plants Review Okra (Abelmoschus esculentus L.) as a Potential Functional Food Source of Mucilage and Bioactive Compounds with Technological Applications and Health Benefits Thamires Lacerda Dantas 1,2, Flávia Carolina Alonso Buriti 1,2,* and Eliane Rolim Florentino 1,2,* 1 Programa de Pós-Graduação em Ciências Farmacêuticas, Universidade Estadual da Paraíba, Campina Grande 58429-600, PB, Brazil; [email protected] 2 Núcleo de Pesquisa e Extensão em Alimentos, Universidade Estadual da Paraíba, Campina Grande 58109-790, PB, Brazil * Correspondence: fl[email protected] (F.C.A.B.); [email protected] (E.R.F.) Abstract: Abelmoschus esculentus has fruit popularly known as okra and belongs to the Malvaceae family. It is commonly used in cooking but also in traditional medicine in the treatment of worms, dysentery, inflammation, and also irritation of the stomach, intestines, and kidneys, as it is a potential functional food. Its mucilage is a highly viscous polysaccharide that is mostly composed of monosac- charides D-galactose, L-rhamnose, and galacturonic acid, as well as proteins and minerals. The functional properties of okra mucilage have been widely studied, mainly for its potential antidiabetic activity; thus, its use as adjuvant or nutraceutical therapy for diabetes is very promising. Due to its rheological properties, it is a potential resource for pharmaceutical and food applications. Okra mucilage can be extracted by several methods, which can directly influence its physicochemical characteristics and biological activity. Features such as low cost, non-toxicity, biocompatibility, and high availability in nature arouse the interest of researchers for the study of okra mucilage. The Citation: Dantas, T.L.; Alonso Buriti, survey of research on the applications of okra mucilage highlights the importance of using this F.C.; Florentino, E.R. Okra promising source of bioactive compounds with interesting technological properties. The potential (Abelmoschus esculentus L.) as a of okra as a functional food, the properties of okra mucilage, and its technological applications are Potential Functional Food Source of Mucilage and Bioactive Compounds discussed in this review. with Technological Applications and Health Benefits. Plants 2021, 10, 1683. Keywords: Abelmoschus esculentus; okra; functional food; polysaccharides; gum; mucilage https://doi.org/10.3390/ plants10081683 Received: 16 July 2021 1. Introduction Accepted: 11 August 2021 Abelmoschus esculentus L. is popularly known as okra or lady’s finger. It belongs Published: 16 August 2021 to the Malvaceae family, native to Africa, and is cultivated in tropical, subtropical, and warm temperate climates in different countries from Africa to Asia, Southern Europe, and Publisher’s Note: MDPI stays neutral America [1,2]. with regard to jurisdictional claims in Okra, originating in Ethiopia and propagated in North Africa, the Mediterranean, published maps and institutional affil- Arabia, and India is of great economic importance in the subtropical regions of the world [3]. iations. As food, okra can be eaten fresh or cooked and used as an additive in soups, salads, and stews [4]. Okra fruit has a high moisture content, it is rich in nutrients, and it is a great source of vitamins and minerals. Carbohydrates are present in okra mainly in the form of mucilage [5], commonly applied in different industrial segments and for Copyright: © 2021 by the authors. medicinal purposes [6]. The fruits, seeds, and leaves of okra have applications due to their Licensee MDPI, Basel, Switzerland. composition and properties (Figure1). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Plants 2021, 10, 1683. https://doi.org/10.3390/plants10081683 https://www.mdpi.com/journal/plants Plants 2021, 10, x FOR PEER REVIEW 2 of 15 Plants 2021, 10, 1683 2 of 14 Figure 1. Utilization of fruits, seeds, an andd leaves from okra. Okra image: authors’ personal archive. Okra isis aa vegetable vegetable widely widely cultivated cultivated in the in world.the world. It is considered It is considered important important through- throughoutout the tropical the tropical and subtropical and subtropical regions regions of Africa of Africa and Asia, and withAsia, anwith annual an annual estimated esti- matedproduction production of six million of six million tons [7]. tons In Pakistan, [7]. In Pakistan, okra crop okra is grown crop is on grown an area on of an 15,081 area haof 15,081with an ha annual with an production annual production of 114,657 tonsof 114,657 [8]. Globally, tons [8]. India Globally, ranks India first in ranks okra first production, in okra production,having an area having of 509 an ha area with of an509 annual ha with production an annual of production 6094.9 million of 6094.9 tons andmillion productivity tons and of 12 million tonnes/ha [9]. productivity of 12 million tonnes/ha [9]. The bioactive potential of okra mucilage and its rheological