Present and Future of High Pressure Processing: A Tool for Developing Innovative, Sustainable, Safe and Healthy Foods

Developed for academic researchers and for those who work in industry, Present and Future of High Pressure Processing: A Tool for Developing Innovative, Sustainable, Safe, and Healthy Foods outlines innovative applications derived from the use of high-pressure processing, beyond microbial inactivation. This content is especially important for product developers as it includes technological, physicochemical, and nutritional perspectives.This book specifically focuses on innovative high-pressure processing applications and begins with an introduction followed by a section on the impact of high-pressure processing on bioactive compounds and bioaccessibility/bioavailability. The third section addresses the ways in which high-pressure processing can assist in the reduction of toxins and contaminants, while the fourth section presents opportunities for the use of high-pressure processing in the development of healthy and/or functional food. This reference concludes with an analysis of the challenges regarding the use of high-pressure processing as an innovative application.

• Explores the use of high-pressure processing as a tool for developing new products
• Outlines the structure and improved functional properties provided by high-pressure processing
• Illustrates potential applications and future trends of high-pressure processing
• Explains the mechanisms that influence the impact of high-pressure processing
• Highlights the optimal conditions for high-pressure processing to develop certain food products
• Defines the challenges and future perspectives in the use of high-pressure processing for food product development

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 22, 2020
• ISBN: 9780128172667

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China

Section 1

Introduction

Chapter 1: An overview of the potential applications based on HPP mechanism

Kashif Ghafoora; Mohsen Gavahianb; Krystian Marszałekc; Francisco J. Barbad; Qiang Xiae; Gabriela I. Denoyaf,g    a Department of Food Science and Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh, Saudi Arabia

b Product and Process Research Center, Food Industry Research and Development Institute, Hsinchu, Taiwan, ROC

c Prof. Wacław Dąbrowski Institute of Agricultural and Food Biotechnology, Department of Fruit and Vegetable Product Technology, Warsaw, Poland

d Preventive Medicine and Public Health, Food Sciences, Toxicology and Forensic Medicine Department, Faculty of Pharmacy, Universitat de València, Valencia, Spain

e Key Laboratory of Animal Protein Food Processing Technology of Zhejiang Province, College of Food and Pharmaceutical Sciences, Ningbo University, Ningbo, China

f National Institute for Agricultural Technology (INTA), Food Technology Institute, Hurlingham, Buenos Aires, Argentina

g National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina

Abstract

Over the last decades, high-pressure processing (HPP) has shown its potential as one of the most relevant technologies for nonthermal food processing mainly due to its application for microbial inactivation while retaining fresh-like characteristics of the food. Moreover, HPP can be considered as a potential tool for developing new food products with new sensorial and functional properties. Apart from food preservation, the application of HPP to improve health attributes (e.g., reducing food contaminants or salt concentration), and to enhance the extraction or fermentation processes, has been an interesting research topic around the world. This chapter intends to show the core-base processing characteristics of HPP, highlight the advantages and limitations of this nonthermal processing, and discuss the potential applications of HPP in the food industry.

Keywords

High-pressure processing; Basic principles; Mechanism of action; Applications

Acknowledgments

Francisco J. Barba acknowledges the EU Commission for the funds provided by the BBI-JU through the H2020 Project AQUABIOPROFIT Aquaculture and agriculture biomass side stream proteins and bioactives for feed, fitness and health promoting nutritional supplements (Grant Agreement no. 790956).

1: Introduction

One of the major targets of different food preservation methods is the inactivation of pathogenic microorganisms and the effectiveness of such methods is of paramount importance to achieve this objective (Barba, de Souza Sant’Ana, Orlien, & Koubaa, 2017).

Foodborne diseases, which are caused due to the presence of certain pathogenic microorganisms and chemicals in foods, are responsible for the illness of huge populations around the globe and, in some cases, these illnesses may prove to be fatal. Pathogenic bacteria such as Salmonella spp., Listeria monocytogenes, Campylobacter spp., and Escherichia coli O157:H7 are examples of the most important causative organisms for such diseases (Barba, Koubaa, do Prado-Silva, Orlien, & Sant’Ana, 2017). The other foodborne microorganisms that may pose different health-related concerns and food product quality include viruses, bacterial spores, and yeast (Barba, Koubaa, et al., 2017; Kultur et al., 2018).

