**2. Physiology and biochemistry of strawberry during ripening**

Fruit ripening involves dramatic changes in the color, texture, flavor, and aroma of fleshy fruits. Both the palatability and nutritional quality of fruit are highly dependent on its consumption at an optimum stage of ripeness. However, ripe fleshy fruits are also perishable commodities, and this presents problems for fruit production, harvesting, storage, and marketing.

The general ripening programmes (**Figure 1**) displayed by strawberry typically include: (i) modification of color through the alteration of chlorophyll, carotenoid, and/or anthocyanin accumulation; (ii) modification of texture via alteration of cell turgor and cell wall structure; (iii) accumulation and modification of acids, sugars and volatiles that affect nutritional quality, aroma and flavor; and (iv) increased susceptibility to pathogens and herbivores [2]. These changes in flavor, color, aroma and texture make fruit ripening a complex process, which must be very tightly regulated. Fruit species are categorized as either climacteric or nonclimacteric, based on physiological differences in their ripening patterns [3].

Strawberry is a nonclimacteric fruit and fast growing, with a short postharvest life. During development, receptacle growth was due to a combination of cell division and cell expansion until seventh day after petal fall, and thereafter, only

#### **Figure 1.**

*Stages of fruit development [1], from left to right color development from tip toward receptacle (anthocyanin development).*

**25**

**Figure 2.**

*Fruit Physiology and Postharvest Management of Strawberry*

cell enlargement occurs [4]. Accumulation of sugars, water and synthesis of cell walls were observed until 21–28 days after petal fall [5]. In strawberry and other fruits like grapes, growth may continue after initiation of ripening process [6]. Fruit enlargement continues until it reaches 25 per cent red or more, when chlorophylls

Auxin, the first plant hormone identified, may act as an inhibitor of ripening in some nonclimacteric fruits [7, 8]. In strawberry, it appears that auxin from the externally located achenes (seeds) inhibits the ripening of the fleshy receptacle [9]. Fruit development continues till the auxin level falls below the critical level in the receptacle and achenes, thus permitting ripening [10]. Therefore, removing the achenes promotes ripening, while treating strawberries with synthetic auxins delays

During ripening, the primary cell wall of fleshy fruits shows structural and compositional change [11], which leads to loss of firmness and facilitates the attack of pathogens, enhancing postharvest decay and reducing the quality of fresh fruit. During ripening, water soluble polyuronides increases (**Figure 2**), whereas, there will be decrease in insoluble, covalently bound pectins. Concurrently, depolymerization of pectins occurs, which has been linked with the action of a number of hydrolases, mostly polygalacturonases (PG) [14]. Xyloglucan, the main component of hemicelluloses in dicotyledons, is also considered to play a vital role in cell wall structure, since it forms cross-linkages among the cellulose polymers. Xyloglucan endotransglycosidases, endoglucanases, and expansins contribute to the depoly-

Three major components of fruit organoleptic quality are flavor, sweetness, and acidity. Fruit with intense flavor also have high titratable acidity and high soluble solids [15]. Fruit soluble solids, sugars, titratable acidity, and organic acids at

*Changes in polyuronides during fruit ripening [13], changes in ethanol insoluble powder, and total polyuronides during strawberry development (o) mg ethanol insoluble powder per gram fruit fresh weight (●) mg powder* 

have been completely degraded and anthocyanins begin to build up.

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

**2.1 Role of hormones in fruit ripening**

**2.2 Softening of fruit during ripening**

merization of xyloglucans at the time of ripening [14].

*per individual fruit (*ە *(mg total polyuronide per individual fruit.*

ripening [11, 12].

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

cell enlargement occurs [4]. Accumulation of sugars, water and synthesis of cell walls were observed until 21–28 days after petal fall [5]. In strawberry and other fruits like grapes, growth may continue after initiation of ripening process [6]. Fruit enlargement continues until it reaches 25 per cent red or more, when chlorophylls have been completely degraded and anthocyanins begin to build up.

