Industrial relevance of Tamarindus indica L. by-products as source of valuable active metabolites

Highlights

• Tamarind by-products are a rich source of phytochemicals with bioactive activity.

• Tamarind peel and seed can be used in different areas of the industrial cycle.

• New extraction technologies are proposed for the sustainable phytochemical recovery.

• Integral management of tamarind by-products is a viable alternative.

• Biorefinery strategy is proposed, with discussion of challenges and trends.

Abstract

Tamarind (Tamarindus indica L.) pulp is highly consumed due to the appreciable sensorial attributes. However, the fruit processing generates from 50 to 70% of residue, corresponding to peel, fiber, and seeds; a biomass still unexplored and usually discarded in the environment. In this perspective, the present review highlights and summarizes the current literature data about the main bioactive compounds associated to by-products from tamarind processing. Then, to balance the lack of information on these residues, an overview on extraction methods is also presented, linked to the recovery of relevant compounds from these residues and possible applications for the resulting products. Phenolic compounds, fatty acids, and polysaccharides are the main classes of substances from tamarind by-products, which, when processed, are submitted to traditional extraction methods (Soxhlet and maceration). To spread the environmental appeal of these residues as viable biomass, non-traditional extraction methods, still underused for tamarind by-products, are valued. These methods are interesting alternatives to obtain valuable compounds adequate for functional foods, packaging formulations, medicines, and cosmetics.

Introduction

Tamarind (Tamarindus indica L.) is an exotic fruit belonging to the Fabaceae family, that adapts easily in semi-tropical regions with low rainfall, which favors fruit development. Although native from Madagascar, tamarind is spread worldwide due to easy adaptability and rapid seeds pollination (Havinga et al., 2010). The fruit can be structurally separated in four parts: the peel, dark brown or gray, composed of cracks arranged longitudinally and horizontally; the fibers, branched woody that sticks to the pulp; the edible pulp, brown, sweet or acid; and the seeds, internal to the endocarp, with long oval shape in bright dark brown (Azad, 2018).

The tamarind pulp, corresponding about 30–50% of the fruit, has been used for a long time as a spice in Asian cuisine, mainly due to the presence of reducing sugars and tartaric acid, which provide the attractive sweet or sour flavors (Rao & Mathew, 2012). The pulp is commercialized in different products such as juice, syrup, frozen pulp, dehydrated fruits, jelly, and sweet products (De Caluwé, Halamová, & Van Damme, 2010). The tamarind industrialization favors the fruit consume all year long and even in nonproductive regions. However, because of the considerable high processing volume, large amounts of by-products are industrially generated because from 11 to 30% of the fruit corresponds to peel, and 25 to 40% corresponds to the seeds. Theses by-products are still commonly used in livestock feed or discarded in the environment (Aengwanich, Suttajit, Srikun, & Boonsorn, 2009; Souza et al., 2018b).

Studies indicate that the tamarind by-products represent a valuable source of nutrients, due to content in carbohydrates, proteins, vitamins, and minerals. Besides that, several bioactive compounds are associated with these biomasses such as phenolics compounds, polysaccharides, polyphenols, alkaloids, and fatty acids (Menezes, Trevisan, Barbalho, & Guiguer, 2016). The bioactive compounds from tamarind seeds present valuable bioactivities like antioxidant, anti-diarrheal, and anti-inflammatory activities (Gupta & Gupta, 2017; Waqas, Akhtar, Bakhsh, Caldeira, & Khan, 2015), while the peel is related to antioxidant and cytotoxic actions (Atawodi, Liman, & Onyke, 2013; Ngwewondo et al., 2018).

Several bioactivities attributed to compounds present in tamarind by-products encourage the use of theses biomasses to produce inputs to food, chemical, pharmaceutical, and textile industries (De Queiroz et al., 2018). Then, to rapidly incorporated these products into the industrial cycle, processes to recover these valuable substances, such as extraction methods, are widely encouraged. Various reports have revealed the use of different processes such as Soxhlet (SOX) (Shirisha & Varalakshmi, 2016), maceration (Ngwewondo et al., 2018), SFE (Reis, Dariva, Vieira, & Hense, 2016), and MAE (Ganesapillai, Venugopal, & Simha, 2017), to obtain bioactive compounds from tamarind by-products. However, due to the nutritional wealth and the components diversity, the selection and the optimization of extraction processes are strategical for a viable and fully exploration of these residues.

At present, tamarind by-products have been reported in review studies as potential sources of health-beneficial substances applied in the pharmacological and cosmetic fields (Ahmad, Ahmad, Zeenat, & Sajid, 2018; Komakech, Kim, Matsabisa, & Kang, 2019). However, the adequate extraction method improves the recovery and separation of compounds from tamarind by-products based on its characterization and quantification. This expands the industrial chain where the recovered extracts can be incorporated. Despite the importance of the processing step to value tamarind by-products, to the best of our knowledge, no review study discusses extraction processes and their effects on bioactive compounds recovered from this biomass.

Then, to cover this void, this review highlights and summarizes the current literature on most bioactive compounds from tamarind by-products, discussing pretreatment and extraction methods, emphasizing recent advances on non-conventional methods. Challenges and trends for the industrial application of these processes and recovered products are also highlighted.