1. Introduction
The ocean represents ca. 95% of the biosphere and is crucial for the planet and humankind, as it provides a plethora of important resources and services
[1,2][1][2]. Although currently recognized as a common provider of social, environmental, and economic benefits
[3], the ocean has faced, and continues to face, several natural and anthropogenic threats. Some of the major threats are related to the overexploitation of marine resources, climate change, pollution, ocean acidification, habitat damage, and management failure
[4]. To mitigate these major threats, it is critical to maintain the balance between the exploitation of marine resources and the ecosystem resilience to such exploitation. This balance should be evident to all, as well as coordinated with and integrated into public policies, governance, finance, and management of global supply chains where ocean resources play a role
[3]. To achieve this goal, sustainable and circular business models, as well as integrated policies that protect marine ecosystem functions and regulate all major activities occurring in the ocean, must be implemented or improved across the globe.
The blue economy reached a Gross Value Added (GVA) of EUR 129.1 billion and a turnover of EUR 523 billion in 2020 across seven different sectors (living resources, non-living resources, marine energy, port activities, shipbuilding and repair, maritime transport, and coastal tourism)
[5]. The marine living resources sector comprises the harvesting and farming of biological resources, as well as their conversion and distribution, and that sector alone generated more than EUR 19.4 billion in GVA and EUR 119 billion in turnover in 2020. Despite this GVA, it may still be underestimating the value of the EU blue bioeconomy as a whole, as this does not encompass sectors such as blue biotechnology. Fisheries and aquaculture, two ocean-related major economic activities, have grown throughout the years, in part due to the increasing demand for food by an expanding human population
[6]. If exploited sustainably, ocean resources potentially have the capacity to regenerate and feed a large proportion of the world’s population. According to the Food and Agriculture Organization of the United Nations (FAO), aquaculture accounted for 122.6 million tonnes of the unprecedented total of 214 million tonnes produced by fisheries and aquaculture in 2020
[6]. In this year, the number of people employed in primary fisheries and aquaculture exceeded 58 million
[6], indicating the importance of these activities in the economic development of multiple countries. Moreover, as marine organisms have evolved for thousands of years to be able to thrive in complex habitats and are exposed to extreme conditions, they produce a wide variety of specific and potent bioactive substances
[7]. Hence, the ocean is a rich and natural source of many bioactive compounds that cannot be found elsewhere. Thousands of marine bioactive compounds have been extracted, identified, and characterized in recent decades
[8]. Indeed, ~7000 of these molecules are already in use or being validated for several purposes, ranging from medicine to industrial applications
[9]. For instance, in 2020 and 2021, 1407 and 1425 new bioactive compounds were reported from marine organisms
[10]. However, the increased extraction and use of such compounds has been exerting even more pressure on the limited natural resources of the marine realm.
Environmental and economic concerns have been increasingly driving the use of eco-friendly alternatives to exploit marine natural resources. In the age of sustainability, where development models are changing towards circularity and zero waste, the fisheries and aquaculture sectors, alongside many of the other sectors they connect with (like fish and seafood transformation industries), are key players in supplying new by- and co-products that work as raw materials for other industries. Examples include the once considered “waste streams” of fish by-catches, the shells and non-edible parts of shellfish and crustaceans, and invasive species such as crabs and starfish, which can serve as raw materials for different bio-based products. Many industries, including the pharmaceutical, veterinary, nutraceutical, cosmetic, biomaterials, and others, benefit from the development of products and/or processes using these marine resources
[11]. Such products may take the form of pharmaceutical drugs, livestock feed formulas, pet food products, specialty foods and nutritional supplements for several human conditions, medical biocomponents, beauty supplements, functional textiles or new fibres, biomaterials used in construction or nature-based building solutions, and additives or enzymes used in manufacturing and industrial processes, just to name a few, to improve productivity with lower environmental impacts
[12,13,14,15][12][13][14][15]. These approaches promote the development of sustainable products, circular (bio)economy models, zero-waste strategies, and reduce environmental pollution.