The development and innovation in food preservation techniques have helped in the commercialization of new products and progresses of the food industry. Pathogens adapt to stressful conditions during preservation and storage of foods and hence continuous improvement and innovation in food processing are essential to ensure food safety. Pasteurization and sterilization (heat application), freezing and chilling (temperature reduction), the addition of salt and sugar and drying (water activity reduction), and the use of preservatives are some of the traditional methods of food preservation (Misra et al., 2017).

The effectiveness of these methods should be explored to ensure that the pathogenic microorganisms are unable to regrow after the process according to the levels determined by food safety organizations (Barba, Koubaa, et al., 2017). Conventional processing methods sometimes negatively affect the consumer acceptance as they are associated with certain deleterious changes in the nutritional, physicochemical, and sensorial attributes of food products (Farahnaky, Azizi, & Gavahian, 2012; Gavahian, Farahnaky, Javidnia, & Majzoobi, 2012). These concerns in addition to other environmental effects of conventional methods have resulted in the development of novel techniques that may be regarded as mild technologies (Barba, Koubaa, et al., 2017; Feng, Ghafoor, Seo, Yang, & Park, 2013; Lee et al., 2015; Misra et al., 2017).

The presence of endogenous enzymes and their activity also affect the storage stability of different food products in addition to microorganisms. For instance, in case of whole fruits, the enzymes and their substrates are segregated in separate compartments. However, in fruit pieces, purées, and juices, some cell compartments are damaged and enzymes could interact with substrates, catalyzing oxidative reactions, which results in poor quality attributes. Polyphenol oxidase (PPO), β-glucosidase (GLC), peroxidases (POD), and lipoxygenase (LOX) are examples of oxidative enzymes responsible for detrimental changes in color, flavor, and nutritional value.

PPO and POD are the most important enzymes responsible for browning of fruit and vegetable products during processing and storage. PPOs lead to hydroxylation of monophenols to o-diphenols as well as the oxidation of diphenols to quinones. All of these chain reactions are responsible for the formation of brown pigments. POD participates in several plant metabolic processes such as the catabolism of auxins, lignification of the cell wall, as well as browning reactions, resulting in products that participate in the oxidation of various electron donors with H2O2 (Marszałek, Doesburg, et al., 2019).

The synergistic effect of PPO and POD to catalyze oxidative reactions have been proved by using substrates such as chlorogenic acid and catechol (Marszałek et al., 2018). Moreover, peroxidases contribute to the processes that lead to the oxidative crosslinking of cell wall polysaccharides. Hence, the inactivation of different quality-deteriorating enzymes is one of the objectives of food preservation in order to ensure shelf-life stability of various food products.

Another example of deteriorating enzymes is related to the texture of fruits and vegetables, which depends on the composition of the cell wall and middle lamella. Pectin methylesterase (PME) and polygalacturonase (PG) are important enzymes with regard to the texture of fresh produce as they are involved in the breakdown of pectin network that surrounds the cellulose backbone of the cell wall. The breakdown of pectin due to synergistic effects of these two enzymes results in textural changes in fruits and vegetables and their products such as juices and purees. These enzymes could also reduce the cloud stability in juices (Chakraborty, Kaushik, Rao, & Mishra, 2014; Marszałek, Krzyżanowska, Woźniak, & Skąpska, 2016).

High-pressure processing (HPP) technology is a novel food preservation method which has started to be implemented widely in meat and fruit and vegetable beverages sectors mainly due to its ability to inactivate tissue enzymes, pathogenic and spoilage microorganism, and simultaneously preserving food products’ nutritional and sensorial quality characteristics (Barba, Terefe, Buckow, Knorr, & Orlien, 2015; Kultur et al., 2018).

