Sea cucumbers, belonging to the class Holothuroidea, are marine invertebrates, habitually found in the benthic areas and deep seas across the world. They have high commercial value coupled with increasing global production and trade. Sea cucumbers, informally named as bêche-de-mer, or gamat, have long been used for food and folk medicine in the communities of Asia and Middle East.
Nutritionally, sea cucumbers have an impressive profile of valuable nutrients such as Vitamin A, Vitamin B1 (thiamine), Vitamin B2 (riboflavin), Vitamin B3 (niacin), and minerals, especially calcium, magnesium, iron and zinc. A number of unique biological and pharmacological activities including anti-angiogenic, anticancer, anticoagulant, anti-hypertension, anti-inflammatory, antimicrobial, antioxidant, antithrombotic, antitumor and wound healing have been ascribed to various species of sea cucumbers. Therapeutic properties and medicinal benefits of sea cucumbers can be linked to the presence of a wide array of bioactives especially triterpene glycosides (saponins), chondroitin sulfates, glycosaminoglycan (GAGs), sulfated polysaccharides, sterols (glycosides and sulfates), phenolics, cerberosides, lectins, peptides, glycoprotein, glycosphingolipids and essential fatty acids. This review is mainly designed to cover the high-value components and bioactives as well as the multiple biological and therapeutic properties of sea cucumbers with regard to exploring their potential uses for functional foods and nutraceuticals.
In recent decades, the concept of functional foods has offered a new and practical approach to achieving optimal health by promoting the use of natural products with physiological benefits thus reducing the risk of various chronic diseases [1,2].
Most of the currently available functional foods and therapeutic agents are derived either directly or indirectly from naturally occurring sources, especially, the terrestrial food plants and marine species [2–4]. Due to the rich oceanic biodiversity, marine organisms are valuable sources of nutritious foods as well as represent novel reservoirs of biologically active components, in particular bioactive peptides, and antimicrobial, anti-inflammatory and anticancer agents [4–6].
Sea cucumbers are one of the marine animals which are important as human food source, particularly in some parts of Asia . They are usually soft-bodied echinoderms comprising a diverse group of flexible, elongated, worm-like organisms, with a leathery skin and gelatinous body, looking like a cucumber. Habitually, they tend to live on the sea floor in deep seas .
A multitude of harvestable sea cucumbers species have been exploited with growing global demand due to their food and pharmaceutical uses [9–13]. The dehydrated sea cucumber is commercially sold, especially in Asian markets with main business in China, followed by Korea and Indonesia and then Japan. On the other hand, these are also exported in appreciable quantities to parts of the United States and northern Australia [14,15]. According to Food and Agriculture Organization of the United Nations (FAO) report Beche-de-mer production and Apostichopus japonicas (Selenka, 1867) catches by various countries for the period 1992–2001 was estimated to be 12,331 t (metric ton) (dry weight) .
Sea cucumbers, commonly known as trepang, beche-de-mer, or gamat, have long been utilized in the food and folk medicine systems of Asia and Middle East communities [17,18]. Sea cucumbers have been well recognized as a tonic and traditional remedy in Chinese and Malaysian literature for their effectiveness against hypertension, asthma, rheumatism, cuts and burns, impotence and constipation [18–23]. Several unique biological and pharmacological activities namely anti-angiogenic , anticancer , anticoagulant [26,27], anti-hypertension , anti-inflammatory [29–31], antimicrobial [32,33], antioxidant , antithrombotic [35,36], antitumor [37,38], and wound healing  have been ascribed to chemical compounds extracted from different sea cucumber species. These medicinal benefits and health functions of sea cucumbers can be attributed to the presence of appreciable amounts of bioactive compounds, especially the triterpene glycosides (saponins) [40–42], chondroitin sulfates , glycosaminoglycan [26,36], sulfated polysaccharides , sterols (glycosides and sulfates) , phenolics , peptides , cerberosides  and lectins [49–51].
As far as we know, previously no comprehensive review article as such has ever been published covering the detailed nutritional, medicinal and pharmacological aspects of sea cucumbers. This review is an attempt to mainly compile an inclusive report covering the description of high-value components and bioactives as well as biological and medicinal properties of these multipurpose marine invertebrates, as one of the potential sources for functional foods and nutraceuticals. An updated overview of the distribution, fishery and trade of sea cucumbers is also presented, worldwide.