**1. Introduction**

According to the FAO, world fishery production has reached around 179 million tons in 2018, of which 156.4 million tons were intended for direct human consumption. This is equivalent to an annual supply estimated at 20.5 kg per inhabitant. While world capture fisheries production stagnates at around 96.4 million tons, aquaculture is experiencing continuous growth in the supply of fish for human consumption, contributing with 46% of the total supply [1].

Unfortunately, despite the expanding demand for fishery and aquaculture products and their importance to the food security of many populations, a large part of the catch is wasted [2–4]. From the catch to the finished product, unused secondary products are generated. Today, some of these by-products are used but a great amount is wasted [5]. In 2016, Jackson & Newton estimated that 11.7 million tons of by-products produced in processing plants around the world are not collected for the production of marine ingredients [6].

In the past, marine by-products were often discarded as waste, used directly as feed for aquaculture, livestock, pets or used in silage and fertilizers [2, 7]. However, in past two decades, other uses of marine by-products have appeared based on their important characteristics and their contents of high value molecules. In some

cases, compounds from by-products are identified higher in value than the starting material [8, 9]. Furthermore, with improved processing technologies, marine by-products can be now used differently and more efficiently.

Several reviews have been previously published discussing the possibilities of using marine by-products to produce high added value compounds [8, 10–15]. Different methods have allowed to produce useful molecules like proteins, gelatin, collagen, enzymes [7, 16, 17], biodiesel and biogas [18–24], natural pigments [25], minerals [26, 27], hydroxyapatite [28], chitin and chitosan [29, 30], creatine and taurine [31, 32].

The possible valorizations of marine by-products can be divided into three main categories: production of marine proteins (fishmeal, silage and hydrolysates), oils rich in polyunsaturated fatty acids (PUFAs) and preparation of high value compounds such as vitamins, enzymes, minerals, taurine and creatine, hydroxyapatite, biodiesel and biogas for human and animal nutrition, industrial or pharmaceutical uses. In this review, we mainly present the sources of marine by-products, their characteristics, and the possible technologies that can be used to produce marine oils and concentrated n-3 fatty acids.

### **2. Marine by-products and their characteristics**

There is no one definition of marine by-products. In the past, marine byproducts have been often considered as fish offal or waste [5, 7]. Actually, the term by-products designates all unused parts that can be recovered during production operations. They designate viscera, heads, trimmings, bones, cartilage, tails, skin, scales, blood, shells, carcasses, or damaged fish. Depending on the fishing period, reproductive elements such as eggs, milt or soft roe may be among these by-products [33].

In some works, the definition of by-products was reserved for feed. In others, the terms fish waste [34–37], waste streams [38], and rest raw material [5] have been used. In all cases, the biomass of by-products can be used to generate an added value unlike waste which has to be composted, burned or destroyed [5].

Generally, by-products can result from all aquatic food processing industries onshore or even during transformation on board. Marine by-products often constitute more than 50% of the body weight of processed fish [2, 4, 7, 39, 40]. However, this amount can reach up to 70% of the catch depending on catching species and area, postharvest conditions and industrial preparation processes [2, 7, 8, 11, 34, 41–44]. Processing operations like filleting, salting and smoking generate the most important amounts of by-products (50–75% of processed fish) [10], followed by the fish canning industry (30–65% of processed fish) and finally, the processing of crustaceans and mollusks [45]. It's estimated that the quantities of fish by-products generated by the processing industries will continue to increase due to the increasing demand for fishery products as source of valuable nutrients and a balanced diet for health [11, 45].

Knowledge of the properties of by-products allows their valorization into highly valuable products that could be higher in value than the fish fillets [8]. Analysis of the composition of by-products has revealed their richness in potentially valuable molecules such as proteins, essential fatty acids, oil, vitamins, minerals but also in bioactive compounds [4, 5, 34, 38, 46–48].

The by-products protein fraction is easily digestible and rich in essential amino acids. It can be used for production of peptides and amino acids, hydrolysates, gelatin and collagen, thermostable protein dispersions and protamine. While marine oils contain n-3 fatty acids [36, 37, 49–51], phospholipids, squalene, fat-soluble

**31**

*Valorization Technologies of Marine By-Products DOI: http://dx.doi.org/10.5772/intechopen.95031*

season [52].

reactions) [53].