The most representative HPP meat products available in the market include sliced ham, turkey or chicken cuts, ready-to-eat products, and whole pieces of cured ham. Fruit and vegetable products, mainly purees, juices, and beverages, represent ≈   40% of the global HPP food market (Barba et al., 2015; Huang, Wu, Lu, Shyu, & Wang, 2017; Misra et al., 2017). Seafood and ready-to-eat products are also really important from a commercial point of view. Moreover, apart from the common HPP application (as a preservation technology), it has the potential to be used for freezing, enzyme control, cold gelatinization of starch, protein unfolding, shucking of shellfish, enhancing mass transfer phenomena (e.g., cell-wall opening for extraction of high-added value compounds), and even for promoting microbial growth under mild processing conditions, thus enhancing fermentation processes and reducing time (Barba et al., 2015; Barba, Esteve, & Frígola, 2012). However, the level of pressure, temperature, and holding time, which are the main processing parameters determining HPP treatment, differ according to the targeted applications, being therefore of great importance to understand the mechanism influencing the different HPP applications as well as to optimize the HPP conditions (Barba, Koubaa, et al., 2017; Mota et al., 2018).

The elucidation of HPP-assisted microbial inactivation mechanisms can be related to the physiological and biochemical effects on the microbial cells (Barba, Criado, Belda-Galbis, Esteve, & Rodrigo, 2014; Barba, de Souza Sant’Ana, et al., 2017; Ghafoor, Kim, Lee, Seong, & Park, 2012). A general interpretation of the resistance to the HPP-assisted inactivation reveals that yeasts and molds are less resistant to this treatment whereas the Gram-positive microorganisms are most resistant within the vegetative form of the cells, possibly due to their cell wall structure. Moderate resistance is shown by Gram-negative microorganisms whereas bacterial spores are extremely resistant to HPP treatment even at very high pressure (1000 MPa). The microbial growth stage is also important for determining their pressure sensitivity. Microorganisms are more sensitive to pressurization treatment during log phase in comparison to the stationary phase. Different physical characteristics and the composition of the food can also affect the pressure-assisted inactivation of microorganisms (Barba, de Souza Sant’Ana, et al., 2017; Barba, Koubaa, et al., 2017).

The main challenge encountered by this treatment is the extension of shelf life of food through the inactivation of native tissue enzymes, which generally present more resistance to the HPP than most of the microorganism (Barba et al., 2012, 2014, 2015; Marszałek, Woźniak, & Skąpska, 2016; Marszałek, Woźniak, Skąpska, & Mitek, 2017). The application of HPP to carry out probiotic bacteria fermentation for producing fermented foods is among the latest trends in this area of the science (Mota et al., 2018).

The industrial application of HPP is increasing worldwide in the food sector and there are more than 300 HPP equipments being utilized, mainly in North America and Mexico (67%), and also in Europe (18%), Asia (8%), Latin America (3%), Oceania (3%), and Africa (1%) (Huang et al., 2017). Avure Technologies (Västerås, Sweden), Hiperbaric (Burgos, Spain), and UHDE High-Pressure Technologies (Hagen, Germany) are the main companies for industrial-scale equipment production, with horizontal and vertical vessel systems available for batch HPP equipment (Barba et al., 2016; Misra et al., 2017).

In batch systems, products have to be packed before HPP treatment for a certain period of time and predefined temperature and pressure to obtain the desired results. The batch process can be used for all kinds of food: liquid, semisolid, and solid. Fruit and vegetable juices, drinks, smoothies, and puree are generally prepacked in plastic bottles of different shapes, designed to fill the pressure chamber with the maximum amount of products. Generally, the products are prepacked at vacuum conditions in flexible packages for the elimination of air bubbles.

The new trend is the production of continuous or semicontinuous HPP equipment with the application of aseptic filing of HPP-treated liquid product. Avure Technologies Company offers semicontinuous systems for liquid beverages treatment such as juices. On the other hand, Hiperbaric has introduced a very recent solution that allows bulk processing of beverages with the largest currently available capacity of 10,000 L/h (Barba et al., 2016; Marszałek, Szczepańska, et al., 2019).

Commercial applications of HPP in the food industry use pressures in the range from 100 to 600 MPa at room temperature, whereas laboratory equipment can achieve pressures up to 1400 MPa, connected with cooling or heating systems. These pressures are extremely high in relation to other pressures observed in nature.

