**4. Stabilization of biomass by obtaining bioenergy and bioproducts**

#### **4.1 Biogas production**

Anaerobic digestion is a microbiological process, in absence of oxygen, where organic matter is progressively degraded by an heterogeneous bacterial population to methane (55–70%) and carbon dioxide (30–45%) [80]. Anaerobic digestion presents some fundamental advantages such as the possibility of working at high rates of organic load, and the produced methane can be used as an energy source due to its heating value (35,793 kJ/m3 , at 1 atm, 0°C), which equals to 1 kg of raw coal or 0.76 kg of standard coal [3, 11]. The use of biogas for energy supply reduces deforestation, soil erosion and environmental pollution [81, 82]. Also, it can improve the energy efficiency of various production processes due to the energetic contribution that provides [82]. In addition, a wet waste called digestate, which is a mixture of partially degraded organic matter, microbial biomass, and inorganic compounds, is produced during biomethanization and could be used as a base for fertilizers or organic amendments [82, 83].

Several studies on anaerobic digestion of strawberries extrudate have been carried out. The results of one these studies reveal that strawberries extrudates have a high level of anaerobic biodegradability (90% in VS, (total volatile solids)) and that a substantial amount of methane can be obtained in this way (312 mL CH4 STP/g added VS) (STP: standard temperature and pressure conditions, i.e. 0°C, 1 atm) at an organic loading rate range of 2.04 to 3.51 kg VS/m3 ·d [84]. In another study of anaerobic digestion of strawberry waste from supermarkets, using an organic loading rate of 0.55–4.4 (g/L·d), the experimental biogas and methane yields were 0.588 and 0.231 L/g, respectively [85]. It has been observed that sometimes it is necessary to codigest strawberry extrudate with a substrate that provides alkalinity, such as sewage sludge [86, 87]. Co-digestion studies of strawberry extrudate with other substrates such as fish waste [3] and glycerol [83] have also been studied. Anaerobic digestion of strawberry extrudate is a promising technique but it should be further studied since low alkalinity of the extrudate together with formation of inhibitory compounds caused by the extraction process could negatively affect the digestion process.

#### **4.2 Compost production**

Composting has been proposed for a long time as a quite cheap option for agricultural waste management [2]. Composting has also been proposed as a post-treatment for the produced digestate after anaerobic digestion [88]. Composting is the biooxidative conversion of organic waste into an organic amendment. According to Gutiérrez et al. (2017) [2], the cost of composting varies in a wide range from \$40 to \$500 per throughput ton depending on the technology. Composting costs vary widely depending on the type of operation, which ranges from the most simple ones, such as opening windrows, to more complex procedures like in-vessel aerobic composting that allows smell emissions to be controlled and prevents environmental pollution [2]. The great disadvantage is that a considerable amount of offensive odors can be emitted during the process due to the generation of volatile organic compounds [89]. Other disadvantages are the long process time and the necessity of a proper monitoring [90]. Co-composting of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent has been successfully proven [2, 89].

#### **4.3 Bioethanol production**

Bioethanol is one of the most produced alcohols from the fermentation of sugars found in fruits and vegetables [7, 91–93]. Theoretically, any organic product with a

**281**

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

hydrolysis, thus improving the efficiency of the entire process [92].

showed the feasibility of using berries for bioplastic production [8].

Biochar is the solid carbonaceous residue produced through organic waste and used as a soil improver [100, 101]. Biochar is produced through several types of methods such as pyrolysis, torrefaction or hydrothermal carbonization [100, 101]. There are no studies reported in the literature dealing with the production of biochar from strawberry extrudates. However, the above-mentioned techniques (pyrolysis, torrefaction and hydrothermal carbonization) could be potentially applied for this substrate. Several studies have been carried out on the hydrothermal carbonization of other agri-food waste, such as olive cuttings and olive pulp [102]; grape marc [103]; olive mill waste, canned artichoke and orange waste [104].

