High-Pressure Processing of Fruits and Fruit Products

C H A P T E R

4 High-Pressure Processing of Fruits and Fruit Products So´nia Marı´lia Castro1,2, Jorge Alexandre Saraiva1 1

QOPNA e Departamento de Quı´mica, Universidade de Aveiro, Campus de Santiago, Aveiro, Portugal; 2CBQF e Centro de Biotecnologia e Quı´mica Fina e Laborato´rio Associado, Escola Superior de Biotecnologia, Universidade Cato´lica Portuguesa/Porto, Rua Dr. Anto´nio Bernardino Almeida, Porto, Portugal

4.1 INTRODUCTION

value and fresh-like sensory attributes of juices, pure´es, and pastes. Together with thermal processing, other conventional preservation technologies, such as freezing, salting, and drying, ensure the safety and shelf life of fruit-derived products but can result in the loss of physicochemical and nutritional quality attributes. However, new methods of processing and packaging continue to emerge that can extend the shelf life and freshness of perishable foods, including plant-based products. High-pressure processing (HPP) has been seen as an alternative technology for fruit processing. To qualify as an alternative method, a new/emerging technology should have significant impact on a product’s quality and safety, while maintaining the cost of technology within feasibile limits. Different commercial combinations of pressure (100e800 MPa), temperature (below 0
C up to 100
C), and time (milliseconds up to 1200 s) can be used to achieve the desired effect on the texture, color, and flavor of foods. The selection of HPP conditions depends on various factors, such as type of food, pH, chemical composition, nature of enzymes, type of microorganisms present, initial microbial load, and reaction kinetics of microbial death and nutrient loss. Moreover, the quality of HPP processed fruits can change during storage due to ongoing chemical reactions if endogenous enzymes or microorganisms are incompletely inactivated. Color, flavor, and texture are important quality characteristics of fruits, and also major factors affecting the sensory perception and consumer acceptance of foods. Foods with a high acid content, including fruits, are

Just as previous technical innovations in the nineteenth and twentieth centuries served the food industry, so will the technological advances of the twenty-first century. Consumers have opinion regarding the direction of food product innovations. Currently, they demand more convenient, innovative, fresh foods, including new “minimally processed”, and raw-like products. In order to meet consumers’ expectations in the twenty-first century, the food industry will utilize novel technologies, whose purpose will be twofold: (1) to provide the new quality attributes demanded by consumers; and (2) and to ensure the all-important and always expected assurance of food safety. Furthermore, new/emerging processes and related equipment, testing procedures, safety systems, and packaging materials will lead to advances in the overall systems for food handling and delivery. Therefore, these innovations should have minimal adverse impact on the color, texture, and other sensory characteristics of food. Many plant-based foods, including fruits, are subjected to cooking or processing to increase their edibility and palatability. Juices are often pasteurized (c. 85
C, 30 s), and the processing conditions for obtaining pure´e/paste from several fruits depend on the physicochemical characteristics of the considered fruit, its maturity, and ripening conditions, as well as the final purpose of the product. The combined effect of depectination and pasteurization decreases the nutritional

Emerging Technologies for Food Processing http://dx.doi.org/10.1016/B978-0-12-411479-1.00004-8

65 Copyright © 2014 Elsevier Ltd. All rights reserved.

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4. HIGH-PRESSURE PROCESSING OF FRUITS AND FRUIT PRODUCTS

particularly good candidates for this technology. HPP could preserve the nutritional value and the fragile sensory properties of fruits and fruit products due to its limited effect on the covalent bonds of low molecular mass compounds. Food treated with HPP technology at or near room temperature will not undergo significant changes. However, to achieve thorough destruction of both vegetative cells and spores in low-acid foods, elevated pressures are often required to achieve commercially sterile conditions. HPP technology is often combined with temperature or other conventional preservation methods in order to enhance microbial inactivation. Lower process intensities can then be used. However, these treatments need low storage and distribution temperatures to preserve the microbial, sensory, and nutritional quality of the treated food. Even so, HPP treatment has the potential to be used for sterilizing food, including low-acid products, if it is applied at elevated temperature (60e90
C) and using the temperature increase due to adiabatic compression. By choosing the appropriate process conditions, it is possible to completely inactivate both vegetative cells and microbial spores and to obtain food products that are shelf-stable (Matser et al., 2004; Black et al., 2007). The principal unwanted changes in processed fruit and fruit products are off-flavors, discoloration, softening (loss of texture or juiciness), and water loss. As perishable products, processed fruit and fruit products are generally characterized by an irreversible loss of quality. Therefore, the sensory quality of this type of product can never improve during further storage; quality can only be retained, or its deterioration can be retarded by using optimal processing and packaging techniques, storage temperatures, and also potentially the application of an enzymatic browning inhibitor (e.g., Guerrero-Beltra´ and Barbosa-Ca´novas, 2004; Mauricio-Iglesias et al., 2011; Perera et al., 2009; Polydera et al., 2005). The effect of HPP can vary depending on processing conditions (pressure, hold time, pH, and temperature) and form (whole fruit, pure´e, or juice). The food matrix can be altered by these variables, consequently impacting the effectiveness of HPP. The type of plant material (i.e., species) is also important, but less is known about the impact of cultivar within species on food quality on the effectiveness of HPP. Fruits and fruit products, like any other food, are complex systems and HPP could have several simultaneous effects, such as cell wall and membrane disruption (e.g., Van Buggenhout et al., 2005), changing enzyme catalyzed conversion processes (e.g., Castro et al., 2006a; Verlent et al., 2004, 2005; Jolie et al., 2012), modification of biopolymers, including enzyme inactivation, protein denaturation, and gel

