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.     

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.     

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.     

Nutritional composition of selected green leafy vegetables,herbs and carrots

Six green leafy vegetables and herbs – spinach, amaranth, bengal gram, cauliflower, mint, coriander and carrots – were analyzed for moisture, protein,ascorbic acid, -carotene, total iron, ionizable iron (as % of total iron) in vitro iron (% of total iron), copper, manganese and zinc. Moisture content of the leaves and carrots varied from 75.1 percent (bengal gram) to 95.4 percent (carrot) and protein from 9.83 percent (carrots) to 30.9 (mint) percent. Ascorbic acid, -carotene, total iron and ionizable iron contents were at a maximum in case of bengal gram leaves whereas level of ionizable iron and in vitro iron as a percent of total iron was highest in carrots. Copper, manganese and zinc contents were maximum in spinach.     

Mycoflora and vitamin content of sun-dried food condiments in Nigeria

The fungi most frequently isolated (of 20–100% incidence) from fresh okra, pepper fruits and melon seeds areBotryodiplodia theobromae, Rhizopus stolonifer, Trichoderma harzianum, Mucor mucedo andFusarium oxysporum. The major mycoflora of the fruits which had been sun-dried for twenty days are comprised ofAspergillus spp andPenicillium spp which initially had formed the minor components (of less than 20% incidence) of the colonising population. The effect of sun-drying on the fruits was a statistically significant (P=0.05) decrease in the riboflavin content and a generally small and non-significant decrease in the concentrations of thiamine, niacin, biotin and ascorbic acid. The effect of mouldiness during sun-drying was to further decrease the concentration of the vitamins.     

Effect of processing and storage on the ascorbic acid (vitamin C) content of some pineapple varieties grown in the Rivers State of Nigeria

Ascorbic acid contents of the juice of four different pineapples species grown in the Rivers State of Nigeria were determined before and after storage of whole pineapple and processing and storage of the juice for two months. Ascorbic acid of the fresh juice ranged from 22.5 mg to 33.5 mg/100 g sample. After storage at room temperature (30–32 °C) of whole pineapple for two weeks, ascorbic acid was reduced to between 59 and 65 percent of the fresh juice. Processing the juice by pasteurisation reduced the ascorbic acid to between 28 and 46 percent while storage in plastic bottles for two months further reduced the ascorbic acid content to between 10 and 21 percent.     

Radiation effect on ascorbic acid and riboflavin biosynthesis in germinating soybean

The influence of irradiation on biosynthesis of ascorbic acid and riboflavin in germinating soybean seeds in tap and distilled water at ambient (25–35°C) conditions was investigated. Ascorbic acid was not detectable in the original seeds and the initial level of riboflavin was 3.3 g/g. The rate of synthesis of these vitamins increased with increasing germination time up to 72–96hr followed by a decreasing pattern depending upon the treatment. The effect of irradiation and germination on the synthesis of these vitamins was statistically significant (P<0.01). Maximum amounts of ascrobic acid 16.2 and 15.0 mg/ 100 g (fresh weight basis) were found in the 0.10 kGy sample after 72 hr of germination in tap and distilled water, respectively. However, a radiation dose of 0.20 kGy resulted in the development of maximum values of riboflavin, 30.0 and 27.0 g/g (dry weight basis) on germination in tap and distilled water respectively.     

Changes in β-carotene and ascorbic acid content of fresh amaranth and fenugreek leaves during storage by low cost technique

Leafy vegetables are highly perishable and their shelf life depends on duration and conditions of storage. A low cost storage structure was used to extend the shelf life of amaranth and fenugreek and their quality was evaluated on the basis of retention of -carotene, ascorbic acid and chlorophyll during storage. Losses of -carotene ranged from 46.5 to 85.0% for amaranth and 24.0 to 73.0% for fenugreek depending on duration and conditions of storage. Similarly ascorbic acid retention varied from 9–32% for amaranth and 23–80% for fenugreek. Results showed that the degradation of quality parameters was faster at ambient conditions and packaging of leaves in low density polyethylene bags was beneficial in improving shelf life and nutritive value. Low cost storage structure was similar to low temperature storage for retention of -carotene, ascorbic acid, chlorophyll content and enhancement of shelf life.     

