Emerging Preservation Methods for Fruit Juices and Beverages

Traditionally, the shelf-life stability of juices has been achieved by thermal processing. Low temperature long time (LTLT) and high temperature short time (HTST) treatments are the most commonly used techniques for juice pasteurization. However, thermal pasteurization tends to reduce the product quality and freshness. Therefore, some non-thermal pasteurization methods have been proposed during the last couple of decades, including high hydrostatic pressure (HHP), high pressure homogenization (HPH), pulsed electric field (PEF), and ultrasound (US). These emerging techniques seem to have the potential to provide “fresh-like” and safe fruit juices with prolonged shelf-life. Some of these techniques have already been commercialized. Some are still in the research or pilot scale. The first part of the chapter will give an update of these emerging non-thermal techniques.


Introduction
This chapter provide a review of traditional and non-traditional food preservation approaches including physical methods (non-thermal pasteurization), chemical methods (natural food preservatives) and their combinations for extension of the shelf life of fruit juices and beverages.
Traditionally, the shelf-life stability of juices has been achieved by thermal processing. Low temperature long time (LTLT) and high temperature short time (HTST) treatments are the most commonly used techniques for juice pasteurization. However, thermal pasteurization tends to reduce the product quality and freshness. Therefore, some non-thermal pasteurization methods have been proposed during the last couple of decades, including high hydrostatic pressure (HHP), high pressure homogenization (HPH), pulsed electric field (PEF), and ultrasound (US). These emerging techniques seem to have the potential to provide "fresh-like" and safe fruit juices with prolonged shelf-life. Some of these techniques have already been commercialized. Some are still in the research or pilot scale. The first part of the chapter will give an update of these emerging non-thermal techniques.
Apart from thermal pasteurization, some chemical preservatives are also widely used for the extension of the shelf-life of fruit juices and beverages. Two of the most commonly used preservatives are potassium sorbate and sodium benzoate. However, consumer demand for natural origin, safe and environmental friendly food preservatives has been increasing since 1990s. Natural antimicrobials such as bacteriocins, organic acids, essential oils and phenolic compounds have shown considerable promise for use in some food products. The second part of the chapter will comprise of applications of these natural antimicrobials in fruit juice preservation.
From scientific literature, it is apparent that some individual non-thermal methods as well as natural antimicrobials are effective to inactivate microorganisms or reduce the log colony forming units (CFU) while not adversely affecting the sensory and nutritional quality. Moreover, the combination of these techniques could also provide synergistic effects on prolonging the shelf-life of fruit juices and beverages and potentially could become replacements for traditional pasteurization methods. The third part of the chapter will provide recent progresses of these combined techniques in fruit juice shelf-life extension.
Generally, there are two principles that govern the behaviour of foods under pressure: the Le Chatelier-Braun principle and the Isostatic principle. The Le Chatelier-Braun principle indicates that any phenomenon (such as phase transition, change in molecular configuration, chemical reaction, etc.) accompanied by a decrease in volume is enhanced by the increase in applied pressure. The isostatic principle means that the distribution of pressure into the sample is uniform and instantaneous. Thus, the process time is independent of sample size and shape (Ramaswamy et al. 2005).
HPP is proven to meet the FDA requirement of a 5-log reduction of microorganisms in fruit juices and beverages without sacrificing the sensory and nutritional attributes of fresh fruits (San Martín et al. 2002). Compared with thermal processing, HHP has many advantages. It can provide safe product with reduced processing time. It can maintain maximum fresh-like flavor and taste in the product due to the lower processing temperatures. Moreover, it is environmentally friendly since it requires only electrical energy and no waste by-products generated (Ramaswamy et al. 2005, Toepfl et al. 2006. Due to these advantages, HHP has been widely used in food product preservation including fruit and beverages in the areas of microbial inactivation (Table 1) and shelf-life extension (

Pulsed electric field (PEF)
Pulsed electric field processing (PEF) applies short bursts of high voltage electricity for microbial inactivation and causes no or minimum effect on food quality attributes. Briefly, the foods being treated by PEF are placed between two electrodes, usually at room temperature. The applied high voltage results in an electric field that causes microbial inactivation. The applied high voltage is usually in the order of 20-80 kV for microseconds. The common types of electrical field waveform applied include exponentially decaying and square wave (Knorr et al. 1994, Zhang et al. 1995, Barbosa-Cánovas et al. 1999).
The principles of PEF processing have been explained by several theories including the trans-membrane potential theory, electromechanical compression theory and the osmotic imbalance theory. One of the most accepted theories is associated with the electroporation of cell membranes. It is generally believed that electric fields induce structural changes in the membranes of microbial cells based on generation of pores of the cell membrane, leading consequently to microbial destruction and inactivation (Tsong 1991, Barbosa-Cánovas et al. 1999.
Compared with thermal processing, PEF processing has many advantages. It can preserve the original sensory and nutritional characteristics of foods due to the very short processing time and low processing temperatures. Energy savings for PEF processing are also important compared with conventional thermal processing. Moreover, it is environmentally friendly with no waste generated (Toepfl et al. 2006). Due to these advantages, PEF processing has been widely used in food product preservation including fruit and beverages in the areas of microbial inactivation (Table 3) and shelf-life extension (  Table 4. Examples of PEF effect on quality attributes of fruit products