formation (e.g., Castro et al., 2006b; Balny et al., 2002; Kolakowski et al., 2001; Kunugi and Tanaka, 2002; Ludikhuyze et al., 2003; Randolph et al., 2002; Van der Plancken et al., 2005), and altering chemical reactions (e.g., Nguyen et al., 2006; Oey et al., 2006). This chapter is intended to review the main findings related to the effect of HPP on fruits and fruit-based products from 2004 onward.

4.2 PHYSICOCHEMICAL PARAMETERS The effect of HPP on a number of physicochemical properties of fruit juices and pure´es/pastes has been reported in several papers. Changes in parameters such as pH, titratable acidity,
Brix, and total soluble solids are compiled in Table 4.1. In general, it seems that the physicochemical parameters are not significantly affected by the applied conditions of HPP immediately. However, several undergo substantial subsequent changes under refrigerated storage, which can mostly be attributed to partial enzyme inactivation of enzymes such as pectin methylesterase (PME) and polygalacturonase (PG), together with rapid microbial growth. However, it is widely reported in the literature that HPP gives better quality and safety parameters compared to thermal processing, as will be further discussed in this chapter. It should be mentioned that part of the efficacy of HPP treatments in food processing is attributed to the pressure-induced pH change (Stippl et al., 2005; Samaranayake and Sastry, 2010; Min et al., 2010). The direction and magnitude of the pH shift must be determined for each food. In general, food samples exhibit a buffering action under pressure-resisting changes in pH, due to the presence of weak acids and other components. According to Samaranayake and Sastry (2013), the pH of fruit juices remained almost unchanged up to 100 MPa, and then gradually dropped and leveled off beyond 500 MPa. There was a maximum pH drop of 0.3 pH units over the entire pressure range (0.1e800 MPa). It is known that reduced pH is beneficial in synergy with pressure in eliminating microorganisms, and these conditions inhibit the recovery or outgrowth of sublethally injured cells (Davidson and Taylor, 2007). Nevertheless, Giron (2005) observed no significant effect on the HPP inactivation of Lactobacillus plantarum when acid antimicrobials were added. Samaranayake and Sastry (2013) reported that the pressure-dependent pH change is apparently independent of the concentration of added antimicrobial acids. So, the addition of these acids to enhance pressure effects should be carefully evaluated.

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4.2 PHYSICOCHEMICAL PARAMETERS

TABLE 4.1 Effect of HPP on Several Physicochemical Properties of Some Fruit and Fruit Products Product

Treatment Conditions

Main Effect

References

Blueberry juice

200e600 MPa/20e42
C/ 5e15 min

No significant changes in pH and
Brix.

Barba et al. (2013)

Navel orange juice

500 and 600 MPa/40
C/4 5 min, followed by storage (0e30
C, 64 days)

Limited cloud loss and small decrease in viscosity, even at elevated storage temperature.

Polydera et al. (2005)

Orange juice

600 MPa/20
C/1 min, followed by storage (4 and 10
C, 12 weeks)

pH,
Brix, TA, and viscosity were not affected immediately after HP and subsequent storage. The degree of clarification and browning index increased significantly over time.

Bull et al. (2004)

Orange juice mixed with milk

100e400 MPa/20e42
C/ 2e9 min

No significant changes in pH and
Brix. Significant decrease in turbidity for all times when pressure was higher than 200 MPa.

Barba et al. (2011)

Passion fruit juice

300 MPa/25
C/5 min

Pressurized juice minimizes loss of sensory and nutritional quality.

Laboissie`re et al. (2007)

Pomegranate juice

350e550 MPa/30e50 s

Changes in pH,
Brix and TA, after 15 days of refrigerated storage.

Varela-Santos et al. (2012)

Pomegranate juice

400 MPa/5 min, followed by storage (4
C, 90 days)

The pH, TSS, and TA did not show significant change immediately after HPP and during storage.