This chapter has reviewed up-to-date literature on the bioactive compounds contained in strawberries, which have an important health and market value. Different extraction and purification techniques to obtain valuable compounds from strawberry extrudate have been reviewed and analyzed. The reviewed techniques present different advantages and drawbacks that were analyzed to facilitate the selection of the most suitable process for each valorisation scenario. Finally,

Fossil fuel depletion, global warming, and problems of pollution of the environment that provoke plastics in its life cycle are encouraging the development of biodegradable plastics [95, 96]. Agri-food waste are usually rich in many useful substances such as lipids, polysaccharides, and aromatics, which could be used for the manufacture of biodegradable polymeric materials. Bioplastics already play an important role in the sectors of packaging, agriculture, consumer electronics and motoring, but still have a very low share in the total production of plastics. Currently, about 1% of the annual tons of plastic are bioplastics [97]. Examples of such bioplastics are exopolysaccharides, polycaprolactone, polybutylene succinate, polybutylene adipate terephthalate, polyhydroxyalkanoates or polyhydroxybutyrates [97, 98]. For obtaining bioplastics from agri-food waste, the waste must be treated to extract or isolate specific macromolecules, such as cellulose, lignin, suberin, starch, or monomers, such as vegetable oils, tannins and terpenes [96, 99]. A study conducted on the production of bioplastics from Murta fruit extract, that is a native Chilean berry,

high content of sugars and starch, such as strawberry extrudate, may be susceptible to obtaining bioethanol [91]. Inedible sources from the strawberry extrudate such as lignocellulosic biomass, which mainly comprises cellulose, hemicellulose, and lignin, can be hydrolysed to produce a mixture of pentoses and hexoses that can be transformed into bioethanol [94]. Bioethanol from agro-waste, such as strawberry extrudate, could be a promising technology that involves four processes, pre-treatment, enzymatic hydrolysis, fermentation and distillation, this final step is crucial for the process to be economically viable on a commercial scale due to high energy consumption in the form of steam to increase the yield of bioethanol production when lignocellulose materials are used as raw material [93]. These processes have several challenges and limitations, such as the efficient pre-treatment process to eliminate lignin from the lignocellulosic agro-residues. The proper pre-treatment process can increase the concentrations of fermentable sugars after enzymatic

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

**4.4 Bioplastics production**

**4.5 Biochar production**

**5. Conclusions**

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

high content of sugars and starch, such as strawberry extrudate, may be susceptible to obtaining bioethanol [91]. Inedible sources from the strawberry extrudate such as lignocellulosic biomass, which mainly comprises cellulose, hemicellulose, and lignin, can be hydrolysed to produce a mixture of pentoses and hexoses that can be transformed into bioethanol [94]. Bioethanol from agro-waste, such as strawberry extrudate, could be a promising technology that involves four processes, pre-treatment, enzymatic hydrolysis, fermentation and distillation, this final step is crucial for the process to be economically viable on a commercial scale due to high energy consumption in the form of steam to increase the yield of bioethanol production when lignocellulose materials are used as raw material [93]. These processes have several challenges and limitations, such as the efficient pre-treatment process to eliminate lignin from the lignocellulosic agro-residues. The proper pre-treatment process can increase the concentrations of fermentable sugars after enzymatic hydrolysis, thus improving the efficiency of the entire process [92].

#### **4.4 Bioplastics production**

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

**4. Stabilization of biomass by obtaining bioenergy and bioproducts**

Anaerobic digestion is a microbiological process, in absence of oxygen, where organic matter is progressively degraded by an heterogeneous bacterial population to methane (55–70%) and carbon dioxide (30–45%) [80]. Anaerobic digestion presents some fundamental advantages such as the possibility of working at high rates of organic load, and the produced methane can be used as an energy source due to

0.76 kg of standard coal [3, 11]. The use of biogas for energy supply reduces deforestation, soil erosion and environmental pollution [81, 82]. Also, it can improve the energy efficiency of various production processes due to the energetic contribution that provides [82]. In addition, a wet waste called digestate, which is a mixture of partially degraded organic matter, microbial biomass, and inorganic compounds, is produced during biomethanization and could be used as a base for fertilizers or

Several studies on anaerobic digestion of strawberries extrudate have been carried out. The results of one these studies reveal that strawberries extrudates have a high level of anaerobic biodegradability (90% in VS, (total volatile solids)) and that a substantial amount of methane can be obtained in this way (312 mL CH4 STP/g added VS) (STP: standard temperature and pressure conditions, i.e. 0°C, 1 atm) at

anaerobic digestion of strawberry waste from supermarkets, using an organic loading rate of 0.55–4.4 (g/L·d), the experimental biogas and methane yields were 0.588 and 0.231 L/g, respectively [85]. It has been observed that sometimes it is necessary to codigest strawberry extrudate with a substrate that provides alkalinity, such as sewage sludge [86, 87]. Co-digestion studies of strawberry extrudate with other substrates such as fish waste [3] and glycerol [83] have also been studied. Anaerobic digestion of strawberry extrudate is a promising technique but it should be further studied since low alkalinity of the extrudate together with formation of inhibitory compounds caused by the extraction process could negatively affect the digestion process.

