1. Introduction
Nutraceuticals, sometimes referred to as functional foods or food supplements, are a wide range of bioactive compounds belonging to families of secondary metabolites generally extracted from plants or microbes [
1]. Widely recognized as products with a beneficial interaction with human metabolism, they have antioxidant and chronic disease-prevention functions. Nutraceuticals show a positive consumption trend, as demonstrated by the increased food-supplement market value, which rose from USD 32 billion (in 2009) to 45 billion (in 2016) [
2]. With a wholesome 2019 market value of USD 424 billion, Daliri and Lee estimated that the nutraceutical market will grow annually by an average of 6.5% in 2021–2027 [
3].
The green transition of nutraceuticals, functional food, and the cosmetics industry is steadily proceeding [
4], pushed by the consumer’s demand for environmentally friendly products, policy tools, and investments to reduce the harmful impact of production on the climate and the environment [
5]. In this context, the integrated biomass–biorefinery approach is one of the most promising production models for recovering raw materials and obtaining energy, food, feed, and polymers with high added value [
6]. However, its feasibility and economic sustainability are limited by the availability of biomass, its quality, the procurement costs, and the conversion yield [
7]. Obtaining chemicals capable of replacing their fossil-based counterparts is the crucial point of biomass-based businesses’ technological and profitability analysis, which must consider additional factors affecting the supply chain efficiency. Land use, the impact on biodiversity and ecosystems, water consumption, GHG emissions, and food competition are just some of the evaluation criteria to consider in the economic decision-making process and industrial feasibility study.
Our study focuses on two important nutraceuticals: chlorogenic acid (CGA) and inulin, which have a compound annual growth rate (CAGR) of current and projected (until 2027) demand of 3.44% and 4%, respectively [
3,
8].
CGA is a polyphenolic molecule belonging to the caffeoylquinic acid family, consisting of a quinic acid bonded at C-5 to a caffeic acid molecule [
9], biosynthesized by the plant in response to stresses caused by bacteria [
10] fungi [
11], insects [
12], wound damage [
13,
14], and ultraviolet exposition [
15,
16]. The growing interest in CGA is due to its beneficial interactions with human metabolisms, such as antioxidant, antimicrobial, hepatoprotective, and anti-obesity activity [
9,
17]. Green coffee (
Coffea spp. L.) is the primary source of CGA [
18], although it is facing a recent market contraction [
8]. Green coffee is cultivated mainly in Brazil and Vietnam [
18] where the most cultivated species are
Coffea canephora and
Coffea arabica [
19]. The
arabica species is more agronomically demanding than
canephora, but its yield and quality are superior [
20].
Although the CGA extraction processes are industrially diversified [
21,
22,
23,
24], the Soxhlet method is widely employed [
24], followed by the more cost-effective, efficient, and scalable microwave-assisted extraction (MAE) [
25,
26,
27,
28]. CGA is commercialized mostly as phyto complex formulations (pills or capsules) [
29], with a diversified pricing policy according to the concentration, branding, and application [
3]. The most expensive formulation is used in the pharmaceutical sector (USD 30/kg), followed by cosmetic (USD 22/kg) and nutraceuticals (USD 14/kg) [
3]. The microencapsulation prevents CGA degradation from digestive oxireductive stress [
29]. Yearly, more than half of the CGA extracted (6437 tons) is consumed as food supplements, followed by 21% used by the pharmaceutical sector (1444 tons/year), and approx. 20% used in cosmetics [
3].
Inulin belongs to the fructans family, consisting of linear (2→1)-linked -d-fructosyl units linked to the fructosyl moiety. Biosynthesized in plant roots, where it exerts an energy reservoir function [
30], inulin’s structure varies from 2 to 60 fructosyl units [
31], according to the vegetative stage, the species, and the environmental conditions [
31]. Inulin has low caloric intake values, making inulin-based products recommended for low-glycemic diets [
32] and in many food preparations (baby foods, bakery, ice creams) [
33]. Furthermore, many studies underline inulin’s ability to reach the gut and act as a prebiotic [
34]. Chicory (
Chichorium intybus), the primary inulin source [
8], is an overwintering herb endemic of the Mediterranean basin, North America, and Africa [
35], whose cultivars are widely employed as food and feed products [
36,
37]. Environmental conditions play a significant role in plant development, as a temperature above 14 °C is required for consistent production [
37]. Chicory needs great cultivation inputs (for example, 750 m
3/year of water), thus causing a high environmental impact (3.75 kg CO
2 eq/kg of biomass) [
18,
38].