Chen et al. (in press)

Several fruit juices

Up to 800 MPa/25
C/2 min

pH of fruit juices remained almost unchanged up to 100 MPa, and then gradually dropped and leveled off beyond 500 MPa. Acidification of tomato juice indicated that the pressuredependent pH change is independent of the concentration of added antimicrobial acids.

Samaranayake and Sastry (2010)

Watermelon juice

300, 600, and 900 MPa/60
C/ 5, 20, 40, and 60 min

Browning was avoided for pressures higher than 600 MPa.

Zhang et al. (2011)

FRUIT JUICES

FRUIT PURE´ES/PASTES Pineapple pulp

300 MPa/25
C/5 min

Pressurized ready to drink juice revealed higher sensory quality, as compared to commercial juices.

Barros-Marcellini (2006)

Avocado paste

600 MPa/23
C/3 min, followed by storage (4
C, 45 days)

Just after pressure, pH changed significantly. pH values continued to decrease during the first 20 days storage, after which remained stable until the end of the storage.

Jacobo-Vela´zquez and Herna´ndez-Brenes (2010)

Guava pure´e

600 MPa/3 min, followed storage (4
C, 45 days)

Pulp pH presented a consistent decline during the first 20 days of storage.

Jacobo-Vela´zquez and Herna´ndez-Brenes (2010)

Nectarine pure´e

450 and 600 MPa/10
C/5 and 10 min, followed by storage (5
C, 60 days)

pH, TA, and
Brix were not affected immediately after subsequent refrigerated storage.

Garcı´a-Parra et al. (2011)

Tomato pure´e

400 MPa/25
C/15 min

pH,
Brix, and viscosity increased after pressure application.

Sa´nchez-Moreno et al. (2006)

Melon pieces

600 MPa/room temperature/ 10 min, followed by storage (4
C)

No impact was observed for
Brix and TA just after pressure. An increase in TA was observed during storage.

Wolbang et al. (2008)

Nectarine halves

200e600 MPa/10
C/3 min, followed by stored (5
C, 30 days).

The pH decreased as a consequence of the AA and calcium lactate addition, while the soluble solids content and the acidity were not affected by HPP.

Miguel-Pintado et al. (in press)

FRUIT PIECES/SLICES

Abbreviations: HP, high pressure; TA, titratable acidity; TSS, total soluble solids; AA, ascorbic acid.

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4. HIGH-PRESSURE PROCESSING OF FRUITS AND FRUIT PRODUCTS

4.3 COLOR Color of fruit and vegetable juices remains a key factor influencing consumers’ acceptability, and it is often evaluated in the quality control procedures of different juice manufacturers. It has also been used by researchers as an indicator of the organoleptic and nutritional quality of foods during preservation/processing treatment and subsequent storage, because it is connected with the perception of some characteristics that appear to be representative of the quality of processed juices. The most important pigments in fruits are the carotenoids and anthocyanins, which are responsible for the orange-yellow and red, and red to blue color of fruits, TABLE 4.2

respectively. Although carotenoids are pressure stable at room temperature, anthocyanins are rather stable during HPP at moderate temperatures (Garcia-Palazon et al., 2004). So, changes in the color attributes of pressure-treated products are closely related not only to the pigments’ stability, but also to the (in)activation of browning-related enzymes under pressure conditions. In many fruit products, including fruit juices, jams, and pure´es, color is generally preserved during HPP at ambient temperature (Guerrero-Beltra´n and Barbosa-Ca´novas, 2004; Guerrero-Beltra´n et al., 2005, 2006), which indicates its limited effect on pigments (Ahmed et al., 2005; Oey et al., 2008b). Pressurized mango pulps (100e400 MPa/20
C/15e30 min) showed

Effect of HPP on Color of Some Fruit and Fruit Products

Product

Treatment Conditions

Main Effect

References

320 MPa/50
C

There was no obvious increase in color.

Guangyuan et al. (2007)

FRUIT JUICES Apple juice

MPa/40
C/45

Navel orange juice

min, 500 and 600 followed by storage (0e30
C, for 64 days)

Lower rates of color change compared at all storage temperatures studied, except at 30
C.

Polydera et al. (2005)

Strawberry juice Tomato juice

300e700 MPa/65
C/60 min, at different pH values (2.5, 3.7, and 5.0)

No significant changes were observed related to color degradation of tomato, while for strawberry samples only at pH 3.7 and 5 there was a significant increase.

Rodrigo et al. (2007a)

Avocado paste

600 MPa/23
C/3 min, followed by storage (4
C, 45 days)

Significant decrease in redness and yellowness in HP-treated avocado paste only at the end of the storage.

Jacobo-Vela´zquez and Herna´ndez-Brenes (2010)

Blackberry and strawberry pure´es

400, 500, 600 MPa/10e30
C/15 min

Color differences were minor for pressure-treated pure´es.

