**Abstract**

This review summarizes and critically analyzes the different types of potential valorization options for strawberry extrudate in order to have a broader overview of the potential management of this waste. Animal feed is commonly used as a management option for the strawberry extrudate; however, most of the strawberry extrudate is disposed in landfills. Strawberry extrudate contains different bioactive compounds that encourage the use of an alternative management approach than landfilled. The present review offers a complete comparative, including the advantages and drawbacks of each reviewed technique, to facilitate the selection of the most suitable technology for the different valorization scenarios. This review has been structured in three sections: 1. Composition of the strawberry extrudate and strawberry especially focused on their content in bioactive compounds. 2. The different techniques of extraction and purification of bioactive compounds. 3. The handling and management of the resulting biomass after the extraction process of bioactive compounds.

**Keywords:** strawberry extrudate, bioactive compounds, bioproducts, extraction techniques, purification

#### **1. Introduction**

In 2016, 8 million tons of strawberry were produced in the world with a value of agricultural gross production of 17,739 million US\$ [1]. Besides its market as fresh product, strawberry is also used to produce many types of by-products, due to its peculiar flavor and aroma. Strawberry by-products are mainly formulated from a strawberry concentrate. The most common technology to obtain the strawberry concentrate is by extrusion. Strawberries are extruded by twin-screws up to several sieves with different mesh sizes. The sieves retain a residual fraction formed by the fibrous part and the achenes, named strawberry extrudate, which accounts about 7% of the manufactured strawberry [2].

Animal feed is commonly used as a management option for the strawberry extrudate, however, most of the strawberry extrudate is disposed in landfills, contributing to greenhouse emissions due to its high organic load [3]. Alternatives for strawberry extrudate management are required to avoid severe environmental

#### *Innovation in the Food Sector Through the Valorization of Food and Agro-Food By-Products*

impacts that cause landfills, such as negative effects on agricultural soil quality, polluting of aquatic ecosystems and atmospheric contamination [4].

Similar to strawberry, strawberry extrudate contains substances of high interest such as bioactive compounds. Some of these bioactive compounds have beneficial health effects on cardiovascular, neurological or cancerous disorders [5]. Due to their health benefits, bioactive compounds have an economic interest for different commercial sectors, such as the pharmaceutical, food and chemical industries [6]. Added to bioactive compounds, strawberry extrudate could be used to obtain other types of resources such as bioenergy [7, 8]. It is also well known the high phenolic composition in the achenes and in the pulp of the strawberry [9].

A general biorefinery scheme as a management option for the strawberry extrudate should look for synergies between unitary processes of extraction of bioactive compounds, purification and the management of the final biomass of the strawberry extrudate after extraction (**Figure 1**).

The extraction of bioactive compounds in agro-waste materials, such as the strawberry extrudate can be performed through various extraction techniques [10]. The main objective at this step consists of solubilizing the compounds of interest, with less possible impurities and making it an economically profitable technique. Extraction techniques in literature can be clustered into two groups: conventional extraction techniques, e.g. hydrothermal treatments, which are widely used at lab and full scale [11], and in recent years, more innovative techniques, e.g. enzyme assisted extraction. Additionally, combined extraction techniques between conventional and innovative techniques are being carried out to achieve high extraction yield [12]. All these extraction techniques will be revised and analyzed in the present chapter.

Any of these extraction techniques usually generate a liquid phase, with the bioactive compounds of interest, and a solid phase with a high amount of organic matter. After purification process of the liquid phase, a new liquid phase remains without the extracted bioactive compounds. Therefore, just the recovery of compounds of interest from the strawberry extrudate does not solve the problem of stabilization of the biomass of the strawberry extrudate and the use of a subsequent

**273**

*Valorization Options of Strawberry Extrudate Agro-Waste. A Review*

treatment is necessary for its stabilization [13]. The liquid phase after purification and the solid phase must undergo a new treatment for stabilization. In addition, extraction and purification processes consume energy which should be valued. The main options for assessing and stabilizing biomass after the extraction and purification process of the bioactive compounds should be focused on obtaining bioenergy

The present chapter aims to summarize the bioactive compounds present in strawberries, to summarizes and critically analyzes the different extraction and purification techniques for the recovery of these bioactive compounds, as well as the different options for the management and stabilization of the strawberry

