells which is irreversible or it can reseal the cell to its initial viable state which is reversible (Barbosa-Canovas, Pothakamury, Palou, & Swanson, 1998, pp. 9–48). The former is complete inactivation while the later is partial inactivation. In general, strong electric fields (10–50 kV/cm) are applied to cause irreversible cell death. The effectiveness of PEF depends on important processing factors such as field strength, pulse width, pulse frequency, treatment time, polarity, temperature applied etc. (Barba et al., 2015). Fruit juice matrix is an important factor in deciding the efficiency of PEF process. Researchers found lesser effectiveness of PEF processing of juices containing high amount of macronutrients such as fats and proteins compared to simple microbial suspensions (Bendicho, Espachs, Arantegui, & MARTÍN, 2002; Ramaswamy & Chen, 2002). Electric conductivity of the medium is also an important parameter as juices with high conductivity will lead to small electric fields that are not suitable for PEF processing (Barbosa-Canovas, Pothakamury, Gongora-Nieto, & Swanson, 1999). The presence of natural antimicrobials can increase the effectiveness of PEF processing of fruit juices (Barbosa Ćanovas and Sepúlveda, 2004). Charateristics of fruit juice such as pH, water activity, and soluble solids are some of the major factors that can effect the PEF technology in terms of microorganism inactivation (Aronsson & Rönner, 2001). The main components of a PEF system are a high voltage power supply, a treatment chamber, a pulse generator, an energy discharging switch to electrodes and a cooling system to balance temperature rise during treatment.

Pulsed electric field (PEF) Ultraviolet irradiation (UV) Ultrasound processing Ohmic heating (OH) High hydrostatic pressure (HHP) High pressure CO2 processing (HPCD) Membrane processing Nano fluid thermal processing (NFT)

2. Microorganisms in watermelon juice Eradication of foodborne pathogens that have the capability to contaminate watermelon tissues and watermelon juice is absolutely necessary to minimize the risk of infections that can come with their consumption. As watermelons grow in the ground, there is always a high level of contamination of pathogens such as Salmonella spp., E. coli O157:H7 and Listeria monocytogenes during processing. There is a need to develop non-thermal pasteurization techniques to eliminate these pathogenic bacteria found in watermelon juice as they are proven to be associated with outbreaks of foodborne infections (Blostein, 1993; Gayler et al., 1995). United States FDA has reported 16% foodborne disease outbreaks associated with melon in the years between 1996 and 2008 with Salmonella spp. responsible for half of it (USDA, 2009). L.monocytogenes is one of the main foodborne pathogen along with Salmonella and E. coli in watermelon juice. Research has shown that L.monocytogenes can grow in watermelon juice at temperatures of 10 and 20 °C (Penteado & Leitao, 2004). Watermelon juice, due to its low acid content offers a suitable environment for pathogens like coliforms to grow. Some of the pathogens found in watermelon juice are Staphylococcus aureus, Bacillus cereus, Klebsiella sp., Escherichia coli, Salmonella sp., Shigella sp., Penicillium sp., Fusarium sp. etc (10.5923/j.microbiology.20170704.03). These microorganisms increase the microbial load in the watermelon juice and make it difficult to increase the shelf life of the juice and store it for longer periods. Researchers have therefore tried to minimize the microbiological activity and retaining the bioactive compounds at the same time using non-thermal processing methods.

3.2. Ultraviolet irradiation Ultraviolet (UV) light processing is one of the most promising nonthermal methods developed in recent times. It is easy to use and is fatal to most of the foodborne pathogens. It is also cost effective compared to most of the other non-thermal processes as it is a dry cold process (Gayán, Serrano, Raso, Álvarez, & Condón, 2012). The range of UV light used for food processing ranges from 100 to 400 nm and are classified as UV- A (320–400 nm), UV-B (280–320) and UV-C (200–280). UV- C radiation is found to be most lethal and is mostly used in fruit juice processing. (Gayán et al., 2012). Because of the germicidal properties of this wavelength region, The United States Food and Drug Administration (USFDA) have approved UV-C irradiation for fruit juice pasteurization purposes (Tremarin, Brandão, & Silva, 2017). Research has shown that UV-C light is able to inactivate bacterial and viral microorganisms in fruit juices. It is a physical treatment and doesn't result in chemical residues. The radiation in UV processing is obtained from an electromagnetic spectrum's UV region. To achieve microbial 235

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inactivation, the juice must be fully exposed to 400 J/m2. The important parameters affecting the efficiency of this process are transmissivity of the product, the power, reactor configuration, wavelength and physical arrangement of the UV source and the radiation path length (Koutchma, 2009). Strain, stage of culture, density of microorganisms, growth media and characteristics such as type and composition of juice also plays a role in assessing the effectiveness of UV irradiation on microorganisms of same species. The germicidal effect of the UV-C light can be explained by the fact that microbial DNA has the tendency to absorb UV-C light photons which leads to generation of crosslinks between cytosine and thiamine molecules in the same DNA strand. This cross linking of DNA is proportional to the amount of UV light exposure (Guerrero-Beltran & Barbosa-Canovas, 2004). UV irradiation causes dimerization of the pyrimidine molecules found in RNA and DNA which results in distortion of the DNA helical structure. Hence replication of nucleic acid becomes difficult which eventually leads to the death of the microorganisms. Studies have shown the UV-C treatment has the capability to reduce microbial load in different fruit juices such as apple (Walkling-Ribeiro et al., 2008), starfruit (Bhat, Ameran, Voon, Karim, & Tze, 2011) and orange juice (Pala & Toklucu, 2013; Tran & Farid, 2004). Researchers have also achieved higher retention of bioactives such as polyphenols and flavonoids in juices after UV-C treatment (Bhat et al., 2011; Pala & Toklucu, 2013).

non toxic gas with anti microbial properties and is permissible in food and beverages. HPCD has recently attracted high interest as an alternative to thermal heating based methods in the fruit juice processing industry (Ross, Griffiths, Mittal, & Deeth, 2003). Scientists have found satisfactory results with HPCD treatment as it was able to inactivate pathogenic microorganisms and enzymes and at the same time retained a high amount of bioactive compounds, color and sensory qualities of fruit juices (Damar & Balaban, 2006; Huang et al., 2009; Liao, Hu, Liao, Chen, & Wu, 2007; Liu et al., 2010). The CO2 pressures applied in this method for preservation of fruit juices are much lower (< 40 MPa) compared to other high pressure processing methods. The temperature for this process ranges from 20 °C to 60 °C so as to avoid thermal degradation of bioactive compounds. The exposure to carbon dioxide increases the lag phase and generation time of microorganisms. The process initiates with pasteurization with CO2 for a particular amount of time for the gas to penetrate into the microbial cells. Subsequently explosive decompression occurs which results in rapid gas expansion within the cells. This leads to rupture of microbial cells of microorganisms. The whole process can be divided into a series of steps as listed below: 1. 2. 3. 4. 5. 6. 7.

3.3. Ultrasound treatment Ultrasonic treatment is a widely used non-thermal method for processing of fruit juices. It is an alternative to conventional thermal pasteurization and sterilization. Exposure of ultrasonic treatment to juice microorganisms results in breaking of their cell membrane and production of free radicals. The extrusion of intracellular matrix leads to the death of microorganisms (Piyasena, Mohareb, & McKellar, 2003). The nonthermal nature of this process relies on the treatment intensity and profile. Pressure and gas bubbles are formed in the liquid medium due to the sound wave. Acoustic cavitation is generated in the cell wall of the microorganisms due to the change in pressure and associated compression and depression of the medium particles. This cavitation process has a bactericidal effect. The cavitation bubbles induce microstreaming and shear stress with a local increase of temperature and pressure. This results in disintegration of microbial cells. This increase in local energy and pressure provides localized pasteurization without causing a rise in macro-temperature (Jiménez-Sánchez, LozanoSánchez, Segura-Carretero, & Fernández-Gutiérrez, 2017). Cavitation also causes intracellular micromechanical shocks which disrupt cell components and thus help in enzyme deactivation (Abid et al., 2013; O’donnell, Tiwari, Bourke, & Cullen, 2010). Deactivation of enzyme is also caused by free radicals generated during sonolysis of water molecules (H2O → OH− + H+) (Mason, Paniwnyk, & Lorimer, 1996). The ultrasonic processing of fruit juices can be divided into zones based on frequency ranges. The one with frequencies higher than 100 kHz and intensities below 1 W/cm2 is called low energy (low-power, low intensity) and the one that uses frequencies between 20 and 500 kHz and has an intensity higher than 1 W/cm2 is termed as high energy ultrasound (Shaheer et al., 2014). Studies have shown that sonication has the potential to achieve a 5 log reduction in foodborne pathogens in fruit juices. Researchers have found positive results in reducing microbial load using ultrasonication in various fruit juices such as orange (500 kHz, 240W for 15 min), apple (25 kHz for 60 and 90 min), and carrot juice (20 kHz, 750W for 2 min) (Abid et al., 2013; Jabbar et al., 2014; Valero et al., 2007).