Jerusalem artichoke (
Helianthus tuberosus L.), also known as topinambur, is an additional source of inulin. Native to North America (36th parallel), the Jerusalem artichoke is a short-day perennial plant. Its adaptability to varying climatic and soil conditions makes it amenable to worldwide cultivation as a warm-season crop with an annual cycle [
39]. The species is also used in the exploitation of marginal lands [
40,
41], albeit harvesting and cultivating practices are yet to be optimized [
42]. The traditional inefficient inulin extraction methods have been substituted by MAE [
43].
Native to the Mediterranean basin, cardoon (
Cynara cardunculus L.) is a perennial herb belonging to the
Asteraceae family [
44]. Minorly cultivated as a vegetable, cardoon is attracting interest thanks to its high concentration of bioactive compounds [
44,
45], biomass yield [
46], and ability to grow on marginal lands under low-input agronomical regimes [
44]. Cardoon favors carbon sequestration, arable crop-system integration [
41], and producing bio-based products, which avoids food competition phenomena [
40,
41]. Another Asteracea, artichoke (
Cynara scolymus), is used for CGA extraction.
The growing demand for CGA and inulin is calling for developing and adopting greener business models along the entire supply chain [
47].
With the goal of identifying the most efficient biomass for CGA and inulin extraction, this study compares the strategic factors affecting profitability and environmental impact by applying a multi-criteria decision analysis (MCDA) methodology. Conventional biomasses used to extract the two compounds of interest—green coffee, chicory, and Jerusalem artichoke—are compared with cardoon. Comparative methods (MCDA based) for biomass performance evaluation and subsequent choice are present in the literature concerning ethanol production [
48], sugarcane varieties [
49], and gasification processes [
50]. Published studies consider only one component (i.e., technical improvements of the biomass or their processing technologies, and sustainability) [
51]. Conversely, this study embraces various methods to optimize the choice among different options and conflicting criteria [
52].
Extensively employed in policy-making decisions [
53], MCDA proved to be suitable even in technical and scientific domains (reviewed in [
54]). MCDA for biomass selection is applied in renewable energy source (RES) analyses [
55] using the analytical hierarchical process (AHP), as described in [
56]. For example, Chatzimouratidis and Pilavachi [
57] used AHP to evaluate power plants’ impact on living standards, whereas Amer and Daimon [
58] evaluated the efficiency of renewable biomasses for energy production. Concerning nutraceuticals and functional foods, a novel MCDA model was proposed to assess the toxicological risks of botanical extracts [
59]. Similarly, an MCDA-based experiment to find the correlation between military multi-nutrient food supplements and chronic disease incidence was recently conducted [
60].
Considering the examples reported above, our novel approach considers technical–economic data from the literature and market reports about inulin and CGA production from renewable biomasses and innovatively applies MCDA to the nutraceuticals and food supplement sector, taking into account the environmental, economic, and social dimensions of CGA and inulin extraction. We aim at providing evidence for the validity of our model in providing an efficient decisional mechanism to promote alternative sustainable solutions for the nutraceutical industry.
Our approach is based on a customized MCDA methodology, which will be further described in the Materials and Methods section, applying an innovative computational model developed by Gatto et al. [
61] to rank and select biomasses for the sustainable extraction of CGA and inulin. This innovative approach is based on quantitative and qualitative data present in the literature, therefore favoring the procedure’s standardization, even in case of niche issues such as the subject of our study. The screened and analyzed literature data considers ultimately only the information useful for CGA and inulin. Based on eight criteria, a set of parameters describing the biomasses’ performance, this approach takes into consideration experts’ judgements in defining their importance by applying, as a part of MCDA, the AHP method, a general theory of measurement to derive ratio scales from paired comparisons that reflects the relative strength of preferences and feelings [
62]. Further details on the AHP model are provided in the Materials and Methods section.
4. Discussion
Global warming, the depletion of natural resources, and a growing environmental awareness are driving the green transition of the manufacturing sector towards sustainable growth, guaranteeing adequate resources and living conditions for future generations. In this context, the European Commission has designed strategies to replace fossil materials with bio-based solutions, reduce environmental pressures, and strengthen green innovation, research, and employment in the EU. Through specific investment measures and strategic plans, such as the New Green Deal and the Next Generation EU, Europe aims to reduce net greenhouse gas emissions by at least 55% by 2030 [
79] and make Europe the first climate-neutral continent by 2050 [
80].