Industrial applications with the highest volume of 687 L and maximum pressure up to 310 MPa or 525 L with maximum pressure up to 600 MPa, generally work at ambient temperature or with mild heating up to 50°C. Semiindustrial applications with volumes below 150 L reaches temperatures up to 95°C and pressures up to 700 MPa (Barba et al., 2016; Barba, de Souza Sant’Ana, et al., 2017; Horita et al., 2018). Some laboratory-scale equipment can reach pressures and temperatures from 600 to 900 MPa and from 80°C to 180°C, respectively (Fig. 1), respectively, but the volume of the HPP chamber does not exceed 5 L. The highest pressure applied for food was 1400 MPa at temperatures up to 110°C in a chamber of 35 mL volume (Reineke, Mathys, Heinz, & Knorr, 2008).

Fig. 1 Laboratory HPP chambers with maximum pressure up to 600 MPa, at 80°C (A) and 900 MPa, at 180°C (B) (UNIPRESS Equipment, Warsaw, Poland).

High pressure can be generated in different ways: by an external pump, by a moving piston, or by heating of the medium in a closed chamber. In Batch systems, the pressure is transmitted by a low compressibility medium (e.g., water) and the process consists in three stages: (i) pressurization, (ii) maintaining the targeted pressure during the holding time, and (iii) depressurization. During the first stage, the liquid medium is pumped into the pressure chamber using pumps and pressure intensifiers. Once the desired level of pressure is achieved, the second stage starts and consists in holding the selected level of pressure during a targeted time.

After completing the holding time, the depressurization is applied, the pressure drops immediately. The level of pressure and holding time are process parameters that can be selected according to the food matrix and the expected final results while the maximum pressure that could be achieved, treatment time, and depressurization time depend on the equipment capabilities. Once the desired pressure is achieved, no additional energy is required and pressure is maintained during the holding time. The system could be chilled or heated by a complementary equipment or by using the transmitting medium at certain temperature to control the temperature during the process (Barba, de Souza Sant’Ana, et al., 2017).

There are three principles that underline the application and effects of HPP: Pascal’s law, adiabatic heat of compression and the Le Chatelier-Braun principle (Barba, Ahrné, Xanthakis, Landerslev, & Orlien, 2017).

The first is Pascal’s law, also known as the isostatic rule, which states that the transmittance of pressure is uniform and instantaneous in the whole system under pressure. The HPP equipment immediately generates stable pressure in the whole volume of the product regardless of its size, shape, and consistency (Barba, Ahrné, et al., 2017). Increase in the pressure occurs in the product at a much faster rate and much homogeneously than in the case of increase in temperature in heat conduction processes.

The second principle is related to the increase in temperature in the system as a consequence of compression heating. This heating is specific to each food constituent and kind of transmitting fluids. For example, the temperature of water increases in a range from 3°C to 5°C per each 100 MPa, whereas that of silicone oil can increase to above 20°C per 100 MPa. Among different foods, oils and fats have the largest heat of compression values that range from 3°C to 9°C per each 100 MPa due to a difference in lipid and water molecular structure. This heat of compression should be taken into account, along with the initial temperature and desired pressure while designing food processing. The heat transfer among pressure transmitting fluid, through the product, and to the high-pressure chamber strongly influence the effect of microbial and enzyme inactivation as well as the final product quality (Barba, Ahrné, et al., 2017).

A considerable amount of water is present in most of the foods that may have a fair resemblance to the pressure-transmitting water that may also reduce adiabatic heating thermal effect. Consequently, fatty foods may undergo a higher temperature rise in comparison to fruit and vegetable (F&V) products (Barba et al., 2016; Barba, de Souza Sant’Ana, et al., 2017). The food product’s initial temperature, the kind of pressure-transmitting fluid, and temperature as well as the pressure vessel initial temperature must be designed and equilibrated before food processing in order to avoid high uncontrolled temperature fluctuations. The adiabatic heating is completely reversible upon pressure release, but the temperature does not return to the initial value, due to the heat transfer to the high-pressure chamber and temperature equilibration during holding time (particularly for longer pressure holding times). Although the increase in temperature is relatively small, it can significantly affect microorganism, especially at the mild temperatures used in experiments.