Pressurized CO2 solubilization in the external liquid phase Modification of cell membrane Decrease of intracellular pH Inactivation of key enzyme Inhibitory effect of molecular CO2 and HCO3− on metabolism Disordering of the intracellular electrolyte balance Vital constituent's removal from cell and cell membranes.

3.5. High hydrostatic pressure High hydrostatic pressure is a non-thermal cold pasteurization technique for fruit juice processing. It is based primarily on two principles: the Le Chatelier principle and the isostatic principle. According to Le Chateliers principle, pressure favors changes and structural reactions that involve a decrease in volume while isostatic principle states that pressure transmission is uniform and proportional in all parts of fluid foods (Heremans, 2002; Toepfl, Mathys, Heinz, & Knorr, 2006; Valdez-Fragoso, Mújica-Paz, Welti-Chanes, & Torres, 2011). Pressure treatment, unlike heat treatment doesn't depend on size and geometry of the product and as a result processing time is minimized (Rastogi, Raghavarao, Balasubramaniam, Niranjan, & Knorr, 2007). The applied pressure for juice processing ranges from 300 to 700 MPa. Operating time can be from milliseconds to 20 min. In this process, pasteurization takes place through direct or indirect compression. An increase in temperature of 3°C occurs for 100 MPa of applied pressure (Morris, Brody, & Wicker, 2007). The inactivation mechanism is based on the breaking of non covalent bonds and damaging of cell membrane. HHP also causes protein denaturation which interrupts cellular functions and eventually leads to cell death (Lopez –Gomez et al., 2009). As it has a miniscule effect on covalent bonds, nutritional and sensory qualities of juice are retained (Ferrari, Maresca, & Ciccarone, 2010). Low temperature of the process also helps in achieving higher percentage of bioactive compounds in the product juice (Chen et al., 2015). Different microorganisms response differently to HHP eg. yeasts and mould are most sensitive, gram negative bacteria has medium sensitivity while gram positive bacterias are the most resistant (Bello, Martínez, Ceberio, Rodrigo, & López, 2014). Researchers have found positive results in HHP processing of different fruit juices such as apple (Juarez-Enriquez, Salmeron-Ochoa, Gutierrez-Mendez, Ramaswamy, & Ortega-Rivas, 2015), orange (Wang et al., 2012), pomegranate (Chen et al., 2013), strawberry (Cao et al., 2012), mango (Hiremath & Ramaswamy, 2012) etc. They were able to achieve high level of microbial activity reduction and preservation of bioactive compounds.

3.4. High pressure carbon dioxide High pressure carbon dioxide (HPCD) treatment is a novel nonthermal technique applied recently for fruit juice processing. CO2 is a 236

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rate of heating also depends on the resistance of the fruit juice. The heating time can be minimized according to the feed juice characteristics by applying a higher voltage gradient. The changes in electrical conductivity in the fruit juice are an important parameter in increasing the efficiency of the heating process (Leizerson & Shimoni, 2005). This process is not applicable to foods having electrical conductivity below 0.01 S/m and above 10 S/m (Piette et al., 2004). However electrical conductivity of fruit juices is high enough to get an efficient heating during ohmic treatment.

3.6. Membrane technology Membrane technology is the most widely used non-thermal processing technique for fruit juice processing. Membrane processing is very effective in reducing heat associated loss of nutritional and functional quality in fruit juices as it is a low temperature operation. Membrane concentration of fruit juices present higher resistance to microbial and chemical deterioration by reducing water activity. It is mainly used for clarification and concentration of fruit juices. Pressure driven membrane processes such as microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO) and nanofiltration (NF) have been widely used for concentrating bioactive compounds in different fruit juices. MF and UF are the most commonly used filtration methods in bioprocessing industry. They are able to separate particles in the approximate size ranges of 0.1–10 μm and 1–100 μm respectively. Microfiltration is mainly used for clarification purposes while ultrafiltration is used for both clarification and concentration. Temperature driven membrane processes such as membrane distillation, osmotic distillation, pervaporation etc are some recent developments in application of membrane methods for juice processing. The separation mechanism for MF/UF/NF is primarily size exclusion based on the pore sizes of the solute particles and membrane material. There can be another mechanism which is based on electrostatic interactions between solutes and membrane material that depends upon solute and membrane material properties. The type of membrane modules used in fruit juice processing is tubular, spiral wound, hollow fiber and flat sheet modules. Polymeric membranes used for juice processing are polyamide, polysulfone, polyethersulfone, polypropylene and poly-vinylidene fluoride (Bhattacharjee, Saxena, & Dutta, 2017a). Some of the advantages membrane technology has over conventional thermal processing are.

4.2. Nanofluid thermal processing In recent times, nanofluid heating has been investigated for fruit juice processing by some researchers. Their specific thermal properties have made them promising in terms of novel thermal pasteurization of liquid foods compared to conventional thermal fluids (steam and hot water). This technique provides the advantage of shortened process time so as to maintain a high percentage of nutritional and sensory components in the final product juice. This method is based on the principal that nanofluids have a much higher thermal conductivity compared to other heating fluids. Metals and oxidized metals have a higher thermal conductivity than conventional fluids. Copper and alumina have a thermal conductivity that is 700 and 60 times higher than water respectively. Therefore when the particles of these oxidized metals are mixed with heating fluids, they are able to impart better heat transfer properties. Nanofluids are stable two phase compounds that are composed of nano particles (dimension less than 100 nm) and base fluids. They can be highly suitable in food processing industries due to their better stability and minimal pressure drop compared to various suspensions (Farajollahi, Etemad, & Hojjat, 2010). Agglomeration, clogging and friction probabilities are minimized by low volume fraction and small size of nano-particles which lead to cost savings in maintenance and fluid transfer. The lower the particle size, the higher the heat transfer and thermal productivity of suspended particles (Eastman, Choi, Li, Yu, & Thompson, 2001). Researchers have found more than 20% increase in thermal conductivity by mixing nanoparticles and base fluids even at low volume fractions (1–5%) (Choi & Eastman, 1995; Xuan & Li, 2000). Sizes, concentration, thermal conductivity, type of base fluid are some of the important parameters that influence the heat transfer augmentation in nano fluid processing of fruit juices.

• Low Temperature Operation • Increase in aroma retention • Clean Process, a substitute for the use of polluting materials (diatomaceous earth, bentonite etc.) • Low amount of waste generated. • Well adapted to treatment of effluents. • Increased juice yield. • Simple cleaning methods and maintenance of the equipment 4. Novel thermal technologies

5. Watermelon juice processing using novel thermal and nonthermal methods

4.1. Ohmic heating Ohmic heating is a novel thermal technique for fruit juice processing. It is also referred to as Joule heating, electrical resistance heating, direct electrical resistance heating, electro-heating, and electro-conductive heating. Internal heat generation is the main difference between ohmic heating and other conventional thermal methods where heat is either transmitted by conduction or convection. Also in ohmic process, the entire volume of food is heated while in microwave heating, heating is achieved only in a certain depth of the product. Its ability to heat foods rapidly and uniformly is its principal advantage (Icier, Yildiz, & Baysal, 2006). In this process the electric current is directly applied to the food instead of external heat. This direct passing of electric current through the food material causes rapid heat dissemination and therefore faster heating of food. The temperature increase throughout the food is uniform as the heating takes place volumetrically. The uniform heating of the juice particles reduces thermal damage and nutritional losses. Therefore it is possible to obtain a juice with acceptable textural properties, minimum aroma loss and high sensory quality (Tempest, 1992). The electrical energy applied in ohmic heating converts instantly to heat inside the fruit juice. In general intensities of applied electrical field do not exceed 1 kV/cm (Sastry, 2008). The heating amount is related to voltage gradient in the field and the electrical conductivity. The

Microorganisms such as Salmonella enteritidis, E coli and Listeria monocytogenes are potential health hazards in watermelon juice due to their low acid content. Watermelon juice is also categorized as a potentially hazardous food by the FDA of USA. Therefore it is essential to deactivate or destroy these pathogens for the juice safety. These microorganisms can be significantly destroyed when they are subjected to pulsed electric field processing. PEF processing (35 kV/cm at 40 °C) was used to reduce the microbial load of watermelon juice to enhance its safety (Mosqueda-Melgar, Raybaudi-Massilia, & Martín-Belloso, 2007). They achieved reductions of 3.56, 3.6 and 3.41 log10 units of Salmonella enteritidis, E coli and Listeria monocytogenes microorganisms in watermelon juice treated for 1727 μs at 188 Hz. They concluded that number of passes and processing time are important parameters in PEF deactivation of these microorganisms. Mosqueda-Melgar, RaybaudiMassilia, and Martin-Belloso (2008) also studied PEF processing of watermelon juice combined with natural antimicrobials (citric acid and cinnamon bark oil). Citric acid has antimicrobial properties linked with chelating metal ions which ensure pH reduction in the medium (Nazer, Kobilinsky, Tholozan, & Dubois-Brissonnet, 2005) Cinnamon bark oil contains some antimicrobial compounds such as maldehyde and eugenol which helps in food preservation (Burt, 2004; Oussalah, Caillet, 237