Chitin, its derivative chitosan, and collagen, are highly relevant marine bioactive compounds to the biomedical, nutraceutical, cosmetic, feed, and wastewater treatment industries, among others
[12,16,17,18,19][12][16][17][18][19]. Both chitin and collagen represent unified templates for biomineralization and skeletogenesis in many organisms and are essential elements for their structural life support functions
[20]. In fact, both biopolymers represent examples of the “scaffolding strategy”, a modern trend of using naturally occurring 3D scaffolds made of chitin and collagen (i.e., in sponges) for tissue engineering and technology derived thereof
[21,22,23][21][22][23]. These naturally occurring compounds, or derivatives, are also used in applications such as preservative food coatings due to their thermal stability and antimicrobial qualities
[24] but also in a wide range of different biomaterials, some even in the framework of extreme biomimetics inspiration
[25,26][25][26].
Chitin is one of the most abundant biopolymers in nature
[27]. It can be extracted from the exoskeletons of crustaceans, molluscs, insects, and fungi. It can also be obtained from some
Porifera, like sponges
[28]. Chitin is classified in three different groups: α-chitin, usually extracted from the exoskeleton of crustaceans such as shrimps and crabs; β-chitin, extracted from squid pens; and γ-chitin, obtained from fungi and yeasts
[29]. Chitin and chitosan properties are highly variable depending on their source, as well as on the deacetylation, protein concentration, and extraction procedures
[30]. The conventional way of making chitin and chitosan include demineralisation, deproteinisation (+deacetylation for chitosan), or electrochemical methods
[31]. Both chitin and chitosan undergo modifications (e.g., deacetylation, quaternization, oxidation) to enhance their physical properties
[32]. Although chitin has poor solubility, its derivative chitosan is a soluble biopolymer in aqueous acidic conditions
[33]. Therefore, chitin is often chemically modified by deacetylation to obtain chitosan.
Collagen has at least 28 types (I-XXVIII) described. The most abundant types are in mammals, fibrillar collagen types I–III, predominantly sourced from commercialized porcine, bovine, ovine, and chicken tissues
[34]. It can also be obtained from marine sponges
[35[35][36],
36], jellyfish, squids, and fishes
[37]. The skin, bones, fins, head, and scales of fish are rich in collagen and account for approximately 75% of the fish wet weight
[38]. Collagen has multiple sources, but an increase in marine-derived collagen is being seen
[39,40][39][40] and its usages range from cosmetic and nutraceutical preparations to tissue engineering, medical or pharmaceutical high-value products
[41[41][42],
42], and even several manufacturing biomaterials applications
[43,44][43][44]. In fact, collagen from marine organisms utilised for biomedical applications has been recognised as a convenient and safe source, and some advantages have been pointed out when compared to collagen from mammalian origin, including (1) less significant religious and ethical constraints; (2) greater absorption due to low molecular weight; (3) low inflammatory response; (4) and minor regulatory and quality control problem
[45]. Even more, it represents an option towards the valorisation of marine by-products and the development of the circular economy concept, as providing new solutions for the reuse of materials is highly targeted on the EU policy making agenda
[46].
As chitin and collagen can be extracted from sources that would otherwise be considered as waste (e.g., non-edible parts of fish and shellfish, fisheries’ by-catch, and invasive species), the use of these compounds represents an opportunity to reinforce circular business models and to reuse and reduce the waste streams derived from marine fisheries, aquaculture, and food processing industries. Chitin and collagen markets currently represent USD ~7900 million and USD 4700 million, respectively
[47], meaning they both have substantial commercial interest. The application and transformation of what was once considered waste has therefore led to new valorisation strategies, creating opportunities to capitalize these co-products and side streams in market segments not yet explored
[12[12][48],
48], building novel business models in new value networks for the marine-derived chitin/chitosan and collagen.
2. Marine Chitin/Chitosan and Collagen Value Chains
2.1. Trends in the Distribution and Number of Publications per Value Chain
The number of peer-reviewed publications (hereafter referred to as publications) related to the chitin/chitosan value chain was almost twice that of publications related to the collagen value chain (138 vs. 84). Four publications contained information relevant for both value chains. Approximately half of the analysed publications were published in top tier (i.e., Q1) journals. For the chitin/chitosan value chain, 49% of the publications analysed (n = 67) were published in journals in Q1 and 31% (n = 43) in Q2. For the collagen value chain, 50% of the publications (n = 42) were published in journals in Q1 and 35% (n = 29) in Q2. Globally, for both value chains, publications were distributed as follows: Q1, 48% (n = 106); Q2, 32% (n = 71); Q3, 12% (n = 26); and Q4, 7% (n = 16).
