**2.1 Role of strawberry as a source of dietary antioxidants compared with similar sources**

Strawberry consumption can help to prevent inflammation, oxidative stress, cardiovascular disease (CVD), certain types of cancers, type 2 diabetes, and obesity. The addition of berries to the diet can positively influence risk factors for CVD by

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*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural…*

**Type Nutrient Per 100 g** Minerals Calcium (mg) 16

Vitamins Vitamin C (mg) 58.8

Proximates Dietary fiber (g) 2.0

Iron (mg) 0.41 Magnesium (mg) 13 Phosphorus (mg) 24 Manganese (mg) 0.386

Folate (μg) 24 Thiamin (mg) 0.024 Lutein + zeaxanthin (μg) 26 Vitamin E, a-tocopherol (mg) 0.29 Vitamin K (μg) 2.2 Vitamin B6 (mg) 0.047

Fructose (g) 2.44

inhibiting inflammation, improving plasma lipid profiles, scavenging free radicals, and increasing LDL resistance to oxidation [18]. The mechanisms by which strawberries exert these positive effects are not completely understood. Among many potential mechanisms, its role as an antioxidant is the most relevant as strawberry supplementation significantly decreases oxidative stress, protecting mononuclear blood cells against DNA damage [19, 20]. Several studies have shown that strawberry generally possesses a high level of antioxidant activity, which is linked to the levels of phenolic compounds in the fruit rather than vitamin C [1, 21–23]. Wang and Jiao [24] showed that strawberry juice extracts exhibited a high level of antioxidant capacity against free radical species. Strawberry extracts also seem to modulate cell signaling in cancer cells by inhibiting proliferation of several types of cancer cells inducing cell cycle arrest and apoptosis and suppressing tumor angiogenesis [25]. An unavoidable result of aerobic metabolism in humans and other organisms is the production of reactive oxygen species (ROS). ROS include free radicals such as the superoxide anion (O2•−) and hydroxyl radical (•OH), as well as nonradical molecules like hydrogen peroxide (H2O2), singlet oxygen (1O2), etc. All ROS can be damaging to organisms at a concentration where its level exceeds the defense mechanism. These excess ROS can put cells in oxidative stress that eventually pose a threat to cells by causing peroxidation of lipids, oxidation of proteins, damage to nucleic acids, and enzyme inhibition. The enhanced production of ROS during physiological stresses can also activate a programmed cell death (PCD) pathway that may lead to cell death [26–33]. Under normal conditions, ROS molecules are unable to cause any damage as they are constantly being scavenged by a range of antioxidative mechanisms [34]. But, the delicate equilibrium between the ROS production and their scavenging by antioxidants is disturbed by multiple stress factors. An efficient antioxidative system that includes nonenzymatic as well as enzymatic antioxidants in a cell can usually scavenge or detoxify excess ROS [35]. The human antioxidant defense system includes endogenous (enzymatic and nonenzymatic) antioxidants and exogenous antioxidants such as vitamin C, vitamin E, anthocyanidins,

*DOI: http://dx.doi.org/10.5772/intechopen.84803*

*Adapted from [17].*

*Nutrient composition of fresh strawberries.*

**Table 1.**


*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural… DOI: http://dx.doi.org/10.5772/intechopen.84803*

#### **Table 1.**

*Strawberry - Pre- and Post-Harvest Management Techniques for Higher Fruit Quality*

quality improvement in strawberry are also discussed.

**2. Nutritional and health benefit profile of strawberry**

iodine, magnesium, copper, iron, and phosphorus (**Table 1**).