Ultrasound (US)
Power ultrasound (US) has emerged as a potential non-thermal technique for preservation of food products over the last decade. Compared with diagnostic ultrasound, power US uses a lower frequency range of 20 to 100 kHz and a higher sound intensity of 10 to 1000 W/cm 2 (Baumann et al. 2005).
The principle of ultrasonic processing could be explained as follows: Firstly, the ultrasonic transducers convert electrical energy to sound energy. Secondly, when the ultrasonic waves propagate in liquid, small bubbles will be formed and collapsed thousands of times per second. This rapid collapse of the bubbles (cavitation) results in high localized temperatures and pressure, causing breakdown of cell walls, disruption of cell membranes and damage of DNA (Manvell, 1997, Knorr et al. 2004, O'Donnell et al. 2010).

70
The application of high power ultrasound in the food industry has been widely investigated. To meet the FDA requirement of a 5-log reduction of microorganisms, a combination of sonication with mild heat treatment and /or pressure is essential (Baumann et al. 2005 effectiveness of ultrasound on inactivation of microorganisms in fruit juices (Table 5). A few studies have been conducted to examine the effect of ultrasound on quality of UStreated fruit juices (Table 6).
Except HHP, PEF and power US, other non-thermal techniques including high pressure homogenization (HPH), membrane filtration and UV-light, among others, are also being investigated.

Ultraviolet light
Ultraviolet light (UV-light) technology utilizes radiation with the electro-magnetic spectrum in the range of 100 to 400 nanometers, between visible light and x-rays. It could be further divided into UV-A (320-400 nm), UV-B (280-320 nm) and . UV-C is known to have biocidal effects and destroys microorganisms by degrading their cell walls and DNA (Ngadi et al. 2003). Therefore, UV-C could be used for the inactivation of microorganisms such as bacteria, yeasts, moulds, among others (Bintsis, Litopoulou-Tzanetaki, & Robinson, 2000). The amount of cell damage depends on the type of medium, microorganisms and the applied UV dose (Ngadi et al. 2003). For fruit juice and beverage processing, the wavelength of 254 nm is widely used (Guerrero-Beltrán & Barbosa-Cánovas, 2004).
As a non-thermal preservation method, UV-C treatment takes the advantages of no toxic or significant non-toxic by-products being formed during the treatment, very little energy being required when compared to thermal pasteurization processes, and maximum aroma and color of the treated fruits being maintained (Tran & Farid, 2004).
UV-C treatment has been successfully applied to reduce the microbial load in different fruit juices and nectars. Under suitable treatment conditions, more than 5-log reduction of some pathogenic microorganism, such as E. coli, in fruit juices could be achieved (Guerrero-Beltrán and Barbosa-Cánovas 2004, Keyser et al. 2008). The minimum treatment condition for clear apple juice was under UV dosage of 230 J L −1 , whereas higher UV dosage levels would be needed for cloudy juices such as orange juice and tropical juices (Keyser et al. 2008).

High pressure homogenization (HPH)
High pressure homogenization (HPH) is considered to be one of the most promising nonthermal technologies proposed for preservation of fruit juice and beverages. The primary mechanisms of HPH has been identified as a combination of spatial pressure and velocity gradients, turbulence, impingement, cavitation and viscous shear, which leads to the microbial cell disruption and food constituent modification during the HPH process. HPH has shown its ability to increase the safety and shelf-life of fruit juices including orange juice (Lacroix et al. 2005;Tahiri et al. 2006;Welti-Chanes et al. 2009), apple juice (Kumar et al. 2009;Pathanibul et al. 2009) and apricot juice (Patrignani et al. 2009). The effectiveness of the treatment depends on many parameters including processing factors such as pressure, temperature, number of passes and medium factors such as type of juice and microorganisms. For example, up to 350 MPa processing pressure was required to achieve an equivalent 5-log inactivation of L. Innocua; however, less pressure is required for E. coli (> 250 Mpa) in carrot juices (Pathanibul et al. 2009). Another instance is that a higher reduction of Saccharomyces cerevisiae 635 was observed in carrot juice (5-log reduction) than in apricot juice. (3-log reduction) with a pressure level of 100 MPa for up to 8 passes (Patrignani et al. 2009).