Patras et al. (2009)

Tomato pure´e

400e600 MPa/20
C/15 min

An increase in total lycopene tomato pure´e.

Qiu et al. (2006)

Color remained unchanged after pressure/temperature treatment.

Rodrigo et al. (2007a)

The total color difference increased as storage time increased. However, this color difference was barely noticeable after 27 days of storage for natural pure´e and pure´es containing ascorbic acid and cysteine.

Guerrero-Beltra´n et al. (2005)

Highest carotenoids extractability was also found in treated at the lowest pressure treatment intensity and holding time (450 MPa/5 min).

Garcı´a-Parra et al. (2011)

600 MPa/3 min, followed by storage (4
C, 45 days)

Instrumental color values did not change significantly during the evaluated storage period.

Jacobo-Vela´zquez and Herna´ndez-Brenes (2010)

600 MPa/20
C/1e5 min, followed by storage (4
C, 4 weeks)

During the 4-week storage in a bag, visible color changes were not observed.

Perera et al. (2009)

FRUIT PASTES/PURE´ES

Mango pure´e, with antibrowning agents

379e586 MPa/0e20 min, followed by storage (31
C, 27 days)

Nectarine pure´e

Guava pure´e

FRUIT PIECES Apple cubes in pineapple juice (0e50% v/v, 20
Brix)

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69

4.4 TEXTURE

no visual color differences immediately after HPP treatment (Ahmed et al., 2005), indicating pigment stability. However, there was a subsequent decrease in color during storage. Significant changes under refrigerated storage are often attributed to incomplete enzyme inactivation (e.g., b-glucosidase, peroxidase, and polyphenol oxidase) (Garcia-Palazon et al., 2004; Suthanthangjai et al., 2005; Patras et al., 2009), enzyme-substrate specificity toward pressure treatments (Gimenez et al., 2001), and the presence of ascorbic acid (AA) (Kouniaki et al., 2004), which can result in undesired biochemical reactions in the food matrix. Table 4.2 summarizes the main recent studies related to color in fruit and fruitrelated products. Although HPP at ambient temperature has a limited effect on pigments, when combined with elevated temperatures it can induce color losses. A recent work related to pelargonidin-3-glucoside, one of the major anthocyanins, was done using strawberry paste (Verbeyst et al., 2010). For all the applied thermal (80e130
C) and pressure/temperature processes (200e700 MPa, 80e130
C), the degradation kinetics followed a firstorder model and there was synergistic effect of temperature and pressure on the degradation rate, although the effect of increasing pressure was smaller than that of increasing temperature. Pressure seemed to play an additional role in enhancing the degradation rate of anthocyanins. The shorter treatment times used during these processes (due to fast heating and cooling rates) might lead to a lower integrated process impact comparison to an equivalent thermal process. According to Van der Plancken et al. (2012), carotenoids are also affected when fruit products are submitted to pressure/elevated temperatures. The effect of temperature in HPP on several pigments is strongly dependent on the effect on carotenoids (e.g., a- or b-carotene and lutein). Color pigments can also interact with food structure and result in both color and translucency/opacity changes. Texture modifications may result in changes in the nature and extent of internally scattered light and the distribution of surface reflectance (Oey et al., 2008b). Besides the instability of color pigments, browning plays an important role in the discoloration of pressure-treated fruit products. Enzymatic browning of phenols, AA oxidation, caramelization, formation of brown-red polymers by oxidized lipids, and Maillard reactions are the main reasons for browning in processed/ stored peeled or sliced fruits, according to Tortoe et al. (2007) and Vaikousi et al. (2008). However, browning by oxidation and polymerization of phenols could be avoided by storing the fruit at low temperatures (Zhou et al., 2008). At low storage temperatures, enzymatic browning occurs due to partial inactivation of polyphenol oxidase, but treatments can be combined with AA and cysteine in order to enhance the storage stability

of HPP fruit products (Guerrero-Beltra´n et al., 2005). In-pack browning of pressure-treated products also depends on the packaging material and its oxygen permeability (Polydera et al., 2003; Perera et al., 2009).

