Sweet potatoes (Ipomoea batatas
) are an exceptionally essential crop in several parts of the world, being produced in more than 100 countries. They are also a main food crop of the tropical and subtropical areas and, therefore, can provide a nutritional advantage to the people of rural and urban regions by enhancing their production and increasing consumption [1
]. Sweet potato is positioned as the seventh most major food crop in the world, fourth in tropical countries [3
] and the fifth most essential food crop on a fresh weight basis in developing countries after rice, wheat, maize and cassava, and it is cultivated in more than 100 developing countries [4
]. It is the fourth most important crop in Bangladesh after rice, wheat and potato.
Malnutrition caused by the deficiency of vitamin A is known to be widespread among the rural people of developing countries, including Bangladesh. This deficiency causes children to succumb to common diseases and leads to the impairment of growth and development, vision impairment, poor immune functions and, in extreme cases, results in blindness and death [5
In pregnant women, vitamin A deficiency (VAD) can have several consequences on pregnancy outcome, such as low birth weight of the baby, higher chance of transmitting HIV/AIDS virus infection and, in certain cases, may result in death of both the mother and child. Research findings concluded that vitamin A plays a vital role in the prevention of maternal mortality and can also prevent mother to fetus transmission of HIV/AIDS virus [5
]. Roughly one million children have clinical signs and symptoms of VAD, and over 0.9 million children <6 years of age suffer from some degree of xerophthalmia; and 30,000 children become blind every year due to severe VAD in Bangladesh [5
]. The high prevalence of micronutrient deficiencies is normally seen in the children of Bangladesh, particularly vitamin A, iron, iodine and zinc deficiency. The prevalence of night blindness among rural preschool-aged children in Bangladesh is 0.67% [5
]. The VAD problem among the women of reproductive age is still considered to be a major problem. Over 2.7%, 2.4% and 2% of pregnant women, lactating women and non-pregnant/non-lactating women respectively are night blind in Bangladesh [5
As most of the rural people cannot afford to buy animal products due to low income, there is a clear need to identify a potential alternative rich food source of vitamin A in terms of land/environmental sustainability, developing the rural economy and increasing the consumption to achieve the better nutritional status of the people of Bangladesh. Orange-fleshed sweet potato (OFSP) is relatively rich in β-carotene (precursor of vitamin A) and subsequently rich in vitamin A [6
]. In addition, OFSP contains significant amounts of minerals (Fe, Zn, Mn), vitamins B and C, fiber and other micronutrients, such as polyphenols and carotenoids [6
]. Polyphenols are widely known for their positive effect on human health. The inclusion of polyphenols in the diet provides protection against heart disease and prevents oxidation of LDL, by acting as ‘scavengers of free radicals’, especially peroxide, breaking its formation chain and neutralizing it [7
]. Several authors have previously stated that the polyphenols in sweet potatoes exhibited antioxidative or free radical scavenging ability, boost humans’ defense mechanism against oxidative stress and, thus, inhibit the development of chronic diseases, like cancer, cardiovascular diseases, liver injury, etc. [7
]. Like polyphenols and vitamin E, carotenoids also exhibit antioxidant activities [8
To overcome the VAD problem, efforts were made to develop varieties that are high yielding, with medium-sized tubers and a high carotene content. Given these facts, the Tuber Crops Research Centre (TCRC), Bangladesh Agricultural Research Institute (BARI), developed seven high yielding varieties of sweet potato since 1988 through introduction, selection and hybridization [9
]. There are now in total nine high-yielding varieties of OFSP in Bangladesh, and they are called BARI SP1, BARI SP2, BARI SP3, BARI SP4, BARI SP5, BARI SP6, BARI SP7, BARI SP8 and BARI SP9. Among the nine varieties of OFSP in Bangladesh, the highest yielding varieties are BARI SP8 and BARI SP9. The tuber yield potential of these two varieties varied between 40 and 45 tonnes per hector and is superior to the other seven varieties in Bangladesh.
Being rich in carotenoids, β-carotene and total polyphenol content (TPC), OFSP is gaining importance as the least expensive source of antioxidants, providing several essential previously mentioned health benefits. Consumption of OFSP roots can also provide sustainable vitamin A, which plays a major role in preventing and treating night blindness [10
]. OFSP has substantial potential to contribute to a food-based approach to managing the problem of modern chronic diseases together with VAD, a major public health concern of the poor people of the world. Thus, there is a greater possibility that OFSP could be included in the normal diet of the consumer food habit to supplement as an alternative staple food source for the poor people in the age of widespread population growth and nutrition crisis. However, a significant proportion of consumers is not aware of the nutritive value of some high-yielding OFSP cultivars. Moreover, the biochemical constituent of OFSP varies among the varieties. Therefore, the assessment of the biochemical composition of different varieties is essential for selecting the cultivars having high amounts of the nutrients. In Bangladesh, no previous study was conducted on the nutritional content of different varieties of OFSP, and thus, the aim of the study was to estimate and compare the selected nutritional content of nine OFSP varieties produced in Bangladesh. This was the first comprehensive and systematic analysis of a large number of OFSP varieties in Bangladesh.