Taro Corms: Comparison
Please note this is a comparison between Version 1 by Vania Paschoalin and Version 3 by Vania Paschoalin.

Taro [Colocasia esculenta (L.) Schott] is an ancient tuberous crop that is cultivated in tropical and subtropical climates as staple food source. The edible part of taro widely used for human consumption is known as corm. Taro corms contarms contain valuable bioactive molecules effective against cancer and cancer-related risk factors, such as carcinogens and biological agents, several pathophysiological conditions, including oxidative stress and inflammation, while controlling metabolic dysfunctions and boosting the immunological response. Such broad effects are achieved by the taro health-influencing compounds displaying antitumoral, antimutagenic, immunomodulatory, anti-inflammatory, antioxidant, anti-hyperglycemic, and anti-hyperlipidemic activities. Although thesTaro bioactivities are attributed to the combination of tarin, taro-4-I polysaccharide, taro polysaccharides 1 and 2 (TPS-1 and TPS-2), A-1/B-2 α-amylase inhibitors, monogalactosyldiacylglycerols (MGDGs), digalactosyldiacylglycerols (DGDGs), polyphenols, and nonphenolic antioxidants. Most of these compounds have been purified and successfully challenged in vitro and in vivo, proving their involvement in the aforementioned activities. Although these health-promoting effects have been recognized since ancient times, as well as other valuable features of taro for food profit, such as hypo-allergenicity, gluten-free, and carbohydrates with medium-glycemic index, taro crop remains underexploited. The popularization of taro intake should be considered a dietary intervention strategy to be applied to improve the overall health status of the organism and as supportive therapy to manage tumorigenesis.

  • Taro Corms
  • Colocasia esculenta
  • tuber crop
  • health-promoting compounds
  • antitumoregenic
  • im-munomodulator
  • metabolic regulator
  • Taro Corms,Colocasia esculenta

1. Introduction

Taro [Colocasia esculenta (L.) Schott] is a perennial herbaceous plant of Asiatic origin that belongs to Araceae family and is classified as a monocotyledonous (Table 1). This herb can reach 1-2 m in height with large heart-shaped leaves, long petioles, an underground starchy structure called corm and the roots (Figure 1). Taro is cultivated in tropical and subtropical climates as staple food source due to its carbohydrate-rich nature. To avoid confusion with other similar plants, Colocasia esculenta species is called taro by the scientific community. Popularly, taro can have distinct names, such as eddoe, cocoyam, tannia, dasheen, inhame, and others, that vary according to the place it is cultivated and consumed \( \)[1].

Figure 1. General characterization of taro plant parts.

Figure 1. General characterization of taro plant parts.

 

Table1. Classification of Colocasia esculenta (L.) Schott.

RankScientific name Common name
Kingdom
Plantae
Plants
 Subkingdom
Tracheobionta
Vascular plants
  Superdivision
Spermatophyta
Seed plants
    Division
Magnoliophyta
Flowering plants
     Class
Liliopsida
Monocotyledons
      Subclass
Arecidae
-
       Order
Arales
-
        Family
Araceae
Arum family
         Genus
Colocasia Schott
Colocasia
          Species
Colocasia esculenta (L.) Schott
Cocoyam and others

Collected from USDA Plant Data Based (https://plants.usda.gov/core/profile?symbol=COES).

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 [2][1].

2. Taro Cultivation and Nutritional Importance

  1. 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 [3][4][5][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 [6][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 [2][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 [7][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 [8][9][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 2Figure 1) [10][11][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 [12] 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/) [13][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 2Table 1).

Figure 21. 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. Taro cultivation in West Africa and China reached >230164 tons followed by the USA, Canada, and Cyprus with production lower than 1600 tons. Uncolored countries represent production areas under 1000 ha. Uncolored countries represent production areas under 1000 ha.

Table 21. Nutritional composition of tarao analyzed raw, cooked and baked taro.

