Yerba mate: cultivation systems, processing and chemical composition. A review

: The unique chemical composition of yerba mate and its functionalities suggest that it needs to be explored for its innovation potential. New uses may boost consumption, surpassing the traditional consumption barrier, and making yerba mate accessible on a global level. Thus, to highlight the importance of yerba mate as a potential source of agro-economic resources, we present a review on its botanical, ecological, and industrial aspects, along with information on the biochemical composition of this species and its biological activity.


Introduction
In recent years, more studies have been conducted on yerba mate (Ilex paraguariensis), focusing mainly on its health effects. Yerba mate has several pharmacological activities, including antioxidant, anti-inflammatory, antimutagenic, anti-obesity, and cardioprotective functions (Gómez-Juaristi et al., 2018). These benefits are related to a unique chemical composition including alkaloids, polyphenols, terpenes, and essential oils, among others Riachi et al., 2018).
Ilex paraguariensis is abundant in the understory of Araucaria forests and has a considerable economic value and a significant importance in agricultural production systems, generating income and playing a strategic role in the preservation of native forest areas in ecosystems with a multiple-use perspective of natural resources (Inventário Florístico Florestal de Santa Catarina, 2013).
However, with some exceptions, scientific evidence shows that implementation of yerba mate had a late onset, while studies on Camelia sinensis and Coffea sp. are numerous. Compared to mate, these species have a similar economic and biological potential and are widely consumed worldwide due to their stimulating effects on the nervous system (Heck and Mejia, 2007;Baeza et al., 2017). The consumption of infusions prepared from the leaves of yerba mate dates back to the XIX century, while studies on this species have only be performed in the last three decades (Heck and Mejia, 2007).
Our current knowledge on yerba mate is rather fragmented, requiring further studies. The species has potential to be used not only as a drink, but also as raw material for the cosmetics, nutraceutical, and pharmaceutical industries (Heck and Mejia, 2007;Bracesco et al., 2011;Berté et al., 2014;Souza et al., 2015;Cardoso Junior and Morand, 2016). Thus, changes are necessary in agronomic research to obtain a highquality raw material through breeding programs, variety selection, as well as improved production strategies in efficient systems that ensure the best chemical composition, thereby, optimizing its biological activities (Cardoso Junior and Morand, 2016).
To emphasize the importance of this species as potential source of agro-economic resources and highlight its versatile chemical composition and the possibility of multiple uses, we conducted a literature review on its botanical, ecological, agronomic, and industrial aspects. In addition, we present information on its biochemical composition and biological activity.
The species are endemic and distributed in the wild exclusively in the forested regions of South America, composed of Mixed Ombrophilous Forest, in the Atlantic Forest biome, always in associations, and clearly evolved with Araucaria angustifolia (Heck and Mejia, 2007). To develop, Ilex requires average annual temperatures between 17 and 21 °C and regular rainfall, with high air and soil humidity. Ilex occurs in the subforest layer in acidic soils of low natural fertility, high aluminum content, low available phosphorus levels, and high organic matter concentration. It tolerates shade at any age and is considered an ombrophilous species with slow or moderate growth, typical of mature forests, where it can reach density of hundreds individuals per hectare (Caron et al., 2014b;Chaimsohn et al., 2014).

Agronomic aspects -cropping systems
The world production of yerba mate in 2016 amounted to 937,310 tons, mainly from Brazil, Argentina, and Paraguay (FAO, 2017). In Araucaria forests, the species is abundant, with a considerable economic value and a significant importance in agricultural production systems, becoming a stabilizing factor of income and having, many times, a strategic preservation function of native forests in their ecosystems with perspective of multiple use of natural resources Pires et al., 2016).  (Bracesco et al., 2011;Cabral et al., 2018). with more than 600 species. Ilex has a predominantly tropical distribution, extending to temperate regions of the northern and southern hemispheres, with East Asia and South America as the global centers of diversity (Yi et al., 2017;Cabral et al., 2018). Yerba mate is the most important commercial species of the genus and occurs in its native state in the subtropical and temperate regions of South America, Yerba mate: cultivation and composition Sci. Agric. v.78, n.5, e20190259, 2021 northern Santa Catarina States in Brazil. These fragments in the region contribute to the landscape formation, composing a mosaic of cultivated areas interspersed by forests (Hanisch et al., 2010).