4.4 TEXTURE The textures of fruits and vegetables are highly dependent on the chemistry and physical properties of the cell walls. Much research has been done on plant cell walls in relation to texture, considering the mechanical properties of plant tissues (e.g., Van Buggenhout et al., 2009). The observed effects are dependent on the pressure/temperature/time conditions and the type of fruit. Thermal processes, such as blanching, cooking, pasteurization, and sterilization, are known to result in softening. Changes in cell biopolymers occur during HPP treatments. Pressure induces changes in polysaccharides, which can affect their functionality and the texture/structure of plant-based food products (Cano and de Ancos, 2005). Softening occurs partly as a result of the solubilization and depolymerization of pectic polymers that are involved in cellecell adhesion (e.g., Van Buggenhout et al., 2009). Basak and Ramaswamy (1998) also concluded that the initial loss of firmness of several fruits and vegetables, such as apples, pears, oranges, pineapples, carrots, celery, and green and red peppers, around 100 MPa, is associated with loss of turgor due to membrane disruption. At 100 MPa, the pear was the most pressure-sensitive fruit followed by apples, pineapples, and oranges, while at 200 MPa, the apple was more sensitive than the pear. During HPP, there are several cell wall polymer transformations which occur due to both enzymatic and nonenzymatic reactions (Sila et al., 2008). Substrates, ions, and enzymes, which are located in different compartments in the cell, can be released and interact with each other during and after pressure treatments. Even though disruption of cellular compartmentalization can be sometimes desired as it may lead to improved bioaccessibility (Verlinde et al., 2008) and the extraction yield (Oey et al., 2008a) of certain compounds, it can have a negative impact on quality parameters. Under certain conditions, pressure can enhance the action of PME (Castro et al., 2006b), lower the activity of PG (mostly at moderate temperature) (Rodrigo et al., 2006), and retard b-elimination (at elevated temperatures). Plant PMEs have different pressure/temperature stability (e.g., Castro et al., 2004, 2006a; Nunes et al., 2006; Rodrigo et al., 2006, 2007a), depending on the type and maturity of the fruit. As a consequence, pressure/temperature combinations can be used to (in) activate some specific texture-related enzymes during processing, in order to create textures that cannot be

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4. HIGH-PRESSURE PROCESSING OF FRUITS AND FRUIT PRODUCTS

formed by thermal processing. Moreover, mild pressure/temperature conditions can also be used as a pretreatment, or as an alternative mode of preserving the textural properties of thermally processed fruits, because it significantly retards the rate of thermal softening (Sila et al., 2004; Shahidul Islam et al., 2007; Castro et al., 2008). Improved texture retention due to mild conditions can be correlated with strengthened intercellular adhesion (Canet et al., 2005). The increased positive effect of temperature, within the range of 40e55
C, when combined with pressures up to 400 MPa, is attributed to the enhancement of PME catalytic activity (Castro et al., 2006b) and, consequently, the extensive modification of pectins in terms of their demethoxylation (Sila et al., 2004, 2008). Moreover, when PG is not present, HPP can be combined with pretreatments, such as infusion with exogenous pectinases (Duvetter et al., 2005) and/or soaking in calcium chloride solutions (Sila et al., 2006; Castro et al., 2007; Sirijariyawat et al., 2012), which can also result in increased firmness of the processed fruits. However, the use of thermal stimulation of endogenous PME in the context of texture engineering of plant-based foods is limited when PG or other detrimental enzymes present in the tissue are also stimulated by the thermal treatment. During treatments up to 400 MPa, the high activities of both tomato PME and tomato PG cause a drastic loss in consistency (Verlent et al., 2007), because PG is able to depolymerize the pectin that has been demethylated by PME. Thus, the level of the pressure treatment should be carefully chosen to obtain the desired rheological properties of tomato-based products. Besides texture, HPP treatments can also affect the rheological properties of fruit products. Ahmed et al. (2005) reported that the viscosity of mango pulp increased after HPP at 100 or 200 MPa (20
C/15 or 30 min), while a reduction in viscosity was observed after HPP at 300 and 400 MPa (20
C/15 or 30 min). For some fruit juices, cloud stability is also an important quality aspect. Pressure-treated orange juice (600 MPa/ 40
C/4 min) showed higher viscosity than samples given a thermal treatment (80
C/60 s) (Polydera et al., 2005). In addition, during storage (0, 5, 10, 15, or 30
C for 64 days), and even at an elevated storage temperature (30
C), limited cloud loss and a small decrease in the viscosity of HPP juice were observed. A few studies have already been conducted at high pressure/high temperatures. Carrots, due to their high pectin content, show drastically altered textures when submitted to high temperature processes. When both thermally and pressure processed at elevated temperatures (80 or 100
C; 600 MPa/80
C), carrots showed an initial texture loss attributed to loss of turgor pressure, and HPP-treated carrots at elevated temperature, unlike thermally treated ones, did not undergo further

softening as the process continued (De Roeck et al., 2008). The improved retention of hardness under pressure could be due to inhibition of b-eliminative depolymerization and development of fortifying networks between the low methoxylated pectin and endogenous Ca2þ ions. In pectin model systems, b-eliminative depolymerization occurred at a lower rate, while demethoxylation took place at a higher rate during HPP at elevated temperatures (500e700 MPa, 90
C), in comparison to thermal heating at ambient pressure (De Roeck et al., 2009). The texture of carrots is predominantly determined by cell wall strength and degree of biopolymer cross-linking, rather than by turgor pressure (Furfaro et al., 2009). De Roeck et al. (2010) showed that, for processing conditions leading to the same microbial impact, both for pasteurization and sterilization purposes, HPP was a better option for retaining carrot hardness. The viscosity of tomato homogenate decreased considerably at pressures lower than 400 MPa, but increased at higher pressure levels, such as 500 MPa, when combined with temperatures up to 60
C (Sa´nchez-Moreno et al., 2006; Verlent et al., 2006).

