1. Introduction

Crops that have been neglected over the years are currently being revalued based on modern technologies used to extract, identify, estimate, and assay a great number of compounds displaying claimed pharmacological effects. The study of the composition of such food matrices has stimulated the recognition and reevaluation of so-called “orphan” crops, reaffirming the knowledge that traditional communities have practiced since ancient times by considering the vital role of those crops not only in supporting diets but also in promoting the health and treating these populations. In most cases, neglected or underutilized species have been substituted by those cultures in huge demand, although sometimes, those crops are poorer not only in nutritional aspects but mainly in bioactive compounds ^[1].

2. Taro Consumption, Cultivation, and Nutritional Importance

2. Taro Consumption, Cultivation, and Nutritional Importance

Even though taro corm (or taro) is a rich source of health-promoting compounds, this crop, as well as tubercle consumption worldwide, is highly neglected probably because it is mainly associated with subsistence agriculture [2,3,4]^[2][3][4]. Moreover, due to poorness, unsustainable farming practices, and climate change, taro crops face many challenges in several underdeveloped countries, such as African Sub-Saharan nations and other countries in Central and South America ^[5]. In general, taro crops, as several subsistence crops, are cultivated in small farms, with low capital endowment, far from urban centers and with no access to capital markets, and low-off farm income ^[1]. The food processing sector can overcome these constraints and enhance taro crop availability and acceptance by urban populations by replacing corn and wheat in processed foods, enhancing raw product commercialization. In addition, this may also lead to attention regarding taro crops as a rich source of remarkable and unique compounds, whose pharmacological activities have been demonstrated both in in vitro and in animal models.

International research centers mainly dedicated to taro studies are still scarce, although they would be helpful to overcome many challenges that have remained unsolved for over ten years. Financial and scientific investments would aid in improving cultivation conditions, creating and maintaining germplasm collections of diverse regions, improving conservation methods, increasing food security, and enhancing the benefits of taro consumption. These efforts would increase the research field and shared information between countries, which might expand taro cultivation, sales, and consumption worldwide, especially in developing countries ^[6].

The most significant taro producers are the West African countries, i.e., Nigeria, Cameroon, and Ghana, followed by China, which contribute respectively 6.7 and 3.9 million tons of taro, corresponding to 83.6% of the worldwide taro production [7,8]^[7][8]. Other nations, such as the USA, Canada, Japan, Turkey, and Central and South American countries, produce about 2 million tons of taro. Brazil has not yet been internationally recognized as a taro producer country, since less than 1000 ha are planted and dispersed, which is probably due to the vast Brazilian territory, where relevant producers are spread throughout the Mid-South region (Figure 1) [9,10]^[9][10]. However, Southeast Brazil boasts a germplasm bank, named INCAPER, which is used to collect and conserve taro cultivars, maintaining the diversity and characteristics of the Brazilian varieties, which include T37 (Macaquinho), T38 (Chinês), T39 (Japonês), T40 (Chinês Regional), T41 (Cem em Um), T42 (São Bento), and T43 (Branco) ^[11]. The neglected and underutilized status of taro crops is noted by comparison to other tubercles, such as potatoes, which are widely consumed worldwide, although displaying superior nutritive importance. For example, in 2018, approximately 12.6 million tons of taro per annum were produced worldwide against 64.7 million tons of potato (Solanum tuberosum L.) (Figure 1) ^[7]. Taro is a healthy alternative of carbohydrate source, as the cooking process does not interfere with their nutritional composition, causing only minimal modifications in nutrient contents, according to Food Data Central from the United States Department Agriculture (USDA) (https://fdc.nal.usda.gov/) ^[12]. The proximate composition of crude, cooked, and baked taro is quite similar regarding vitamins and minerals, except for niacin and calcium levels, as well as protein and total fat amounts, which were lowered by thermal processing (Table 1).

Figure 1. Global distribution of taro production reproduced from FAOSTAT (http://www.fao.org/faostat/en/#data/QC). Quantitative taro production per country in 2018, repreScheme 230. tons followed by the USA, Canada, and Cyprus with production lower than 1600 tons. Uncolored countries represent production areas under 1000 ha.

