**3. Phytochemical and secondary metabolites present in plant foods**

Secondary metabolites present in plant foods, such as alkaloids, phenolic compounds (flavo‐ noids, isoflavonoids and anthocyanins) and terpenoids, have gained importance because of their antioxidant, antiviral, antibacterial and anticancer effects [19]. These phytochemicals are mixtures of several components, including phytophenolics in herbs and spices, phenolics, flavo‐ noids and acids in fruits and glucosinolates in cruciferous vegetables (mustard) [5]. As shown in **Table 1**, *Rubus* (cloudberry and raspberry) extracts have antimicrobial effects against food spoil‐ age and poisoning bacteria [21]. In general, antioxidant compounds have important protection effects from fruit insects and microbial organisms during storage [23]. Secondary metabolites are very important in medicine and agricultural science due to the activity of chemotherapeu‐ tic compounds or pesticides. Phenolics and flavonoids provide very important defense mecha‐ nisms against postharvest diseases [23]. For example, walnut seed coats contain gallic acid which is a phenolic compound that prevents aflatoxin biosynthesis by *Aspergillus flavus* (**Table 1**) [23]. Therefore, polyphenol compounds have antiviral activities to some various types of viruses [23]. One of the other very important phytochemical groups are flavonoids which have anti‐ allergenic, antiviral, antifungal and anti‐inflammatory activity. It is abundant in most of the fruits and vegetables such as apples, grapes, lemons, tomatoes, onions, lettuce, broccoli, etc. [23]. Flavonoids are also known as one of the largest groups of natural phenolic compounds in plants [27]. These natural compounds have important effects against a variety of microorganisms [27]. In addition, flavonoids either have protective effects from microbial attacks or respond as phy‐ toalexins against them. Volatiles are phytochemicals that are either inhibitory or stimulatory to fungal growth. Acetaldehyde, a volatile compound that occurs in fruit during ripening, has a fungicidal effect on postharvest pathogens [23]. As shown in **Table 1**, "Isabella" (*Vitis labrusca* L.) grape variety volatiles have a strong effect on *B. cinerea* development [19].


**Table 1.** The effects of fruit and vegetable extracts on food pathogens.

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‐

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].

**3. Phytochemical and secondary metabolites present in plant foods**

Secondary metabolites present in plant foods, such as alkaloids, phenolic compounds (flavo‐ noids, isoflavonoids and anthocyanins) and terpenoids, have gained importance because of their antioxidant, antiviral, antibacterial and anticancer effects [19]. These phytochemicals are mixtures of several components, including phytophenolics in herbs and spices, phenolics, flavo‐ noids and acids in fruits and glucosinolates in cruciferous vegetables (mustard) [5]. As shown in **Table 1**, *Rubus* (cloudberry and raspberry) extracts have antimicrobial effects against food spoil‐ age and poisoning bacteria [21]. In general, antioxidant compounds have important protection effects from fruit insects and microbial organisms during storage [23]. Secondary metabolites are very important in medicine and agricultural science due to the activity of chemotherapeu‐ tic compounds or pesticides. Phenolics and flavonoids provide very important defense mecha‐ nisms against postharvest diseases [23]. For example, walnut seed coats contain gallic acid which is a phenolic compound that prevents aflatoxin biosynthesis by *Aspergillus flavus* (**Table 1**) [23]. Therefore, polyphenol compounds have antiviral activities to some various types of viruses [23]. One of the other very important phytochemical groups are flavonoids which have anti‐ allergenic, antiviral, antifungal and anti‐inflammatory activity. It is abundant in most of the fruits and vegetables such as apples, grapes, lemons, tomatoes, onions, lettuce, broccoli, etc. [23]. Flavonoids are also known as one of the largest groups of natural phenolic compounds in plants [27]. These natural compounds have important effects against a variety of microorganisms [27]. In addition, flavonoids either have protective effects from microbial attacks or respond as phy‐ toalexins against them. Volatiles are phytochemicals that are either inhibitory or stimulatory to

tion of carotenoids, phenolics and flavonoids [16].

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