As for the evolution of the number of publications related to each value chain (Figure 1), the first scientific publication approaching the chitin/chitosan value chain was published in 1990, a second in 1992, and a third in 1993 (Figure 1a). After a 7-year gap, a fourth publication was published in 2000; after a period of intermittent publication from 2001 to 2009, publications related to the chitin/chitosan value chain have been published yearly, with an increasing trend being recorded over the years (Figure 1a). The maximum number of publications (n = 28) was observed in 2022, with 20 being published in Q1 journals.
Figure 1. Number of publications per year and quartile (Q1–Q4). (a) Number of publications for the chitin/chitosan value chain; (b) number of publications for the collagen value chain. Quartile classification according to SCImago.
The first scientific publication approaching the collagen value chain was published in 1969, followed by a second and third publication in 1971 and 1972, respectively, and a fourth and fifth in 1994 and 2000 (Figure 1b). After a 5-year gap, a publication was published in 2006, but only since 2009 have publications been published on this topic on a yearly basis. An increasing trend has been observed since 2009 (Figure 1b), with the maximum number of publications in 2022. In this year, 12 of the 21 publications were published in Q1 journals.
2.2. Trends in the Geographical Origin of Publications per Value Chain
The scientific publications related to each value chain were differently distributed based on the country of the corresponding author(s). Publications related to the chitin/chitosan value chain originated from 43 countries (Figure 2), whereas those related to the collagen value- chain originated from 25 countries (Figure 3). Most publications related to the chitin/chitosan value chain were from India (n = 20), while most publications related to the collagen value chain originated from China (n = 13), closely followed by India (n = 12). Asia was the most relevant region, with 43% and 57% of the corresponding authors of publications related to the chitin/chitosan and collagen value chains, respectively, being based in Asian countries.
Figure 2.
Geographic distribution of the chitin/chitosan value chain-related publications based on the country of the corresponding author(s).
Figure 3.
Geographic distribution of the collagen value chain-related publications based on the country of the corresponding author(s).
2.3. Trends in the Origin of the Marine Raw Materials and Feedstock per Value Chain
The origin of the raw material(s) used differed considerably between the two value chains, based on the information provided by the analysed publications (
Figure 4). For the chitin/chitosan value chain, the “food processing industry” and “fisheries” were the most frequent sources of raw materials used in publications (34% and 31%, respectively) (
Figure 4a). The source “aquaculture” showed a low value (6%), considering the rising interest in this sector related to the aquaculture production of species that may be a source of chitin and its derivatives, such as chitosan (i.e., crustaceans)
[6]. For the collagen value chain, most publications used raw materials from “fisheries” (52%) followed by the “food processing industry” (22%) (
Figure 4b). Although “aquaculture” was also the least frequent source of raw materials in collagen value chain publications, its relative contribution was twice that calculated for the chitin/chitosan value chain (12% vs. 6%, respectively). Globally, “fisheries” have been the most relevant source of raw materials for both value chains. It is worth noting that “undisclosed” was the third most common source on both value chains; furthermore, in the chitin/chitosan value chain, its value (29%) was similar to that of the two most common sources (
Figure 4a).
Figure 4. Origin of the raw materials as their frequency of occurrence in the publications analysed for each value chain. (a) Chitin/chitosan value chain; (b) collagen value chain. Blue, fisheries; orange, food processing industry; yellow, aquaculture; grey, undisclosed.
For the chitin/chitosan value chain, “crustacean waste” was the most used feedstock in the studies analysed (71%), especially “shrimp waste” (35%) (
Figure 5a). The percentage obtained for “algae and seagrasses” (15%) resulted from a single publication that mentioned endophytic fungi isolated from 19 different species of algae and 10 different species of seagrasses
[56][49]. Regarding the collagen value chain, “fish scales, skin, and bones” were the feedstock used in 62% of the analysed publications (
Figure 5b). Globally, fish and crustacean wastes were the most used feedstock in the studies related to both value chains.
Figure 5. Feedstock used as source of extraction and their frequency of occurrence in the publications analysed for each value chain. (a) Chitin/chitosan value chain; (b) collagen value chain.