Strawberries are an excellent source of essential and health benefitting nutrients

**2.1 Role of strawberry as a source of dietary antioxidants compared with similar** 

Strawberry consumption can help to prevent inflammation, oxidative stress, cardiovascular disease (CVD), certain types of cancers, type 2 diabetes, and obesity. The addition of berries to the diet can positively influence risk factors for CVD by

(**Table 1**) and low in total calories with a 100 g serving providing only 32 kcal. Their sweet flavor makes them a delicious alternative to processed foods. Dietary fiber present in strawberries may contribute to regulating blood sugar levels by slowing digestion. Fiber content may also control calorie intake by its satiating effect. Strawberries contain fat-soluble vitamins (i.e., vitamin A and tocopherol) and carotenoids (i.e., lutein and zeaxanthin), but one of the aspects of major nutritional relevance is the extremely high content of vitamin C, even higher than citrus fruits. Together with vitamin C, folate plays a crucial role in the nutritional quality of strawberry as it is one of the richest natural sources of this essential micronutrient, and folate is an important factor in health promotion and disease prevention [15, 16]. Strawberry is a source of several other vitamins such as thiamin, vitamin B6, vitamin K, vitamin A, and vitamin E although to a lesser extent (**Table 1**). It is also an excellent source of manganese providing more than 20% of the daily adequate intake (AI) for this mineral per serving. The same amount of strawberries can provide about 5% of the AI for potassium and is known as a good source of

researchers have been testing novel, sustainable approaches to improve the quality and antioxidant properties of strawberries to increase health benefits. One of the reasons for strawberry demand and consumption has been going up as this fruit is an excellent source of natural antioxidants, such as carotenoids, phenolics, vitamins, anthocyanins, and flavonoids with remarkably high capacity of scavenging free radicals [4]. Improving fruit quality and yield sustainability without synthetic inputs is a research priority for this nutritious fruit. Beneficial microorganisms that are used as bio-fertilizers or bio-stimulants possess the ability to colonize the rhizosphere, plant roots, or both when applied to seeds or plant organs that are used for vegetative propagation (strawberry tips). Some of these microbes have shown potential to promote strawberry plant growth by the release of metabolites into the rhizosphere that may inhibit various pathogens as biocontrol agents [5–8]. However, Tomic et al. [9] found that the response to bacterial inoculation is cultivar-related in strawberries. These microbes were reported to improve plant nutrition and support plant development under natural or stressed conditions as well as increase yield and quality of many important crops and thus may play a crucial role in sustainable crop production in the future [10–12]. A small but significant body of literature also suggests that these microbes can increase strawberry fruit quality in terms of taste and nutritional value and thereby have a positive impact on human health with associated reduction of healthcare costs [13, 14]. The objective of this review is to update our knowledge on the research conducted on improving yield and quality of strawberry by using natural products and beneficial microbes around the globe. Major focus of the review is to relate bio-fortified strawberry fruit with human health benefit. Some novel eco-friendly approaches and potential mechanisms involved with yield and

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**sources**

*Nutrient composition of fresh strawberries.*

inhibiting inflammation, improving plasma lipid profiles, scavenging free radicals, and increasing LDL resistance to oxidation [18]. The mechanisms by which strawberries exert these positive effects are not completely understood. Among many potential mechanisms, its role as an antioxidant is the most relevant as strawberry supplementation significantly decreases oxidative stress, protecting mononuclear blood cells against DNA damage [19, 20]. Several studies have shown that strawberry generally possesses a high level of antioxidant activity, which is linked to the levels of phenolic compounds in the fruit rather than vitamin C [1, 21–23]. Wang and Jiao [24] showed that strawberry juice extracts exhibited a high level of antioxidant capacity against free radical species. Strawberry extracts also seem to modulate cell signaling in cancer cells by inhibiting proliferation of several types of cancer cells inducing cell cycle arrest and apoptosis and suppressing tumor angiogenesis [25]. An unavoidable result of aerobic metabolism in humans and other organisms is the production of reactive oxygen species (ROS). ROS include free radicals such as the superoxide anion (O2•−) and hydroxyl radical (•OH), as well as nonradical molecules like hydrogen peroxide (H2O2), singlet oxygen (1O2), etc. All ROS can be damaging to organisms at a concentration where its level exceeds the defense mechanism. These excess ROS can put cells in oxidative stress that eventually pose a threat to cells by causing peroxidation of lipids, oxidation of proteins, damage to nucleic acids, and enzyme inhibition. The enhanced production of ROS during physiological stresses can also activate a programmed cell death (PCD) pathway that may lead to cell death [26–33]. Under normal conditions, ROS molecules are unable to cause any damage as they are constantly being scavenged by a range of antioxidative mechanisms [34]. But, the delicate equilibrium between the ROS production and their scavenging by antioxidants is disturbed by multiple stress factors. An efficient antioxidative system that includes nonenzymatic as well as enzymatic antioxidants in a cell can usually scavenge or detoxify excess ROS [35]. The human antioxidant defense system includes endogenous (enzymatic and nonenzymatic) antioxidants and exogenous antioxidants such as vitamin C, vitamin E, anthocyanidins,

