**1. Introduction**

Fruits and vegetables are consumed as fresh or processed and known to be among the most important sources of phytochemicals for the human diet. About 200,000 phytochemicals are known so far and 20,000 of them have been identified as originating from fruits, vegetables and grains [1]. Phytochemicals has many health effects as antioxidants against many diseases or antibacterial, antifungal, antiviral, cholesterol‐lowering, antithrombotic, or anti‐inflam‐ matory effects [2]. Phytochemicals are used for various purposes such as pharmaceuticals, agrochemicals, flavors, fragrances, coloring agents, biopesticides and food additives [1]. Their chemical structures composed of phytochemicals such as phenolics, alkaloids, sapo‐ nins and terpenoids [1]. These compounds are known as secondary metabolites having vari‐ ous identifiable structures, although a benzene ring with one or more hydroxyl groups is a common feature. They are commonly classified as flavonoids (anthocyanins, flavan‐3‐ols,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

flavonols, proanthocyanidins or flavones, non‐hydrolyzable tannins, isoflavones and flava‐ nones) and non‐flavonoids (hydroxycinnamic, hydroxybenzoic acid, hydrolyzable tannins, benzoic acids and stilbenes) [3]. Sugars, acids and polysaccharides are an important source of phytochemicals, secondary metabolites of plants also known as their antioxidant activ‐ ity and other properties [4]. Lately, there are many investigations on plant "antimicrobial," "antiviral," or "antibacterial" effects [1]. In addition, phytochemicals are some of the most important natural preservation structures to reduce and inhibit pathogenic microorganism growth and preserve the overall quality of food products [5]. These antimicrobials can protect food products, extending the shelf life naturally [5]. Chilling, fermentation, freezing, acidifi‐ cation, nutrient restriction, water activity reduction, synthetic antimicrobials and pasteuriza‐ tion have been used in food preservation technology and phytochemicals such as flavonoids, polyphenols, anthocyanins and carotenoids are also used to preserve and control microbial spoilage in foods traditionally [6]. In general, food antimicrobials can be classified as natu‐ ral and synthetic substances depending on their origin. Synthetic antimicrobials are found in fruits naturally such as benzoic acid in cranberries, tartaric acid in grapes, sorbic acid in rowanberries, malic acid in apples and citric acid in lemons [6]. Secondary metabolites are in close contact through sophisticated communication involving metabolic attacks by plants on their pathogens [7]. Fruits and vegetables have phenolics which are biologically active compounds. Fruits and vegetables have a special phytochemical group which protect plants from their environment stress such as pollution, pathogens, or various abiotic stresses [2]. Even if secondary metabolites having different structures, they can have similar functions. First, plant‐defensive metabolites include phytoalexins biosynthesized to respond to biotic and abiotic stresses with the effect of both protecting the plant and controlling the pathogen growth [7]. Secondly, most of these metabolites are responsible for the organoleptic and quali‐ tative properties of foods originating from such plants. For example, anthocyanins constitute a pigment group responsible for the color of a great variety of fruits, flowers and leaves [8] and flavan‐3‐ols are polyphenols involved in the bitterness and astringency of tea, grapes and wine [9, 10]. Thirdly, these compounds are unique sources of industrial material in the form of food additives, pharmaceuticals and flavors [11]. Finally, they are considered to be benefi‐ cial for health, mainly due to their antioxidant activity. Many studies have suggested that a high intake of polyphenol‐rich foods may have cardiovascular benefits and provides some level of cancer chemopreventive activities and beneficial effects against other less prevalent but devastating illnesses, such as urinary bladder dysfunctions and Alzheimer's disease [12]. Furthermore, food scientists and nutrition specialists suggest that phytochemicals offer many health benefits when consumed as part of the usual human diet [13].