**3.1 Production of marine oils**

inflammatory diseases [57, 80–82].

and DHA [85, 86].

vitamins, and cholesterols. Additionally, other valuable components can be

[8], chitin and chitosan [25, 30], creatine and taurine [10, 15].

extracted from marine by-products including nucleic acids, calcium, phosphorous, and hydroxyapatite [14, 28, 35] and other bioactive compounds such as astaxanthin

There are significant compositional differences between parts composing byproducts [38]. In cases where the separation between the different parts of marine by-products is possible, the valorization will be optimal. For example, prioritizing the extraction of protein derivatives from the skin of the fish or oil from viscera and/or heads. Fatty fish by-products present an important raw material for the fish oil extraction industries especially during the high fat season. Aidos and co-authors studied the possibility of oil extraction and quality of oil from salted by-products of the maatjes herring (heads, frames, skin, viscera, etc.) by demonstrating that salt does not prevent the production of an oil of good quality [47]. A recent study showed that sardine cooking condensate and cooked by-products have a high potential for the recovery of oil with yields that can reach 32.9% during the fatty

The greatest valorization of these by-products depends on their handling according to the hygiene rules applied for food production [33]. Special care must be taken to maintain the temperature low during storage and transport to avoid alteration and to preserve their nutritional qualities as marine by-products are highly sensitive to degradation (oxidation, microbial spoilage and enzymatic

Marine oils are rich in PUFAs, especially, eicosapentaenoic acid (EPA, 20: 5 n-3) and docosahexaenoic acid (DHA, 22: 6 n-3) [52, 54–59]. These n-3 fatty acids have valuable benefits and medicinal properties. Numerous articles have described the benefits of n-3 fatty acids in regard to blood pressure, prevention and treatment of coronary artery disease [60, 61], atherosclerosis and thrombosis [62–64], hypertriglycemia [64, 65], schizophrenia and memory [66], stress and depression [67] and foetal development [57, 68–71]. However, the most widely discussed benefits relate to cardiovascular health [61, 65, 72–79] and the prevention and treatment of

These fatty acids are of marine origin, found mainly in fatty fish and seafood.

They are obtained by consumption of algae, fungi and phytoplankton [83]. However, certain human groups, such as premature babies and ill people, are unable to synthesize them. Even in people not belonging to these groups, the amount of EPA and DHA synthesized by the body may not be enough because the biosynthesis of these two acids becomes slow with age as well as with bad habits such as smoking, alcohol intake and poor fitness habits [11, 84]. In this case, a diet based on marine lipids (fish and its derivatives) provides the needed intake of EPA

Marine oils are mainly composed of mixtures of fatty acids esterified with glycerol in triacylglycerides [11]. They are the main natural source of n-3 PUFAs particularly, EPA and DHA [37, 50, 51]. **Table 1** summarizes some variation intervals of EPA and DHA in certain oils extracted from fatty marine by-products. The variation depends on type of by-products used, the species, the catching season and

the processing technology used for extraction and purification.

**3. Main valorization technologies of marine by-products**

*Valorization Technologies of Marine By-Products DOI: http://dx.doi.org/10.5772/intechopen.95031*

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

by-products can be now used differently and more efficiently.

taurine [31, 32].

by-products [33].

oils and concentrated n-3 fatty acids.

bioactive compounds [4, 5, 34, 38, 46–48].

**2. Marine by-products and their characteristics**

cases, compounds from by-products are identified higher in value than the starting material [8, 9]. Furthermore, with improved processing technologies, marine

Several reviews have been previously published discussing the possibilities of using marine by-products to produce high added value compounds [8, 10–15]. Different methods have allowed to produce useful molecules like proteins, gelatin, collagen, enzymes [7, 16, 17], biodiesel and biogas [18–24], natural pigments [25], minerals [26, 27], hydroxyapatite [28], chitin and chitosan [29, 30], creatine and

The possible valorizations of marine by-products can be divided into three main categories: production of marine proteins (fishmeal, silage and hydrolysates), oils rich in polyunsaturated fatty acids (PUFAs) and preparation of high value compounds such as vitamins, enzymes, minerals, taurine and creatine, hydroxyapatite, biodiesel and biogas for human and animal nutrition, industrial or pharmaceutical uses. In this review, we mainly present the sources of marine by-products, their characteristics, and the possible technologies that can be used to produce marine