#### **2.1 Role of hormones in fruit ripening**

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

embedded, which are popularly called seeds.

in postharvest management of strawberry.

production, harvesting, storage, and marketing.

and require cool dry storage.

fruit of strawberry is "accessory fruit" and is not a true berry. The flesh consists of the greatly enlarged flower receptacle in which many true fruits, or achenes, are

Strawberries are commercially cultivated both for immediate consumption and for processing as frozen, canned, or preserved berries or as juice. Due to the perishable nature of the berries and the improbability of mechanical picking, the fruit is generally grown near centers of consumption or processing and where sufficient labor is available. The berries are handpicked directly into small baskets and crated for marketing or put into trays for processing. Early crops can be produced under controlled conditions (glass or plastic covering). Strawberries are very perishable

To innovate a new technology for extending storage life of strawberry fruits in the postharvest area, it is necessary to understand the physiology and biochemistry of fruits. This chapter reviews fruit physiology, recent trends and future prospects

Fruit ripening involves dramatic changes in the color, texture, flavor, and aroma

The general ripening programmes (**Figure 1**) displayed by strawberry typically include: (i) modification of color through the alteration of chlorophyll, carotenoid, and/or anthocyanin accumulation; (ii) modification of texture via alteration of cell turgor and cell wall structure; (iii) accumulation and modification of acids, sugars and volatiles that affect nutritional quality, aroma and flavor; and (iv) increased susceptibility to pathogens and herbivores [2]. These changes in flavor, color, aroma and texture make fruit ripening a complex process, which must be very tightly regulated. Fruit species are categorized as either climacteric or nonclimacteric,

Strawberry is a nonclimacteric fruit and fast growing, with a short postharvest

*Stages of fruit development [1], from left to right color development from tip toward receptacle (anthocyanin* 

life. During development, receptacle growth was due to a combination of cell division and cell expansion until seventh day after petal fall, and thereafter, only

of fleshy fruits. Both the palatability and nutritional quality of fruit are highly dependent on its consumption at an optimum stage of ripeness. However, ripe fleshy fruits are also perishable commodities, and this presents problems for fruit

**2. Physiology and biochemistry of strawberry during ripening**

based on physiological differences in their ripening patterns [3].

**24**

**Figure 1.**

*development).*

Auxin, the first plant hormone identified, may act as an inhibitor of ripening in some nonclimacteric fruits [7, 8]. In strawberry, it appears that auxin from the externally located achenes (seeds) inhibits the ripening of the fleshy receptacle [9]. Fruit development continues till the auxin level falls below the critical level in the receptacle and achenes, thus permitting ripening [10]. Therefore, removing the achenes promotes ripening, while treating strawberries with synthetic auxins delays ripening [11, 12].

#### **2.2 Softening of fruit during ripening**

During ripening, the primary cell wall of fleshy fruits shows structural and compositional change [11], which leads to loss of firmness and facilitates the attack of pathogens, enhancing postharvest decay and reducing the quality of fresh fruit. During ripening, water soluble polyuronides increases (**Figure 2**), whereas, there will be decrease in insoluble, covalently bound pectins. Concurrently, depolymerization of pectins occurs, which has been linked with the action of a number of hydrolases, mostly polygalacturonases (PG) [14]. Xyloglucan, the main component of hemicelluloses in dicotyledons, is also considered to play a vital role in cell wall structure, since it forms cross-linkages among the cellulose polymers. Xyloglucan endotransglycosidases, endoglucanases, and expansins contribute to the depolymerization of xyloglucans at the time of ripening [14].

Three major components of fruit organoleptic quality are flavor, sweetness, and acidity. Fruit with intense flavor also have high titratable acidity and high soluble solids [15]. Fruit soluble solids, sugars, titratable acidity, and organic acids at

#### **Figure 2.**

*Changes in polyuronides during fruit ripening [13], changes in ethanol insoluble powder, and total polyuronides during strawberry development (o) mg ethanol insoluble powder per gram fruit fresh weight (●) mg powder per individual fruit (*ە *(mg total polyuronide per individual fruit.*

maturity are quantitatively inherited [16, 17]. Numerous biochemical changes are observed during strawberry development and especially during fruit ripening [18]. The major soluble constituents of maturing and ripe strawberries are soluble sugars and organic acids [6, 19].

