*3.2.1 Adsorbents*

There are many studies that show the properties of adsorbents to separate, concentrate and purify various compounds [66, 67]. Functionality, porosity, irregularities, surface area, tightly bonded impurities, internal porous structure, particle size, ionic strength, pH, and temperature all influence physical adsorption [66]. The temperature influences the adsorption in two ways, increasing the transport


**279**

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

nuclear magnetic resonance spectroscopy methods.

*3.2.2 Countercurrent-chromatography*

offered by the different solvent systems [70].

*3.2.3 Two-phase aqueous system*

speed through the outer boundary layer and inside the pores due to the decrease in the viscosity of the solution, and changing the capacity of the adsorbent. However, high temperatures can promote irreversible interactions [67]. Another important parameter for purification with adsorbents is pH. For example, at acid pH, the adsorption of phenolic compounds by different adsorbents increases because the phenols are not dissociated and dispersion interactions predominate [66]. At alkaline pH, the adsorption decreases due to the dissociation of hydroxyl groups and carboxyl groups [66]. There are many types of adsorbents such as activated carbons, mineral adsorbents, synthetic polymeric adsorbents, ion exchange resins, lignin and lignocellulosic materials, adsorbents based on polysaccharides and others [66]. Among the available adsorbents Amberlite XAD adsorbents are widely used in the concentration of polyphenols [68]. Zhang et al. [69] reported the isolation and structural characterization of 10 phenolic compounds from strawberry extracts using a combination of Amberlite XAD-16 and C18 columns, HPLC-UV, and

Countercurrent chromatography is a technique widely used in the purification of natural products [70]. Countercurrent chromatography is a liquid–liquid partition chromatography process in which both the mobile phase and the stationary phase are liquid [70]. The main advantage of countercurrent chromatography, when compared to equivalent techniques such as low pressure liquid chromatography, is that there are no adsorption losses in the stationary phase [70]. The range of selectivity offered by chromatographic resins is equivalent to the range of selectivity

Several studies have shown the importance of countercurrent chromatography

for the purification of bioactive compounds from strawberry. The compound 2,5-dimethyl-4-hydroxy-3[2H]-furanone 6′O-malonyl-β-d-glucopyranoside was isolated from a strawberry glycosidic extract (Fragaria × *ananassa*, cv. Senga Sengana) by countercurrent chromatography [71]. Peonidin-3-glucoside and malvidin-3-glucoside were obtained from grapes in a single step, while in a second step, cyanidin-3-glucoside was isolated [72]. In another research, the separation of anthocyanin monomers of high purity from mulberry fruits was developed [73].

Two-phase aqueous system is a liquid–liquid fractionation technique that is usually formed by mixing two polymers in aqueous media, for example, polyethylene glycol and dextran or maltodextrin, or by a polymer and a salt, such as polyethylene glycol and salts of phosphates, citrates or sulphates [74–76]. This method has advantages over other purification techniques due to a comparatively low consumption of energy and time, as well as the possibility to be designed for a continuous operation. Moreover, two-phase aqueous systems are effective for many types of substances, especially for the concentration and purification of bioactive compounds [74, 75]. Several studies have demonstrated the suitability of this technique for the purification of bioactive compounds such as phenolic compounds from fig fruits (*Ficus carica* L.) [76], or the purification of gallic acid from natural matrices with ionic liquids [77]. Furthermore, two-phase aqueous system has been applied for the purification of polyphenols from a model solution of gallic acid and three real samples of red and white wine, and orange juice in combination with macro and micro extractors [78]. Polyphenols have been also extracted from *Aronia melanocarpa* berries, using ultrasound-assisted extraction in combination with the two-phase aqueous system [79].

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

#### **Table 1.**

*Summary table of characteristics for comparing extraction techniques.*

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

speed through the outer boundary layer and inside the pores due to the decrease in the viscosity of the solution, and changing the capacity of the adsorbent. However, high temperatures can promote irreversible interactions [67]. Another important parameter for purification with adsorbents is pH. For example, at acid pH, the adsorption of phenolic compounds by different adsorbents increases because the phenols are not dissociated and dispersion interactions predominate [66]. At alkaline pH, the adsorption decreases due to the dissociation of hydroxyl groups and carboxyl groups [66]. There are many types of adsorbents such as activated carbons, mineral adsorbents, synthetic polymeric adsorbents, ion exchange resins, lignin and lignocellulosic materials, adsorbents based on polysaccharides and others [66]. Among the available adsorbents Amberlite XAD adsorbents are widely used in the concentration of polyphenols [68]. Zhang et al. [69] reported the isolation and structural characterization of 10 phenolic compounds from strawberry extracts using a combination of Amberlite XAD-16 and C18 columns, HPLC-UV, and nuclear magnetic resonance spectroscopy methods.