**2. Bioactive compounds in strawberry extrudate and strawberries**

Strawberry extrudate presents similar nutrients composition than strawberry [15]. The strawberry has high concentration of dietary fibrous (2 g fibrous/100 g raw strawberry), such as lignin, hemicellulose, cellulose, and pectin, containing small amounts of protein (0.4–0.5 g protein/100 g raw strawberry) and fat (0.1 g

The strawberry contains high concentrations of vitamin C, contributing to 24% to the antioxidant capacity of strawberries [16]. The recommended daily intake of vitamins (100–150 mg/day) can be satisfied with an average of 100 g of strawberries per day [18]. Furthermore, strawberry is a source of many other vitamins in smaller amounts, such as vitamin E, vitamin A, vitamin B6, vitamin K, thiamine, riboflavin, folate acid, and niacin (0.01–0.4 g vitamin/100 g raw strawberry) [5, 19]. Strawberry is also rich in manganese, potassium, and a good source of iodine, magnesium, cop-

The sugar composition of strawberries varies with the degree of maturity of the fruit [20], being glucose, fructose, and sucrose the main sugars in strawberries [5]. Sugars in strawberries are involved in the taste of the fruit and are responsible for the caloric value of the strawberries. Organic fatty acids such as citric acid, malic acid, succinic acid, tartaric acid, oxalic acid, and fumaric acid are ones of the response of the taste, texture, pH, and color of the strawberry, and can alter the

**Figure 2** shows a general scheme for the classification of phytochemical compounds that can be founded in the strawberry extrudate. Phytochemicals are widely studied, mainly due to the extensive types of compounds that have potential biological benefits in humans. The main phytochemicals in strawberries are the flavonoids, followed by the hydrolysable tannins and the phenolic acids and, as

Flavonoids are divided into two groups, i.e. anthocyanins, and anthoxanthines. Anthoxanthines, in turn, are grouped into five subclasses, i.e. flavones, flavonols, flavanones, flavanols, and isoflavones [21]. The three main classes of flavonoids in

*DOI: http://dx.doi.org/10.5772/intechopen.93997*

and other bioproducts of interest [14].

extrudate after the extraction process.

fat/100 g raw strawberry) [16, 17].

per, iron, and phosphorus [5, 16].

sensory quality of this fruit [6].

minor constituents, the condensed tannins [5].

strawberries are anthocyanis, flavonols, and flavanols [22].

**2.2 Phytochemicals**

*2.2.1 Flavonoids*

**2.1 Nutrients**

#### **Figure 1.**

*General scheme of a biorefinery approach as a valorisation option for strawberry extrudate.*

*Valorization Options of Strawberry Extrudate Agro-Waste. A Review DOI: http://dx.doi.org/10.5772/intechopen.93997*

treatment is necessary for its stabilization [13]. The liquid phase after purification and the solid phase must undergo a new treatment for stabilization. In addition, extraction and purification processes consume energy which should be valued. The main options for assessing and stabilizing biomass after the extraction and purification process of the bioactive compounds should be focused on obtaining bioenergy and other bioproducts of interest [14].

The present chapter aims to summarize the bioactive compounds present in strawberries, to summarizes and critically analyzes the different extraction and purification techniques for the recovery of these bioactive compounds, as well as the different options for the management and stabilization of the strawberry extrudate after the extraction process.

## **2. Bioactive compounds in strawberry extrudate and strawberries**

#### **2.1 Nutrients**

*Innovation in the Food Sector Through the Valorization of Food and Agro-Food By-Products*

impacts that cause landfills, such as negative effects on agricultural soil quality,

A general biorefinery scheme as a management option for the strawberry extrudate should look for synergies between unitary processes of extraction of bioactive compounds, purification and the management of the final biomass of the

The extraction of bioactive compounds in agro-waste materials, such as the strawberry extrudate can be performed through various extraction techniques [10]. The main objective at this step consists of solubilizing the compounds of interest, with less possible impurities and making it an economically profitable technique. Extraction techniques in literature can be clustered into two groups: conventional extraction techniques, e.g. hydrothermal treatments, which are widely used at lab and full scale [11], and in recent years, more innovative techniques, e.g. enzyme assisted extraction. Additionally, combined extraction techniques between conventional and innovative techniques are being carried out to achieve high extraction yield [12]. All these extraction techniques will be revised and analyzed in the

Any of these extraction techniques usually generate a liquid phase, with the bioactive compounds of interest, and a solid phase with a high amount of organic matter. After purification process of the liquid phase, a new liquid phase remains without the extracted bioactive compounds. Therefore, just the recovery of compounds of interest from the strawberry extrudate does not solve the problem of stabilization of the biomass of the strawberry extrudate and the use of a subsequent