4.5 FLAVOR Fruit juices are often pasteurized, and irreversible changes are produced in the flavor of the juice as a result of chemical reactions that are initiated or occur during thermal processing. The changes in flavor are also associated with a number of deteriorative reactions that take place during storage, giving rise to the development of off-flavors. As the effect of HPP on flavor is concerned, it is common to assume that HPP limits its major impact to noncovalent bonds, because the structure of small molecular compounds is not affected during processing. Therefore, HPP is often seen as a technology that can maintain the original products’ flavor. However, as previously mentioned, HPP can enhance and retard enzymatic and chemical reactions. In this sense, it could indirectly alter the concentrations of some flavor compounds, mainly during storage, and these changes could be sufficient to disturb the whole balance of flavor composition in fruits and fruit products. Rodrigo et al. (2007b) attributed different pressure stability to lipoxygenase and hydroperoxide lyase, which are naturally present in tomato and partly responsible for the development of the rancid taste often reported for tomato-related products e because they catalyze the oxidation of polyunsaturated fatty acids. Jacobo-Vela´zquez and Herna´ndez-Brenes (2010) used a trained panel to determine the sensory shelf-lifelimiting factor of HPP (600 MPa/23
C/3 min) avocado paste during refrigerated storage (4
C, 45 days). Sour and rancid favors were identified as the main sensory

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4.6 VITAMINS

descriptors (critical descriptors) that were able to discriminate stored from untreated samples. In contrast, the odor of the strawberry pure´e treated at 800 MPa at ambient temperature was perceived to be very similar to that of the untreated pure´e (0.1 MPa, 20
C) (Lille et al., unpublished). Also, Baxter et al. (2005) observed no differences in the concentration of volatile flavor compounds between freshly frozen, heat-treated (85
C/25 s), and HP-treated (600 MPa/18e20
C/60 s) navel orange juice. The results of the chemical analysis were supported by the results of a trained sensory panel and a consumer panel, which did not find any differences in odor or flavor between the differently treated orange juices. When HPP is applied at elevated temperatures (800 MPa, 60
C, 10 min), the overall flavor of strawberry pure´e showed a clear increase in dried fruit- and tea-like odor and a loss of acidity (Lille et al., unpublished). In tomato pure´e treated at 800 MPa (20 and 60
C, 10 min), a reduction in the intensity of fresh tomato odor was coupled with a decrease in the amounts of unsaturated aldehydes and other compounds present (Viljanen et al., 2011). Simultaneously with the loss of fresh tomato odor, an increased intensity of cooked tomato odor and tea aroma was perceived in HPP-treated samples processed at higher temperatures (800 MPa, 60
C). Sampedro et al. (2009) have studied the stability of aroma compounds under moderately thermal HPP (650 MPa, 2 min, 68
C after pressurization), and report that an increase of approximately 20
C led to a significant loss in 12 aroma compounds found in orange juice. Overall, HPP at ambient temperatures does not directly affect the flavor of fruit or fruit product. However, other factors should be taken into consideration, such as enzyme (in)activation, which could indirectly affect flavor. HPP at elevated temperature does not appear to be the ideal substitute for thermal processing with regard to either tomato or strawberry flavor. In addition, a lot of research needs to be conducted to explore the effect of both pressure treatment and the packaging material on the volatility profile of in-pack food products due to interactions between food and packaging, such as permeation, sorption, and migration. It seems that temperature might be a critical parameter in in-pack HPP food products (Mauricio-Iglesias et al., 2011).

4.6 VITAMINS Several reports concerning the loss of bioactive compounds, such as vitamins, and antioxidant activities in fruit and fruit products after HPP have been published. Vitamins can be categorized as either water- and