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findings. The thermosonication operational parameters were 20 kHz, 24.1–60 μm amplitude level at a temperature of 25–45 °C for 2–10 min. They found that the sonicated juice had a higher percentage of bioactives such as vitamin C and lycopene than the thermally treated juice at the same temperature, although sonication at a higher temperature of 45 °C catalyzed the degradation process of lycopene and ascorbic acid. Phenolic content reduction was also observed as the temperature rose from 25 to 45 °C. The authors attributed this degradation to oxidation of these compounds by OH radicals generated by sonochemical reactions. High amplitude levels were reported to be not suitable with regards to lycopene retention. Increase in processing times and amplitude level (10 min and 60 μm) had brought the largest increase in lightness (L*) value. Saikia et al. (2016) used sonication to study bioactive compound retention in watermelon juice and found satisfactory retention of bioactive compounds. Hundred millilitres of fresh watermelon juice was sonicated for half an hour at 50 °C in a ultrasonic cleaning bath. The operating parameters were 30 ± 3 Hz frequency and 100 W power. The TPC showed a significant increment from 7 mg GAE/100 ml for fresh juice to 17.5 mg GAE/100 ml for sonicated juice. Total flavonoid content also increased from 5.5 to 6.58 mg QE/100 ml after sonication. Makroo, Saxena, Rastogi, and Srivastava (2017) used ohmic heating to inactivate PPO in watermelon juice for minimizing enzymatic browning. Their result showed significant reduction in PPO activity in watermelon juice at 90 °C for 15–60 s with maximum reduction occurring in the first 30 s. The inactivation rate slowed down during the latter half of the 1 min OH treatment. Comparing with conventional heating, the authors came to the conclusion that OH provided higher rates of inactivation in much shorter processing time. The reduction in total phenolic content (TPC) was found to be 39.7% after OH treatment at 90 °C for 1 min which was 3% lower than conventional heating. The signification change in pH was attributed to electrochemical effects of OH treatment. Color stability (ΔE) was found to be more in OH treatment than thermal heating at the same temperature. The reduction in lycopene was also less in ohmic heating especially in the initial part than hot water heating. The changes in lycopene were 2.35–3.94% and 1.67–4.27% in hot water heating and OH treatment (0–60 s) respectively. Ishita and Athmaselvi, (2017) analyzed changes in pH and color of watermelon juice after ohmic heating treatment. The pH of the processed juice increased after OH treatment for 1 and 3 min while after 5 min treatment it decreased slightly from the feed juice value of 5.2. Increase in voltage gradient during storage reduced the juice pH. The increase in OH voltage gradient from 10 to 20 V/cm for 1 min treatment reduced the increase of pH from 3.8 to 1.92%. The authors linked juice hydrolysis during OH treatment to this variation in pH. The corrosion of OH electrodes due to voltage fluctuations and continuous heating can also be a factor in pH variations. The authors also found effect of voltage gradient in color stability of the juice. The L value of the processed juice decreased with an increase in voltage gradient and processing time. Liu et al. (2013b) used high hydrostatic pressure for processing watermelon juice and achieved positive results. They observed maximum inactivation values of 88 and 42% for PPO and POD respectively at 600 MPa and 25 °C for an hour of HHP treatment. They linked this reduction in enzymatic activity to the pressure induced structural changes in protein. Primary structure of the proteins remained intact as covalent bonds were unaltered by high pressures at 25 °C, but the high pressures broke the hydrogen bonds which led to change of secondary structure of the enzymatic protein. They reported no significant changes in titratable acidity, pH, TSS, lycopene and phenolic contents of HHP processed juice at 200, 400 and 600 MPa for 5, 15, 30, 45 and 60 min. The browning degree of the juice was found to decrease with the increase in pressure and treatment time. The color change (ΔE) value of juice was found to be lower than 2 in most of the HHP processing conditions. The authors attribute this color stability to the absence of pigment degradation or browning reaction due to the low

Saucier, & Lacroix, 2007). Their main target was to inactivate potential health hazard microorganisms such as Salmonella enteritidis, E coli and Listeria monocytogenes. They were successful in reducing microbial populations of watermelon juice (35 kV/cm for 1682 μs at 193 Hz and 4 μs pulse duration) containing 1.5% of citric acid by more than 5.0 log10 CFU/ml. They inactivation process revealed that Listeria monocytogenes was more resistant than Salmonella enteritidis and E coli. This mixing of antimicrobials with PEF produced a synergistic effect leading to high level of pathogen inactivation. Similar results were reported for apple juice by Raybaudi-Massilia, Mosqueda-Melgar, and MartinBelloso (2006) by using malic acid as an antimicrobial. Aguiló-Aguaiyo et al., (2010a,b) analyzed PEF processing for reducing the pectolytic activity of watermelon juice. They carried out PEF treatments at 250 Hz and pulse width from 5.5 to 7 μs and found that the processed watermelon juice has the lowest residual PME values in bipolar (15%) and monopolar (21%) modes. Similar results were found by Elez-Martinez et al., (2003) for orange juice where bipolar pulses led to higher PME inactivation. These reductions achieved by PEF processing can ensure minimal loss in viscosity and higher cloud stability of watermelon juice. Oms-Oliu, Odriozola-Serrano, Soliva-Fortuny, and Martín-Belloso (2009) studied the effect of PEF on the bioactive compounds of watermelon juice. Their results suggested that bipolar treatment was more effective than mono-polar treatment with regards to retention of antioxidant capacity in watermelon juice. Retentions of antioxidant capacity increased as frequency and pulse width were increased from 50 to 200 Hz and from 1 to 7 μs respectively. Maximum lycopene content was attained with 7 μs bipolar pulses for 1050 μs at 35 kV/cm and 200–250 Hz frequencies. They also found an increase in lycopene retention with an increase in pulse width and same decreases at low electric field strength. Monopolar mode had a more positive effect on vitamin C retention compared to bipolar mode treatment. The authors attributed this to the inactivation of enzymes responsible for oxidation of vitamin C. Aguiló-Aguaiyo et al. (2009) investigated the effect of PEF processing on the non-enzymatic browning of watermelon juice. The compound 5-hydroxymethyl furfural (HMF) is responsible for undesirable brown color development in watermelon juice (Bozkurt, Gögüs, & Eren, 1999). The authors found that PEF had a significant effect on color changes (ΔE) of the watermelon juice. The treatment also affected the HMF concentration as was evident with the high level of color preservation of the processed juice. Mono polar mode was found to be more successful than bipolar mode with regards to color preservation and HMF minimization. The authors also concluded that PEF was more effective in retaining the original color of the juice than conventional thermal techniques. Feng, Ghafoor, Seo, Yang, and Park (2013) treated watermelon juice with UV-C irradiation and reported 2.6-log, 1.47-log and 0.99-log reductions in coliforms, yeast and molds and minimal changes in physicochemical properties and bioactive compounds. They were able to maintain a low microbial activity for the storage period of one month. The load was lower than 6.0 log CFU/ml. Increase in UV-C doses had a negative effect on the juice color. They observed a significant increase of pH and total soluble solids content after 25 days of storage. The authors were able to extend the shelf life of watermelon juice up to 31 d, by means of a UV treatment using helix Teflon -coil UV-C reactor. Zhang et al. (2011) studied the effectiveness of UV-C treatment in enzyme inactivation in watermelon juice. The compared UV-C and thermal methods for PME deactivation and reported that the former needed much lesser time to attain a same PME residual level. UV-C treatment (4.8 kJ/L) has taken 5 min to reduce the PME content by 25% while heat treatment at 60 °C took 20 min for the same. They concluded that the same inactivation time can be further reduced by increasing the energy density of the lamp and flow rate of the treatment. Although they noticed that a higher exposure to the treatment increased the browning degree which can lead to increased color changes (ΔE). Rawson et al. (2011) analyzed the effect of thermosonication on the bioactive compounds of watermelon juice and reported significant 238