#### **2.3 Sugars**

The major soluble sugars in strawberries are glucose [1.4–3.1% fresh weight (FW)], fructose (1.7–3.5% FW), and sucrose (0.2–2.5% FW) [6]. Glucose and fructose concentrations increase continuously during fruit development, while sucrose accumulates mostly during maturation [19].

#### **2.4 Organic acids**

The major organic acid is citrate, and its concentration ranges from 4 to 12 mg·g<sup>−</sup><sup>1</sup> FW. This acid contributes greatly to fruit titratable acidity, which declines gradually during fruit development. The sugar/organic acid ratio is a major parameter of strawberry taste [6].

### **2.5 Amino acids**

Of the other soluble constituents of strawberries, amino acids may also directly affect fruit taste, as was shown by the sensory evaluation of another fleshy fruit, peach [*Prunus persica* (L.) Batsch] [20]. Moreover, some amino acids are flavor precursors [20]. The major amino acids in strawberries are asparagine, glutamine, and alanine [21]. Anthocyanins (0.5–1.5 mg/g fruit weight) are a major component of the fruit, while ascorbic acid (0.3–1.2 mg/g fruit weight) makes an important contribution to the fruit nutritional value. Among the insoluble constituents, starch is present in young fruit and disappears before ripening [5].

#### **3. Harvesting**

Harvesting is generally practiced after 3–4 months from planting. Strawberries are the sweetest when they are fully ripened on the plant. It is better to leave them on the plant for a day or two till they turn red. To ensure ripeness, taste test can be made. During harvesting berries, care should be taken as ripe ones bruise very easily. For harvesting, snap the stem just above the berry to remove them from the plant. Store harvested berries out of direct sunlight in some cool place, such as a refrigerator immediately after picking to increase the storage time. Strawberries can be consumed fresh or preserved by freezing or dehydrating and canning.

#### **3.1 Robotic harvesting**

The pericarp of a strawberry is so soft that workers must harvest the fruits carefully to avoid damage. The fruits are harvested early in the morning, before the temperature of the fruits rises and they become soft; workers need to select mature red fruits from among the many fruits that have set. These factors result in long working hours during the harvest period. Mechanical harvesting trials have been conducted on the assumption of once-over picking, but utilization of this strategy is not yet widespread [13]. The commonly used selective harvesting method requires high-tech and sophisticated robot technology. In short, it is essential to design an

**27**

precooling at 4°C and storage at 4°C, respectively.

requirements.

**Figure 3.**

**4. Precooling**

*Fruit Physiology and Postharvest Management of Strawberry*

smart robot with human-like perceptive capabilities; for example, the machine would need to analyze fruit position, assess maturity level and pick the fruit without injuring the pericarp. Basic studies on robotic harvesting were initiated with orchard fruits [22]; since then, such studies have been ongoing in a number of countries [23]. This skill has then been used for vegetable fruits. Tillett [24] reviewed various robot prototypes and clarified the importance of the manipulator design and its application to practical use. Several studies have applied robotic technology to fields in greenhouses for instance, cucumber harvesting [25], strawberry harvesting (**Figure 3**) [1] tomato harvesting [26], aubergine harvesting [27] and de-leafing [28]. However, the performance and cost have not met commercial

*Robotic harvesting in strawberry [1]: (a) high tech sophisticated harvester from a distance and (b) enlarged* 

Rapid removal of field heat from freshly harvested commodities is called precooling. It slows down ripening, respiration, senescence, decay, and water loss, thus helping for quality maintenance and prolonging shelf life [29]. Rapid precooling is most essential for produce such as strawberry which has a high rate of metabolism. The process of removal of field heat can be achieved by different methods that includes room cooling (RC), forced-air cooling (FA), hydrocooling (HC) contact icing, and vacuum cooling, each differing in efficiency of heat removal. Strawberries are typically cooled used forced air cooling. Delay in cooling of harvested strawberries results in reduction of number of marketable berries due to increased water loss, softening, and losses of sugars and vitamin C [30]. Thus it is usually recommended that strawberries should be cooled to temperatures near 0°C as soon as possible (within 1 h) after harvest to limit deterioration and decay [31, 32]. However, for commercial strawberry operations, this idea is rarely achieved due to factors such as the volume of strawberries handled, cooling and handling equipment availability, and capability, economics, energy, and market conditions. Hydro-cooling is a more rapid precooling method, but strawberries are not hydro-cooled commercially, due to decay problems by the water left on the berries after Hydro-cooling [29, 32]. Park et al. [33] proved that effectiveness for keeping the freshness of strawberries was best achieved by