Nutritional Composition
Principle *Nutrient per 100 g of Dry Weight
Crude TaroCooked TaroBaked Taro with Salt
Water70.64 g63.8 g60.98 g
Energy112 kcal142 kcal144 kcal
Carbohydrates26.46 g34.6 g34.09 g
Protein1.5 g0.52 g1.93 g
Total fat0.20 g0.11 g0.26 g
Cholesterol0 mg0 mg0 mg
Dietary fibers4.1 g5.1 g5.3 g
Ash1.2 g0.97 gna
Vitamins *   
Folates0.022 mg0.019 mg0.023 mg
Niacin0.600 mg0.510 mg0.734 mg
Pantothenic acid0.303 mg0.336 mgna
Pyridoxine0.283 mgNana
Riboflavin0.025 mg0.028 mg0.031 mg
Thiamin0.095 mg0.107 mg0.110 mg
Vitamin A0.004 mg0.004 mg0.005 mg
Vitamin C4.5 mg5 mg4.3 mg
Vitamin E2.38 mg2.93 mg3.07 mg
Vitamin K0.001 mg0.0012 mg0.0013 mg
Electrolytes *   
Sodium11 mg15 mg475 mg
Potassium591 mg484 mg762 mg
Minerals *   
Calcium43 mg18 mg56 mg
Copper0.172 mg0.201 mg0.222 mg
Iron0.550 mg0.720 mg0.710 mg
Magnesium33 mg30 mg43 mg
Manganese0.383 mg0.449 mgna
Selenium0.0007 mg0.0009 mg0.0009 mg
Zinc0.230 mg0.270 mg0.300 mg
Starch ** (g starch/100 g)  
Total starch18.814.2na
Resistant Starch—RS5.22.1na
Slowly digestible starch—SDS13.6 (SDS+RDS)2.5na
Rapidly digestible starch—RDS9.6na
Glycemic Index **naMediumMedium
Nutritional Composition
Principle *Nutrients per 100 g of Dry Weight
Crude TaroCooked TaroBaked Taro with Salt
Water70.64 g63.8 g60.98 g
Energy112 kcal142 kcal144 kcal
Carbohydrates26.46 g34.6 g34.09 g
Protein1.5 g0.52 g1.93 g
Total fat0.20 g0.11 g0.26 g
Cholesterol0 mg0 mg0 mg
Dietary fibers4.1 g5.1 g5.3 g
Ash1.2 g0.97 gna
Vitamins *   
Folates0.022 mg0.019 mg0.023 mg
Niacin0.600 mg0.510 mg0.734 mg
Pantothenic acid0.303 mg0.336 mgna
Pyridoxine0.283 mgNana
Riboflavin0.025 mg0.028 mg0.031 mg
Thiamin0.095 mg0.107 mg0.110 mg
Vitamin A0.004 mg0.004 mg0.005 mg
Vitamin C4.5 mg5 mg4.3 mg
Vitamin E2.38 mg2.93 mg3.07 mg
Vitamin K0.001 mg0.0012 mg0.0013 mg
Electrolytes *   
Sodium11 mg15 mg475 mg
Potassium591 mg484 mg762 mg
Minerals *   
Calcium43 mg18 mg56 mg
Copper0.172 mg0.201 mg0.222 mg
Iron0.550 mg0.720 mg0.710 mg
Magnesium33 mg30 mg43 mg
Manganese0.383 mg0.449 mgna
Selenium0.0007 mg0.0009 mg0.0009 mg
Zinc0.230 mg0.270 mg0.300 mg
Starch ** (g starch/100 g)  
Total starch18.814.2na
Resistant Starch—RS5.22.1na
Slowly digestible starch—SDS13.6 (SDS+RDS)2.5na
Rapidly digestible starch—RDS9.6na
Glycemic Index **naMediumMedium
* FoodData Central in USDA (https://fdc.nal.usda.gov/) [13][12]. na—Not applied ** [14][15][13,14].

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 [14][16][17][18][13,15,16,17].

3. Taro Consumption Worldwide

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 [11][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 [3][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 [19][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 [20][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 [21][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 [22][23][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 [23][24][25][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 [26][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 [27][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 [14][16][17][28][29][30][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.

4. Bioactive Compounds and Pharmacological Properties of Taro corms

The use of taro to treat multiple unhealthy conditions and diseases such as diabetes, hemorrhage, diarrhea, arterial hypertension, alopecia, among others, dates from ancient times [31][1]. Taro’s health-promoting potential has been confirmed by in vitro and in vivo preclinical assays, by assaying raw or cooked corms and taro derivatives in the form of flour or extracts (Table 3) [14][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69].