#### *3.2.2 Countercurrent-chromatography*

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

enhanced yields with pulsed electric fields. For instance, a comparison study between a heat treatment at 90°C for 60 or 30 seconds and high intensity pulsed electric field in strawberries juice, showed that strawberry juice treated with high intensity pulsed electric field maintained greater amount of phenolic acids and total anthocyanins than thermally treated juices [63, 64]. Likewise, the recovery of phenols from the shell of the pomegranate by pulsed electric field has been assayed, resulting in a similar antioxidant extraction yields and an energy saving of 50%

compared to an ultrasound extraction technique [65].

target compounds to be recovered or the required extraction yield.

There are many studies that show the properties of adsorbents to separate, concentrate and purify various compounds [66, 67]. Functionality, porosity, irregularities, surface area, tightly bonded impurities, internal porous structure, particle size, ionic strength, pH, and temperature all influence physical adsorption [66]. The temperature influences the adsorption in two ways, increasing the transport

> **Ability to release compounds**

**Degradation of bioactive compounds**

**x x x x**

**x x x x x**

**x x x x x**

**x x x x x x**

**Intracellular attack**

**Breaks of bonds**

**High cost**

**3.2 Purification techniques of bioactive compounds**

**Specificity Possibility of** 

*Summary table of characteristics for comparing extraction techniques.*

**x x**

**combination**

*3.1.6 Extraction techniques comparison*

*3.2.1 Adsorbents*

**Extraction technique**

Solvents extraction

Hydrothermal extraction

Microwave assisted extraction

High hydrostatic pressure extraction

Pulsed electric fields extraction

**Table 1.**

Several studies on the extraction of antioxidant compounds in agri-foods show

After reviewing the different extraction techniques that have been applied to the strawberry and strawberry extrudate, a summary describing their most interesting aspects is shown in **Table 1**. The aspects that have been compared are: the specificity of the extraction techniques with the bioactive compounds, the possibility of combining with other extraction techniques, the ability to release bioactive compounds, the potential degradation of bioactive compounds, possibility of intracellular attack, bonds breakage and whether the technique has a high operational and investment cost. The choice of the best technique for the strawberry extrudate is a tailor-made solution for each situation that will depend of the investment capacity,

**278**

Countercurrent chromatography is a technique widely used in the purification of natural products [70]. Countercurrent chromatography is a liquid–liquid partition chromatography process in which both the mobile phase and the stationary phase are liquid [70]. The main advantage of countercurrent chromatography, when compared to equivalent techniques such as low pressure liquid chromatography, is that there are no adsorption losses in the stationary phase [70]. The range of selectivity offered by chromatographic resins is equivalent to the range of selectivity offered by the different solvent systems [70].

Several studies have shown the importance of countercurrent chromatography for the purification of bioactive compounds from strawberry. The compound 2,5-dimethyl-4-hydroxy-3[2H]-furanone 6′O-malonyl-β-d-glucopyranoside was isolated from a strawberry glycosidic extract (Fragaria × *ananassa*, cv. Senga Sengana) by countercurrent chromatography [71]. Peonidin-3-glucoside and malvidin-3-glucoside were obtained from grapes in a single step, while in a second step, cyanidin-3-glucoside was isolated [72]. In another research, the separation of anthocyanin monomers of high purity from mulberry fruits was developed [73].

#### *3.2.3 Two-phase aqueous system*

Two-phase aqueous system is a liquid–liquid fractionation technique that is usually formed by mixing two polymers in aqueous media, for example, polyethylene glycol and dextran or maltodextrin, or by a polymer and a salt, such as polyethylene glycol and salts of phosphates, citrates or sulphates [74–76]. This method has advantages over other purification techniques due to a comparatively low consumption of energy and time, as well as the possibility to be designed for a continuous operation. Moreover, two-phase aqueous systems are effective for many types of substances, especially for the concentration and purification of bioactive compounds [74, 75]. Several studies have demonstrated the suitability of this technique for the purification of bioactive compounds such as phenolic compounds from fig fruits (*Ficus carica* L.) [76], or the purification of gallic acid from natural matrices with ionic liquids [77]. Furthermore, two-phase aqueous system has been applied for the purification of polyphenols from a model solution of gallic acid and three real samples of red and white wine, and orange juice in combination with macro and micro extractors [78]. Polyphenols have been also extracted from *Aronia melanocarpa* berries, using ultrasound-assisted extraction in combination with the two-phase aqueous system [79].
