**2. Strawberry fruit quality**

Strawberry fruit quality is a composite of sensory characteristics (color, appearance, texture, mechanical properties, diseases, and defects) that give value and enjoyment to consumers [10]. Currently, strawberry producers and handlers are lengthening shelf life through early harvesting of firm fruit with less developed color. This process pays little attention to flavor, taste, and nutritional quality of harvested fruit and yet repeat purchases by consumers have been shown to depend on taste and eating quality of fruits. Therefore, the challenge is to encourage consumers to be willing to pay more for local fruit and varieties with higher quality (because they often require more careful handling and have lower yield), and producers and handlers to pay more attention to maturity, sugar content, taste and flavor of harvested strawberries [2].

Like other fresh produce, strawberry fruit quality is a product of the interaction between variety and preharvest factors. Preharvest factors such as climatic conditions and cultural practices determine the inherent quality of strawberries and the interaction of genetic characteristics, and preharvest factors determine the ultimate quality of the fruit [11]. Because strawberry fruit quality cannot be improved after harvest, the role of preharvest factors must be understood in order to improve consumer acceptance and shelf life [12]. This is because the ripening process in strawberries stops at harvest, and fruit should be picked when fully ripe to ensure good flavor and quality [13].

Maturity indices are important for deciding when to harvest strawberries. Color, soluble solids content (SSC), and titratable acidity (TA) are used as harvest indices in strawberries with >2/3 of fruit surface showing pink or red color, minimum SSC of 7% and maximum TA of 0.8% accepted as a minimum standard for timing of harvest [14]. Once strawberries ripen, they require quick marketing and careful handling to minimize injury and spoilage [13], and the indices provide some marketing flexibility to ensure that eating quality is attained by the time the fruit reaches the consumer while at the same time limiting postharvest losses. The necessity to ship strawberries to distant markets often results in harvesting at less than ideal maturity meaning less optimum quality for the consumer [13].

Berry fruits are extremely perishable and have a short market life. Several studies have shown that strawberry fruits harvested slightly under-ripe are firmer, have less decay and a longer shelf-life, and would ship better than fully ripe strawberries [15]. Because they are nonclimacteric fruit, strawberries produce very small amounts of ethylene and do not respond to ethylene treatment [13]. Therefore, ripened fruit should be kept at 0°C until time for display at retailers [14].

Sugars and organic acids have an important impact on the sensory quality of strawberry fruit. For example, a strawberry with very low sugar and acid content tastes flat [16]. Strawberry fruit contains reducing sugars such as fructose, glucose, and sucrose, comprising >65% of total fruit SSC [16]. Glucose and fructose are found in almost equal concentrations [17], while sucrose levels are generally much lower [18, 19]. The proportions of fructose, glucose, and sucrose are important in the perception of fruit quality since fructose is 1.8 times sweeter than sucrose, [20] and sucrose is about 1.7 times sweeter than glucose [16, 21].

**3**

*The Effect of Preharvest Factors on Fruit and Nutritional Quality in Strawberry*

polyphenols or tannins, which are responsible for astringency [19, 28].

factors acting only to modify the expression of textural traits [30].

concentration appears to be independent of genotype [31].

Nutritive composition of sugar, organic acid, and phenolic compounds in strawberries is very diversely distributed. To obtain the best nutritive values, the interaction between genotype and environment not only needs to be optimized, ideal harvest and post-harvest storage conditions must also be maintained.

Results indicate that the effect of genotype on strawberry fruit and nutritional quality is stronger than that of growing conditions [29]. Strawberry cultivars vary greatly in their rate of softening and overall texture [30]. It has been found that genetic factors have a direct influence on strawberry texture with environmental

Studies have shown that that genotype affects total organic acid content [31], while vitamin C content in strawberry varies among cultivars and between tissues. For example, Nelson et al. [32] found a range from 19.3 to 71.5 mg/100 g ascorbic acid in six strawberry cultivars from four locations [33], while Ezell et al. [34] found a higher rate of 38.9–88.9 mg/100 g in 28 named varieties and 16 numbered selections. Nelson et al. [32] and Ezell et al. [34] reported an average of 45 and 60 mg/100 g, respectively with Ezell et al. [34] concluding that the ascorbic acid average of 60 can be increased to 80 or more through breeding. However, malic acid