The effect of high pressure on biomolecules can be explained by the third rule, the Le Chatelier-Braun principle. The principle of this rule is that under equilibrium conditions, any chemical reaction, phase transformation, molecular transformation, etc., that implies a decrease in volume is favored when the pressure increases. Generally, high pressure can influence large molecules (polymers), including proteins, enzymes, and polysaccharides, due to changes in noncovalent bonds, such as hydrogen, ionic, and hydrophobic bonds, which are more sensitive to pressure changes than covalent bonds. Pressure up to 1200 MPa has no effect on covalent bonds but can lead to permanent changes in hydrogen and ionic bonds as well as in hydrophobic interactions responsible for the secondary and tertiary structure of proteins (Balny, Hayashi, Heremans, & Masson, 1992). The destruction of the enzymes’ primary structure under HPP under pressure up to 900 MPa were excluded in the research under the evaluation of the application of HPP on oxidoreductive enzymes structural changes (Marszałek, Doesburg, et al., 2019).

Smaller molecules like amino acids, vitamins, pigments, or flavor substances are generally not sensitive to pressure (Barba et al., 2015; Butz et al., 2003; Cao et al., 2011). In F&V, vitamins C, B1, B2, E, and provitamin A do not undergo any significant changes as a result of HPP but the processing temperature and the reactions during storage time can change these components (Sancho et al., 1999). HPP coupled with process temperature higher than 20°C could produce a negative effect on the content of anthocyanin pigments and vitamin C, whereas the process run at temperature below 20°C has no or only slight impact on their level (Corrales, Toepfl, Butz, Knorr, & Tauscher, 2008; Garcia-Palazon, Suthanthangjai, Kajda, & Zabetakis, 2004; Marszałek, Mitek, & Skąpska, 2015; Marszałek, Woźniak, Kruszewski, & Skapska, 2017). The color of F&V products treated by HPP can be even more intensive than before pressurization, and thus more attractive. This phenomenon is generally explained by the extraction of pigments from tissues to the intercellular juice (Otero & Préstamo, 2009).

The principles presented above justify why low-molecular-weight compounds, responsible for the nutritional and sensorial characteristics, are not affected by pressure whereas high-molecular-weight compounds are pressure sensitive (Barba et al., 2012, 2015). HPP accelerates the chemical or physical reactions, which cause reductions in the volume of reactions products, whereas reactions that cause an increase in the total volume of the products are retarded (Barba et al., 2016; Barba, de Souza Sant’Ana, et al., 2017).

Products treated by pressures of 10–1000 MPa suffer changes in their volume that reach from 4% to 15%, depending on the pressure applied, structure, and composition of food (Barba et al., 2016; Barba, de Souza Sant’Ana, et al., 2017). It is important to highlight that these changes are not permanent, because the impact of pressure on product’s structure is generally reversible. In addition, if the food structure does not contain air (that is highly compressible), the isostatic action of pressure from all directions with the same intensity does not induce shearing forces that could result in tissue damage (Dervisi, Lamb, & Zabetakis, 2001).

The biggest advantage of HPP is the possibility of reducing the activity of tissue enzymes by changing their structure and the inactivation of microorganisms by damaging the structure of their cell proteins while maintaining the nutritional quality and fresh-like flavor of the products. However, in some cases, microbial growth and enzymatic activity can be enhanced by stress conditions under HPP, thus being a useful tool in fermentation processes (Barba et al., 2015; Marszałek, Woźniak, Skąpska, et al., 2017; Mota et al., 2018).

Regarding packaging materials, it should be noted that a pressure of 600 MPa cause water compression which can result in about 15% reduction in the product volume. Hence the packaging material should be flexible in a way to transmit the pressure, withstand this compression, and retain its original geometry upon decompression. In addition, packaging material migration to the food products must be avoided. Plastic pouches, containers, semirigid trays with at least one flexible interface, and bottles are usually used for HP processing, while metal cans and glassware are obviously not (Barba, de Souza Sant’Ana, et al., 2017).

There are two major limitations to the further development of HPP. First is the level of pressure possible to achieve at the industrial scale. The current research on the tissue enzyme inactivation shows that pressurization even up to 900 MPa is not enough for total inactivation of oxidoreductive enzymes (Marszałek et al., 2018). The proper use of kinetic data of HPP-induced inactivation of deteriorative food enzymes is indispensable for the design, evaluation, and optimization of process parameters to ensure maximum reduction in the activity of targeted enzymes (Hendrickx, Ludikhuyze, Van Den Broeck, & Weemaes, 1998). The temperature and the pressure required for 90% reduction of decimal reduction time (D-value) for enzyme activity (zt-value and zp-value), activation energy (Ea), and activation volume (Va), indicate that inactivation of tissue enzymes is not comprehensive enough to ensure the reliability of HPP at available pressures as an alternative to thermal processing. The high baroresistance of bacterial spores is also a matter of concern. Secondly, development of a continuous pressure food processor still remains an engineering challenge (Barba et al., 2016; Marszałek, Krzyżanowska, et al., 2016). Semicontinuous processing can be achieved using multiple sequential chambers connected in series. In this case, while some chambers are under pressurization, others are unloaded or loaded (Barba et al., 2016; Barba, de Souza Sant’Ana, et al., 2017).

