Elsevier

Food Chemistry

Volume 68, Issue 3, 15 February 2000, Pages 359-367
Food Chemistry

Analytical, Nutritional and Clinical Methods Section
Nutritive evaluation on chemical components of leaves, stalks and stems of sweet potatoes (Ipomoea batatas poir)

https://doi.org/10.1016/S0308-8146(99)00206-XGet rights and content

Abstract

For the effective use of leaves, stalks and stems of two kinds of sweet potatoes, we determined their chemical components and evaluated their nutritive values. Some parts of this plant, which are not usually used, were found to be rich in nutritive and functional components. In particular, leaves contain a large amount of protein, showing high amino acid score. Any part of sweet potatoes was rich in dietary fiber and in particular, leaves were soluble dietary fiber and stems were insoluble dietary fiber, respectively. Mineral content, particularly iron, and vitamin content such as carotene, vitamin B2, vitamin C and vitamin E were high in leaves in comparison with other vegetables. Furthermore, polyphenol content in leaves was comparatively high. These results suggest that the whole parts of sweet potatoes should be utilized as valuable foodstuffs to cope with future changes in food supply and demand, particularly in developing countries.

Introduction

At present in advanced countries, overeating or an unbalanced diet rather than shortage of food is a major concern as a health hazard. However, from a global perspective, there is a shortage of food production and supply because of the population increase in developing countries and the decrease in cultivated field due to desertization. From these points of view, revaluation of the crops, which are tolerant to environmental changes such as drought, storms and floods, and which can be cultivated in waste land and tropical areas, is necessary. One such crop is sweet potatoes (Ipomea batatas poir) which originated from Central America. China is the leading country of sweet potato production, and the global yield was 134, 244t in 1996 [Food and Agriculture Organization (FAO), 1997], which was about 1/2 of that of potatoes (Solanum tuberosum L.) and 1/4 of that of wheat, meaning that sweet potatoes are one of the major food crops. In Japan, sweet potatoes have been cultivated as a hardy plant since the early 1700's, not only its tubers but also leaves, stalks and stems are edible. However, at present, other parts than tubers of sweet potatoes are not used as a food material in any areas except southeast Asia including Okinawa and Formosa, and detailed reports on the effective components in the leaves, stalks and stems are scarce. Therefore, an attempt to use other parts than the tubers would be meaningful to insure future food resources. In particular, leaves of sweet potatoes are dark green and expected to have nutritive components like the dark green and yellow vegetables. Generally, vegetable leaves such as spinach or alfalfa are considered to be a notable protein source (Standard Tables of Food Composition in Japan, 1995, Sun et al., 1979) and studies on the nutritive value of the leaf proteins and the technics for food use are gradually in progress. Then we examined various nutritive components of each part of sweet potatoes and revaluated the characteristics of them.

Section snippets

Materials

Two varieties of sweet potatoes, Koganesengan (KS) and Beniazuma (BA) cultivated at the experimental farm in the university campus, were used. KS is widely cultivated in mainly southern areas of Japan, and BA in Japan except Hokkaido. Both varieties were planted late in May, harvested early in October, and separated into leaves (10–15 cm from the base to the tip), stalks (15–25 cm), stems and tubers (150–200 g with the skins on) as shown in Fig. 1.

For reference, Table 1 shows the character of

Analysis of CRM 383: Haricots Verts (Beans)

Certified components in CRM 383 samples were analyzed by various analytical methods used in the present experiment.

The results are shown in Table 2. The data are expressed as the mean of four trials. All the values obtained by our analytical methods coincided well with the certified values and also not certified ones. Thus, the accuracy of our analytical methods in this study was ensured by these results.

General composition

Table 3 shows the general composition. The amount of protein in 100 g of leaves (numerals

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