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energy savings for 2 and 4% nanofluid heating were 25 and 49%. So, 4% nanofluid heating reduced the energy consumption by almost half when compared to water heating. Lycopene is one of the most valuable antioxidants found in watermelon juice. The molar mass of lycopene is 536.85 Da. Pressure driven membrane processes have been used to concentrate and purify lycopene in watermelon juice in recent times. Rai, Rai, Majumdar, De, and Dasgupta (2010) achieved threefold increase in lycopene concentration in retentate by performing microfiltration of watermelon juice. Similar results were also obtained by Gomes et al. (2013) when they subjected watermelon juice to MF. They reported an increase of 402.8% and 416.3% in lycopene concentration and antioxidant capacity of the final juice. Researchers find negligible change in the amount of total soluble solids (TSS) after MF of watermelon juice (Chhaya et al., 2008; Rai et al., 2010). Bhattacharjee, Saxena, and Dutta (2017b) used ultrafiltration to analyze its effect on sugar and ascorbic acid in watermelon juice concentrate. They observed that the TSS content increased with the volumetric concentration factor (VCF) but the ascorbic acid content decreased with the increase in VCF. They attributed this behavior to oxidation of ascorbic acid due to the continuous recycle of the juice thorough the flat plate membrane module. Nanofiltration has also been used by researchers to concentrate lycopene from watermelon juice (Arriola et al., 2014). They observed an increase of the antioxidant capacity with an increase of volumetric reduction factor. They also found good correlation between the contents of lycopene, ascorbic acid and vitamin C and antioxidant capacity in the final juice. Oliveira et al. (2016) combined MF and RO with diafiltration and were able to obtain a product juice with 17 time's higher lycopene content than the fresh juice. The diafiltration step helped in increasing the antioxidant capacity of the final product. Bhattacharjee, Saxena, and Dutta (2018) used 50 kDa polyethersulfone UF membrane for clarification of watermelon juice. They were able to obtain a clarified juice free of suspended solids with minimal losses w.r.t. TSS and ascorbic acid. Chaparro et al. (2016) combined enzymatic maceration, MF, diafiltration and centrifugation for purifying and concentrating lycopene from watermelon juice. They obtained an extract that had 41 times more lycopene concentration than the feed juice. Temperature driven membrane processes have also been investigated for processing watermelon juice (Vaillant et al., 2005). The authors observed 30% loss of phenolic compounds in the processed juice. Table 1 shows the results of recent studies of nonthermal processing of watermelon juice.

temperature of the HHP process. Therefore the authors concluded that HHP processing was successful in maintaining the original color of juice. PME inactivation in watermelon juice by using HHP was studied by Liu et al. (2013b) and Zhang et al. (2011). Their inactivation values were 77% and 65% at 600MPa/60 min/25 °C and 900 MPa/40 or 60 min/60 °C respectively. Liu et al. (2013b) observed first order inactivation model to be more suitable for PME in watermelon juice. Zhang et al. (2011) also compared HHP processing with thermal and UV irradiation and found that HHP was more successful as it produced lowest changes to color, viscosity, browning degree and lycopene content. The main feature of HHP processing is the fact that only non covalent bonds are affected which means organoleptic properties of juice remain unaltered. When compared to thermal treatments, HPP affects only noncovalent bonds (hydrogen, ionic, and hydrophobic bonds) and has little effect on chemical constituents associated with desirable food qualities such as taste, flavor, color, or nutritional content and, therefore, the processed products stay quite close to a ‘freshlike’ product (Hayashi, 1990; Balci and Wilbey, 1999). Liu et al. (2013b) used HPCD treatment to process watermelon juice and analyzed its ability to inactivate PPO enzyme. They observed drastic decline of PPO residual activity to 4.2% after half an hour treatment at operating parameters of 50 °C and 30 MPa. They conducted kinetic analysis and concluded that the juice is comprised of labile and stable fraction. They found that the labile fraction was vulnerable to temperature but more resistant to pressure and labile fraction PPO inactivated more easily than the stable one. The authors attributed this inactivation to the lowering of pH which triggers structural changes in the enzyme protein. Therefore they suggested that the combination of factors such as pressure, treatment time, temperature, pH reduction and antimicrobial properties of CO2 were responsible for PPO reduction. Liu, Hu, Zhao, and Song (2012) investigated combination of high pressure CO2 and mild heating for processing watermelon juice. They found significant reduction in residual activities of PME and PPO enzymes with treatment during the first 5 min. PPO activity declined rapidly at the beginning which slowed down with time while PME activity was found to be decreasing linearly for an hour during the treatment. The lowest PME residual activity was reported to be 14.5% at 30 MPa and 50 °C for 60 min. They linked this reported activity to the inability to inactivate the liable isoenzyme proportion of PME which could be large. They also found that the combined treatment was able to minimize the browning degree of the watermelon juice more efficiently than thermal treatment which was related to the ability of the former to inactivate PPO and PME activity. The authors observed a slight decrease of lycopene in the processed juice after the HPCD treatment. The decrease in enzyme activity due to HPCD can be attributed to the changes in structure of protein, stability of enzymes and/ or enzyme-substrate interactions under processing conditions. Jafari, Saremnejad, and Dehnad (2017a) used alumina nano particles for nano fluid thermal processing of watermelon juice and were able to achieve 6 and 10% higher levels of vitamin C and lycopene concentration in the final juice by substituting 4% nanofluids for water in the heat exchanger compared to normal heating. They attributed this enhancement to the lower processing time due to the higher thermal conductivity of the nanufluid. Color change values (ΔE) of 2.21 and 1.14 after 2 and 4% nanofluid processing were minimal compared to 3.26 when processed by water heating. This showed the effectiveness of this process in maintaining color stability by minimizing the degree of browning. Minimal changes were reported by the authors in pH and TSS after nanofluid processing compared to thermal pasteurization and PEF processing of watermelon juice by other researchers. Jafari, Saremnejad, Dehnad, and Rashidi (2017b) also studied the energy efficiency of the nano fluid heating process of watermelon juice. Heat transfer enhancements of 8 and 13% were reported with nanoparticle concentrations of 2 and 4%. The authors found that for all Reynolds numbers, 4% nanofluid had the highest overall heat transfer coefficient. It also enhanced the efficiency of the heat exchangers by 58.65%. The

6. Critical observations The main parameters impacting the performance of PEF inactivation of microorganisms are electric field strength, pulse width and shape, treatment time, energy density input, pulse frequency, the microbial characteristics, electrical conductivity of the juice etc. Shorter pulse width and mono polar mode processing produced more color stability in the processed juice. Bioactive compounds such as lycopene content retention increased with higher values of electric field strength and frequency. In fact, because PEF treatment induces cell permeability and increases the release of bioactive components from cells to juice, there may be an opportunity to maximize both the yield and extraction of bioactive compounds. Higher food temperatures also lead to higher antimicrobial effect of the PEF process although it can have a negative effect on the physicochemical characteristics of the juice. Research has showed that the level of microbial inactivation increased with the increase in electric field strength. Combination of mild heat with PEF processing can augment the microbial and enzyme deactivation process at feasible temperatures while maintaining an acceptable level of nutritional components in the product juice. Some microorganisms such as L. monocytogenes offer high resistance to PEF processing as observed by researchers. The thicker peptidoglycan layer of the cell envelope in the gram positive bacteria is attributed to this higher resistance. PEF has also been successful in retaining higher percentage of anthocyanins 239

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Table 1 Recent studies in non-thermal processing of watermelon juice. Method

Operating conditions

Key findings

References

PEF

35 kV/cm/188 Hz/1727 μs/ < 35 °C

Aguilo-Aguayo at al. (2010b)

PEF

35 kV/cm/250 Hz/5.5–7 μs/ < 35 °C

No HMF formation, POD inactivation, increased lightness of juice, enhancement of viscosity High PME inactivation

PEF

35 kV/cm/50–250 Hz/1–7 μs/ < 40 °C

Mono polar mode more effective in maintaining color stability and minimizing HMF formation

PEF

35 kV/cm/50 to 200 Hz/1 to 7 μs

PEF

35 kV/cm/100–250 Hz/ < 30 °C

PEF

35 kV/cm for 1727 μs at 188 Hz and 4 μs pulse duration 11 kV/cm/20 μs/ < 72 °C

Bipolar mode favoured lycopene content while monopolar mode had a positive effect on ascorbic acid, increase in lycopene retention with an increase in pulse width Reductions of 3.56, 3.6 and 3.41 log10 units of Salmonella enteritidis, E coli and Listeria monocytogenes microorganisms More than 5.0 log10 CFU/ml inactivation of E coli and Listeria monocytogenes Complete inactivation of E. coli, L. innocua, Lb plantarum and S. cerevisiae 2.6-log, 1.47-log and 0.99-log reductions in coliforms, yeast and molds, minimal changes in quality parameters Reduction of PME residual activity by 25% in 5 min of treatment Lycopene retention decreased with high amplitude levels, reduction of phenolics was observed as temperature was increased from 25 to 45 °C TPC increased from 7 mg GAE/100 ml for fresh juice to 17.5 mg GAE/100 ml for sonicated juice, flavonoid content also increased from 5.5 to 6.58 mg QE/100 ml. 39.7% reduction in total phenolic content, high color stability, minimal changes in lycopene Voltage gradient had a significant effect on pH and color stability Inactivation values of 88 and 42% for PPO and POD, no significant changes in titratable acidity, pH, TSS, lycopene and phenolic contents PME inactivation value of 65%, minimal changes in color, viscosity and lycopene Prolonged exposure decreased protein absorption