carotenoids, flavonols, and polyphenols, with the diet being the main source [36–39]. Exogenous antioxidants play a key role in this delicate equilibrium between oxidation and antioxidation in living systems [36, 37, 40, 41]. Under physiological conditions, the human antioxidative defense system allows the elimination of excess ROS. However, our endogenous antioxidant defense systems are incomplete without exogenous reducing compounds such as vitamin C, vitamin E, carotenoids, and polyphenols. Therefore, there is a continuous demand for exogenous antioxidants to prevent oxidative stress.

Strawberry polyphenolic phytochemicals perform nonessential functions in plants but have large impacts on humans. Of the polyphenolic compounds, anthocyanins in strawberries are the best-known and quantitatively the most important. Studies have determined total anthocyanin content as 150–600 mg/kg of fresh weight. [17]. Strawberries also contain small amounts of other phenolic compounds as shown in **Table 2**. Evidence from in vitro studies shows that strawberry phenolics may have anti-inflammatory effects and suppress mutagenesis through antioxidative and genoprotective properties. Additionally, the content and composition of flavonols have been studied [42], and these compounds are identified as derivatives of quercetin and kaempferol, with quercetin derivatives being the most abundant [43]. The contents of the flavonoid groups, flavonols, and anthocyanins in strawberry extracts have been associated indirectly and directly, respectively, with the total antioxidant capacity for low-density lipoproteins [21]. Flavonoids in strawberries exhibit antioxidant [44, 45] and anticancer properties as well [46]. Elevated levels of these secondary metabolites should provide better health benefits to the consumers of strawberry.

Among numerous studies conducted on antioxidant contents in fruits and vegetables, results have shown that strawberry possessed a high level of antioxidant activity compared with others in the same group, and the activity was directly linked to the levels of phenolic compounds in the fruit [1, 21, 22]. A comparative study on the antioxidant activity of strawberry extract with other fruits based on the oxygen radical absorbance capacity assay indicated that its antioxidant capacity was higher than extracts from plum, orange, red grape, kiwifruit, pink grapefruit, white grape, banana, apple, tomato, pear, and honeydew melon [47]. However, Sun et al. [22]


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*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural…*

ranked fruit differently for antioxidant contents based on total antioxidant oxyradical scavenging assay. These results put strawberry behind cranberry, apple, and grape but before peach, lemon, banana, pear, orange, grapefruit, and pineapple in terms of antioxidant activity of fruit extracts. Total antioxidant activity of strawberry can also relate to the contents of anthocyanins, which are typically present at high levels in this fruit [47]. Great interest has developed in strawberries due to the extremely high content of vitamin C, which makes them an important source of this vitamin for human nutrition. Relatively high content of ellagic acid is also a reason of interest for strawberries to consumers. Ellagic acid is an antioxidant that has been proposed to exert antimutagenic and anticarcinogenic effects [48, 49]. Nutritional quality of strawberry is reflected in its high levels of vitamin C, folate, and phenolic constituents [17], most of which show relevant antioxidant capacities in vitro and in vivo [50]. Moreover, strawberries are economically feasible and commercially important, and are widely consumed as fresh or in processed forms such as jam, juice, and jelly. Due to the high nutritional quality, taste, and health benefits, strawberries are among the most studied berries from the aspects of horticultural,