Table 1. Nutritional composition of taro analyzed raw, cooked and baked.

Additionally, taro is a rich source of antioxidants, mainly phenolic compounds, both regarding diversity and quantity, distributed in the edible portion of taro. In addition to antioxidants, taro phytochemicals display immunomodulatory, antioxidant, antitumoral, antimetastatic, antimutagenic, anti-hyperglycemic, and anti-hypercholesterolemic bioactivities. Moreover, taro is a potential alternative staple source, with a lower glycemic index than potato, and its consumption may decrease the incidence and prevalence of several diseases, including certain types of cancers [13,15,16,17]^{[13][15][16][17]}.

Despite being considered an orphan crop, taro is a sacred food in some cultures, such as in Hawaii, Melanesia, and Micronesia, where it is known as a Gift of Ancient Gods. In these places, taro is consumed daily and included in several special occasions and rituals due to its symbolic importance ^[10]. Taro is formulated according to the cultural traditions of each local population. For example, taro stems, petiole, corms, and leaves can be consumed as a common practice in Hawaii. However, taro corms are conventionally considered the edible portion of this plant, and they are consumed worldwide ^[2]. Some cultivars can exhibit high calcium oxalate contents, which is considered an antinutritional factor that confers an acrid taste to the tubercles, causes skin irritation, and can decrease calcium absorption ^[18]. For this reason, taro should be preferentially consumed after cooking in order to avoid these undesired effects.

In Hawaii, taro is cooked and smashed with a little water to prepare a starchy paste, which may be consumed immediately (fresh poi) or after 2–3 days of fermentation producing a sour taste paste (sour poi), which is a typical Hawaiian dish ^[19]. Achu, another ancient taro paste, preferentially prepared by women, is mostly consumed in Africa. Taro and bananas are boiled together, peeled, and pounded to form a smooth and homogeneous starchy paste. Then, typical sauces are mixed in, such as yellow sauce (achu soup), jaune sauce, black sauce (black soup), and pepper sauce ^[20].

In other parts of the world, especially Brazil, taro can be served fried or steamed, prepared as a soup, or mashed. The corms are also marketed in a variety of commercial products such as flour, chips, fermented alcoholic beverage, ice bar, ice cream and canned taro, among others [21,22]^[21][22]. These taro derivatives are not globally available, as taro crops are concentrated in China, Taiwan, and Hawaii. Taro flour can be used as an ingredient for many other preparations including bread, cakes, cookies, noodles, and cereals, or even as a partial substitute for traditional whey flour [22,23,24]^[22][23][24].

The main carbohydrate present in taro is starch found in polygonal and small granules, averaging 1.3–2.2 µm in diameter, although granules measuring 5 µm can be observed ^[25]. As a starchy vegetable, taro presents part of the starch in resistant form, which can escape small intestine digestion and be directed to colon fermentation. This resistant-starch results in several health effects, including the augmented absorption of minerals, contribution in controlling blood glycemia, and reduction in plasma triglycerides and cholesterol ^[26].

Since taro is free of gluten and displays low protein and high calorie content, as well as low fat levels, taro consumption can benefit individuals with dietary restrictions such as those presenting allergies, especially in children and gluten-intolerant individuals, while contributing to reduce the risk of obesity and type II diabetes. In addition, the presence of soluble and non-soluble dietary fibers can improve intestinal transit and possibly aid in colorectal cancer prevention. As a result of its gluten-free nature, taro flour has arisen as a promising substitute for wheat flour, boosting the Brazilian market for gluten-free derivatives [13,15,16,27,28,29]^{[13][15][16][27][28][29]}.

To encourage and reinforce the importance of taro consumption, this study aims to discuss the benefits of the biofunctional compounds found in taro in promoting health, especially considering their potential against cancer, as well as in the control of other physiopathological conditions that compose the risk factors for cancer burden, including obesity and type II diabetes.