*General scheme of a biorefinery approach as a valorisation option for strawberry extrudate.*

Similar to strawberry, strawberry extrudate contains substances of high interest such as bioactive compounds. Some of these bioactive compounds have beneficial health effects on cardiovascular, neurological or cancerous disorders [5]. Due to their health benefits, bioactive compounds have an economic interest for different commercial sectors, such as the pharmaceutical, food and chemical industries [6]. Added to bioactive compounds, strawberry extrudate could be used to obtain other types of resources such as bioenergy [7, 8]. It is also well known the high phenolic

polluting of aquatic ecosystems and atmospheric contamination [4].

composition in the achenes and in the pulp of the strawberry [9].

strawberry extrudate after extraction (**Figure 1**).

present chapter.

**272**

**Figure 1.**

Strawberry extrudate presents similar nutrients composition than strawberry [15]. The strawberry has high concentration of dietary fibrous (2 g fibrous/100 g raw strawberry), such as lignin, hemicellulose, cellulose, and pectin, containing small amounts of protein (0.4–0.5 g protein/100 g raw strawberry) and fat (0.1 g fat/100 g raw strawberry) [16, 17].

The strawberry contains high concentrations of vitamin C, contributing to 24% to the antioxidant capacity of strawberries [16]. The recommended daily intake of vitamins (100–150 mg/day) can be satisfied with an average of 100 g of strawberries per day [18]. Furthermore, strawberry is a source of many other vitamins in smaller amounts, such as vitamin E, vitamin A, vitamin B6, vitamin K, thiamine, riboflavin, folate acid, and niacin (0.01–0.4 g vitamin/100 g raw strawberry) [5, 19]. Strawberry is also rich in manganese, potassium, and a good source of iodine, magnesium, copper, iron, and phosphorus [5, 16].

The sugar composition of strawberries varies with the degree of maturity of the fruit [20], being glucose, fructose, and sucrose the main sugars in strawberries [5]. Sugars in strawberries are involved in the taste of the fruit and are responsible for the caloric value of the strawberries. Organic fatty acids such as citric acid, malic acid, succinic acid, tartaric acid, oxalic acid, and fumaric acid are ones of the response of the taste, texture, pH, and color of the strawberry, and can alter the sensory quality of this fruit [6].

#### **2.2 Phytochemicals**

**Figure 2** shows a general scheme for the classification of phytochemical compounds that can be founded in the strawberry extrudate. Phytochemicals are widely studied, mainly due to the extensive types of compounds that have potential biological benefits in humans. The main phytochemicals in strawberries are the flavonoids, followed by the hydrolysable tannins and the phenolic acids and, as minor constituents, the condensed tannins [5].

#### *2.2.1 Flavonoids*

Flavonoids are divided into two groups, i.e. anthocyanins, and anthoxanthines. Anthoxanthines, in turn, are grouped into five subclasses, i.e. flavones, flavonols, flavanones, flavanols, and isoflavones [21]. The three main classes of flavonoids in strawberries are anthocyanis, flavonols, and flavanols [22].

**Figure 2.** *General scheme of phytochemicals contained in strawberries.*

The most relevant flavonoids present in strawberries are the anthocyanins due to their high concentration, approximately 20–47 mg/100 g raw strawberry [16]. More than 25 different pigments of anthocyanins have been described in the different varieties of strawberries [5]. Anthocyanins are responsible for the red color in strawberries [16]. The most important anthocyanins of the strawberry belong to the family of pelargonidin aglycones and cyanidin aglycones [23–25]. According to several studies, pelargonidin-3-glucoside is the dominant anthocyanin in strawberries [16, 24, 26–28]. The interest in anthocyanins have recently increased because of its pharmacological and therapeutic properties [5]. Anthocyanins have shown to positive effect toward reduction of coronary diseases, anticancer, antitumor, anti-inflammatory and anti-diabetic effects; as well as improving visual acuity and cognitive behavior [29]. These therapeutic effects of anthocyanins are connected to their high antioxidant activity [29]. In addition, anthocyanins can be used as a pigment in the food industry [29].

The second most important group of flavonoids in strawberries are flavonols, with approximately 1.5–3.4 mg/100 g raw strawberry [5, 16, 30, 31]. The most important flavonols of the strawberry belong to the family of quercetin and kaempferol, being the quercetin-derivatives the most abundant flavonols in strawberries [5, 17, 25–27]. Quercetin, in particular, is a potent antioxidant, cytoprotective, and anti-inflammatory [30].