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

*view with different parts of robotic harvester.*

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

**Figure 3.**

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

and organic acids [6, 19].

**2.3 Sugars**

**2.4 Organic acids**

**2.5 Amino acids**

**3. Harvesting**

dehydrating and canning.

**3.1 Robotic harvesting**

eter of strawberry taste [6].

12 mg·g<sup>−</sup><sup>1</sup>

maturity are quantitatively inherited [16, 17]. Numerous biochemical changes are observed during strawberry development and especially during fruit ripening [18]. The major soluble constituents of maturing and ripe strawberries are soluble sugars

The major soluble sugars in strawberries are glucose [1.4–3.1% fresh weight (FW)], fructose (1.7–3.5% FW), and sucrose (0.2–2.5% FW) [6]. Glucose and fructose concentrations increase continuously during fruit development, while

The major organic acid is citrate, and its concentration ranges from 4 to

gradually during fruit development. The sugar/organic acid ratio is a major param-

Of the other soluble constituents of strawberries, amino acids may also directly affect fruit taste, as was shown by the sensory evaluation of another fleshy fruit, peach [*Prunus persica* (L.) Batsch] [20]. Moreover, some amino acids are flavor precursors [20]. The major amino acids in strawberries are asparagine, glutamine, and alanine [21]. Anthocyanins (0.5–1.5 mg/g fruit weight) are a major component of the fruit, while ascorbic acid (0.3–1.2 mg/g fruit weight) makes an important contribution to the fruit nutritional value. Among the insoluble constituents, starch

FW. This acid contributes greatly to fruit titratable acidity, which declines

sucrose accumulates mostly during maturation [19].

is present in young fruit and disappears before ripening [5].

Harvesting is generally practiced after 3–4 months from planting.

Strawberries are the sweetest when they are fully ripened on the plant. It is better to leave them on the plant for a day or two till they turn red. To ensure ripeness, taste test can be made. During harvesting berries, care should be taken as ripe ones bruise very easily. For harvesting, snap the stem just above the berry to remove them from the plant. Store harvested berries out of direct sunlight in some cool place, such as a refrigerator immediately after picking to increase the storage time. Strawberries can be consumed fresh or preserved by freezing or

The pericarp of a strawberry is so soft that workers must harvest the fruits carefully to avoid damage. The fruits are harvested early in the morning, before the temperature of the fruits rises and they become soft; workers need to select mature red fruits from among the many fruits that have set. These factors result in long working hours during the harvest period. Mechanical harvesting trials have been conducted on the assumption of once-over picking, but utilization of this strategy is not yet widespread [13]. The commonly used selective harvesting method requires high-tech and sophisticated robot technology. In short, it is essential to design an

**26**

*Robotic harvesting in strawberry [1]: (a) high tech sophisticated harvester from a distance and (b) enlarged view with different parts of robotic harvester.*

smart robot with human-like perceptive capabilities; for example, the machine would need to analyze fruit position, assess maturity level and pick the fruit without injuring the pericarp. Basic studies on robotic harvesting were initiated with orchard fruits [22]; since then, such studies have been ongoing in a number of countries [23]. This skill has then been used for vegetable fruits. Tillett [24] reviewed various robot prototypes and clarified the importance of the manipulator design and its application to practical use. Several studies have applied robotic technology to fields in greenhouses for instance, cucumber harvesting [25], strawberry harvesting (**Figure 3**) [1] tomato harvesting [26], aubergine harvesting [27] and de-leafing [28]. However, the performance and cost have not met commercial requirements.