71

fat-soluble. Water soluble vitamins, including vitamin C and those of the vitamin B group, are generally more unstable than fat-soluble vitamins (including vitamins A, D, E, and K). Vitamin A is often reported in relation to the total or specific carotenoid content. Total carotenoids found in fruits and vegetables are relatively stable to preservation by HPP and conventional thermal processing, as previously discussed. The vitamin A content of persimmon pure´e increased 45% as a result of the application of HPP (de Ancos et al., 2000). Vitamin C and vitamins B1 (thiamin) and B3 (folate) are some of the most unstable toward heat, light, and/ or oxygen. No significant loss of vitamin B1 and B2 content has been reported due to HPP (400e600 MPa/ 25
C/30 min) in model solutions (Sancho et al., 1999), and retention was higher than following thermal treatment. Thiamin, an extremely heat sensitive vitamin was unaffected by HPP in the same model system. Vitamin C, especially in orange juice, has received much attention when aiming at evaluating the effect of new/emerging processing technologies on phytochemicals. Researchers have used AA as a quality indicator in fruits because it is a sensitive bioactive compound that provides an indication of the loss of other vitamins and therefore acts as a valid criterion to evaluate the impact of the treatment on other organoleptic or nutritional components. Numerous researchers have investigated the effect of HPP on the stability of AA in controlled buffer/model systems, as well as in food products. AA is not significantly affected by HPP in a number of fruit products (Sa´nchez-Moreno et al., 2009). In buffer solution, a higher AA degradation rate, through the aerobic pathway, has been observed during adiabatic heating/ pressure build up, taking place at relatively low pressure level, around 100 MPa (Oey et al., 2006). Mild pressures (100e400 MPa) when combined with mild temperatures (30e60
C) maintain AA content in orange juice (Plaza et al., 2006; Sa´nchez-Moreno et al., 2006). When the pressure level is increased (400e600 MPa) and the temperature decreased to around room temperature, the AA content is also preserved (Bull et al., 2004; Torres et al., 2011). Increasing pressure level and/or prolonging pressure treatment has no/little effect on AA degradation for mild pressure-temperature conditions. In addition, HPP orange juices better maintained the vitamin C during more days of refrigerated storage than low pasteurized treated juice (70
C/30 s) (Plaza et al., 2006). However, AA loss was found to be higher during HPP (400 MPa/ 42
C/5 min) for orange juice samples when compared to high pasteurized samples (90
C/20 s) (Esteve and Frı´gola, 2008), which could be due to limited enzyme inactivation, and possibly pressure activation, at the applied conditions. Nevertheless, it has been reported that a small decrease occurs in the AA content during refrigerated storage (Bull et al., 2004; Plaza et al., 2006). Differences

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in AA pressure stability during storage could be explained by the initial oxygen content, and possibly endogenous prooxidative enzyme activity, especially ascorbate oxidase and peroxidase. To date, few studies have been carried out to evaluate the effect of HPP on phytochemicals of fruit juice-milk beverages. High AA retention (91%) in an orange juice-milk beverage after HPP (100e400 MPa/2e9 min) treatment was reported (Barba et al., 2011). In general, it can be concluded that AA is unstable at high-pressure levels when combined with high temperatures (above 65
C), and the major degradation is caused by oxidation, especially during adiabatic heating. Therefore, eliminating the oxygen from the packaging can decrease the AA degradation during processing and subsequent storage (Oey et al., 2008a).

4.7 MICROORGANISMS Contamination sources for fresh-cut fruits and vegetables include raw materials and contact with processing equipment. Spoilage microorganisms exploit the host using extracellular lytic enzymes that degrade these polymers to release water and the plant’s other intracellular constituents, to be used by the microorganisms as nutrients for their growth. Fungi, in particular, produce an abundance of extracellular pectinases and hemicellulases that are important factors in fungal spoilage (Miedes and Lorences, 2004). Successful implementation of a novel technology for food preservation relies on progress in mechanisms of inactivation. HPP has the potential to produce high-quality foods that are microbiologically safe and have an extended shelf life. As a food preservation technology, the utility of HPP is due to the destruction suffered by the microbial population, which allows a substantial increase in shelf life and improves food safety (Considine et al., 2008). To determine the appropriate conditions (pressure range, processing temperature, initial temperature of sample, holding time, and packaging type) for HPP, it is essential to know the precise tolerance levels of different microbial species regarding pressure, and also the mechanisms by which this tolerance level can be minimized. The high acidity (pH < 4.6) of most fruit juices does not allow the growth of pathogens and most bacterial spores. However, unpasteurized fresh juices with low acidity (pH > 4.6) and high water activity (Aw > 0.85) can support the growth of a variety of pathogenic microorganisms. Still, pressurization of food causes an increase in ionization, which leads to a decrease in pH (Patterson, 2005), which can act synergistically with the processing conditions to eliminate microorganisms and inhibit the recovery or outgrowth of sublethally injured cells. The inappropriate use of HPP