#### **2. Commonly used methods of treating plant foods**

Many fresh fruits especially small berries and vegetables are highly perishable after harvest. During the harvest, bruising can reduce shelf life, influencing both color and texture of fresh products. The freshness of fruits and vegetables can be maintained in storage through reduc‐ tion of temperature and/or oxygen levels, increase in carbon dioxide levels, use of modi‐ fied atmosphere packaging or edible coatings, or treatment with gamma irradiation or high  pressure. These can also be combined with treatments of 1‐MCP, ozone and ultraviolet (UV) irradiation to further prevent losses. One of the most basic treatments used to lengthen the shelf life of fresh commodities during storage is to store in a low temperature and high rela‐ tive humidity conditions. It has been known and used to extend the shelf life of fruits and vegetables since antiquity [14]. Moreover, exposure to low temperature during storage opti‐ mizes produce appearance and has the additional benefit of protecting nonappearance qual‐ ity attributes, such as texture, nutrition, aroma and flavor [14]. There are many chemical and natural preservative treatments used to reduce postharvest losses and extend the shelf life of fresh commodities. Using plant extracts with known antimicrobial properties can be of great importance in food preservation. There are some chemical substances in plants that pro‐ duce a definite action on the microbiological, chemical and sensory quality of foods and these phytochemicals have been grouped in several categories including polyphenols, flavonoids, tannins, alkaloids, terpenoids, isothiocyanates, lectins, polypeptides, or their oxygen‐substi‐ tuted derivatives [6]. On the other hand, alternative sources of natural products, such as plant extracts, either as pure compounds or as standardized extracts, provide unlimited opportu‐ nities for control of microbial growth owing to their chemical diversity. The use of natural antimicrobials as phytochemicals is organic acids, essential oils, or plant extracts and could be a good alternative to ensure food safety [6]. To inactivate or inhibit the growth of spoilage and pathogenic microorganisms during preservation of food, there are several processing techniques used including the use of chemical preservatives and synthetic antimicrobials [5]. However, these techniques have not been considered natural antimicrobial agents in food preservation. But, naturally derived compounds in plant extracts can be good control agents for pathogenic microorganisms. The use of synthetic chemicals is increasingly restricted in many countries. Nowadays, the recent trend has been for the use of natural preservatives due to the adverse health effects of synthetic ones. The alternative methods preserve foods and reduce pest and pathogen injury, with the use of resistant varieties or integrated crop‐ ping strategies in which plant secondary metabolites may improve crop protection [6]. The major goals of such natural antimicrobials are to protect the food from food poisoning and spoilage microorganisms that cause off‐odors, off‐flavors and discoloration quality losses [6]. Antimicrobials are called traditional when they have been used for many years and many countries approve them for inclusion in foods. Although many synthetic antimicrobials are found naturally (benzoic acid, sorbic acid, citric acid, malic acid, tartaric acid), the perception of natural has become important for many consumers. The safety and shelf life of food ingre‐ dients can also be improved by application of novel technologies to avoid or delay micro‐ bial growth like packaging in modified atmosphere, nonthermal treatments, activated films, irradiation, etc. [6]. The use of fruits and vegetables as a source of certain phytochemicals, such as ascorbic acid (AA), carotenoids, phenols and flavonoids, has not only health‐pro‐ moting effects but also widely used to restrict oxidation‐induced degenerative changes in cell physiology and aging [15] and is well known due to their significant impact on the food industry [16]. Both glucosinolates and leaf surface waxes are important phytochemicals that also play an important role in protecting plants from pest and pathogen injury [17]. These factors that positively affect plant protection also minimize crop damage by pests and patho‐ gens. B‐Carotene, lycopene, lutein and zeaxanthin are known to exhibit antioxidant activity. Increasing oxidative stress results in produce losing keeping quality, not only in terms of