PEF (combined with heat treatment) UV

UV-C/2.7 and 37.5 J/ml

UV

UV-C/4.8 kJ/L

Sonication

1500 W/24.4–60 μm/20 kHz/2–10 min/25-45 °C

Sonication

100 W/30 ± 3 Hz/50 °C/30 min

OH

90 °C/15–60 s

OH

95 °C/1,3 and 5 min/50 Hz

HHP

600 MPa and 25 °C for an hour

HHP

900 MPa/40 or 60 min/60 °C

HHP HPCD

20–600 MPa/20 min/400 MPa/20 to 60 min or 10–40 min/30 °C 30 MPa/2.5–30 min/30-50 °C

HPCD

10, 20 and 30 MPa/5, 15, 30, 45 and 60 min/50 °C

NFTP

2 and 4% nanofluid conc./75, 80 and 85 °C/15, 30 or 45 s

NFTP

2 and 4% nanofluid conc./75, 80 and 85 °C/15, 30 or 45 s

MF MF

CA membrane/0.2 μm/30 ± 2 °C/15.2 cm2/136.5, 204.7, and 276 kPa Ceramic/3 bar/6 m/s/30 °C/tubular

MF

CA membrane/0.2 μm/2 bar/30 °C/1 m/s

UF

5 kDa PES/3 bar/30 °C/flat plate module

UF

50 kDa PES/3 bar/30 °C/flat plate module

NF

PVDF membrane/150 and 300 Da/25 ± 2 °C/600 kPa/1 m/s MF- ceramic/0.2 μm/2bar/35 °C RO- PA membrane/ 35 °C/60 bar/P&F module Ceramic/tubular/50 and 60 °C/6 m/s/0.2, 0.5, 0.8, and 1.4 μm/0.5 and 2.0 bar PP membrane/10 m2/0.2 m/s/26 °C

MF/RO/DF Enzymatic treatment/MF/ DF/centrifugation OE

Maximum inactivation of PPO reduction was 95.8%, labile fraction PPO inactivated more easily PME residual activity was reported to be 14.5% at 30 MPa and 50 °C for 60 min, slight decrease in lycopene content 6 and 10% higher levels of vitamin C and lycopene concentration with 4% nanofluid, greater color stability, minimal changes in pH and TSS 2 and 4% nanoparticles could enhance heat transfer coefficients of base fluids by 8 and 13%, respectively, energy savings for 2 and 4% nanofluid heating were 25 and 49%. 3 times increase of lycopene in the product juice Increase of 402.8% and 416.3% in lycopene concentration and antioxidant capacity of the final juice Removal of suspended solid and turbidity, minimal change in TSS content Vitamin C and sugar content increased in the juice concentrate Satisfactory level of juice clarification with minimal changes in pH and TSS, lycopene content decreased in the clarified juice Increase of the antioxidant capacity with an increase of volumetric reduction factor Product juice had a lycopene content that is 17 times more than feed juice The extract had 41 times more lycopene concentration than the feed juice. 30% loss of phenolic compounds in the processed juice

240

Aguiló-Aguayo, SolivaFortuny, and Martín-Belloso (2010a) Aguiló-Aguayo, SolivaFortuny, and Martín-Belloso (2009) Oms-Oliu et al. (2009)

Mosqueda-Melgar et al. (2007) Mosqueda-Melgar et al. (2008) Aganovic et al. (2017) Feng et al. (2013) Zhang et al. (2011) Rawson et al. (2011)

Saikia et al. (2016)

Makroo et al. (2017) Ishita and Athmaselvi, (2017) Liu et al., 2013b

Zhang et al. (2011) Liu et al. (2014) Liu et al. (2013a) Liu et al. (2012)

Jafari et al. (2017a)

Jafari et al. (2017b)

Rai et al. (2010) Gomes et al. (2013) Chhaya et al. (2008) Bhattacharjee et al. (2017b) Bhattacharjee et al. (2018)

Arriola et al. (2014) Oliveira et al. (2016) Chaparro et al. (2016) Vaillant et al. (2005)

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process. Researchers were able to achieve a high rate of heating for shorter periods which helped in retaining a higher amount of nutritional and sensory components in the processed juice while saving energy at the same time. Membrane processes have the ability to concentrate the essential bioactive compounds in watermelon juice e.g. lycopene successfully.

in various juices. PEF processing has been the most widely used nonthermal processing technique for watermelon juice processing as compared to other methods as it proves to be highly effective in retaining bioactive compounds in the final product along with microbial inactivation. Processes such as sonication, OH etc. are less effective as there is less retention of nutritional components in the final juice. High pressure processes such as HHP are also quite successful in this aspect as there are minimal changes in content of bioactive compounds in the final product. Despite the large quantity of scientific data available in the literature about the benefits of PEF processing and various technology transfer projects, there is still very little industrial implementation of PEF for pasteurization of fruit juices. UV irradiation has the ability to reduce the bacterial population of coliforms, aerobes, yeast and mould in watermelon juice and extend its shelf life. UV irradiation is not detrimental to the nutritional component of fruit juices when it is used at doses needed to attain 5-log reductions of microorganisms. Research has shown that, compared to thermal processes, UV irradiation is better suited for retention of bioactive compounds in the juices. Vitamin C, phenolic content and antioxidant capacity are very minimally affected by UV processing. Lycopene content of watermelon juice also remain mostly unaffected by UV treatment although some researchers found oxidation and isomerization of lycopene with the increase in radiation intensity and exposure time. The efficiency of ultrasound processing of fruit juices depend upon the temperature, pH, intensity of ultrasound, processing time, food matrix etc. Although high amplitude and higher processing times can increase the level of enzyme inactivation, this will negatively affect bioactive compound of the fruit juices. Researchers found low retention of bioactives such as vitamin C, lycopene and polyphenols in watermelon juice when high intensity and longer processing times were applied. High processing temperature during sonication can also have a negative impact on nutritional aspects of the processed juice. The rate of PPO inactivation increases with an increase in voltage gradient of ohmic heating. But high voltage gradients can degrade bioactive compounds because of electrochemical reactions. Lycopene content was not significantly affected during ohmic heating of watermelon juice, but the phenolic content was decreased. Ohmic heating can maintain better color stability than conventional thermal techniques. HHP processing with more than 400 MPa and processing times of 5 or more minutes can achieve higher than 6 log reductions of most bacterial microorganisms while yeasts and molds are inactivated in mild processing conditions of less than 400 MPa. HHP processing had a little impact on bioactive compounds of watermelon juice while a high percentage PPO inactivation was achieved. Juice vitamin C content upon high-pressure treatment has been shown to be similar to that of fresh juice after 12 weeks of refrigerated storage. Depending on the operating parameters and the scale of operation, the cost of high pressure treatment (HHP) is typically around US$ 0.05–0.50/L or kg, the lower value being comparable to the cost of thermal processing. HHP has been scaled up to industrial level in recent times mostly in Europe to treat fruit juices. Currently, the main suppliers of HHP installations are Avure technologies (USA), Hiperbaric (Spain), HPBioTech (France), Multivac (Germany), ThyssenKrupp (Germany), and Steribar HPP (Hydrolock, France). HPCD treatment is capable of achieving more than 5-log reductions of most of the microorganisms. High percentage of PPO inactivation was observed for watermelon juice using HPCD although a decrease in lycopene content was reported. The most important advantage of HPCD is the possibility of microbial and tissue enzymes inactivation under much lower pressures compared to HHP technique. Still, the exact mechanism of enzyme inactivation still remains unclear; one of the main hypothesis describes the conformational changes of the enzymes. The possibility of inactivation of tissue enzymes by HPCD is significantly higher compared to traditional HPP technique probably due to decreasing of pH of treated sample. Industrial installations are still in development stage for HPCD processing although patented systems exist. Nano-fluid thermal processing (NFT) can increase the efficiency of conventional heating