Vitamin values ofPleurotus mushrooms

Ascorbic acid, thiamine, niacin, riboflavin, pantothenic acid and folic acid contents were determined in four different species ofPleurotus mushroom grown on wet chopped unfermented rice straw. The estimated values for the respective vitamins ranged from 92–144, 1.36–2.23, 60.6–73.3, 6.66–8.97, 21.1–33.3 mg and 1222–1412 µg per 100g mushrooms on dry weight basis. These vitamin values were comparable with those ofAgaricus bisporus, but were higher than those ofAuricularia, Lentinus andVolvariella.     

Biosynthesis of ascorbic acid in germinating rapeseed cultivars

Biosynthesis of ascorbic acid in irradiated and unirradiated germinating rapeseed cultivars was studied at ambient room temperature (20–35 °C). Appreciable quantities of ascorbic acid (19.8–24.1 mg/100 g) were detected in the seeds and synthesis of this vitamin increased significantly (three fold) with increasing germination time depending upon rapeseed cultivars (p<0.05). Soaking of seeds in tap water (1:2) for 24 hours resulted in the decrease of the vitamin in each case. Among the radiation treatments (0.05–0.20 kGy), maximum amounts of ascorbic acid were found in 0.10 kGy (342.1 mg/100 g dry weight) and 0.15 kGy (113.8 mg/100 g wet weight) samples after 96 hours of germination. An overall significant linear relation (r=0.96) was observed between vitamin biosynthesis and germination time upto 96 hours in rapeseed.     

Vitamin contents of cereal grains as affected by storage and insect infestation

There were substantial losses in thiamine, riboflavin and niacin contents of wheat, maize and sorghum grains at three infestation levels (25, 50 and 75%) caused by releasing two insect species viz.,Trogoderma granarium andRhizopertha dominica separately and mixed population. Losses were to the extent of 65 to 69% (thiamine), 50 to 67% (riboflavin) and 10 to 32% (niacin) due toT. granarium and 23 to 29% (thiamine), 13 to 18% (riboflavin) and 4 to 14% (niacin) due toR. dominica at 75% level of infestation in three cereal grains. Storage of grains (1–4 months) in insect free conditions did not show appreciable changes in the vitamin contents.     

Content of antinutrients and in vitro protein digestibility of the African yambean,pigeon and cowpea

The protein, trypsin inhibitor (TI), tannin, phytate, phytic acid phosphorus and in vitro protein digestibility (IVPD) of cultivars of the African yambean (Sphenostylis stenocarpa) — AYB, pigeon pea (Cajanus cajan) — PP and cowpea (Vigna unguiculata) — CP were determined. The protein content of CP (24–28.0%) was higher than those of PP (21–22.5%) and AYB (21–22.5%). The cream and speckled AYB contained more TI (30.9 and 25.3 mg/g) than PP (7.5–14.1 mg/g) and CP (9.8–20.5 mg/g). Apart from the white CP cultivar, they contained more tannin (1.24–1.42 mg/g) than PP (0.14–0.97 mg/g) and AYB (0.71–1.17 mg/g). Phytate was lowest in the AYB (6.30–7.49 mg/g) than PP (8.31–11.31 mg/g) and CP (8.40–9.92 mg/g). Phytic acid contributed 67–74% of the phosphorous in the AYB, 66–75% in PP and 54–59% in CP. The IVPD of the AYB (73.3±0.7%) was significantly lower (p<0.05) than those of PP (76.34±0.2%) and CP (77.8±0.4%). There was a significant negative correlation between TI and IVPD (r=–0.63,p<0.05). There was no significant correlation between IVPD and phytate and tannin contents. There was a positive correlation between protein content and IVPD (r=0.69**) for the legumes under study. These legumes may pose no serious problems to populations consuming them especially when heat treatment is applied before consumption.     