parameters may adversely affect the outcome of this technology. The cell membrane is often considered to be the first site of injury in pressure-inactivated bacteria. However, membrane damage in some bacterial strains appears later than cell death (Ananta and Knorr, 2009), indicating that the loss of the integrity of the cell membrane is not enough to explain the pressure inactivation process of bacteria. The internal cell structure is also modified, as mentioned by Moussa et al. (2007), after the application of pressure (up to 550 MPa, at room and sub-zero temperatures) to Escherichia coli. Moreover, gram-positive bacteria are more resistant to environmental stresses than are gram-negative bacteria, due to the complexity and abundance of protein, phospholipids, and lipopolysaccharide in the gram-negative outer wall (Patterson, 2005; Pilavtepe-Celik et al., 2008). Cocci are also more resistant than rod or spirochete-shaped bacteria (Patterson, 2005). In general, the larger and more complex the organism, the easier it is to inactivate. Bacterial spores are the most resistant group and they cannot be significantly inactivated by pressure alone. Therefore, combined pressure and temperature treatments have been proposed as a method of producing shelf-stable low-acid foods (Patterson, 2005). Temperatures in the range of 45e50
C appear to increase the rate of inactivation of food pathogens and spoilage microorganisms. Temperatures ranging from 90 to 110
C in combination with pressure 500e700 MPa have been used to inactivate spore-forming bacteria, such as Clostridium botulinum and Bacillus amyloliquefaciens (e.g., Margosch et al., 2006). Also, spores from Alicyclobacillus acidoterrestris, one of the major problems in spoilage in the fruit industry worldwide, were reported by (Silva et al., 2012) to inactivate at 45
C and 600 MPa in orange juice, and at 65
C only 200 MPa was needed to achieve a reduction in spore numbers. Pressure treatments of 600 MPa at 80
C (one cycle of 15 min, three cycles of 5 min, or five cycles of 3 min) were reported to achieve 5.7 log cycles inactivation in pineapple juice (Aw 0.93) and nectar (Aw 0.94) (Ferreira et al., 2009). Castro et al. (2008) showed that pressurized (100 and 200 MPa, 10 and 20 min) green and red pepper samples presented a microbial content for total mesophilic counts, enterobacteriaceae and total and fecal coliforms, comparable to those obtained by thermal blanching and below the maximum acceptable values, indicating conformity of the processed peppers for consumption. Higher pressures (800e900 MPa) can still be used to discriminate the spore strains according to their pressure resistance (Ramaswamy et al., in press). In contrast to bacteria, yeasts are eukaryotic cells and thus possess mitochondria. Besides cell membrane injury/disruption, it appears that mitochondria could be one of the elements

I. HIGH PRESSURE PROCESSING

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which are altered by the pressure inactivation process (Brul et al., 2000). Yeasts, molds, and vegetative bacteria vary in their response to pressure, depending on factors such as species, strain, processing temperature, and substrate. Ascospores of heat-resistant molds appear to be more pressure resistant, and many of them are not inactivated in the pressure range 300e800 MPa. Most often there is a need for minimal pressure level of 600 MPa for 10e15 min in combination with temperatures of 60e90
C for their inactivation (Ferreira et al., 2009). Their vegetative counterparts are much more pressure sensitive, having sensitivities similar to yeasts (Ludwig, 2003). It is hypothesized that pressure acts on the permeability and rigidity of the ascospores wall that, in turn, increases their permeability to water. This rehydration is the first step in the course of spore germination (Black et al., 2007). Currently, high-pressure processed products are low pH fruit juices (grapefruit juice, mandarin juice, and apple and orange juice), jams, jellies, fruit dressing, and avocado (Ohlsson, 2002). HPP is, in general, effective in inactivating most vegetative pathogenic and spoilage microorganisms at pressures above 200 MPa at chilled or process temperatures less than 45
C, but the rate of inactivation is strongly influenced by the peak pressure (Patterson, 2005; Lau and Turek, 2007). Commercially, higher pressures are preferred as a means of accelerating the inactivation process, and current practice is to operate at 600 MPa, with the exception of those products in which protein denaturation needs to be avoided. The pressure resistance of vegetative microorganisms often reaches a maximum at ambient temperatures, so the initial temperature of the food prior to HPP can be reduced or elevated to improve inactivation at processing temperature.

4.8 CONCLUSIONS Since the appearance of the first fruit juices pasteurized by high pressure on the commercial market, in the early 1990s in Japan, several other fruit-based products processed by high pressure have entered the market. These types of products have shown a high rate of commercial expansion in the last few years, mainly due to their natural, fresh, and raw-like characteristics (sensorial, nutritional, and functional), which can be obtained after cold high-pressure pasteurization. Two examples are elucidative. First, Starbucks entered this business in the first quarter of 2012, having acquired a company (Evolution Fresh) that was already producing high-pressure pasteurized fruit juices. Second, a few months ago, another company (Harmless Harvest) launched commercially a “raw” tea, produced by extraction under pressure.

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It is expected that this sector will show very interesting commercial developments, as well as the appearance of novel products, in the near future.

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I. HIGH PRESSURE PROCESSING