7. Conclusion Consumers demand for fresh and nutritional fruit juices has resulted in the growth of non-thermal processing of fruit juices which can retain the authenticity and at the same time can ensure more safety. As watermelon products are regarded as potentially hazardous foods by FDA due to their low acid content (pH = 5–6), there is a need to process the juice so as to minimize the microbial spoilage and maximize the retention of nutritional components for longer periods. The effect of these non-thermal processes on watermelon juice has been reviewed in the paper. Non-thermal processing of watermelon juice has able to produce a product that has minimal activity of enzymes and microorganisms and resembling the original juice in terms of nutritional and sensorial aspects. Non-thermal processes such as PEF, UV, HPCD, HHP etc have been analyzed by researchers for inactivation of various microorganisms such as E. coli, L. innocua, Salmonella enteritidis, Listeria monocytogenes etc. and have found positive results. The combination of mild heat treatment with some of these non-thermal methods also delivered promising results. There is a dearth of consistency in operating conditions of some of these processes for juice processing as they are still in laboratory scale. While high pressure (HHP) has been shown to effectively inactive various kinds of microorganisms, the issue of foodborne viruses still need to be further addressed. The need for fundamental understanding of these processes and their mode of inactivation is essential to optimize process design and ensuring desired standard products. Most of these non-thermal processes are currently applied at a lab or pilot scale, thus inducing higher production cost than large scale industrial thermal devices. Researchers will be focussing more on the underlying mechanisms of inactivation and the necessary parameters for achieving the best quality juice in near future. Albeit the ability of non-thermal processes to reduce foodborne pathogens and enhance nutritional qualities and shelf life, the high fixed costs limits their use in fruit juice processing industries. Inability to handle large volumes of juice is another reason of their limited use along with lack of in-depth knowledge of mechanisms of inactivation. Further research is required in terms of cost optimization and scalability of these processes to fulfill the needs of both the industry and consumer. References Abid, M., Jabbar, S., Wu, T., Hashim, M. M., Hu, B., Lei, S., & Zeng, X. (2013). Effect of ultrasound on different quality parameters of apple juice. Ultrasonics Sonochemistry, 20(5), 1182–1187. Aganovic, K., Smetana, S., Grauwet, T., Toepfl, S., Mathys, A., Loey, A. V., & Heinz, V. (2017). Pilot scale thermal and alternative pasteurization of tomato and watermelon juice: An energy comparison and life cycle assessmen. Journal of Cleaner Production, 141, 514–525. Aguiló-Aguayo, I., Soliva-Fortuny, R., & Martín-Belloso, O. (2009). Avoiding non-enzymatic browning by high-intensity pulsed electric fields in strawberry, tomato and watermelon juices. Journal of Food Engineering, 92(1), 37–43. Aguiló-Aguayo, I., Soliva-Fortuny, R., & Martín-Belloso, O. (2010a). Optimizing critical high-intensity pulsed electric fields treatments for reducing pectolytic activity and viscosity changes in watermelon juice. European Food Research and Technology, 231(4), 509–517. Aguiló-Aguayo, I., Soliva-Fortuny, R., & Martín-Belloso, O. (2010b). Color and viscosity of watermelon juice treated by high-intensity pulsed electric fields or heat. Innovative Food Science & Emerging Technologies, 11(2), 299–305. Aronsson, K., & Rönner, U. (2001). Influence of pH, water activity and temperature on the inactivation of Escherichia coli and Saccharomyces cerevisiae by pulsed electric fields. Innovative Food Science & Emerging Technologies, 2(2), 105–112. Arriola, N. A., dos Santos, G. D., Prudêncio, E. S., Vitali, L., Petrus, J. C. C., & Castanho Amboni, R. D. (2014). Potential of nanofiltration for the concentration of bioactive compounds from watermelon juice. International Journal of Food Science and Technology, 49(9), 2052–2060.

241

Trends in Food Science & Technology 93 (2019) 234–243

C. Bhattacharjee, et al. Balci, A. T., & Wilbey, R. A. (1999). High pressure processing of milk – the first 100 years in the development of new technology. International Journal of Dairy Technology, 52, 149–155. Barba, F. J., Parniakov, O., Pereira, S. A., Wiktor, A., Grimi, N., Boussetta, N., & Lebovka, N. (2015). Current applications and new opportunities for the use of pulsed electric fields in food science and industry. Food Research International, 77, 773–798. Barbosa-Canovas, G. V., Pothakamury, U. R., Gongora-Nieto, M. M., & Swanson, B. G. (1999). Preservation of foods with pulsed electric fields. Elsevier. Barbosa-Canovas, G. V., Pothakamury, U. R., Palou, E., & Swanson, B. G. (1998). Nonthermal preservation of foods. New York: Marcel Dekker9–48 53–110, 113–136, 139–159. Barbosa-Ćanovas, G. V., & Sepúlveda, D. (2004). Present status and the future of PEF technology. In M. Pilar Cano, M. S. Tapia, & G. V. Barbosa-C´anovas (Vol. Eds.), Novel food processing technologies: Vols. 1–0, (pp. 1–44). Boca Raton, FL: CRC Press. Bello, E., Martínez, G., Ceberio, B., Rodrigo, D., & López, A. (2014). High pressure treatment in foods. Foods, 3(3), 476–490. Bendicho, S., Espachs, A., Arantegui, J., & MARTÍN, O. (2002). Effect of high intensity pulsed electric fields and heat treatments on vitamins of milk. Journal of Dairy Research, 69(1), 113–123. Bharate, S. S., & Bharate, S. B. (2014). Non-enzymatic browning in citrus juice: Chemical markers, their detection and ways to improve product quality. Journal of Food Science and Technology, 51(10), 2271–2288. Bhat, R., Ameran, S. B., Voon, H. C., Karim, A. A., & Tze, L. M. (2011). Quality attributes of starfruit (Averrhoa carambola L.) juice treated with ultraviolet radiation. Food Chemistry, 127(2), 641–644. Bhattacharjee, C., Saxena, V. K., & Dutta, S. (2017b). Watermelon juice concentration using ultrafiltration: Analysis of sugar and ascorbic acid. Food Science and Technology International, 23(7), 637–645. Bhattacharjee, C., Saxena, V. K., & Dutta, S. (2017a). Fruit juice processing using membrane technology: A review. Innovative Food Science & Emerging Technologies, 43, 136–153. Bhattacharjee, C., Saxena, V. K., & Dutta, S. (2018). Analysis of fouling and juice quality in crossflow ultrafiltration of watermelon juice. Food Science and Technology, 38(supl.1), 71–76. Blostein, J. (1993). An outbreak of “Salmonella joviana” associated with consumption of watermelon. Journal of Environmental Health, 29–31. Bozkurt, H., Gögüs, F., & Eren, S. (1999). Nonenzymic browning reactions in boiled grape juice and its models during storage. Food Chemistry, 64(1), 89–93. Burt, S. (2004). Essential oils: Their antibacterial properties and potential applications in foods—a review. International Journal of Food Microbiology, 94(3), 223–253. Cao, X., Bi, X., Huang, W., Wu, J., Hu, X., & Liao, X. (2012). Changes of quality of high hydrostatic pressure processed cloudy and clear strawberry juices during storage. Innovative Food Science & Emerging Technologies, 16, 181–190. Chaparro, L., Dhuique-Mayer, C., Castillo, S., Vaillant, F., Servent, A., & Dornier, M. (2016). Concentration and purification of lycopene from watermelon juice by integrated microfiltration-based processes. Innovative Food Science & Emerging Technologies, 37, 153–160. Chen, D., Pang, X., Zhao, J., Gao, L., Liao, X., Wu, J., et al. (2015). Comparing the effects of high hydrostatic pressure and high temperature short time on papaya beverage. Innovative Food Science & Emerging Technologies, 32, 16–28. Chen, D., Xi, H., Guo, X., Qin, Z., Pang, X., Hu, X., & Wu, J. (2013). Comparative study of quality of cloudy pomegranate juice treated by high hydrostatic pressure and high temperature short time. Innovative Food Science & Emerging Technologies, 19, 85–94. Chhaya, C., Rai, P., Majumdar, G. C., Dasgupta, S., & De, S. (2008). Clarification of watermelon (Citrullus Lanatus) juice by microfiltration. Journal of Food Process Engineering, 31(6), 768–782. Choi, S. U., & Eastman, J. A. (1995). Enhancing thermal conductivity of fluids with nanoparticles. IL (United States): Argonne National Lab No. ANL/MSD/CP-84938; CONF951135-29. Cortés, C., Esteve, M. J., & Frígola, A. (2008). Color of orange juice treated by high intensity pulsed electric fields during refrigerated storage and comparison with pasteurized juice. Food Control, 19(2), 151–158. Cserhalmi, Z., Sass-Kiss, A., Tóth-Markus, M., & Lechner, N. (2006). Study of pulsed electric field treated citrus juices. Innovative Food Science & Emerging Technologies, 7(1–2), 49–54. Damar, S., & Balaban, M. O. (2006). Review of dense phase CO2 technology: Microbial and enzyme inactivation, and effects on food quality. Journal of Food Science, 71(1), R1–R11. Eastman, J. A., Choi, S. U. S., Li, S., Yu, W., & Thompson, L. J. (2001). Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles. Applied Physics Letters, 78(6), 718–720. Edwards, A. J., Vinyard, B. T., Wiley, E. R., Brown, E. D., Collins, J. K., Perkins-Veazie, P., & Clevidence, B. A. (2003). Consumption of watermelon juice increases plasma concentrations of lycopene and β-carotene in humans. Journal of Nutrition, 133(4), 1043–1050. Esteve, M. J., Barba, F. J., Palop, S., & Frígola, A. (2009). The effects of non-thermal processing on carotenoids in orange juice. Czech Journal of Food Sciences, 27, S304–S306. Farajollahi, B., Etemad, S. G., & Hojjat, M. (2010). Heat transfer of nanofluids in a shell and tube heat exchanger. International Journal of Heat and Mass Transfer, 53(1–3), 12–17. Feng, M., Ghafoor, K., Seo, B., Yang, K., & Park, J. (2013). Effects of ultraviolet-C treatment in Teflon®-coil on microbial populations and physico-chemical characteristics of watermelon juice. Innovative Food Science & Emerging Technologies, 19, 133–139. Ferrari, G., Maresca, P., & Ciccarone, R. (2010). The application of high hydrostatic

