**5. Postharvest treatments**

### **5.1 Physical treatments**

Physical methods include high or low temperature treatments**,** irradiation and use of modified or controlled atmospheres.

#### *5.1.1 High-temperature treatments*

High temperature treatments can control insect pests, prevent pathogen infection, induce resistance to chilling injury, slow fruit ripening, and extend postharvest shelf life [34, 35]. Application of thermal treatments reduced the fungal development, ripening rate and extended the shelf life in strawberry [36]. Strawberry shelf life may be improved by an appropriate thermal treatment that could be used instead of fumigation to allow a more advantageous usage of this fruit in the commercial chain.

#### *5.1.2 Low temperature*

Freezing of fruits and vegetable is one of the most common ways for maintaining the quality of these products. Frozen storage of strawberry, at 18°C after 7 months, had a specific effect on color but no significant different in total anthocyanin was observed [37]. Decrease of anthocyanin content in frozen storage strawberry, at 20°C after 6 months, depending on variety was 11–27.5% [38]. The storage temperatures of 18 and 24°C were best for preserving the qualitative characteristics (color, texture, flavor and wholeness) of the strawberries [39].

#### *5.1.3 Irradiation*

Alternative control methods that do not leave residues, such as postharvest UV-C radiation, have been shown to prevent decay and improve fruit quality [40–44]. Ultraviolet C (UV-C) radiation is known for preventing fungal decay and enhancing phytochemical content in fruit when applied postharvest. Additionally, it has been reported that postharvest UV-C radiation induces secondary metabolites production that protect fruit against abiotic and biotic stresses [45]. Furthermore, these metabolites (phenolic compounds, anthocyanins, carotenoids) also play an important role in fruit quality with impact on human health [46]. UV-treated fruits had a lower respiration rate, higher titratable acidity and anthocyanin content, and were firmer than the untreated fruits. The percentage of free sugars increased faster in UV treated fruits at the beginning of the storage period [40]. Freshly harvested strawberries of cv. Kent, at 25–50% red were exposed to UV-C at doses of 0.25 and 1.0 kJ/m2 and stored at 4 or 13°C after exposure which has resulted in controlling the decay caused by *Botrytis cinerea* at both storage temperatures and extended the shelf-life of the fruits by 4–5 days [40].

#### **5.2 Chemical treatments**

#### *5.2.1 Fumigation*

Methyl bromide fumigation is the current treatment for postharvest strawberry disinfestation of pests such as western flower thrips [*Frankliniella occidentalis* (Pergande)] and two-spotted spider mite (*Tetranychus urticae* Koch). Due to the reduced availability and increased cost of methyl bromide (as a result of its phase out in 2005 for all uses except quarantine treatments), an alternative treatment is

**29**

*Fruit Physiology and Postharvest Management of Strawberry*

desirable. Low molecular weight volatile compounds such as ethyl formate (EF) are produced by several fruits and vegetables which are important components for flavor and aroma and also have been revealed to have insecticidal and fungicidal properties [47]. Before the product reaches the market, these low molecular weight volatile compounds can potentially undergo degradation to biogenic levels in the tissues of treated commodities which is an advantage over conventional chemicals,

Ethyl formate is currently in the process of being formulated with CO2 for commercial use in Australia and New Zealand. Simpson et al. [48] showed that CO2 in combination with Ethyl formate significantly reduced pest population (Western flower thrips and Red spider mite) without causing any damage to the fruit quality. Nitrous oxide (NO) has been found to be ubiquitous in postharvest climacteric and nonclimacteric fruit, vegetables and flowers, with higher levels present in unripe than in ripe tissues [49, 50]. Since ethylene accumulation initiates ripening of climacteric produce and enhances senescence of nonclimacteric produce, it was speculated that application of NO might retard ripening and senescence in postharvest tissues [51]. Strawberries are a high value fruit but marketing is limited by a short postharvest life. The postharvest life can, however, be extended by minimiz-

ing the concentration of ethylene in the atmosphere around fruit [51, 52]. Wills et al. [53] performed fumigation in strawberry in an atmosphere of anaerobic nitrogen for up to 2 h at 20°C with nitric oxide concentrations ranging

dative role in enhancing postharvest shelf life of strawberry fruits [54].

weight loss and decay, higher firmness and hue angle than control [57].