The current cost of employing HP treatment in food preservation depends on many factors, including equipment costs and its amortization, production capacity, and running costs (labor and energy) (Barba et al., 2016). The production rate (process flow: kg or L of product per year) is determined by the cycle time and the volumetric packaging efficiencies in the pressure chamber. The better the packing density, the lower the cost of production per kg or L. The cost of HPP-preserved foods is calculated to be around 0.3 €/kg and is much higher in relation to conventional pasteurization (0.05 €/kg), but often significantly lower in comparison to well-known traditional methods like drying (5 €/kg), smoking (2 €/kg), or brining (1 €/kg) (Heinz & Buckow, 2010). Nowadays many consumers accept higher costs of HPP products due to their better quality.

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Section 2

Impact of HPP on bioactive compounds content and bioaccessibility/bioavailability

Chapter 2: HPP for improving preservation of vitamin and antioxidant contents in vegetable matrices

Ana B. Baranda; Paula Montes    AZTI, Food Research, Basque Research and Technology Alliance (BRTA), Derio, Spain

Abstract

The permanent consumer demand for processed vegetable products with characteristics similar to the fresh ones has led to the increase in high-pressure processing (HPP) vegetable products in the market due to the advantages compared to those produced by conventional thermal pasteurization. This chapter presents scientific data that assess the effect of HPP technology on vitamins and antioxidants in vegetable matrices and their comparison with thermal processing. Also, different forms of HPP vegetable products, currently available in the market, are discussed.

Keywords

High-pressure processing; HPP; Vitamins; Antioxidants; Fruits; Vegetables

Acknowledgment

The authors thank the Basque Government, the Spanish Government, and the European Commission for partially supporting the research on high-pressure processing carried out at AZTI during the last years. The authos thank also Beandbejuice and Mintel for images and information of the HHP commercial products shown in this chapter.

1: Introduction

The processing of vegetable food products and their subsequent storage conditions may have a positive or negative influence on the stability of compounds. Fruits and vegetables play an important role in human nutrition and health due to their constituents (Blasa, Gennari, Angelino, & Ninfali, 2010). They are the sources of vitamins, minerals, dietary fiber, and phytochemicals; strong antioxidants are strongly associated with health benefits such as the improvement in gastrointestinal health, good vision, and a reduced risk of heart disease, stroke, chronic diseases such as diabetes, and some forms of cancer. Thermal pasteurization and sterilization, the conventional methods for the inactivation of plant enzymes and inhibition of microorganisms, result in the loss of these physicochemical and nutritional quality attributes (Petruzzi et al., 2017). To overcome these problems, high-pressure processing (HPP) has been suggested as an alternative to the processing of fruit and vegetable products.

2: Main vitamin and antioxidant compounds in vegetable matrices

Vitamins are compounds that are essential, in small quantities, for the normalfunctioning of metabolism in the body. Since they cannot usually be synthesized by the body but occur naturally in certain foods, they must be obtained from the daily diet. There are two types of vitamins: water-soluble (vitamins B1, B2, B3, B6, B12, C, biotin, and folate) and fat-soluble (vitamins A, D, E, and K). Of these, the main vitamins found in fruit and vegetables are C, A (carotenoids), E, and folate (Combs & McClung, 2017).

Antioxidants are molecules capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that can produce free radicals, leading to chain reactions that may damage cells. Antioxidants either immediately neutralize free radicals or interfere with the free radical’s path of destruction and prevent or reduce the amount of damage. Moreover, antioxidants cope with reactive oxygen species (ROS) which are produced during normal oxygen metabolism or are induced by exogenous damage. Free radicals and ROS are also implicated in a phenomenon called oxidative stress, related with the development of chronic and degenerative illness such as cancer, autoimmune disorders, aging, cataract, rheumatoid arthritis, cardiovascular, and neurodegenerative diseases (Blasa et al., 2010).