Chemical composition of indigenous wild herbs,spices, fruits,nuts and leafy vegetables used as food

Thirty wild fruits, nuts, herbs, spices and leafy vegetables were characterized and their chemical composition determined. Some of them were not only used for food, but for medicine in minor aliments by the natives. Results of the proximate analysis showed that on dry weight basis, the crude protein content ranged from 4.6 to 22.1 percent for spices and herbs, 3.2 to 43.1 percent for fruits and nuts, and 15.9 to 35.7 percent for leafy vegetables. The fat (ether extract) ranged from 7.5 to 36.0 percent for spices and herbs, 1.8 to 72.6 percent for fruits and nuts and 10.6 to 22.6 percent for leafy vegetables. Total carbohydrate content ranged from 34.6 to 71.9 percent for spices and herbs, 11.3 to 76.1 percent for fruits and nuts, and 24.6 to 51.4 percent for leafy vegetables. The wild fruits, nuts and leafy vegetables are high in ascorbic acid (Vitamin C.) Ascorbic acid content ranged from 18 mg/100 g dry sample to 113 mg/100 g sample for fruits and nuts, and 23 mg/100 g to 232 mg/100 g sample for leafy vegetables. The levels for peroxide value and free fatty acids (as percent oleic acid) of the spices are generally low indicating good storage stability of these plant materials. The flavour imparting essential oils (as percent oleoresin) content of the spices/herbs were fairly high and ranged from 0.1 to 5.2 percent.     

Effects of wilting,blanching and storage temperatures on ascorbic acid and total carotenoids content of some Nigerian fresh vegetables

Four fresh vegetables (fluted pumpkin leaf, okra, African spinach, and water leaf) were studied. Determinations were made of the amounts of ascorbic acid and total carotenoids in fresh, wilted and blanched begetables as well as in fresh and blanched vegetables stored at ?10°C and 5°C. Results showed that wilting accounted for the highest losses in both ascorbic acid and carotenoids in all vegetables investigated. The least losses in the two nutrients were observed in blanched vegetables. In general carotenoid was more stable to the different treatments than ascorbic acid.     

Proximate composition and functional properties of four cultivars of bambara groundnut ( Voandezeia subterranea)

Proximate composition and selected functional properties of four cultivars of bambara groundnut ( Voandezeia subterranea Thoura) were ascertained. Crude protein ranged from 17.5 to 21.1 percent; crude fat 7.3–8.5 percent; total ash 4–5 percent; crude fiber 1.8–2.0 percent; carbohydrate and moisture content for the different cultivars were 53.0–60.8 percent and 7.5–12.3 percent, respectively. The results of functional property determinations indicated that the bulk density ranged from 0.65 to 0.75 g/ml; water binding capacity 2.1–2.9 g/2g sample; oil binding capacity 0.9–1.6 g/2g sample; emulsifying activity 55.-1–60.0 percent and emulsifying stability 10–12 percent. The results show that bambara groundnut has great potential for incorporation into various human foods where it could provide useful plant proteins.     

Investigations into the thiamine and riboflavin content of malt and the effects of malting and roasting on their final content

A simple and effective method for the analysis of thiamine (B₁) and riboflavin (B₂) vitamers, in unmalted and malted grains, by high performance liquid chromatography (HPLC) has been developed. This method makes use of trichloroacetic acid (TCA) as an extraction medium to effectively clean up the sample and analyze the vitamer content with high accuracy (R² > 0.9992; %RSD < 5%). This method was employed in the routine analysis of a wide range of malted and unmalted grains, and it was found that lighter colored malts contain higher concentrations (2–5 times higher) of thiamine and riboflavin vitamers compared to darker colored malts. The malting process has no effect on the overall riboflavin content; however, both steeping and kilning processes cause increases in thiamine vitamer content. Roasting profiles show that thiamine and riboflavin vitamer concentrations are significantly effected when the temperature reaches 120 °C, which explains why roasted products have lower vitamer content than paler malts.     