characteristics have The bioactive potential of okra mucilage and its rheological characteristics have been been the subject of several studies and reported in current bibliographic surveys [10,11]. the subject of several studies and reported in current bibliographic surveys [10,11]. How- However, the importance of okra as a low-cost functional food still deserves to be more ever, the importance of okra as a low-cost functional food still deserves to be more under- underlined. Functional foods represent an important segment for innovation, as they lined. Functional foods represent an important segment for innovation, as they are in- are intended not only to satisfy hunger and provide human beings with the necessary tended not only to satisfy hunger and provide human beings with the necessary nutrients nutrients but also to prevent nutrition-related illnesses and increase consumers’ physical but also to prevent nutrition-related illnesses and increase consumers’ physical and men- and mental well-being [12]. The richest sources of compounds with beneficial health tal well-being [12]. The richest sources of compounds with beneficial health effects are effects are vegetables due to their richness in polyphenols, a very efficient source of vegetables due to their richness in polyphenols, a very efficient source of antioxidants [13]. antioxidants [13]. In this sense, this paper aims to highlight the benefits of this fruit as a In this sense, this paper aims to highlight the benefits of this fruit as a low-cost raw mate- low-cost raw material and a promising natural alternative in several areas, including its rialuse and as a a functional promising food, natural particularly alternative the in use seve ofral okra areas, mucilage including as a technologicalits use as a functional resource food,with interestingparticularly properties the use of for okra industry mucilage use. as a technological resource with interesting properties for industry use. 2. Composition, Cost, and Main Uses of Okra 2. Composition,Several in natura Cost, and foods Main are consumedUses of Okra daily in dishes in their raw state or included in theirSeveral cooked in natura state infoods dishes are consumed and regional daily preparations; in dishes in mosttheir raw people state are or unawareincluded ofin theirtheir cooked potential state health in dishes benefits and [14 regional]. However, preparations; industrialized most functionalpeople are foods unaware have of added their potentialproduction health value, benefits which [14]. raises However, their final industrialized cost to consumers. functional This foods higher have price added is in pro- part ductiondue to the value, various which health raises benefits their final they provide,cost to consumers. in part to theThis production higher price costs, is in and part also due in topart the to various the marketing health benefits carried outthey on provide, them by in companies part to the toproduction win over consumers,costs, and also seeking in part to togive the greater marketing emphasis carried so thatout on people them keep by companies in mind that to theywin areover investing consumers, in good seeking health to giveand qualitygreater ofemphasis life [15]. so that people keep in mind that they are investing in good health and quality of life [15]. Plants 2021, 10, 1683 3 of 14 An alternative for the population is to take advantage of the potential of in natura and minimally processed foods, such as fruits, vegetables, cereals, and legumes. Vegetables, such as okra, have functional properties, and, in addition to being produced on a large scale, most of them have a low cost for the consumer. The functional properties of okra are not just limited to the fruit. Studies show that parts of the plant, such as the leaves, flowers, and seeds, have bioactives in their composition [16–19]. Fauza et al. [20] highlighted the phenols and flavonoids present in okra fruits as being the main components responsible for their beneficial properties. Assessing the biological activity of okra fruit flour in vivo, a decrease in glucose levels was observed by the same authors. According to the last agricultural census of the Brazilian Institute of Geography and Statistics (IBGE) [21], the production of okra in Brazil reached 111.967 tons, being grown in 43,341 agricultural establishments, located mainly in the Northeast and South- east regions. The Brazilian production value of okra corresponded to 2.29% of the total spent on vegetables. The price of okra in Brazil by May 2021 ranged between 3.8 and 7.2 BRL/Kg (0.69–1.29 USD/kg), with the lowest price found in the Northeast and South- east regions [22]. Okra is a nutrient-rich food and its inclusion in one’s diet can bring many bene- fits. Dietary fibers are the most abundant macronutrients (8.16 g/100 g fresh weight), followed by carbohydrates (4.86 g/100 g fresh weight) and proteins (3.55 g/100 g fresh weight) [23].