The main anthocyanin found in strawberries is pelargonidin 3-glucoside, with cyanidin 3-glucoside and pelargonidin 3-rutinoside present as minor components [35]. Differences have also been reported for other quality attributes. For instance, Anagnostou [36] reported that fruit from the cultivar "Fern" had better color and more anthocyanins than from "Selva." When evaluated for firmness, "Carlsbad" was the firmest and "Rosalinda" the softest [37], confirming that firmness is mainly cultivar dependent [36]. In the same study, Anagnostou [36] also found that TA was not significantly affected by cultivar. Differences in the incidence of albino fruit production as reported by Sharma [38] can be attributed to genetic variability among cultivars. It has also been shown that relative distribution of phenolic compounds varies with genotype. Up to a 4-fold difference in flavonol content was observed between cultivars but with only slight variations associated with growing environment [39]. These results suggest that different cultivars can be used for different purposes. Some such as "Toyonoka" are firmer and more suitable for distant markets but may have lower vitamin C, anthocyanins, phenolics and flavonols, others like "Oso Grande" with good nutritional values are suitable for fresh consumption, while some like "Mazi" with high anthocyanin and flavonol content but lower levels of vitamin C, citric acid, and

total soluble solids (TSS) may be valued for their functional properties [35].

Nutritional quality can be considered an inheritable trait that can be improved through breeding [29], and breeding and biotechnology programs are working to produce new varieties with improved fruit and nutritional qualities combined with

citric) was found to be positively correlated with TA [16].

Citric acid forms the major organic acid found in strawberry fruit [22], representing 88% of the total organic acids in ripe fruit [23]. Malic acid is the second most prominent organic acid in the fruit [23], and the organic acid level (malic +

The major phenolic compounds in strawberries include anthocyanins and proanthocyanidins, ellagitannins and ellagic acid conjugates, cinnamic acid conjugates and hydroxycinnamic acid derivatives, catechin, flavan-3-ols, flavonols, and flavons [24]. These compounds have numerous health benefits [25] such as antioxidation and anti-inflammatory activities [26, 27]. Also present in the strawberry fruit are

*DOI: http://dx.doi.org/10.5772/intechopen.84619*

**3. Genetic variation**

*The Effect of Preharvest Factors on Fruit and Nutritional Quality in Strawberry DOI: http://dx.doi.org/10.5772/intechopen.84619*

Citric acid forms the major organic acid found in strawberry fruit [22], representing 88% of the total organic acids in ripe fruit [23]. Malic acid is the second most prominent organic acid in the fruit [23], and the organic acid level (malic + citric) was found to be positively correlated with TA [16].

The major phenolic compounds in strawberries include anthocyanins and proanthocyanidins, ellagitannins and ellagic acid conjugates, cinnamic acid conjugates and hydroxycinnamic acid derivatives, catechin, flavan-3-ols, flavonols, and flavons [24]. These compounds have numerous health benefits [25] such as antioxidation and anti-inflammatory activities [26, 27]. Also present in the strawberry fruit are polyphenols or tannins, which are responsible for astringency [19, 28].

Nutritive composition of sugar, organic acid, and phenolic compounds in strawberries is very diversely distributed. To obtain the best nutritive values, the interaction between genotype and environment not only needs to be optimized, ideal harvest and post-harvest storage conditions must also be maintained.

## **3. Genetic variation**

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

Some review papers exist on the effect of preharvest factors on strawberry fruit quality [6–9], but the most recent one [9] addresses major temperate berry crops and does not focus solely on strawberry. Also, since then many new research papers have been published. Therefore, this chapter will review recent publications and elaborate on the effect of preharvest factors on strawberry fruit and nutritional

Strawberry fruit quality is a composite of sensory characteristics (color, appearance, texture, mechanical properties, diseases, and defects) that give value and enjoyment to consumers [10]. Currently, strawberry producers and handlers are lengthening shelf life through early harvesting of firm fruit with less developed color. This process pays little attention to flavor, taste, and nutritional quality of harvested fruit and yet repeat purchases by consumers have been shown to depend on taste and eating quality of fruits. Therefore, the challenge is to encourage consumers to be willing to pay more for local fruit and varieties with higher quality (because they often require more careful handling and have lower yield), and producers and handlers to pay more attention to maturity, sugar content, taste and

Like other fresh produce, strawberry fruit quality is a product of the interaction between variety and preharvest factors. Preharvest factors such as climatic conditions and cultural practices determine the inherent quality of strawberries and the interaction of genetic characteristics, and preharvest factors determine the ultimate quality of the fruit [11]. Because strawberry fruit quality cannot be improved after harvest, the role of preharvest factors must be understood in order to improve consumer acceptance and shelf life [12]. This is because the ripening process in strawberries stops at harvest, and