There is no one definition of marine by-products. In the past, marine byproducts have been often considered as fish offal or waste [5, 7]. Actually, the term by-products designates all unused parts that can be recovered during production operations. They designate viscera, heads, trimmings, bones, cartilage, tails, skin, scales, blood, shells, carcasses, or damaged fish. Depending on the fishing period, reproductive elements such as eggs, milt or soft roe may be among these

In some works, the definition of by-products was reserved for feed. In others, the terms fish waste [34–37], waste streams [38], and rest raw material [5] have been used. In all cases, the biomass of by-products can be used to generate an added

Generally, by-products can result from all aquatic food processing industries onshore or even during transformation on board. Marine by-products often constitute more than 50% of the body weight of processed fish [2, 4, 7, 39, 40]. However, this amount can reach up to 70% of the catch depending on catching species and area, postharvest conditions and industrial preparation processes [2, 7, 8, 11, 34, 41–44]. Processing operations like filleting, salting and smoking generate the most important amounts of by-products (50–75% of processed fish) [10], followed by the fish canning industry (30–65% of processed fish) and finally, the processing of crustaceans and mollusks [45]. It's estimated that the quantities of fish by-products generated by the processing industries will continue to increase due to the increasing demand for fishery products as source of valuable nutrients and a balanced diet for health [11, 45]. Knowledge of the properties of by-products allows their valorization into highly valuable products that could be higher in value than the fish fillets [8]. Analysis of the composition of by-products has revealed their richness in potentially valuable molecules such as proteins, essential fatty acids, oil, vitamins, minerals but also in

The by-products protein fraction is easily digestible and rich in essential amino acids. It can be used for production of peptides and amino acids, hydrolysates, gelatin and collagen, thermostable protein dispersions and protamine. While marine oils contain n-3 fatty acids [36, 37, 49–51], phospholipids, squalene, fat-soluble

value unlike waste which has to be composted, burned or destroyed [5].

**30**

vitamins, and cholesterols. Additionally, other valuable components can be extracted from marine by-products including nucleic acids, calcium, phosphorous, and hydroxyapatite [14, 28, 35] and other bioactive compounds such as astaxanthin [8], chitin and chitosan [25, 30], creatine and taurine [10, 15].

There are significant compositional differences between parts composing byproducts [38]. In cases where the separation between the different parts of marine by-products is possible, the valorization will be optimal. For example, prioritizing the extraction of protein derivatives from the skin of the fish or oil from viscera and/or heads. Fatty fish by-products present an important raw material for the fish oil extraction industries especially during the high fat season. Aidos and co-authors studied the possibility of oil extraction and quality of oil from salted by-products of the maatjes herring (heads, frames, skin, viscera, etc.) by demonstrating that salt does not prevent the production of an oil of good quality [47]. A recent study showed that sardine cooking condensate and cooked by-products have a high potential for the recovery of oil with yields that can reach 32.9% during the fatty season [52].

The greatest valorization of these by-products depends on their handling according to the hygiene rules applied for food production [33]. Special care must be taken to maintain the temperature low during storage and transport to avoid alteration and to preserve their nutritional qualities as marine by-products are highly sensitive to degradation (oxidation, microbial spoilage and enzymatic reactions) [53].

### **3. Main valorization technologies of marine by-products**

#### **3.1 Production of marine oils**

Marine oils are rich in PUFAs, especially, eicosapentaenoic acid (EPA, 20: 5 n-3) and docosahexaenoic acid (DHA, 22: 6 n-3) [52, 54–59]. These n-3 fatty acids have valuable benefits and medicinal properties. Numerous articles have described the benefits of n-3 fatty acids in regard to blood pressure, prevention and treatment of coronary artery disease [60, 61], atherosclerosis and thrombosis [62–64], hypertriglycemia [64, 65], schizophrenia and memory [66], stress and depression [67] and foetal development [57, 68–71]. However, the most widely discussed benefits relate to cardiovascular health [61, 65, 72–79] and the prevention and treatment of inflammatory diseases [57, 80–82].