The agroforestry system is the yerba mate cultivation associated with logging and/or agricultural activities. These systems are composed of plant species in the arboreal and/or herbaceous-shrub layer and managed in a way that favors the production of yerba mate in the understory. The species planted have different cycles, sizes, and functions, resulting in an increased biodiversity, which promotes physical-chemical, hydrological, and microbiological improvements of the soil, besides generating income (Barbosa et al., 2017).
Monocultures allow cultivation of more plants in an area, generating higher yields, and enabling mechanized harvesting. However, trees are exposed to full sun, which can lead to alterations in their metabolic processes and damages in leaf quality. These species have evolved as Ombrophilous species and are subjected to physiological stresses when cultivated in open places, making them more susceptible to pest attacks and diseases .
Maintenance of native herbs in traditional systems (extractive and intercropped with native forests) can represent an important stimulus for environmental conservation to ensure maintenance of the forest and In general, herbs occur is diverse habitats, based on their adaptability to different light conditions and management strategies, enabling different designs of production systems. In this sense, we highlight the extractive systems, consorted with native forests, agroforestry, and monoculture (full sun) Vogt et al., 2016).
The extractive activity of a natural forest (Araucaria Forest or Mixed Ombrophilous Forest) is considered the traditional system of cultivation, mainly in terms of native herbs. Yerba mate produced in this system is extracted sustainably from the most significant native forest areas of southern Brazil. In this system, management or cultural treatments are not common and crops are harvested periodically Vogt et al., 2016).
A system in consortium with native forest, also called "mixed cultivation" or "caívas", is traditionally the exploration of forest remnants where yerba mate grows naturally or in cultivations managed in association with other plant species, usually native species, and in some cases even associated with cattle livestock. This system also has economic, social, and environmental importance, since it contributes to the preservation of forest remnants and generates income to the farmer (Chaimsohn et al., 2014).
Most of these caívas are forest fragments of different sizes in rural properties of southern Paraná and its significant economic value, providing monetary value to forest remnants. In addition, such systems generally have fewer phytosanitary problems, favoring plant production without the use of agrochemicals (Marques et al., 2012;Chaimsohn et al., 2014). Characteristics of the consortium system are common, such as shading of plants, presence of other forest species, and sometimes conservation of the original material of mate .
In addition to the significant volume of yerba mate produced in traditional and agroforestry systems, the product obtained from these systems has a higher value, since the shading provided by other tree species results in a product with a better flavor, more accepted in the Brazilian and Uruguayan markets (major yerba mate consumers in the world) (Marques et al., 2012). Industrial demands for this type of weed have increased markedly in recent years (Caron et al., 2014a;Caron et al., 2014b).
Composition of yerba mate varies considerably depending on factors, such as seasonality, temperature, water and nutrient availability, cultivation system, and adopted management practice, with effects on its physiological effects. Thus, studies that elucidate the relationship between its composition and its constituent factors are necessary to determine the association between health benefits, mate consumption, and maintenance of sustainable supply chains with forest preservation (Berté et al., 2014;Pires et al., 2016;Cardoso Junior and Morand, 2016;Kahmann et al., 2017;Riachi et al., 2018).

Processing and uses
The first explorers of yerba mate were the native inhabitants of northeastern Argentina, southern Brazil, Paraguay, and Uruguay, who consumed mate due to its stimulating and medicinal properties. Several tribes, such as the Guaranis, the Amerindians (Incas and Quechuas), and the Caingangues, consumed its leaves, infused, or chewed. Infusion of leaves became a popular drink and, nowadays, the product obtained from dry leaves, also called mate or maté, is used in several types of infusions, such as the chimarrão, tereré, and mate tea (roasted leaves) (Holowatt et al., 2016;Lima et al., 2016).