**3. Enhancement of yield and antioxidant contents in strawberry by** 

To overcome the challenge of increasing strawberry production with a significant reduction of agrochemical use and environmental pollution (especially from synthetic chemicals), a great deal of interest and research has been devoted to natural products and beneficial microbes in recent days. Many growers and researchers are actively looking for ways to create a more sustainable production system through use of natural inputs while simultaneously improving yield and antioxidant properties. A large body of literature suggested that integration of these products with conventional management tools could significantly reduce chemical use and make strawberry production more sustainable. Various natural products have been tested in strawberry production to improve yield and quality by preventing disease and stimulating growth and development. Among the natural products, chitosan is the most tested that has shown growth and yield stimulating effect together with efficacy against diseases in strawberries and other crops [51]. Chitosan is a polysaccharide derived from chitin outer skeletons of shell fish and crustaceans such as crab, crayfish, lobster, and shrimp. As chitin is deacetylated by sodium hydroxide to obtain chitosan, it is slightly basic and is soluble in dilute aqueous acidic solution (pH < 6.5). Once dissolved, it can be further diluted with water to apply on plants at all different growth stages. In general, it is nontoxic to humans and considered safe for agricultural uses due to its quick degradation in the environment. Once chitosan or its derivatives come in contact with plants, they bind with the cell plasma membrane and elicit defense responses through expression of pathogenesis-related (PR) genes, accumulation of phytoalexins, callose, oxidative burst, and formation of reactive oxygen species. Expression of these PR genes and accumulation of antimicrobial phytoalexins are believed to play a major role in controlling pre- and postharvest pathogenic diseases. A large body of published reports supports antimicrobial activities of chitosan against a wide range of phytopathogens [52]. Similar studies also found that the biostimulant chitosan promoted plant growth and development and provided enhanced disease suppression capability to plants through multiple mechanisms including induced systemic resistance [51, 53]. Chitosan has been widely used as fruit coatings to enhance storability and preserve anthocyanin and other antioxidants in strawberry [51], and various other fruit mainly for protection

*DOI: http://dx.doi.org/10.5772/intechopen.84803*

genomic, and sustainable production practices.

**various natural products including chitosan**

#### **Table 2.**

*Polyphenol composition reported in strawberries.*

*Improving Yield and Antioxidant Properties of Strawberries by Utilizing Microbes and Natural… DOI: http://dx.doi.org/10.5772/intechopen.84803*

ranked fruit differently for antioxidant contents based on total antioxidant oxyradical scavenging assay. These results put strawberry behind cranberry, apple, and grape but before peach, lemon, banana, pear, orange, grapefruit, and pineapple in terms of antioxidant activity of fruit extracts. Total antioxidant activity of strawberry can also relate to the contents of anthocyanins, which are typically present at high levels in this fruit [47]. Great interest has developed in strawberries due to the extremely high content of vitamin C, which makes them an important source of this vitamin for human nutrition. Relatively high content of ellagic acid is also a reason of interest for strawberries to consumers. Ellagic acid is an antioxidant that has been proposed to exert antimutagenic and anticarcinogenic effects [48, 49]. Nutritional quality of strawberry is reflected in its high levels of vitamin C, folate, and phenolic constituents [17], most of which show relevant antioxidant capacities in vitro and in vivo [50]. Moreover, strawberries are economically feasible and commercially important, and are widely consumed as fresh or in processed forms such as jam, juice, and jelly. Due to the high nutritional quality, taste, and health benefits, strawberries are among the most studied berries from the aspects of horticultural, genomic, and sustainable production practices.