pressure for the stabilization of functional foods: Pomegranate juice. Journal of Food Engineering, 100(2), 245–253. Gayán, E., Serrano, M. J., Raso, J., Álvarez, I., & Condón, S. (2012). Inactivation of Salmonella enterica by UV-C light alone and in combination with mild temperatures. Applied and Environmental Microbiology, 78(23), 8353–8361. Gayler, G. E., MacCREADY, R. A., Reardon, J. P., & McKernan, B. F. (1955). An outbreak of salmonellosis traced to watermelon. Public Health Reports, 70(3), 311. Giovannucci, E. (2002). A review of epidemiologic studies of tomatoes, lycopene, and prostate cancer. Experimental Biology and Medicine, 227(10), 852–859. Gomes, F. S., Costa, P. A., Campos, M. B., Tonon, R. V., Couri, S., & Cabral, L. M. (2013). Watermelon juice pretreatment with microfiltration process for obtaining lycopene. International Journal of Food Science and Technology, 48(3), 601–608. Guerrero-Beltran, J. A., & Barbosa-Canovas, G. V. (2004). Advantages and limitations on processing foods by UV light. Food Science and Technology International, 10(3), 137–147. Hayashi, R. (1990). Application of high pressure to processing and preservation: Philosophy and development. In W. E. L. Spiess, & H. Schubert (Eds.). Engineering and food (pp. 815–826). London: Elsevier Applied Science. Heremans, K. (2002). High pressure bioscience and biotechnology: A century and a decade perspective. TRENDS IN HIGH PRESSURE BIOSCIENCE AND BIOTECHNOLOGY, PROCEEDINGS, 19(C), 1–6. Hiremath, N. D., & Ramaswamy, H. S. (2012). High‐pressure destruction kinetics of spoilage and pathogenic microorganisms in mango juice. Journal of Food Processing and Preservation, 36(2), 113–125. Huang, H., Zhang, Y., Liao, H., Hu, X., Wu, J., Liao, X., et al. (2009). Inactivation of staphylococcus aureus exposed to dense‐phase carbon dioxide in a batch system. Journal of Food Process Engineering, 32(1), 17–34. Icier, F., Yildiz, H., & Baysal, T. (2006). Peroxidase inactivation and colour changes during ohmic blanching of pea puree. Journal of Food Engineering, 74(3), 424–429. Ishita, C., & Athmaselvi, K. A. (2017). Changes in pH and colour of watermelon juice during ohmic heating. International Food Research Journal, 24(2). Jabbar, S., Abid, M., Hu, B., Wu, T., Hashim, M. M., Lei, S., & Zeng, X. (2014). Quality of carrot juice as influenced by blanching and sonication treatments. LWT-Food Science and Technology, 55(1), 16–21. Jafari, S. M., Saremnejad, F., & Dehnad, D. (2017a). Nano-fluid thermal processing of watermelon juice in a shell and tube heat exchanger and evaluating its qualitative properties. Innovative Food Science & Emerging Technologies, 42, 173–179. Jafari, S. M., Saremnejad, F., Dehnad, D., & Rashidi, A. M. (2017b). Evaluation of performance and thermophysical properties of alumina nanofluid as a new heating medium for processing of food products. Journal of Food Process Engineering, 40(5) e12544. Jiménez-Sánchez, C., Lozano-Sánchez, J., Segura-Carretero, A., & Fernández-Gutiérrez, A. (2017). Alternatives to conventional thermal treatments in fruit-juice processing. Part 1: Techniques and applications. Critical Reviews in Food Science and Nutrition, 57(3), 501–523. Juarez-Enriquez, E., Salmeron-Ochoa, I., Gutierrez-Mendez, N., Ramaswamy, H. S., & Ortega-Rivas, E. (2015). Shelf life studies on apple juice pasteurised by ultrahigh hydrostatic pressure. LWT-Food Science and Technology, 62(1), 915–919. Koutchma, T. (2009). Advances in ultraviolet light technology for non-thermal processing of liquid foods. Food and Bioprocess Technology, 2(2), 138–155. Leizerson, S., & Shimoni, E. (2005). Effect of ultrahigh-temperature continuous ohmic heating treatment on fresh orange juice. Journal of Agricultural and Food Chemistry, 53(9), 3519–3524. Liao, H., Hu, X., Liao, X., Chen, F., & Wu, J. (2007). Inactivation of Escherichia coli inoculated into cloudy apple juice exposed to dense phase carbon dioxide. International Journal of Food Microbiology, 118(2), 126–131. Liu, X., Gao, Y., Xu, H., Hao, Q., Liu, G., & Wang, Q. (2010). Inactivation of peroxidase and polyphenol oxidase in red beet (Beta vulgaris L.) extract with continuous high pressure carbon dioxide. Food Chemistry, 119(1), 108–113. Liu, Y., Hu, X., Zhao, X., & Song, H. (2012). Combined effect of high pressure carbon dioxide and mild heat treatment on overall quality parameters of watermelon juice. Innovative Food Science & Emerging Technologies, 13, 112–119. Liu, Y., Hu, X. S., Zhao, X. Y., & Zhang, C. (2013a). Inactivation of polyphenol oxidase from watermelon juice by high pressure carbon dioxide treatment. Journal of Food Science and Technology, 50(2), 317–324. Liu, Q., Wang, R. F., Zhang, B. B., Zhao, X. Y., Wang, D., & Zhang, C. (2014). Protein secondary structure changes of watermelon juice treated with high hydrostatic pressure by FTIR spectroscopy. Journal of Food Process Engineering, 37(6), 543–549. Liu, Y., Zhao, X. Y., Zou, L., & Hu, X. S. (2013b). Effect of high hydrostatic pressure on overall quality parameters of watermelon juice. Food Science and Technology International, 19(3), 197–207. López-Gómez, A., Fernández, P. S., Palop, A., Periago, P. M., Martinez-López, A., MarinIniesta, F., et al. (2009). Food safety engineering: An emergent perspective. Food Engineering Reviews, 1(1), 84–104. Makroo, H. A., Saxena, J., Rastogi, N. K., & Srivastava, B. (2017). Ohmic heating assisted polyphenol oxidase inactivation of watermelon juice: Effects of the treatment on pH, lycopene, total phenolic content, and color of the juice. Journal of Food Processing and Preservation, 41(6) e13271. Mason, T. J., Paniwnyk, L., & Lorimer, J. P. (1996). The uses of ultrasound in food technology. Ultrasonics Sonochemistry, 3(3), S253–S260. Morris, C., Brody, A. L., & Wicker, L. (2007). Non‐thermal food processing/preservation technologies: A review with packaging implications. Packaging Technology and Science: International Journal, 20(4), 275–286. Mosqueda-Melgar, J., Raybaudi-Massilia, R. M., & Martín-Belloso, O. (2007). Influence of treatment time and pulse frequency on Salmonella Enteritidis, Escherichia coli and Listeria monocytogenes populations inoculated in melon and watermelon juices

