**4. Phytochemicals as natural preservatives and antimicrobials**

Natural preservatives derived from plant extracts such as phytochemicals and essential oils are used against fungal development in many fruits and vegetables after harvest [28]. The efficiency of an antimicrobial treatment depends on many factors, such as type, genus, spe‐ cies and strain of the main microorganism, in addition to environmental factors such as pH, water activity, temperature, atmospheric composition and an initial microbial load of the food materials [6]. Therefore, other important subject to know is type of the microorganism(s) owing to usually combinations of antimicrobials are more effective than adding just one. The natural antimicrobial preservative activity is not clear since there are many influencing fac‐ tors, one of the most important being the interaction between phytochemicals and growth of microorganisms [6]. Processing of foods containing phytochemicals is expected to result in some changes in their phytochemical content. Phytochemicals present in many food stuffs are lost by heat processing such as sterilization, pasteurization and dehydration [6].

Many investigations have evaluated phytochemical effects on antifungal activity. The potential use of plant extracts as natural antimicrobial agents in food preservation forms the basis for many applications such as grape seed or rosemary extracts that have been used as food preservatives [22]. Researchers reported that grape extracts of Riesling *Vitis vinifera* L. grapes showed strong preservative effects against some of the Gram‐positive food‐borne pathogens [5]. The alkaloids, steroids, tannins, flavonoids, saponins and gly‐

cosides which were secondary metabolites showed various biological activities and act in plant defense mechanisms. Flavonoids usually occur as glycosides and aglycones in plant tissue which have significant antioxidant properties and antimicrobial and insect‐repel‐ lent properties as well [15]. Flavonoids and their antimicrobial effect are useful as a food preservative to extend the shelf life and safety of foods. Flavonoids play important roles in biological activities, including antiallergenic, antiviral and antifungal effects [23]. It is also present in various common fruits and vegetables (apples, grapes, lemons, tomatoes, onions, lettuce and broccoli). The following flavonoids are antifungal agents in plants: iso‐ flavonoids, flavans flavanones. However, the antifungal activity of flavonoid compounds plays an important role between plant‐microorganism and host plant's defensive systems [8]. Saponin and flavonoids are found in fruits and vegetables and in general they form a soapy lather after extracted from parts of plants [5]. Mandalari et al. [24] reported that Bergamot fruit extract which is rich in flavonoid has an effective on the yeast *Saccharomyces cerevisiae* (**Table 1**).

Okwu et al. [25] also showed that the antifungal activity of both citrus species and grape has an important effect against *Fusarium oxysporum* (**Table 1**). Thiosulfinates come from hydrolysis products of garlic and onion. They have a strong potential of producing antimi‐ crobial effects against pathogenic microorganisms [5]. Broccoli, Brussels' sprouts, cabbage mustard and horseradish have glucosinolates that also have a wide range of antibacterial effects. Moreover, olive leaves (*Olea europaea*) are rich in phenolic compounds, with dem‐ onstrated strong antimicrobial effects and can be potentially used in food processing [5]. Al‐Zoreky [29] reported that phenolics and flavonoids present in pomegranate fruit peels demonstrated strong antimicrobial activity against some food pathogen microorganisms. In addition, *Psidium guajava* has phenolic, flavonoid, carotenoid, terpenoid and triterpenes that demonstrated strong antimicrobial activity [30]. Salas et al. [31] reported that flavonoids extracted from citrus species, not only naringin, hesperidin and neohesperidin but also enzy‐ matically modified derivatives of these compounds, have strong antifungal activity [31]. The limonoid compounds have important antibacterial and antiviral activity as shown in **Table 1** [1]. Vikram et al. [32] reported that seeds of grapefruits have significant inhibitory effect on pathogenic *Escherichia coli* O157:H7. Black raspberry and Chardonnay seed extracts have also antibacterial activity to inhibiting growth of some food pathogen microorganisms [33]. Tehranifar et al. [26] reported that high percentage of phenolic content in the peel and seed of pomegranate fruit has high antifungal activity especially on postharvest fungi (*Penicillium italicum*, *Rhizopus stolonifer* and *Botrytis cinerea*). Another study showed that berry extracts exhibit selective inhibitory properties against intestinal bacteria [1]. Recently, antifungal activity has been found in all tissue types of strawberry fruit due to the phenolic compounds that inhibit the growth of fungi [23].

#### **5. Other beneficial properties of plant phytochemicals**

In the last decade, the results of many research have shown the positive effects of phytochemicals in human health. There is a strong correlation of antioxidant consumption with lower risk of many diseases such as cardiovascular cancer, diabetes and hypertension diseases as well as other medical conditions [34, 35]. Fruits and vegetables have phenolic compounds, pigments and natural antioxidants; these compounds protect many diseases like cancer and heart disease [36]. The importance of antioxidant effects on cardiovascular diseases and cancer is especially important [23] and these antioxidants can be found in var‐ ious fruits, vegetables and herbs. Phenolics as flavonoids have an important effects such as antimicrobial, anti‐inflammatory, antioxidant, antiviral, antiallergic, anticancer, antiulcer, antidiabetic, antiplasmodial, antihypertensive, anticonvulsant and all reducing risks for severe human diseases [27]. Antioxidants in fruits and vegetables have defensive effects and are three main groups: vitamins, phenolics and carotenoids [35]. Vitamin C (l‐ascorbic acid, AA) and the oxidized form (dehydroascorbic acid, DHAA), carotenoids and pheno‐ lic compounds prevent cardiovascular disease, cancer and cataracts which are associated with the oxidative damage of lipids, DNA and proteins [4]. Moreover, some carotenoids also have antioxidant activity (AOA) and shown beneficial effects on the reduction of car‐ diovascular diseases [4]. The fruits and vegetables that have phytochemicals are also not only low in fat and saturated fat, cholesterol and calories but also are rich in potassium and sodium, fiber, folic acid and AA [34]. One of the most important flavonols is quercetin, which is higher in onion (red and yellow), broccoli, kale, French beans, apple, red grapes and cherries. Quercetin is anticarcinogenic and inhibits low‐density lipoprotein (LDL) oxidation activities [34].