Yerba mate exploration is based on the use of selected leaves and branches, which are subjected to thermal bleaching (sapeco) for enzyme inactivation, followed by drying, grinding, and separation. These last two steps allow obtaining a product with standard particle size, followed by milling and aging for up to 24 months, depending on the desired product ( Figure 4). Intensity, grinding type, and the aging period result in products with differentiated standards (Meinhart et al., 2010).
The agro-industrial processing of yerba mate has not been significantly altered since the beginning of its economic exploration, with disadvantages related to its high energy requirement, difficulties in controlling its variables and, consequently, in the standardization of the final product. Another negative aspect concerns the oxidative environment of the bleaching and drying process, which potentially contributes to the degradation of the biochemical compounds of the leaves. Thus, Figure 4 -Traditional processing of yerba mate (Berté et al., 2014;Silveira et al., 2017;Riachi et al., 2018). Yerba mate: cultivation and composition Sci. Agric. v.78, n.5, e20190259, 2021 the development of new technological processes for preserving its compounds is a strategy that must be considered (Meinhart et al., 2010;Cardoso Junior and Morand, 2016).
Mate is consumed as leaf infusion, with variations in the manufacturing and preparation of the beverage. The leaves are infused in hot water and sipped through a tube and gourd. Tereré is a cold drink, while mate tea is obtained from the roasted leaves and consumed hot or cold (Bracesco et al., 2011;Cardoso Junior and Morand, 2016).
Roasted mate can also be subjected to the extraction of soluble solids with hot water, followed by drying in a spray-dryer, resulting in soluble roasted mate. Soluble solid extraction from the crushed green yerba mate yields the soluble green mate; both products are intended primarily for export and present as market innovation (Berté et al., 2014).
The per capita consumption of yerba mate in Uruguay, Argentina, and Brazil is estimated at 8 to 10 kg yr -1 , 5 to 6 kg yr -1 , and 1.2 to 5 kg yr -1 , respectively (Berté et al., 2014;Cardoso Junior and Morand, 2016). In Brazil, the state of Rio Grande do Sul is the largest consumer of herb for chimarrão (70,000 t yr -1 ), while Rio de Janeiro is the largest consumer of roasted mate tea (1,500 t yr -1 ). In Brazil, the entire yield is exported, mainly to Uruguay and Chile, followed by the United States, Europe, and Asia, which receive the product as whole or ground dried leaves or extracts for the pharmaceutical industry (Anesine et al., 2012;Lima et al., 2016).
In the last decade, along with the traditional use, yerba mate has been grown for raw material in the production of beers, soft drinks, cosmetics, sweets, and functional cheeses as well as other non-traditional uses (Table 1). In the case of functional cheeses, a recent study showed that the addition of yerba mate, besides increasing the biological activities due to the interaction between herb polyphenols and milk proteins, increases the sensorial characteristics, with good acceptance by consumers (Marcelo et al., 2014;Saraiva et al., 2019).
Leaves are also used to produce energy drinks as an alternative to coffee, widely appreciated in Europe and the United States because of their high levels of antioxidants and nutritional benefits (Bercher et al., 2011;Bergottini et al., 2017). However, studies on new uses, such as food preservatives, food supplements, dyes, or hygiene and cosmetics products, need to be conducted to allow consumption to exceed the traditional barrier and become increasingly accessible in Latin America, which is also interesting for innovations in the agroindustrial sector (Table 1) (Cardoso Junior and Morand, 2016).
As a secondary use, yerba mate wood produces a blade of excellent quality (Table 1). However, the species is considered inadequate to produce energy, pulp, and paper. Its residue, after processing, has been used by horticultural workers as organic fertilizer and in animal feed, providing forage with 13 % crude protein. In addition, the species is highly recommended because of its ornamental value and biological properties, mainly for afforestation, gardening, and the ecological restoration of degraded ecosystems (Embrapa, 2019).
Rodríguez-Arzuaga and Piagentini (2017) optimized yerba mate concentrations in an aqueous dipping solution to maximize the antioxidant capacity and minimize the browning occurrence without affecting the sensory quality of freshly cut apples. Our results suggest that chemical treatment with yerba mate applied to apples cut freshly was successful in delaying enzymatic browning development, providing compounds with antioxidant capacity with potential benefit for human health (Table 1). Biodegradable and edible starch-glycerol based films containing different concentrations of a natural antioxidant as yerba mate extract were evaluated to obtain promising biodegradable edible films to be used as packaging. The study demonstrated that yerba mate extract acted as a plasticizer when incorporated as an antioxidant into starch-glycerol based films. Besides, the use of the extract improved biodegradability of the films in compost and preserved their stability (Medina Jaramillo et al., 2016).