2.4. Trends in the Perception of Sustainability for Chitin/Chitosan and Collagen Value Chains
The sustainability, as expressed in the scientific publications, for each value chain was categorized into economic, environmental, and social. Economic sustainability is mostly related to the improved cost efficiency of the extraction methods, especially regarding them being cheaper than previously established methods or capable of achieving a higher quality or higher quantity of compounds. Environmental sustainability is related to environmentally friendly methods of compound extraction and to waste reduction and reuse. Social sustainability refers to practices that may improve society well-being and reduce inequalities, such as those related to consumer cultural or dietary needs.
Overall, more economic, environmental, and social sustainability practices have been applied in the chitin/chitosan value chain than in the collagen value chain, particularly environmental and economic sustainability practices (
Figure 6). Environmental practices are the most referred to in publications related to both value chains, such as environmentally friendly methods of extraction
[57[50][51],
58], reduce/reuse of waste
[59[52][53][54],
60,61], or reduction in environmental harm
[62][55], followed by economical practices, such as cheaper consumables
[57[50][56],
63], cheaper methodologies
[64,65,66[57][58][59][60],
67], more cost-efficient processes
[68,69,70,71,72][61][62][63][64][65], and new potential products
[19,73,74][19][66][67].
Figure 6. Percentage of publications referring to each of the three categories of sustainable practices per value chain. (a) Chitin/chitosan value chain; (b) collagen value chain. Economical mentions refer to cheaper consumables; cheaper methodologies; high cost equipment; more cost-efficient process; new potential product; not cost-efficient method; product that does not justify its use. Sustainability mentions refer to consumer aversion; more employment/income opportunities; social equality. Environmental mentions refer to environmentally friendly methods of extraction; environmental harm; reduce/reuse of waste.
2.5. Trends in Market Applications for Each Value Chain
Regarding the market applications of chitin/chitosan and collagen, several different sectors were mentioned as both present and future applications. Overall, collagen products are currently less used than chitin/chitosan products (
Figure 7), and an increased use of both types of products is expected, as described by the authors of the screened publications. Chitin/chitosan products are mostly used in the industrial sector, newly derived and purified compounds, food applications, and wastewater treatment (
Figure 7)
[56,71,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94][49][64][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87]. An increased use in these sectors, as well as in biomedical applications
[95[88][89][90][91],
96,97,98], is envisioned. However, in the analysed scientific publication, the authors state that more time is needed to assess how the use of chitin/chitosan products in biomedical applications will evolve
[99,100][92][93]. Collagen products are mostly used in biomedical applications
[68,101][61][94] and as purified compounds (
Figure 7)
[68[61][95],
102], and a substantial rise in biomedical, cosmetic, and pharmaceutical applications is suggested by the authors in many of the analysed publications
[37,61,62,103,104][37][54][55][96][97].
Figure 7. Number of current (block colour) and future (striped pattern) applications reported by sectors for chitin/chitosan (a) and collagen (b) products. The resulting bars correspond to the exact number of each application field mentioned as current or future applications in the analysed publications dataset.
2.6. Trends in Data Distribution per Category of Information per Value Chain
There is a high degree of information discrepancy between the different categories of information presented in Figure 8, with more information presented in the categories relating to raw material origin, feedstock, pre-processing, and processing. While the sources and processes for obtaining chitin/chitosan or collagen were documented in >70% of the publications related to each value chain, market information related to the current applicability of both products and their derivatives was scarce (~23% in the case of the chitin/chitosan value chain and ~20% for the collagen value chain) (Figure 8). Moreover, the applicability of these products is generally documented as a possibility rather than a reality, and very few publications have mentioned patents, profitability, or marketability. Even when considering future perspectives, ~60% of the publications refer to products but only ~5% refer to market growth or profitability.
Figure 8.
Percentage of publications referring to each category of extracted information for chitin/chitosan (
a
) and collagen (
b
) value chains.
Although the economic and environmental sustainability of the chitin/chitosan value chain has been addressed in ~40% of the analysed publications, this value was much higher than that found for the collagen value chain (~30% for environmental sustainability and ~20% for economic sustainability) (Figure 8). Social sustainability was only seldom referred to for both value chains (<10% of publications).