Salicylic acid (SA) is a simple phenolic compound. It is recognized as a plant growth regulator, because of its external application effect on many plant growth physiological processes [55]. Salicylic acid (2 mM) effectively increased strawberry ascorbic acid content, fruit total antioxidant potential, total soluble solids and prevented fungal contaminations [56]. They also studied the reversible effect of SA and recommended plant SA treatment in all different growth stages like vegetative, fruit development and postharvest stage. Fruits of the plants of strawberry cv. Camarosa which received SA (0.03 mM) after 7 days at 28°C in their nutrient solution had less

Among secondary nutrients, calcium acts a major role in maintaining the quality of fruit and vegetables. Increasing the "Ca" content in the cell wall of fruit tissue

then held at 20 and 5°C in air containing 0.1 ml l<sup>−</sup><sup>1</sup>

Hydrogen sulfide acts as an important gaseous regulator in plants like nitrous oxide. Fumigation with hydrogen sulfide (H2S) gas released from the H2S donor NaHS increased the postharvest shelf life of strawberry fruits depending on dose used [54]. Strawberry fruits fumigated with various doses of H2S has resulted in significantly lower rot index, maximum fruit firmness, and minimum respiration intensity and polygalacturonase activities than controls. Treatment with H2S maintained higher activity levels of enzymes catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase and lowers the activities of lipoxygenase relative to untreated (controls). It also reduced hydrogen peroxide, malondialdehyde, and superoxide anion to levels below control fruits during storage. Furthermore, H2S treatment maintained higher contents of soluble proteins, reducing sugars, free amino acid, and endogenous H2S in fruits. This interprets that H2S plays an antioxi-

ethylene

*DOI: http://dx.doi.org/10.5772/intechopen.84205*

which can persist as residues in food products.

which had resulted in extension of postharvest life.

from 1.0 to 4000 ml l<sup>−</sup><sup>1</sup>

*5.2.2 Salicylic acid*

*5.2.3 Calcium dips*

#### *Fruit Physiology and Postharvest Management of Strawberry DOI: http://dx.doi.org/10.5772/intechopen.84205*

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

Physical methods include high or low temperature treatments**,** irradiation and

High temperature treatments can control insect pests, prevent pathogen infection, induce resistance to chilling injury, slow fruit ripening, and extend postharvest shelf life [34, 35]. Application of thermal treatments reduced the fungal development, ripening rate and extended the shelf life in strawberry [36]. Strawberry shelf life may be improved by an appropriate thermal treatment that could be used instead of fumigation to allow a more advantageous usage of this fruit in the commercial chain.

Freezing of fruits and vegetable is one of the most common ways for maintaining the quality of these products. Frozen storage of strawberry, at 18°C after 7 months, had a specific effect on color but no significant different in total anthocyanin was observed [37]. Decrease of anthocyanin content in frozen storage strawberry, at 20°C after 6 months, depending on variety was 11–27.5% [38]. The storage temperatures of 18 and 24°C were best for preserving the qualitative characteristics

Alternative control methods that do not leave residues, such as postharvest UV-C

and stored at 4 or 13°C after exposure which has resulted in controlling

the decay caused by *Botrytis cinerea* at both storage temperatures and extended the

Methyl bromide fumigation is the current treatment for postharvest strawberry

disinfestation of pests such as western flower thrips [*Frankliniella occidentalis* (Pergande)] and two-spotted spider mite (*Tetranychus urticae* Koch). Due to the reduced availability and increased cost of methyl bromide (as a result of its phase out in 2005 for all uses except quarantine treatments), an alternative treatment is

radiation, have been shown to prevent decay and improve fruit quality [40–44]. Ultraviolet C (UV-C) radiation is known for preventing fungal decay and enhancing phytochemical content in fruit when applied postharvest. Additionally, it has been reported that postharvest UV-C radiation induces secondary metabolites production that protect fruit against abiotic and biotic stresses [45]. Furthermore, these metabolites (phenolic compounds, anthocyanins, carotenoids) also play an important role in fruit quality with impact on human health [46]. UV-treated fruits had a lower respiration rate, higher titratable acidity and anthocyanin content, and were firmer than the untreated fruits. The percentage of free sugars increased faster in UV treated fruits at the beginning of the storage period [40]. Freshly harvested strawberries of cv. Kent, at 25–50% red were exposed to UV-C at doses of 0.25 and

(color, texture, flavor and wholeness) of the strawberries [39].

**5. Postharvest treatments**

*5.1.1 High-temperature treatments*

use of modified or controlled atmospheres.