These fatty acids are of marine origin, found mainly in fatty fish and seafood. They are obtained by consumption of algae, fungi and phytoplankton [83]. However, certain human groups, such as premature babies and ill people, are unable to synthesize them. Even in people not belonging to these groups, the amount of EPA and DHA synthesized by the body may not be enough because the biosynthesis of these two acids becomes slow with age as well as with bad habits such as smoking, alcohol intake and poor fitness habits [11, 84]. In this case, a diet based on marine lipids (fish and its derivatives) provides the needed intake of EPA and DHA [85, 86].

Marine oils are mainly composed of mixtures of fatty acids esterified with glycerol in triacylglycerides [11]. They are the main natural source of n-3 PUFAs particularly, EPA and DHA [37, 50, 51]. **Table 1** summarizes some variation intervals of EPA and DHA in certain oils extracted from fatty marine by-products. The variation depends on type of by-products used, the species, the catching season and the processing technology used for extraction and purification.


**33**

**Species**

Hake, Orange roughy,

Salmon Jumbo squid *Sardinella lemuru*

*Sardina pilchardus*

Salmon Black scabbardfish (*Aphanopus carbo*)

Sardine (Sardina pilchardus)

Salmon

**By-products**

Offcuts

Offcuts

Offcuts

Livers

Head

1.84

15.95

Solvent extraction

11.87

12.97

10.3 11.3 6.2

Enzymatic hydrolysis

Enzymatic hydrolysis

Enzymatic hydrolysis

[93]

[94]

[95]

1.73

2.76

9.3 9.3 2.7

Intestine

liver

Heads Frames without heads

Heads, viscera, frames, skin,

trimmings

Heads, viscera, frames,

—

—

Enzymatic hydrolysis

Pressing CO2 supercritical extraction

[97]

[96]

trimmings)

Belly part Belly part Trimmed muscle

Frame bone

Skin Belly part Trimmed muscle

Frame bone

Skin Skin

Indian mackerel (*Rastrelliger kanagurta*)

3.17 4.45 3.53 4.27 3.87 3.12 3.22 3.85 2.79 11.91–12.31

12.22

3.85 3.62 3.46

3.60

3.26

3.23 3.98

4.32

3.09

13.15–14.47

13.86

CO2 supercritical extraction

Soxhlet extraction

[98]

n-Hexane extraction

**EPA**

—

**DHA**

—

**Process** CO2 supercritical extraction/Cold

extraction/ Wet reduction/enzymatic

extraction

**Ref** [50]

*Valorization Technologies of Marine By-Products DOI: http://dx.doi.org/10.5772/intechopen.95031*

[37]

#### *Valorization Technologies of Marine By-Products DOI: http://dx.doi.org/10.5772/intechopen.95031*

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

**32**

**Species** *Sardinella maderensis*

*Sardinella aurita*

*Cephalopholis taeniops*

Cod (*Gadus morhua*)

Saithe (*Pollachius virens*)

Haddock (*Melanogrammus aeglefinus*)

Tusk (*Brosme brosme*)

*Sardina pilchardus*

Tuna (*Thunnus obesus*)

**By-products**

Liver

skin

Liver

skin

Liver

skin

Liver

Viscera

Trimming

Liver

Viscera

Trimming

Liver

Viscera

Trimming

Liver

Viscera

Trimming

cooked by-products

Skins

Scales

Bones

Skins

Scales

Bones

Heads, gut content, fins

Precooked heads

Non precooked heads

*Sardina pilchardus*

*Skipjack tuna*

**EPA**

4.7

20.5

1.8

10.4

1.6

3.1

8.6–11.4

10.6–12.6

14.2–16.5

10.3–11.5

7.3–13.6

10.5–17.1

13.1–14.8

11.7–12.0

14.6–16.6

5.0

7.0

6.8

20.5–25.0

4.2

4.8

5.1

3.6

4.5

4.7

14.20

0.1 0.1

**DHA**

4.8

4.2

1.4

2.5

1.1

6.9

11.8–16.2

Solvent extraction

[89]

[88]

20.0–25.6

30.4–33.8

15.5–15.9

9.5–23.2

11.3–35.5

15.2

23.2–23.7

33.3–35.7

14.2

25.5

34.8

4.6–10.2

23.6

23.5

21.6

21.8

Hexane Soxhlet extraction

21.5

20.0

18.59

25.5 18.8

Wet reduction method

Wet reduction method

[91]

[92]

Batch hydraulic pressing

CO2 supercritical extraction

[52]

[90]

**Process** Solvent extraction

**Ref**

[87]