Membrane filtration
Ultrafiltration (UF) and microfiltration (MF) are the most commonly used membrane filtration techniques for fruit juice processing. They have been used commercially for the clarification of fruit juices. Through this processing, a "pasteurized" product could be produced with flavours better than thermally treated products (Tallarico et al. 1998;Ortega-Rivas et al. 1998;Cassano et al. 2003). The effectiveness of the treatment depends on many parameters including processing factors such as types of membrane, pore size, transmembrane pressure and medium factors such as type of juice and microorganism. For example, an ultrafiltration (UF) unit, with polysulphone membranes of 10 kDa and 50 kDa pore sizes and trans-membrane pressures of up to 155 kPa, were used to treat apple juices. Results indicated that pH, acid content, and soluble solids did not change but presented less variability for the smaller pore membrane treatment. Relative colour changes were observed for both membranes, which was more detectable for the larger pore membrane treatment (Zarate-Rodriguez et al. 2001). Another application example was to use an ultrafiltration membrane of 15 kDa pore size to filter carrot and citrus juices. Then the clarified juices could be further processed by reverse osmosis and osmotic distillation (Cassano et al. 2003).

Chemical methods (natural antimicrobials)
Apart from physical methods, some chemical preservatives are widely used for the shelf-life extension of fruit juices and beverages. The most commonly used preservatives are potassium sorbate and sodium benzoate. However, consumer demand for natural origin, safe and environmental friendly food preservatives is increasing. Natural antimicrobials such as bacteriocins, lactoperoxidase, herb leaves and oils, spices, chitozan and organic acids have shown feasibility for use in some food products (Gould 2001, Corbo et al. 2009). Some of them have been considered as Generally Recognized As Safe (GRAS) additives in foods. Table 7 lists some natural antimicrobials and their status for GRAS.

Bacteriocins
Bacteriocins are series of antimicrobial peptides which are readily degraded by proteolytic enzymes in the human body. Among them, nisin is the most commonly used food preservative and the GRAS additives permitted by the Food Additive Status List (USFDA, 2006). Apart from dairy, it has been used to preserve fruit and vegetable juices (Yuste & Fung 2004, Settanni & Corsetti, 2008.

Lactoperoxidase
Lactoperoxidase is an enzyme that is widely distributed in colostrum, raw milk and other body liquid. It is an oxidoreductase and catalyses the oxidation of thiocyanate with the consumption of H 2 O 2 , to produce intermediate products with antibacterial properties (Corbo et al. 2009). These products have been indicated to be bactericidal for some spoilage and pathogenic microorganisms and yeasts (Gould 2001). Not much information had been found on the application of lactoperoxidase in fruit juices. Until recently, it was used for the preservation of tomato juice and mongo fruits (Touch et al. 2004, Le Nguyen et al. 2005.

Herb, spice and flavor oils
Some herbs and spices contain essential oils, which are natural antimicrobials. The main elements of these antimicrobials are phenolic compounds, including caffeic, cinnamic, ferulic and gallic acids, oleuropein, thymol and eugenol (Gould 2001 Table 7. Selected natural antimicrobials and their status for GRAS additives* Among them, sage (Salvia officinalis), rosemary (Rosemarinus officinalis), clove (Eugenia aromatica), coriander (Coriandrum sativum), garlic (Allium sativum) and onion (Allium cepa)) were listed as potential antimicrobials for food use (Deans and Ritchie 1987).  -Palmer et al. 1998). It is believed that Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. www.intechopen.com