The bioactivities found in taro corms include antitumoral, immunomodulatory, anti-mutagenic, anti-hyperglycemic, anti-hypercholesterolemic and antioxidant, which have been mainly attributed to its polyphenols, proteins, mucilage, polysaccharides, lipids, and non-polyphenol antioxidants. Many of these bioactive principles have already been identified and singly assayed, proving their participation in these claimed activities. Bioactive molecules identified in taro include tarin, taro-4-I polysaccharide, taro polysaccharides 1 and 2 (TPS-1/TPS-2), A-1/B-2 α-amylase inhibitors, monogalactosyldiacylglycerols (MGDGs), and digalactosyldiacylglycerols (DGDGs). Together, these data clearly indicate that the biological effects exerted by taro are possibly a synergic effect of multiple compounds displaying effectiveness not only against several cancer cell lines but also against some of the main external cancer risk factors, such as free radicals, mutagenic and carcinogenic agents, and physiopathological conditions such as obesity and type II diabetes (Table 3).

Interestingly, many of the bioactivities were demonstrated with cooked taro formulations, even following oral administration, suggesting that the recommendation to include taro in the daily human diets, alongside other healthy eating habits, could contribute to the efforts to reduce cancer risks.

Table 3. Protective and therapeutic potential of taro corms.

Taro corm preparation
 
Bioactive Compound Class
Active principle
Property
Reference
Poi extract
--
Antitumoral and Antimetastatic
[32][33][34][35][36][37]
Crude taro extract


 
Protein
 
Tarin
Tarin nano-liposomal capsules
Polysaccharide
Taro-4-I
Ethanolic crude taro extract
--
poi extract
--
Immunomodulatory
[32][34][36][38][39][40][41][42]
Crude taro extract
Polysaccharide
Taro-4-I
TPS-1 and TPS-2
Protein
Tarin
--
Taro flour
Flavonoid; Alkaloid; saponin; tannin
-
Anti-hyperglycemic
[43][44][45][46][47][48]
Methanolic extract of taro flour
Alkaloid; flavonoid; steroid
-
Mucilage-rich extract from crude taro flour
Neutral sugar; protein, polyphenols
-
Extract from defatted crude taro flour
Protein
A-1 and B-2
Taro flourFlavonoid; Alkaloid; saponin; tannin-
Anti-hypercholesterolemic or Anti-hyperlipidemic
[43][45][47][49][50][51]
Extract from cooked taro flour--
Mucilage-rich extract from crude taro flourNeutral sugar; protein, polyphenols-
Ethanolic extract from crude taroLipid
Extract
MGDG 1-3
DGDG 1-4
Mucilage-rich extract from taro flourPolysaccharideArabinogalactan
Dietary fiber-rich extract from crude taro
Polysaccharide
-
Anti-mutagenic
[52][53][54]
Crude taro extract
--
Heptane extract from cooked taro
--
Distinct raw or cooked taro extracts in aqueous or organic solutions
Polyphenols and non-polyphenols
-
Antioxidant
[14][43][44][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69]

To date, there is a scarcity of clinical studies leaving gaps in the translation of the positive health effects identified in preclinical studies to human beings. The better exploitation and understanding of taro bioactivities, following dietary interventions in humans, could be helpful in developing new functional compounds.

Clinical trials on healthy non-diabetic young adults evidenced that taro shows a medium glycemic index, low glycemic load, and moderate glycemic response [70]. Moreover, the addition of other food components, such as vegetables, oils, and rich protein food, during cooking, can reduce the taro glycemic index to a lower rate [71].

Taro is reported to have anticancer potential through several preclinical analyses, as aforementioned. The Japanese population traditionally consumes starchy roots, such as taro, that are associated with a decrease in the risk of kidney cancer death [72][73][74][75][76].

Taken together, the intake of taro or their derivatives can provide bioactive compounds capable of promoting health benefits, especially in the control of hypercholesterolemia, which is not only a complication of diabetes and overweight but also a risk for cerebrovascular and cardiovascular diseases, which are important causes of death worldwide, along with cancer [75][76]. Moreover, the overall benefit against type II diabetes and obesity could certainly aid in reducing the risk factors for cancer.

5. Conclusions and Prospects

Taro is a valuable source of several health-promoting compounds, such as taro lectin or tarin, bioactive-complex carbohydrates, and natural polyphenols and other antioxidants. In general, these molecules act through individual or synergic pathways, contributing to ameliorate systemic health status by managing oxidative stress imbalance, reducing systemic inflammation, modulating metabolic dysfunctions, and boosting the immune response. Many mechanisms remain to be elucidated to better exploit taro extracts, taro derivatives, or individual taro components. The non-toxicity of these molecules toward healthy cells turns taro components into potential candidates for supportive target therapies when associated with traditional drug treatments. In addition, since taro is a food matrix rich in bioactive compounds, spreading its benefits worldwide may enhance its consumption and consequently production while resulting in better population health maintenance.

 

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