**5.1 Physical treatments**

*5.1.2 Low temperature*

*5.1.3 Irradiation*

1.0 kJ/m2

shelf-life of the fruits by 4–5 days [40].

**5.2 Chemical treatments**

*5.2.1 Fumigation*

**28**

desirable. Low molecular weight volatile compounds such as ethyl formate (EF) are produced by several fruits and vegetables which are important components for flavor and aroma and also have been revealed to have insecticidal and fungicidal properties [47]. Before the product reaches the market, these low molecular weight volatile compounds can potentially undergo degradation to biogenic levels in the tissues of treated commodities which is an advantage over conventional chemicals, which can persist as residues in food products.

Ethyl formate is currently in the process of being formulated with CO2 for commercial use in Australia and New Zealand. Simpson et al. [48] showed that CO2 in combination with Ethyl formate significantly reduced pest population (Western flower thrips and Red spider mite) without causing any damage to the fruit quality.

Nitrous oxide (NO) has been found to be ubiquitous in postharvest climacteric and nonclimacteric fruit, vegetables and flowers, with higher levels present in unripe than in ripe tissues [49, 50]. Since ethylene accumulation initiates ripening of climacteric produce and enhances senescence of nonclimacteric produce, it was speculated that application of NO might retard ripening and senescence in postharvest tissues [51]. Strawberries are a high value fruit but marketing is limited by a short postharvest life. The postharvest life can, however, be extended by minimizing the concentration of ethylene in the atmosphere around fruit [51, 52].

Wills et al. [53] performed fumigation in strawberry in an atmosphere of anaerobic nitrogen for up to 2 h at 20°C with nitric oxide concentrations ranging from 1.0 to 4000 ml l<sup>−</sup><sup>1</sup> then held at 20 and 5°C in air containing 0.1 ml l<sup>−</sup><sup>1</sup> ethylene which had resulted in extension of postharvest life.

Hydrogen sulfide acts as an important gaseous regulator in plants like nitrous oxide. Fumigation with hydrogen sulfide (H2S) gas released from the H2S donor NaHS increased the postharvest shelf life of strawberry fruits depending on dose used [54]. Strawberry fruits fumigated with various doses of H2S has resulted in significantly lower rot index, maximum fruit firmness, and minimum respiration intensity and polygalacturonase activities than controls. Treatment with H2S maintained higher activity levels of enzymes catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase and lowers the activities of lipoxygenase relative to untreated (controls). It also reduced hydrogen peroxide, malondialdehyde, and superoxide anion to levels below control fruits during storage. Furthermore, H2S treatment maintained higher contents of soluble proteins, reducing sugars, free amino acid, and endogenous H2S in fruits. This interprets that H2S plays an antioxidative role in enhancing postharvest shelf life of strawberry fruits [54].

### *5.2.2 Salicylic acid*

Salicylic acid (SA) is a simple phenolic compound. It is recognized as a plant growth regulator, because of its external application effect on many plant growth physiological processes [55]. Salicylic acid (2 mM) effectively increased strawberry ascorbic acid content, fruit total antioxidant potential, total soluble solids and prevented fungal contaminations [56]. They also studied the reversible effect of SA and recommended plant SA treatment in all different growth stages like vegetative, fruit development and postharvest stage. Fruits of the plants of strawberry cv. Camarosa which received SA (0.03 mM) after 7 days at 28°C in their nutrient solution had less weight loss and decay, higher firmness and hue angle than control [57].

#### *5.2.3 Calcium dips*

Among secondary nutrients, calcium acts a major role in maintaining the quality of fruit and vegetables. Increasing the "Ca" content in the cell wall of fruit tissue

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

can aid to delay softening and mold growth and decrease the occurrence of physiological disorders [58]. Common techniques like dipping and vacuum or pressure infiltrations are used to increase cell wall Ca content of fruit tissue after harvest. The firming effect can be explained by the crosslinks formation between the carboxyl groups of polyuronide chains found in the middle lamella of the cell wall; Ca also increases cell turgor pressure [59, 60] and stabilizes the cell membrane [61]. Calcium dips have been employed to improve firmness and extend the postharvest shelf-life of a wide range of fruit and vegetables. In strawberries, CaCl2 dips in combination with heat treatment or modified atmosphere storage and refrigeration increase calcium content and fruit firmness and delay postharvest decay [62, 63]. Calcium dips were effective in decreasing surface damage and delaying both fungal decay and loss of firmness in strawberries, compared to untreated fruit [64].