242

Trends in Food Science & Technology 93 (2019) 234–243

C. Bhattacharjee, et al. treated by pulsed electric fields. International Journal of Food Microbiology, 117(2), 192–200. Mosqueda-Melgar, J., Raybaudi-Massilia, R. M., & Martin-Belloso, O. (2008). Combination of high-intensity pulsed electric fields with natural antimicrobials to inactivate pathogenic microorganisms and extend the shelf-life of melon and watermelon juices. Food Microbiology, 25(3), 479–491. Nazer, A. I., Kobilinsky, A., Tholozan, J. L., & Dubois-Brissonnet, F. (2005). Combinations of food antimicrobials at low levels to inhibit the growth of Salmonella sv. Typhimurium: A synergistic effect? Food Microbiology, 22(5), 391–398. Odumeru, J. A. (2012). Microbial safety of food and food products. In B. K. Simpson, L. M. L. Nollet, F. Toldra, S. Benjakul, G. Paliyath, & Y. H. Hui (Eds.). Food biochemistry and food processing (pp. 787–797). (2nd ed.). UK: John Wiley & Sons. Oliveira, C. S., Gomes, F. S., Constant, L. S., Silva, L. F., Godoy, R. L., Tonon, R. V., et al. (2016). Integrated membrane separation processes aiming to concentrate and purify lycopene from watermelon juice. Innovative Food Science & Emerging Technologies, 38, 149–154. Oms-Oliu, G., Odriozola-Serrano, I., Soliva-Fortuny, R., & Martín-Belloso, O. (2009). Effects of high-intensity pulsed electric field processing conditions on lycopene, vitamin C and antioxidant capacity of watermelon juice. Food Chemistry, 115(4), 1312–1319. Oussalah, M., Caillet, S., Saucier, L., & Lacroix, M. (2007). Inhibitory effects of selected plant essential oils on the growth of four pathogenic bacteria: E. coli O157: H7, Salmonella typhimurium, Staphylococcus aureus and Listeria monocytogenes. Food Control, 18(5), 414–420. O’donnell, C. P., Tiwari, B. K., Bourke, P., & Cullen, P. J. (2010). Effect of ultrasonic processing on food enzymes of industrial importance. Trends in Food Science & Technology, 21(7), 358–367. Pala, Ç. U., & Toklucu, A. K. (2013). Microbial, physicochemical and sensory properties of UV-C processed orange juice and its microbial stability during refrigerated storage. LWT-Food Science and Technology, 50(2), 426–431. Penteado, A. L., & Leitao, M. F. (2004). Growth of Listeria monocytogenes in melon, watermelon and papaya pulps. International Journal of Food Microbiology, 92(1), 89–94. Piette, G., Buteau, M. L., De Halleux, D., Chiu, L., Raymond, Y., Ramaswamy, H. S., et al. (2004). Ohmic cooking of processed meats and its effects on product quality. Journal of Food Science, 69(2), fep71–fep78. Piyasena, P., Mohareb, E., & McKellar, R. C. (2003). Inactivation of microbes using ultrasound: A review. International Journal of Food Microbiology, 87(3), 207–216. Puértolas, E., & Barba, F. J. (2016). Electrotechnologies applied to valorization of byproducts from food industry: Main findings, energy and economic cost of their industrialization. Food and Bioproducts Processing, 100, 172–184. Rai, C., Rai, P., Majumdar, G. C., De, S., & Dasgupta, S. (2010). Mechanism of permeate flux decline during microfiltration of watermelon (Citrullus lanatus) juice. Food and Bioprocess Technology, 3(4), 545–553. Ramaswamy, H. S., & Chen, C. R. (2002). Maximising the quality of thermally processed fruits and vegetables. In W. Jongen (Ed.). Fruit and vegetable processing (pp. 188–214). Cambridge: Woodhead Publishing Riener, J., Noci, F., Cronin, D.A., Morgan, D.J., Lyng, J.G., 2009. Effect of high intensity pulsed electric fields. Rastogi, N. K., Raghavarao, K. S. M. S., Balasubramaniam, V. M., Niranjan, K., & Knorr, D. (2007). Opportunities and challenges in high pressure processing of foods. Critical Reviews in Food Science and Nutrition, 47(1), 69–112. Rawson, A., Tiwari, B. K., Patras, A., Brunton, N., Brennan, C., Cullen, P. J., et al. (2011). Effect of thermosonication on bioactive compounds in watermelon juice. Food Research International, 44(5), 1168–1173. Raybaudi-Massilia, R. M., Mosqueda-Melgar, J., & Martin-Belloso, O. (2006). Antimicrobial activity of essential oils on Salmonella enteritidis, Escherichia coli, and Listeria innocua in fruit juices. Journal of Food Protection, 69(7), 1579–1586.

Ross, A. I., Griffiths, M. W., Mittal, G. S., & Deeth, H. C. (2003). Combining nonthermal technologies to control foodborne microorganisms. International Journal of Food Microbiology, 89(2–3), 125–138. Saikia, S., Mahnot, N. K., & Mahanta, C. L. (2016). A comparative study on the effect of conventional thermal pasteurisation, microwave and ultrasound treatments on the antioxidant activity of five fruit juices. Food Science and Technology International, 22(4), 288–301. Sastry, S. (2008). Ohmic heating and moderate electric field processing. Food Science and Technology International, 14(5), 419–422. Señorans, F. J., Ibáñez, E., & Cifuentes, A. (2003). New trends in food processing. Critical Reviews in Food Science and Nutrition, 43(5), 507–526. Shaheer, C. A., Hafeeda, P., Kumar, R., Kathiravan, T., Kumar, D., & Nadanasabapathi, S. (2014). Effect of thermal and thermosonication on anthocyanin stability in jamun (Eugenia jambolana) fruit juice. International Food Research Journal, 21(6). Teissie, J., Golzio, M., & Rols, M. P. (2005). Mechanisms of cell membrane electropermeabilization: A minireview of our present (lack of?) knowledge. Biochimica et Biophysica Acta (BBA) - General Subjects, 1724(3), 270–280. Tempest, P. (1992). Experience with ohmic heating and aseptic packaging of particulate foodsCrawley, UK: APV Baker Ltd., Automation Process Division Technical Report. No. PT/FBD1368. Toepfl, S., Mathys, A., Heinz, V., & Knorr, D. (2006). Potential of high hydrostatic pressure and pulsed electric fields for energy efficient and environmentally friendly food processing. Food Reviews International, 22(4), 405–423. Tran, M. T. T., & Farid, M. (2004). Ultraviolet treatment of orange juice. Innovative Food Science & Emerging Technologies, 5(4), 495–502. Tremarin, A., Brandão, T. R., & Silva, C. L. (2017). Inactivation kinetics of Alicyclobacillus acidoterrestris in apple juice submitted to ultraviolet radiation. Food Control, 73, 18–23. USDA (2009). Guidance for industry: Guide to minimize microbial food safety hazards of melons; Draft Guidance. Cited 16/05/2011 http://www.food-label-compliance.com/ Sites/5/Downloads/USFDA-Draft-Guidance-MELONS-issued-073109-complete-text. pdf. Vaillant, F., Cisse, M., Chaverri, M., Perez, A., Dornier, M., Viquez, F., et al. (2005). Clarification and concentration of melon juice using membrane processes. Innovative Food Science & Emerging Technologies, 6(2), 213–220. Valdez-Fragoso, A., Mújica-Paz, H., Welti-Chanes, J., & Torres, J. A. (2011). Reaction kinetics at high pressure and temperature: Effects on milk flavor volatiles and on chemical compounds with nutritional and safety importance in several foods. Food and Bioprocess Technology, 4(6), 986–995. Valero, M., Recrosio, N., Saura, D., Muñoz, N., Martí, N., & Lizama, V. (2007). Effects of ultrasonic treatments in orange juice processing. Journal of Food Engineering, 80(2), 509–516. Walkling-Ribeiro, M., Noci, F., Cronin, D. A., Riener, J., Lyng, J. G., & Morgan, D. J. (2008). Reduction of Staphylococcusaureus and quality changes in apple juice processed by ultraviolet irradiation, pre-heating and pulsed electric fields. Journal of Food Engineering, 89(3), 267–273. Wang, L., Pan, J., Xie, H., Yang, Y., Zhou, D., & Zhu, Z. (2012). Pasteurization of fruit juices of different pH values by combined high hydrostatic pressure and carbon dioxide. Journal of Food Protection, 75(10), 1873–1877. Wouters, P. C., Alvarez, I., & Raso, J. (2001). Critical factors determining inactivation kinetics by pulsed electric field food processing. Trends in Food Science & Technology, 12(3–4), 112–121. Xuan, Y., & Li, Q. (2000). Heat transfer enhancement of nanofluids. International Journal of Heat and Fluid Flow, 21(1), 58–64. Zhang, C., Trierweiler, B., Li, W., Butz, P., Xu, Y., Rüfer, C. E., & Zhao, X. (2011). Comparison of thermal, ultraviolet-c, and high pressure treatments on quality parameters of watermelon juice. Food Chemistry, 126(1), 254–260.

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