flavonols, proanthocyanidins or flavones, non‐hydrolyzable tannins, isoflavones and flava‐ nones) and non‐flavonoids (hydroxycinnamic, hydroxybenzoic acid, hydrolyzable tannins, benzoic acids and stilbenes) [3]. Sugars, acids and polysaccharides are an important source of phytochemicals, secondary metabolites of plants also known as their antioxidant activ‐ ity and other properties [4]. Lately, there are many investigations on plant "antimicrobial," "antiviral," or "antibacterial" effects [1]. In addition, phytochemicals are some of the most important natural preservation structures to reduce and inhibit pathogenic microorganism growth and preserve the overall quality of food products [5]. These antimicrobials can protect food products, extending the shelf life naturally [5]. Chilling, fermentation, freezing, acidifi‐ cation, nutrient restriction, water activity reduction, synthetic antimicrobials and pasteuriza‐ tion have been used in food preservation technology and phytochemicals such as flavonoids, polyphenols, anthocyanins and carotenoids are also used to preserve and control microbial spoilage in foods traditionally [6]. In general, food antimicrobials can be classified as natu‐ ral and synthetic substances depending on their origin. Synthetic antimicrobials are found in fruits naturally such as benzoic acid in cranberries, tartaric acid in grapes, sorbic acid in rowanberries, malic acid in apples and citric acid in lemons [6]. Secondary metabolites are in close contact through sophisticated communication involving metabolic attacks by plants on their pathogens [7]. Fruits and vegetables have phenolics which are biologically active compounds. Fruits and vegetables have a special phytochemical group which protect plants from their environment stress such as pollution, pathogens, or various abiotic stresses [2]. Even if secondary metabolites having different structures, they can have similar functions. First, plant‐defensive metabolites include phytoalexins biosynthesized to respond to biotic and abiotic stresses with the effect of both protecting the plant and controlling the pathogen growth [7]. Secondly, most of these metabolites are responsible for the organoleptic and quali‐ tative properties of foods originating from such plants. For example, anthocyanins constitute a pigment group responsible for the color of a great variety of fruits, flowers and leaves [8] and flavan‐3‐ols are polyphenols involved in the bitterness and astringency of tea, grapes and wine [9, 10]. Thirdly, these compounds are unique sources of industrial material in the form of food additives, pharmaceuticals and flavors [11]. Finally, they are considered to be benefi‐ cial for health, mainly due to their antioxidant activity. Many studies have suggested that a high intake of polyphenol‐rich foods may have cardiovascular benefits and provides some level of cancer chemopreventive activities and beneficial effects against other less prevalent but devastating illnesses, such as urinary bladder dysfunctions and Alzheimer's disease [12]. Furthermore, food scientists and nutrition specialists suggest that phytochemicals offer many

176 Superfood and Functional Food - An Overview of Their Processing and Utilization

health benefits when consumed as part of the usual human diet [13].

Many fresh fruits especially small berries and vegetables are highly perishable after harvest. During the harvest, bruising can reduce shelf life, influencing both color and texture of fresh products. The freshness of fruits and vegetables can be maintained in storage through reduc‐ tion of temperature and/or oxygen levels, increase in carbon dioxide levels, use of modi‐ fied atmosphere packaging or edible coatings, or treatment with gamma irradiation or high

**2. Commonly used methods of treating plant foods**

microbial contamination, excessive softening and browning but also in terms of significant depletion of phytochemicals, such as phenolics, flavonoids, ascorbic acid and carotenoids. The addition of AA minimizes oxidative deterioration in processed fruits and vegetables. Exogenous treatment of AA in minimally processed fruits and vegetables reduces or stops enzymatic browning and oxidation‐susceptible degenerative changes such as the deteriora‐ tion of carotenoids, phenolics and flavonoids [16].

Phenolics and their metabolites are common constituents of fruits and vegetables that play an important role as to provide astringency and aroma constituents [15]. Polyphenolic compounds are important as food preservatives that inactivate free radicals giving them an important role fighting against pathogenicity, infestation and photooxidation [1, 15]. In general, antibacterial activity of phenolic acids is stronger against Gram‐positive bacteria than Gram‐negative bac‐ teria [1]. The main problems for such antimicrobials are food‐poisoning microorganisms and spoilage microorganisms that are metabolic end products causing off‐odors, off‐flavors, texture problems and discoloration of food [1]. Phytochemicals, such as phenolic compounds, are of great importance as antithrombotic, anticarcinogenic and anti‐inflammatory agents. However, due to the possible negative effects of synthetic antioxidants, food industries prefer natural ones and can be used as food additives or pharmaceutical supplements [13]. First of all, they protect plants from biotic and abiotic stress factors. Indeed, such phenolic compounds are only induced when stress factors are present and so‐called phytoalexins are specifically involved in defense mechanisms and are synthesized after pathogen or predator attack or injury [18].