Yerba mate was used for dyeing silk, wool, linen, and cotton fabrics. Dyed silk fabrics presented the highest color strength (Yoo and Jeon, 2012). Giacomini et al. (2016) investigated the best dyeing conditions, such as pH, temperature, and dyestuff concentration of silk fabric using roasted yerba mate. The authors concluded that silk fabrics can be dyed easily with yerba mate, providing a yellowish brown color, and the best silk dyeing result was achieved at 90 °C, pH 3.0 and 20 g L -1 dye concentration. Bulut and Akar (2012) used some oil-free yerba mate wastes to dye cotton and wool yarn previously cationized without metal salts. Fabrics were dyed successfully with high color strength.
Another study evaluated the effectiveness of extracts of unripe yerba mate fruits for chemical control of piped apple snail (Pomacea canaliculata) and nontarget species, such as South American catfish (Rhamdia quelen), under laboratory conditions. The extracts were particularly attractive considering the source of compounds and their effectiveness as molluscicides (Brito et al., 2018).

Chemical aspects, bioactive compounds and their functionalities
Much attention has been dedicated to yerba mate due to its potential health benefits ( Figure 5). These benefits seem to be related to the phytochemical variability, determining the unique chemical composition. Studies have detected different chemical groups, such as polyphenols, saponins, alkaloids, and essential oils (Tables 2, 3 and 4). The leaves also contain vitamins (A, C, B1, and B2), magnesium, calcium, iron, zinc, sodium, and potassium (Heck and Mejia, 2007;Berte et al., 2014).
Compounds, such as polyphenols, saponins, alkaloids, and essential oils from the secondary metabolism of plants and, because of their chemical diversity, these compounds have a variety of functions in plants. Numerous substances act as defense against herbivores and pathogens, while others play a role in mechanical support, as a pollinator or in fruit disperser attraction, protection against ultraviolet radiation, or growth reduction of adjacent competing plants (Taiz et al., 2017;Neugart et al., 2018).
In addition, caffeine, theophylline and theobromine alkaloids are important active components of yerba mate, derived from xanthine and known as methylxanthines (Table 4). They all have the stimulating effect on the central nervous system in common, with caffeine as the most potent representative. Methylxanthines also affect the cardiovascular system, with theophylline generating the strongest effect. Thus, caffeine, theophylline, and theobromine concentrations in yerba mate beverages is generally of great interest (Holowaty et al., 2016;Friedrich et al., 2017;Konieczynski et al., 2017).
The biochemical composition of yerba mate varies according to the locality, cultivation system or processing method. Yerba mate contents can vary widely (Table 2), and environmental conditions to which the plants are submitted (seasonality, temperature, water and nutrient availability, radiation) determine their biosynthesis (Dutra et al., 2010;Pires et al., 2016).
Thus, cultivation and management systems greatly affect the levels of these substances (Dutra et al., 2010;Berté et al., 2014); thereby, affecting quality of the final product and its effect on human health. However, studies that interrelate these factors are still scarce (Heck and Mejia, 2007;Neugart et al., 2018;Riachi et al., 2018).

Final Remarks
Consumption statistics show that the production chain of yerba mate is based on the use of traditional drinks, such as the chimarrão and the tereré. However, the innovation potential of yerba mate still needs to Yerba mate: cultivation and composition Sci. Agric. v.78, n.5, e20190259, 2021 Figure 5 -Some potential health benefits associated with yerba-mate consumption (in vitro and vivo tests). be explored, considering its chemical composition and functionalities. The implementation of new uses, such as food preservatives, food supplements, dyes, hygiene and cosmetic products, leads to the increase of yerba mate consumption worldwide. In addition, studies that explain the effects of crop systems on chemical composition and product quality need to be developed.