Maturity indices are important for deciding when to harvest strawberries. Color, soluble solids content (SSC), and titratable acidity (TA) are used as harvest indices in strawberries with >2/3 of fruit surface showing pink or red color, minimum SSC of 7% and maximum TA of 0.8% accepted as a minimum standard for timing of harvest [14]. Once strawberries ripen, they require quick marketing and careful handling to minimize injury and spoilage [13], and the indices provide some marketing flexibility to ensure that eating quality is attained by the time the fruit reaches the consumer while at the same time limiting postharvest losses. The necessity to ship strawberries to distant markets often results in harvesting at less than

fruit should be picked when fully ripe to ensure good flavor and quality [13].

ideal maturity meaning less optimum quality for the consumer [13].

and sucrose is about 1.7 times sweeter than glucose [16, 21].

Berry fruits are extremely perishable and have a short market life. Several studies have shown that strawberry fruits harvested slightly under-ripe are firmer, have less decay and a longer shelf-life, and would ship better than fully ripe strawberries [15]. Because they are nonclimacteric fruit, strawberries produce very small amounts of ethylene and do not respond to ethylene treatment [13]. Therefore, ripened fruit should be kept at 0°C until time for display at retailers [14].

Sugars and organic acids have an important impact on the sensory quality of strawberry fruit. For example, a strawberry with very low sugar and acid content tastes flat [16]. Strawberry fruit contains reducing sugars such as fructose, glucose, and sucrose, comprising >65% of total fruit SSC [16]. Glucose and fructose are found in almost equal concentrations [17], while sucrose levels are generally much lower [18, 19]. The proportions of fructose, glucose, and sucrose are important in the perception of fruit quality since fructose is 1.8 times sweeter than sucrose, [20]

**2**

quality.

**2. Strawberry fruit quality**

flavor of harvested strawberries [2].

Results indicate that the effect of genotype on strawberry fruit and nutritional quality is stronger than that of growing conditions [29]. Strawberry cultivars vary greatly in their rate of softening and overall texture [30]. It has been found that genetic factors have a direct influence on strawberry texture with environmental factors acting only to modify the expression of textural traits [30].

Studies have shown that that genotype affects total organic acid content [31], while vitamin C content in strawberry varies among cultivars and between tissues. For example, Nelson et al. [32] found a range from 19.3 to 71.5 mg/100 g ascorbic acid in six strawberry cultivars from four locations [33], while Ezell et al. [34] found a higher rate of 38.9–88.9 mg/100 g in 28 named varieties and 16 numbered selections. Nelson et al. [32] and Ezell et al. [34] reported an average of 45 and 60 mg/100 g, respectively with Ezell et al. [34] concluding that the ascorbic acid average of 60 can be increased to 80 or more through breeding. However, malic acid concentration appears to be independent of genotype [31].

The main anthocyanin found in strawberries is pelargonidin 3-glucoside, with cyanidin 3-glucoside and pelargonidin 3-rutinoside present as minor components [35]. Differences have also been reported for other quality attributes. For instance, Anagnostou [36] reported that fruit from the cultivar "Fern" had better color and more anthocyanins than from "Selva." When evaluated for firmness, "Carlsbad" was the firmest and "Rosalinda" the softest [37], confirming that firmness is mainly cultivar dependent [36]. In the same study, Anagnostou [36] also found that TA was not significantly affected by cultivar. Differences in the incidence of albino fruit production as reported by Sharma [38] can be attributed to genetic variability among cultivars.

It has also been shown that relative distribution of phenolic compounds varies with genotype. Up to a 4-fold difference in flavonol content was observed between cultivars but with only slight variations associated with growing environment [39].

These results suggest that different cultivars can be used for different purposes. Some such as "Toyonoka" are firmer and more suitable for distant markets but may have lower vitamin C, anthocyanins, phenolics and flavonols, others like "Oso Grande" with good nutritional values are suitable for fresh consumption, while some like "Mazi" with high anthocyanin and flavonol content but lower levels of vitamin C, citric acid, and total soluble solids (TSS) may be valued for their functional properties [35].

Nutritional quality can be considered an inheritable trait that can be improved through breeding [29], and breeding and biotechnology programs are working to produce new varieties with improved fruit and nutritional qualities combined with high plant production efficiency [29]. Wild species like *F. virginiana* spp. glauca and *F. vesca* are good sources of bioactive compounds. *F. virginiana* spp. glauca is also an important genetic source of nutritional quality and other unique traits such as day neutrality, and plant and disease resistance [29]. Breeding for improved nutritional and fruit quality parameters offers the possibility of new commercial varieties that can yield high-quality fruit at reasonable cost [29].