Food Additive 74
Cinnamon as an antimicrobial agent has been used in apple juice (Yuste and Fung 2004;Friedman et al. 2004), apple cider (Ceylan et al. 2004) and fresh-cut apple slices (Muthuswamy et al. 2008). Ground cinnamon (0.3%) could inhibit the growth of Staphylococcus aureus, Y. enterocolitica and Salmonella typhimurium in apple juice (Yuste and Fung 2004), whereas oils of cinnamon leaf or bark inactivated Salmonella enterica and E. coli O157:H7 in apple juice (Friedman et al.2004). Ethanol extract of cinnamon bark (1% to 2% w/v) and cinnamic aldehyde (2 mM) could reduce E. coli O157:H7 and L. innocua in vitro. Ethanol extract of cinnamon bark (1% w/v) reduced significantly the aerobic growth of bacteria inoculated in fresh-cut apples during storage at 6ºC up to 12 days. It was also found that cinnamic aldehyde has greater antimicrobial activity than potassium sorbate (Muthuswamy et al. 2008).
Citrus fruits extracts have also been applied successfully to fruits and vegetables (Fisher & Phillips, 2008). For example, lemon extract was applied for the inhibition of some spoilage microorganisms, such as Bacillus licheniformis, Lactobacillus spp., Pichia subpelliculosa, Saccharomyces cerevisiae and Candida lusitaniae, the minimum inhibition concentration is 100 to 150 ppm (Conte et al. 2007). The growth of pathogenic bacteria, Escherichia coli O157:H7, Listeria innocua and the food spoilage fungus, Penicillium chrysogenum were suppressed by three phenolic compounds (catechin, chlorogenic acid and phloridzin) at 25 mM but the growth of food spoilage yeast Saccharomyces cerevisiae was inhibited only by chlorogenic acid and phloridzin . Vanillin, the predominant phenolic compound present in vanilla beans, has shown a concentration dependent response and the minimal inhibitory concentration (MIC) of 6 to 18 mM for pathogenic and spoilage microorganisms (Rupasinghe et al., 2006).

Chitozan
Chitosan is a modified, natural carbohydrate polymer derived by deacetylation of chitin [poly-β-(1 → 4)-N-acetyl-D-glucosamine] (No & Meyers, 1995). It is widely produced from crab, shrimp and crawfish, with different deacetylation grades and molecular weights which contribute to different functionalities .
Chitosan has attracted attention as a potential food preservative of natural origin due to its antimicrobial activity against a wide range of microorganisms (Sagoo and others 2002). The principles of the antimicrobial activity of chitosan could be explained by several hypotheses. One hypothesis is that the positively charged chitosan molecules could interact with the negatively charged microbial cell membranes, which would affect the cell permeability and lead to the leakage of intracellular compounds (Fang et al., 1994). Another hypothesis is that the interaction of diffused hydrolysis substances with microbial DNA could lead to the inhibition of the mRNA and protein synthesis of the microorganisms (Sudarshan et al., 1992).
A limited works have been done to assess the antimicrobial properties of chitosan in fruit juices (Roller and Covill 1999;Rhoades and Roller 2000). Chitosan glutamate was reported to be an effective preservative against spoilage yeasts in apple juice. Chitosan glutamate in apple juice from 0.1 to 5 g/L inhibited the growth of all spoilage yeasts at 25°C. The most sensitive strain, Z. bailii, was completely inactivated by chitosan at 0.1 and 0.4 g/L for 32-day of storage at 25°C. The most resistant strain, S. ludwigii, required 5 g/L of chitosan for complete inactivation and for maintaining yeast-free conditions in apple juice for 14 days at 25°C (Roller and Covill 1999). Another study by Rhoades and Roller (2000) showed that 0.3 g/L of Chitosan eliminated all the yeasts in pasteurized apple-elderflower juice during a 13-day of storage at 7°C. However, the total bacterial counts and the lactic acid bacterial counts increased slower than the control (Rhoades and Roller 2000). Chitosan has been approved as a food additive in Japan in 1983 and in Korea in 1995. However, it is so far not a GRAS approved food additive by the FDA. As long as receiving the FDA approval for GRAS status, Chitosan as a food additive and its applications in food systems will certainly have a brighter future.

Combination of physical and chemical methods
It is proved that some individual non-thermal methods as well as natural antimicrobials are effective in inactivating microorganisms and at the same time do not adversely affect the sensory and nutritional quality of the fruit juice and other products. Moreover, the combination of these techniques could provide synergistic effects on prolonging the fruit juice shelf-life and potentially as replacement for traditional pasteurization methods. Table 8 and Table 9 list some examples of recent progresses in these combined techniques for the microbial inactivation (Table 8) and shelf-life extension (  Table 9. Examples of combined preservation methods on quality attributes of fruit products

Conclusions
Non-thermal processing is a promising and useful approach for fruit juice and beverage preservation. The products based on these techniques show many advantages such as the retention of sensorial qualities and nutritional values over traditional thermal processing. However, among these non-thermal techniques, only high pressure processing has been adopted by the food industry so far. Additional pilot-scale testing may require for these non-thermal preservation methods to become a real alternative for thermal processing.
Similarly, the application of natural antimicrobial compounds in fruit juice and beverages is in the laboratory scale. But the potential benefits of these compounds would lead to a fast growth of scale-up and commercial application in food industry.
proven records for effective inhibition of microorganisms and shelf-life extension of fruit juices and beverages.