Influence of sundrying on the chemical composition,aflatoxin content and fungal counts of two pepper varieties —Capsicum annum andCapsicum frutescens

Samples of sundried, matured red pepper,Capsicum annum with a moisture content (MC) of 12.7–26.8 percent had on dry weight basis, vitamin C, 5.0–6.4 mg/100 g; crude protein, 0.8–1.2 percent; total soluble solids, 3.3–4.1 percent, and fungal counts of log 4.4–4.5/g. Ordinary matured redC. annum had MC, 75.7–78.2 percent vitamin C, 36.1–38.5 mg/100 g; crude protein, 2.4–2.8 percent; total soluble solids, 9.3–9.9 percent and fungal count of log 3.32–3.39/g. Sundried matured redC. frutescens had corresponding values of 9.4–18.7 percent; 5.8–6.3 mg/100 g; 0.8–1.1 percent; 0.9–2.6 percent and log 3.2–3.4/g. No aflatoxins were detected in sundried, matured redC. frutescens, but aflatoxin B₁ values obtained fromC. annum varied from non-detectable to 2.2 µg/kg. Dominant fungi isolated fromC. annum andC. frutescens wereRhizopus oryzaze,Aspergillus niger,A. flavus,Geotrichum candidum andSaccharomyces spp.     

Display practices and changes in riboflavin content of non-fermenting palm juice

Changes in riboflavin content of industrially bottled palm juice stored at different light intensities similar to display patterns practised by traders was studied. The loss of riboflavin in the first 24 hours was significantly higher than in the second 24 hours in both transparent (P<0.001) and green bottles (P<0.02) exposed to bright sunlight. Riboflavin loss from samples stored in transparent bottles occurred at a faster rate (24–71% of initial) than from samples in green bottles (0–29%) over a 36-hour period. Further loss of riboflavin did not occur over the next 36 hours due to cool weather conditions. In contrast, only 6% of initial riboflavin was lost after 72 hours of continuous exposure to fluorescent light: this increased by 53% by the ninth week. The data showed that riboflavin loss from bottled palm juice varied with the container, the environmental conditions and period of storage. It is recommended that palm juice should be displayed in dark bottles and protected from bright light.     

Effect of processing on flatus producing oligosaccharides in cowpea (Vigna unguiculata) and the tropical African yam bean (Sphenostylis stenocarpa)

The effect of dehulling, soaking and soaking/cooking on sucrose, raffinose and stachyose in mature dry seeds of nine varieties of cowpea (Vigna unguiculata) and one variety of tropical African yam bean (Sphenostylis stenocarpa) were investigated. The results showed a progressive decrease in sucrose, raffinose, and stachyose contents. Soaking for 12 hours and cooking for 30 min eliminated most of the sucrose, raffinose and stachyose. The sugar contents in whole raw cowpea were sucrose 0.73–4.58%, raffinose 0.71–6.86% and stachyose 2.38–3.87%, and for tropical African yam bean sucrose 4.08%, raffinose 1.08% and stachyose 4.14% while the seeds soaked for 12 hours and cooked for 30 min had for cowpea sucrose 0.03–0.81%, raffinose 0.04–0.20% and stachyose 0.12–0.72%, and tropical African yam bean sucrose 0.70%, raffinose 0.40% and stachyose 0.41%.     

Investigations on the effect of traditional food processing,preservation and storage methods on vegetable nutrients: A case study in Tanzania

The effect of traditional food proceesing, preservation and storage methods on vegetable nutrients was studied using cassava, pumpkin and mwage leaves. Traditional cooking method for 90 min for cassava, 50 min for pumpkin and mwage leaves resulted in significant losses in protein, fats and vitamins. Sundrying using traditional mats caused losses of vitamin A of 36.3%, 38.0% and 50.3% for cassava pumpkin and mwage leaves respectively. Storage using earthenware pots for six weeks resulted in significant losses of vitamin C. In general, traditional methods for processing, preservation and storage of vegetables cause significant losses of nutrients, an effect that could account for poor, nutritional status in Morogoro region (Tanzania).