Effect of traditional processing practices on the content of total carotenoid, β-carotene, α-carotene and vitamin A activity of selected Tanzanian vegetables

The α-carotene, β-carotene and total provitamin A carotenoids and the effect of traditional processing practices on the retention of these provitamins were studied using amaranth, cowpea, peanut, pumpkin and sweet potato leaves. Results of this study indicated that the content of total carotenoids, β-carotene and α-carotene were in the range of 26.79–44.74 mg, 4.16–19.12 mg, and 0.99–10.26 mg per 100 g of dry vegetables, respectively. The vitamin A activities were 4.042, 3.124, 0.829, 2.025 and 1.581 mg RE per 100 g of dry amaranth, cowpea, peanut, pumpkin and sweet potato leaves, respectively. The traditional processing practices of sun drying and storage in ventilated containers resulted in a significant (p<0.05) decrease in the concentration of total carotenoids, β-carotene and α-carotene for all the vegetables. Conventional blanching and cooking resulted in a significant (p<0.05) increase in the concentration of carotenoids in the cowpea, peanut and pumpkin leaves while in amaranth and sweet potato greens, thermal processing resulted in a significant (p<0.05) decrese in the concentration of these nutrients.     

Nutritional composition and micronutrient status of home made and commercial weaning foods consumed in Tanzania

About 50% of young children in Tanzania suffer from protein-energyundernutrition (PEU) while more than 45% of children under the age offive suffer from various micronutrient deficiency disorders. The immediatecause of these conditions is inadequate intake and poor utilization ofnutrients, which begins in the weaning period and amplifies in thesubsequent years. This study was conducted to assess the potential of somehome made and commercial weaning foods commonly consumed in Tanzania tosupply adequate amounts of both macro- and micronutrients as recommendedin the Tanzania and FAO/WHO Codex Alimentarius Standards forcereal/milk-based weaning foods. Six types of home made weaning foods,maize, cassava, millet, sorghum and millet-sardine-peanut composite gruelsand plantain pap, and four types of commercial weaning foods, Cerelac-1,Cerelac-2, Lactogen-1 and Lactogen-2, popularly consumed in Tanzania, werechemically assayed for proximate composition, energy and mineral density.Results of the study indicated that, both the home made and commercialweaning foods were good sources of macro- and micronutrients. Whencompared with the Codex Alimentarius and Tanzania Bureau of Standardsspecifications for weaning foods, both home made and commercial weaningfoods had some shortcomings in terms of nutrient composition and energybalance. Many of the foods were low in fat, Fe, Ca, Zn and P but high incrude fiber, carbohydrate and magnesium. Ca, Fe and Zn were the mostcommon deficient macro/micronutrients in the home made weaning foods. Inspite of these shortcomings, most of the home made and commercial weaningfoods were nutritionally sound since they could provide reasonablepercentages of the recommended daily allowances for macro/micronutrientsand energy. It is suggested that, more efforts must be directed towardsincreasing the concentration of Ca, Fe and Zn in the home made weaningfoods through supplementation of the starchy staples with mineral richfoods. Meanwhile, the parents, caretakers and health workers should beeducated on the selection and preparation of nutritious, balanced weaningfoods and good weaning practices.     

Effect of blanching on the content of antinutritional factors in selected vegetables

The effect of blanching on the antinutritional content was studied in cabbage, turnip, collard, sweetpotato and peanut leaves. All the vegetables contained various amounts of phytic acid, tannic acid and/or oxalic acid. Tannic acid was found in largest amounts ranging from 1266.00 mg/100 g in cabbage to 491.00 mg/100 g in sweetpotato. Phytic acid content ranged from 0.31 mg/100 g in sweetpotato to 3.97 mg/100 g in collard. Oxalic acid was in trace amounts in cabbage and turnip; but high concentrations were found in sweetpotato (469.67 mg/100 g) and peanut greens (407.00 mg/100 g). Levels of both tannic acid and phytic acid were significantly (p<0.05) reduced by conventional and microwave blanching methods while oxalic acid levels were not significantly (p<0.05) reduced in most of the treatments by either of the blanching methods. In general, blanching is recommended as an effective method for reducing the antinutritional factors in green vegetables, however, further investigation on the heating times for both conventional and microwave blanching methods has been suggested.     

