The potential of sweet potato (ipomoea batatas l.) leaves in contribution to vitamins and minerals in the diets of children in Tanga, Tanzania

Abstract

cross-sectional survey and laboratory analysis was undertaken in Tanga Municipality, Tanzania from January to March 2001. The main objective of the study was to determine the potential of sweet potato (Ipomoea hatatas) leaves in contribution of micronutrients (specifically vitamins A and C, and minerals iron and calcium) to the children aged 2-5 years (24-59 months). A random sample of 243 households with children aged 24-59 months in Chumbageni and Ngamiani divisions was selected. A structured questionnaire was used to collect data on demography, frequency of vegetable consumption, knowledge, beliefs and food preservation methods. Dietary intakes were estimated using 24-hour dietary recall in 60 households. Focus group discussions and researcher observations were also carried out. Proximate composition of commonly consumed varieties of sweet potato leaves was determined. The content of iron, vitamin C, calcium and vitamin A in raw, cooked and traditionally preserved sweet potato leaves as well as of the anti-nutrients oxalates and polyphenolic compounds was determined. Sweet potato leaves were found to be the second most commonly consumed vegetable after Amaranths. Thin, soft and non-hairy sweet potato leaves were preferred. Most of the mothers were aware of the importance of vegetable consumption. Preservation of vegetables was practised by few (5.3%). More mothers (40%) preserved cassava leaves than those who preserved sweet potato leaves (35%). Seventy (70%) and eighty three (83%), of the dietary intakes were met for iron and vitamin C. Mean intake of iron (lO.20mg), vitamin A (276.51 RE), calcium (200.27mg) and vitamin C (35.74mg) were 102%,69%,40% and 179% of the RDA respectively. About 23% of vitamin A intake was from p-carotene, the rest was from animal sources. Sweet potato leaves contributed xvi 70% of the vitamin C, 48% of calcium, 45% of vitamin A and 34 % of iron intakes from consumed vegetables. The purple midrib sweet potato leaves (PMSPL) had higher protein (37 mg/lOOgm DMB) and ash (20mg/lOOg) contents than the green midrib sweet potato leaves (GMSPL) (with 26 mg/lOOg and 13mg/100g respectively). The dry salted PMSPL had higher vitamin C retention (40%) than non-salted (15%). The p-carotene retention in the salted dried PMSPL (61%) was higher than non-salted ones (47%). Vitamin C in PMSPL cooked with lemon juice was also higher than the ones cooked without. p-Carotene loss was significantly higher (18%) in PMSPL cooked with than the one cooked without lemon juice (10 %). Oxalate levels in GMSPL (3731 mg/lOOgm) were significantly (p<0.05 higher than in PMSPL (2902mg/100gm) while polyphenolics were significantly lower (p<0.05) (5.28% vs. 22.16%). The level of oxalate decreased after cooking but practically, equal amount was retained (44% and 46%) when the PMSPL was cooked with and without lemon respectively. On the other hand, polyphenolic compounds content decreased by 54% in GMSPL cooked with lemon juice and by 19% without the lemon juice. Decrease in oxalate content of salted dried PMSPL (14%) was significantly higher than of nonsalted (9%) (p<0.05). However, polyphenolic compounds decreased from 22.16 ± 0.04% in the raw vegetable to 9.21±0.02% and 2J.25±0.028% when the vegetable was dried with and without salt respectively. The results from this study indicate that there is a need to educate the community on improved methods of SPL preservation such as the use of improved solar driers. The cooking of sweet potato leaves for short time with addition of lemon juice is encouraged as it results to the increase of vitamin C in the cooked SPL. Promotion for increased consumption of fresh and dehydrated sweet potato leaves is recommended as it is easily accessible source of micronutrients for children aged 2-5 years.