Main antioxidants in vegetable food include some enzymes, vitamins (C, E, A), minerals (selenium and zinc), and diverse groups of phytochemicals such as polyphenols, carotenoids, allylsulfides, sulfur-containing compounds, betalains, saponins, phytosterols, and capsaicinoids (Pennington, 2002). Table 1 presents food sources of common vitamins and antioxidants in vegetable matrices.

Table 1

3: Effect of HPP on vitamin and antioxidants in vegetable products

Traditional thermal treatments use high temperatures to preserve and ensure the safety of food based on the effect of microbial destruction and enzyme inactivation (Petruzzi et al., 2017). The two main thermal processes employed in the food processing are pasteurization and sterilization. The first process is a relatively mild heat treatment in which food is heated to <   100°C and in the second process, temperatures above 100°C, usually ranging from 110°C to 121°C, must be reached inside the product. In pasteurization processes the severity of treatment and the resulting extension of shelf life are determined mostly by pH of the food. For sterilization, products are kept for a defined period of time at temperature levels required depending on type of product and size of container. Therefore, heat treatment may lead to a decrease in essential nutrients and food components relating color, flavor, and consequently reduces the nutritional value and other quality parameters of vegetable products. This results in reduced bioavailability/bioactivity and antioxidant capacity (Micali & Fiorino, 2016).

HPP treatment has been suggested as an alternative to thermal pasteurization for fruit and vegetable products (Bevilacqua et al., 2018; Houska et al., 2006; Martínez-Monteagudo & Balasubramaniam, 2016). Due to its limited effect on the covalent bonds of low-molecular-mass compounds such as vitamins, color, and flavor compounds, HPP treatment could preserve nutritional value and the sensory properties of fruits and vegetables. The low energy levels involved in HPP (19 kJ for the compression of 1 L of water at 400 MPa versus 21 kJ for heating 1 L of water at 20–25°C) explain why the covalent bonds of the constituents of foods are usually less affected than weak interactions. Consequently, the primary structure of low-molecular-weight molecules (vitamins, amino acids, volatile compounds, pigments, etc.) is not affected, allowing a better retention of the nutritional and organoleptic properties of foods (Kadam, Jadhav, Salve, & Machewad, 2012). This limited effect on covalent bonds represents a unique feature of this technology and of interest for its application.

Recently, the use of HPP for sterilization of foods has been studied as an alternative method (although without industrial implementation so far) (Ramaswamy, 2011). The sterilization intensity is realized through an innovative approach that exploits the effect of pressures above or equal to 600 MPa, accompanied with elevated process temperatures (90–121°C), a processing method called high-pressure/high-temperature (HPHT) processing. The main potential benefit of the HPHT processing is the fast and volumetric heating in the center of the product to the targeted temperature, which reduces the holding time thus improving food quality. It has been associated with a better retention of quality characteristics such as nutrients content and color.

HPP studies have been performed with a wide range of fruit and vegetable products in different forms such as pieces, purees, or beverages to know the perspectives of HPP regarding retention of vitamins and bioactive compounds (Augusto, Tribist, & Cristianini, 2017; Barrett & Lloyd, 2012; Gopal, Kalla, & Srikanth, 2017; Houska et al., 2006; Jimenez-Sánchez, Lozano-Sánchez, Seguera-Carretero, & Fernández-Gutiérrez, 2017; Rastogi, 2013). Most relevant findings are summarized in Tables 2–4 considering fruits and vegetables minimally processed, blended, and in a beverage form, respectively. Detailed information is given for the experimental conditions under which the studies have been performed. Experimental designs have been carried out to evaluate the influence of processing conditions and to establish kinetic models. Also, comparative studies against conventional thermal processing have been done with processes from mild pasteurization to strong sterilization, for which HPP has been carried out at elevated temperatures (HPHT). In many studies, microbiological safety and enzymatic inactivation influence have been included to evidence the whole quality of the products. Moreover, since the quality of products must be evaluated at the end of the shelf life, most of the studies have followed the behavior of HPP processed products during their storage at different temperatures.

Table 2