Finally, the third group of flavonoids in strawberries are flavanols. Flavanols are the only class of flavonoids that do not naturally occur as glycosides. They are found in strawberries as monomeric compounds, such as catechins, and in

**275**

*Valorization Options of Strawberry Extrudate Agro-Waste. A Review*

polymeric form, which are called condensed or non-hydrolysable tannins [5, 25]. These compounds can be difficult to measure in the strawberry because they are usually presented as part of a complex mixture of phenolic substances. Because of this, the amount of catechins present is sometimes overestimated [31]. At low concentrations flavanols particularly the catechins, are used as sweetening and/ or flavoring additives. These flavonols improve taste and sweetness but are not substitutes for sweeteners and flavorings as they do not have taste and are a little astringent. Some authors have pointed out that their role is to make the receptors in the mouth more sensitive to sweeteners, thus lowering the levels of the sweeten-

Tannins are classified into two groups: non-hydrolysable or condensed tannins and hydrolysable tannins (**Figure 2**). The condensed tannins are also called proanthocyanins, and are bound to the flavanols [33]. The content of condensed tannins in strawberries is approximately 54–163 mg/100 g raw strawberry [16]. In strawberries, the most relevant condensed tannins are procyanidins from catechin and its polymers. Condensed tannins are commonly found in the pulp of strawberries and achenes [5]. Due to the variety of physiological activities, they have been reported to possess, directly and indirectly, antioxidant, antimicrobial, anti-allergic and antihypertensive properties, as well as to inhibit the activities of some enzymes and

The most common hydrolysable tannins in strawberries are ellagitannins, specifically sanguiin H-6 and ellagic acid [5, 26–28]. The content of ellagitannins in strawberries is approximately 10–23 mg/100 g raw strawberry [16]. Ellagic acid is an ellagitannin present in the secondary metabolism of vegetables, its main characteristic is its antioxidant, antimicrobial, antimutagenic, anticarcinogenic and antiviral capacity [16]. The content of ellagic acid in strawberries is approximately 1–2 mg/100 g raw strawberry [16]. Due to the phenolic nature of ellagic acid, this compound tends to react by forming complexes with other molecules of proteins, alkaloids, and polysaccharides, so that it is usually found as ellagitannins esterified with glucose, because of this it is difficult to find it free [20]. The properties of ellagic acid are also exploited in the food industry, so it is used in the manufacture of nutraceutical drinks and food supplements. Likewise, the application of ellagic acid for food preservation is of great impact for the perishable food industry, using its antioxidant activity for microorgan-

Strawberries contain a variety a of phenolic acids which are presented as derivatives of the hydroxycinnamic acid, such as caffeic acid, and hydroxybenzoic acids such as gallic acid [5]. The content of phenolic acids in strawberries is approximately 0.8–6.7 mg/100 g raw strawberry [16]. The major hydroxycinnamic acid in strawberries is p-coumaroylhexose, but ferulic acid and caffeic acid glycosides have also been identified in strawberries [26, 27]. Hydroxycinnamic acid derivatives are responsible for the bitter taste of the strawberry, and it is used in the manufacture of creams [33, 36]. The primary derivative of hydroxybenzoic acid is p-hydroxybenzoic glycoside [28]. The p-hydroxybenzoic glycoside is widely used in the synthesis of organic compounds and their esters, known as parabens, which are

*DOI: http://dx.doi.org/10.5772/intechopen.93997*

ers and flavorings used [21, 32].

physiological receptors [34].

isms inhibition [35].

*2.2.3 Phenolic acids*

used as preservatives in cosmetics [37].

*2.2.2 Tannins*

#### *Valorization Options of Strawberry Extrudate Agro-Waste. A Review DOI: http://dx.doi.org/10.5772/intechopen.93997*

polymeric form, which are called condensed or non-hydrolysable tannins [5, 25]. These compounds can be difficult to measure in the strawberry because they are usually presented as part of a complex mixture of phenolic substances. Because of this, the amount of catechins present is sometimes overestimated [31]. At low concentrations flavanols particularly the catechins, are used as sweetening and/ or flavoring additives. These flavonols improve taste and sweetness but are not substitutes for sweeteners and flavorings as they do not have taste and are a little astringent. Some authors have pointed out that their role is to make the receptors in the mouth more sensitive to sweeteners, thus lowering the levels of the sweeteners and flavorings used [21, 32].