Composting has been proposed for a long time as a quite cheap option for agricultural waste management [2]. Composting has also been proposed as a post-treatment for the produced digestate after anaerobic digestion [88]. Composting is the biooxidative conversion of organic waste into an organic amendment. According to Gutiérrez et al. (2017) [2], the cost of composting varies in a wide range from \$40 to \$500 per throughput ton depending on the technology. Composting costs vary widely depending on the type of operation, which ranges from the most simple ones, such as opening windrows, to more complex procedures like in-vessel aerobic composting that allows smell emissions to be controlled and prevents environmental pollution [2]. The great disadvantage is that a considerable amount of offensive odors can be emitted during the process due to the generation of volatile organic compounds [89]. Other disadvantages are the long process time and the necessity of a proper monitoring [90]. Co-composting of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent has been successfully proven [2, 89].

Bioethanol is one of the most produced alcohols from the fermentation of sugars found in fruits and vegetables [7, 91–93]. Theoretically, any organic product with a

, at 1 atm, 0°C), which equals to 1 kg of raw coal or

·d [84]. In another study of

**4.1 Biogas production**

its heating value (35,793 kJ/m3

organic amendments [82, 83].

**4.2 Compost production**

**4.3 Bioethanol production**

an organic loading rate range of 2.04 to 3.51 kg VS/m3

**280**

Fossil fuel depletion, global warming, and problems of pollution of the environment that provoke plastics in its life cycle are encouraging the development of biodegradable plastics [95, 96]. Agri-food waste are usually rich in many useful substances such as lipids, polysaccharides, and aromatics, which could be used for the manufacture of biodegradable polymeric materials. Bioplastics already play an important role in the sectors of packaging, agriculture, consumer electronics and motoring, but still have a very low share in the total production of plastics. Currently, about 1% of the annual tons of plastic are bioplastics [97]. Examples of such bioplastics are exopolysaccharides, polycaprolactone, polybutylene succinate, polybutylene adipate terephthalate, polyhydroxyalkanoates or polyhydroxybutyrates [97, 98]. For obtaining bioplastics from agri-food waste, the waste must be treated to extract or isolate specific macromolecules, such as cellulose, lignin, suberin, starch, or monomers, such as vegetable oils, tannins and terpenes [96, 99]. A study conducted on the production of bioplastics from Murta fruit extract, that is a native Chilean berry, showed the feasibility of using berries for bioplastic production [8].

#### **4.5 Biochar production**

Biochar is the solid carbonaceous residue produced through organic waste and used as a soil improver [100, 101]. Biochar is produced through several types of methods such as pyrolysis, torrefaction or hydrothermal carbonization [100, 101].

There are no studies reported in the literature dealing with the production of biochar from strawberry extrudates. However, the above-mentioned techniques (pyrolysis, torrefaction and hydrothermal carbonization) could be potentially applied for this substrate. Several studies have been carried out on the hydrothermal carbonization of other agri-food waste, such as olive cuttings and olive pulp [102]; grape marc [103]; olive mill waste, canned artichoke and orange waste [104].

#### **5. Conclusions**

This chapter has reviewed up-to-date literature on the bioactive compounds contained in strawberries, which have an important health and market value. Different extraction and purification techniques to obtain valuable compounds from strawberry extrudate have been reviewed and analyzed. The reviewed techniques present different advantages and drawbacks that were analyzed to facilitate the selection of the most suitable process for each valorisation scenario. Finally,

different stabilization options for the biomass remaining after extraction have also been reviewed. Stabilization is required to avoid severe environmental impacts, and additionally could be an economically beneficial aid for balancing the cost of the extraction of high value-added compounds. As usually for any waste management option, selection of the best extraction, purification and stabilization technique for the strawberry extruded is a tailor-made solution for each situation.