Proximate composition and mineral content of selected Tanzanian vegetables and the effect of traditional processing on the retention of ascorbic acid,riboflavin and thiamine

Proximate composition, mineral content and the effect of traditional processing practices on the retention of ascorbic acid, riboflavin and thiamine were studied using amaranth, cowpea, peanut, pumpkin and sweetpotato leaves. Results of this study indicated that, crude protein, crude fat, carbohydrate and ash contents were in the range of 20.64–46.56 percent, 2.57–4.34 percent, 35.43–63.50 percent and 8.92–15.69 percent respectively. The mineral content per 100 g of fresh vegetables was in the range of 83.64–229.34 mg, 145.97–780.19 mg, 11.56–21.31 mg, 43.02–110.30 mg, 0.96–5.90 mg and 0.40–2.24 mg for Ca, K, Na, Mg, Fe and Zn respectively. For ascorbic acid, riboflavin and thiamine, concentrations in 100 g of fresh vegetables were in the range of 43.78–89.00 mg, 0.62–1.71 mg and 0.09–0.30 mg respectively. The traditional processing practices of sun/shade drying and storing in ventilated containers resulted in a significant (P<0.05) decrease in ascorbic acid, riboflavin and thiamine for all vegetables. Conventional blanching and cooking for up to 15 minutes resulted in a significant (P<0.05) increase in riboflavin content in cowpea, peanut and pumpkin greens while in amaranth and sweetpotato leaves, thermal processing resulted in a significant (P<0.05) decrease in the vitamin. Based on the results of this study, the vegetables were good dietary sources of minerals, carbohydrate and protein.     

Nutritive value and effect of blanching on the trypsin and chymotrypsin inhibitor activities of selected leafy vegetables

Proximate composition, energy, mineral and vitamin contentsand the effect of blanching methods and times on the trypsinand chymotrypsin inhibitor activities were studied usingcabbage, collard, turnip, peanut, and sweet potato leaves.Results of this study indicated that, crude protein, crudefat, carbohydrate and ash contents were in the range of 15.5–25.6%, 1.4–6.5%, 60.4–73.1% and 6.8–7.5%,respectively. Total dietary fiber was lowest in cabbage (28.2 g/100 g) and highest in the collard leaves (43.1%)while energy content per 100 g of vegetables was highestin sweet potato leaves (402 kcal) and lowest in cabbage(379 kcal). The mineral content per 100 g of vegetableswere in the range of 33.4–249.8 mg, 241.2–471.2 mg,12.1–75.1 mg, 14.9–98.9 mg, 0.5–3.5 mg and 0.9–3.1 mgfor Ca, K, Na, Mg, Fe and Zn, respectively. For ascorbicacid, riboflavin, thiamin and total carotenoids, concentrations in 100 g of vegetables were in the range of45.1–112.7 mg, 0.2–0.3 mg, 0.3–0.8 mg and 2.0–7.3 mg,respectively. The trypsin inhibitory activity per gram ofthe vegetables was highest in collard (60.1 TIU/g) andlowest in peanut leaves (41.0 TIU/g). Chymotrypsin inhibitoractivity was highest in the peanut (69.6 CIU/g) but lowestin the collard leaves (48.0 CIU/g). Both trypsin and chymotrypsin inhibitor activities were significantly (p<0.05) reduced by most of the treatments in eitherthe conventional or microwave blanching methods. In the conventional blanching method, trypsin inhibitor activitywas reduced by 0.5, 6.8, 11.9, 9.0 and 19.3 percent in cabbage, collard, turnip, sweet potato and peanut leaves,respectively, when the vegetables were blanched for 2.5 minutes but after blanching for 10 minutes, the trypsininhibitor activity was reduced by 29.7, 34.9, 54.3, 52.3and 65.6 percent in cabbage, collard, turnip, sweet potatoand peanut greens, respectively. For the microwave ovenblanching, trypsin inhibitor activity was reduced by 3.8,3.3, 32.7, 5.0 and 9.5 percent in cabbage, collard, turnip,sweet potato and peanut leaves, respectively when thevegetables were blanched for 30 seconds. When blanched for60 seconds, trypsin inhibitor activity was reduced by 16.2,45.8, 46.2, 51.0 and 42.4 percent in cabbage, collard, turnip, sweet potato and peanut greens, respectively.Similar trends in the reduction of chymotrypsin inhibitoractivity were observed when the vegetables were conventionally blanched for 2.5, 5 and 10 minutes andwhen blanched by microwave oven for 30, 45 and 60 seconds.Based on the results of this study, the vegetables weregood dietary sources of minerals, vitamins, carbohydrateand proteins. Also, blanching was an effective method forreducing the trypsin and chymotripsin inhibitor activitiesin the leafy vegetables, however, further investigation onthe heating times for both conventional and microwaveblanching methods is suggested.