The transition to a greener economy also involves the nutraceutical sector. Innovation and a growing focus on health care and disease prevention, medical advances, and increasing life expectancy define this market’s steady and tangible upward trend [
1]. However, CGA and inulin are currently extracted from unsustainable biomasses due to food competition, high cultivation requirements, and logistical costs.
We aimed to identify alternatives to current raw materials for the extraction of CGA and inulin as an essential step to achieving social, economic, and environmental sustainability.
The MCDA approach employed in this study provides recommendations on which sources of CGA and inulin are more sustainable, based on economic, social, and technological criteria. This study paves the way for using the MCDA methodology in the nutraceutical industry.
The “process costs” and “inulin concentration” criteria were considered exclusively for CGA and inulin, respectively. In the case of inulin, process evaluation was unnecessary since competitor biomasses are morphologically similar, and the same can thus be assumed for process settings and costs. CGA concentration was not included because of contradictory data reported in the literature. The inclusion of this criterion would have risked biasing the study.
This study identified
Cynara cardunculus as the most promising biomass for the extraction of CGA and inulin, qualifying it as an eco-sustainable, low-input alternative in marginal lands at risk of desertification in the Mediterranean basin. Desertification affects about 75% of the world’s soil, and in Europe, the problem affects 13 countries for a total of 645,000 km
2 [
81]. Cultivation in marginal and abandoned lands is environmentally efficient, and it favors the economic and social growth of these regions. Furthermore, cardoon is not an edible crop and does not compete with the food industry, thus supporting the growing demand for food and the global demand for bio-based products.
However, the current extraction of CGA and inulin from Cynara cardunculus is not economically nor technically competitive with the traditional, industrial biomasses, mainly green coffee and chicory. In the selection phase, expert heterogeneity was purposedly sought to include the broadest overview possible. Therefore, due to their different backgrounds and specific interests, the variability in expert judgments was relevant. Nevertheless, an agreement was recorded about the importance of the final price to consumers in evaluating the ranking of the biomasses for nutraceutical extraction.
CGA from cardoon is sold at almost double the price of green coffee. The reasons behind the expensiveness of CGA cardoon are biomass shortages, scarce cultivation employment and seasonality, and extraction process inefficiencies. The latter is a consequence of the use of conventional methodologies. To reduce process impact on the extraction, further implementation of unconventional extraction methods, such as MAE or UAE, is recommended.
When analyzing inulin production, the environmental sustainability of Jerusalem artichoke is comparable or superior to cardoon. However, the shortcomings of Jerusalem artichoke, such as the reduced inulin concentration and the low process yield, still make cardoon the first choice. It is, however, worth noting that cardoon has a low crop yield both on standard and marginal lands. The extraction process cost was not included in this analysis since all the species used for inulin extraction have similar morphological features and undergo extraction protocols. The reasons for inulin’s market price stability (independent from the biomass considered) could be due to the treatment and process homogeneity required to obtain the inulin powder independently from the final application. Another reason could be that inulin powder is a pure compound, and therefore does not need expensive testing of formulates [
8].
Our study demonstrates that
Cynara cardunculus is a very promising crop for extracting nutraceutical compounds. However, further studies are needed to improve its economic and technical feasibility, supported by dedicated national and European funds. For example, efforts should be dedicated to improving the efficiency of the CGA extraction process to reduce the process’s cost and the final product’s price. The innovative extraction methodologies (MAE, UAE, and Supercritic-CO
2 extraction) can reduce process costs and environmental impact while increasing extraction yields. Inulin research should focus on increasing yield and biomass availability through improved cultivation methods and advanced breeding methodologies [
82].
Farmers could use cardoon to diversify their production, exploit underutilized and marginal land, and, therefore, explore new market segments and find new sources of income. The cultivation of marginal and non-irrigated soils could maintain biodiversity and soil fertility, thus supporting the local economy [
83]. Finally, nutraceutical companies could bring new innovative bio-based products to market, meeting consumer demand for functional and effective compounds that are both sustainable and environmentally friendly [
84].
To ensure that consumers purchase sustainable cardoon-based nutraceutical products over already-marketed products, it would be necessary for the companies to involve the consumer in the purchasing decision, increasing awareness through transparency and promoting sustainability initiatives. Many studies have demonstrated that consumers are willing to pay more for a sustainable product as long as they know the environmental benefits and its sustainability index [
85,
86]. Developing a sustainability certification label for nutraceuticals could award a premium value to the final product. The label should contain clear information on the products’ sustainable features, such as the low-input demand for its cultivation and the possibility of growing cardoon on marginal lands.