In-depth analysis of N2O fluxes in tropical forest soils of the Congo Basin combining isotope and functional gene analysis

Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N₂O) or elemental nitrogen (N₂). The release of N₂O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N₂O; however, despite being the world's second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N₂O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N₂O fluxes in the Congo Basin's lowland forests (0.97 ± 0.53 kg N ha^-1 year^-1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha^-1 year^-1). Measurements of soil pore air N₂O isotope data at multiple depths suggests that a microbial reduction of N₂O to N₂ within the soil may account for the observed low surface N₂O fluxes and low soil pore N₂O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N₂O, N₂) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N₂ via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.

Proteolytic activities in togwa, a Tanzanian fermented food

Proteolytic activities were investigated in sorghum-based togwa prepared by natural fermentation and using starter cultures previously isolated from the native product, i.e., Lactobacillus brevis, Lactobacillus cellobiosus, Lactobacillus fermentum, Lactobacillus plantarum, Pediococcus pentosaceus, and Issatchenkia orientalis in coculture with either L. brevis or L. plantarum. Both proteinase and aminopeptidase activities were substantially higher in naturally fermented togwa than in those with starters (14-30%, 12-70%, respectively). A variable but substantial part of the proteinase activity followed the particulate fraction of togwa; aminopeptidase activity was mainly in that fraction. The breakdown of relatively high molecular mass protein (64 kDa) in togwa was detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE); the products were mainly in the 14-30 kDa range. Reversed-phase fast-protein liquid chromatography (RP-FPLC)-protein/peptide patterns changed during fermentation with some variation between togwa of different cultures. Supplementation of gruel with malt increased the concentration of total protein [from 9.5% to 11.0% (w/w) on dry weight basis)] and of most of the free amino acids. Fermentation had no effect on total protein content; however, the concentration of most of the amino acids was reduced, except for the proline content that increased. Natural fermentation also increased the concentration of glutamic acid and ornithine. Fermentation by P. pentosaceus increased aspartic acid, while L. cellobiosus, L. fermentum, and L. brevis in coculture with I. orientalis increased the concentration of citrulline.

Use of starter cultures of lactic acid bacteria and yeasts in the preparation of togwa, a Tanzanian fermented food

Starter cultures of lactic acid bacteria (Lactobacillus brevis, Lactobacillus cellobiosus, Lactobacillus fermentum, Lactobacillus plantarum and Pediococcus pentosaceus) and yeasts (Candida pelliculosa, Candida tropicalis, Issatchenkia orientalis and Saccharomyes cerevisiae) isolated from native togwa were tested singly or in combination for their ability to ferment maize-sorghum gruel to produce togwa. All species of bacteria showed an ability to ferment the gruel as judged by lowering the pH from 5.87 to 3.24-3.49 and increasing the titratable acidity from 0.08% to 0.30-0.44% (w/w, lactic acid) in 24 h. Yeasts used singly showed little activity within 12 h, but lowered the pH to 3.57-4.81 and increased the acidity to 0.11-0.21% in 24 h. Yeasts in co-culture with lactic acid bacteria (LAB) had a modest effect on the final acidity (P<0.05). The number of lactic acid bacteria and yeasts increased while the Enterobacteriaceae decreased with fermentation time. The pH was lowered and lactic acid produced significantly (P<0.05) fastest in natural togwa fermentation and in samples fermented by L. plantarum or L. plantarum in co-culture with I. orientalis. The content of fermentable sugars was reduced during fermentation. Most volatile flavour compounds were produced in samples from fermentation by P. pentosaceus and I. orientalis in co-culture with either L. plantarum or L. brevis.

Microbiological and fermentation characteristics of togwa, a Tanzanian fermented food

Selected microbiological and metabolic characteristics of sorghum, maize, millet and maize-sorghum togwa were investigated during natural fermentation for 24 h. The process was predominated by lactic acid bacteria (LAB) and yeasts. The mesophiles, lactic acid bacteria, and yeasts increased and the Enterobacteriaceae decreased to undetectable levels within 24 h. The isolated microorganisms were tentatively identified as Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus cellobiosus, Pediococcus pentosaceus, Weissella confusa, Issatchenkia orientalis, Saccharomyces cerevisiae, Candida pelliculosa and Candida tropicalis. The pH decreased from 5.24-5.52 to 3.10-3.34. Maltose increased initially and then decreased, fructose decreased and glucose levels increased during the first 12 h of fermentation. The organic acids detected during fermentation included DL-lactic, succinic, formic, pyruvic, citric, pyroglutamic and uric acid. Lactate was the predominant acid and increased significantly with time. The volatile organic compounds (VOC) detected included acetaldehyde, 2-methyl-propanal, 2-methyl-butanal, 3-methyl-butanal, ethanol, 2-methyl-1-propanol, 2-methyl-1-butanol, 3-methyl-1-butanol, diacetyl and acetoin. Ethanol was the predominant VOC and it increased significantly with time.

Identification and nutrient composition of indigenous vegetables of Tanzania

Thirty types of indigenous vegetables commonly utilized in rural areas of Tanzania were collected, identified and their nutrient compositions analyzed. High values up to 249.6, 266 and 7.7 mg/100 g of vitamin C, calcium and iron, respectively, were recorded. Protein content ranged from 0.6 to 5.0 and fat content 0.1 to 1.0 percent. Generally most of the vegetables were preferred by 50 to 90 percent of the persons surveyed.

Evaluation of the nutritional quality and acceptability of sorghum-based tempe as potential weaning foods in Tanzania

Six types of sorghum (Sorghum bicolor)-based tempe were developed by blending with various combinations and quantities of either bambara groundnut, sesame, cowpea, pigeonpea, common bean, mungbean, soybean, or groundnut (peanut) seeds. Their mixtures were then soaked and solid-state fermented by Rhizopus oligosporus to produce tempe. Soaking resulted in the loss of minerals. Mould fermentation did not change the proximate and mineral composition, but increased the in vitro protein digestibility by 10 to 14.1%. Tempe processing reduced the tannin content by 30.4 to 94.0%. The protein content of tempe ranged from 16.0 to 18.6%; the amino acid score, 63.0 to 69.0%; protein energy, 14.2 to 16.8%; net dietary protein energy, 7.3 to 8.4%; and total energy, 416.0 to 441.0 Kcal/100 g of tempe. The developed tempe had protein quality and energy recommended for weaning foods. The deep-fried snacks were mildly acceptable. More research work and promotion are proposed in order to improve the acceptability of sorghum-based tempe as potential weaning or supplementary foods in Tanzania.

Evaluation of the nutritional quality and acceptability of fingermillet-based tempe as potential weaning foods in Tanzania

Six types of fingermillet (Eleusine coracana)-based tempe were developed by incorporating either commonbeans, groundnuts, cowpeas, mungbeans, chickpeas, sesame and/or their mixtures and fermented by Rhizopus oligosporus. The proximate and mineral composition was not changed significantly by fermentation. The protein content of tempe ranged from 13.3 to 15.7%; the total energy, 374.1 to 434.3 Kcal/100 g; the protein energy, 13.0 to 15.6%; the net dietary protein energy, 7.2 to 8.7%; and the chemical score, 61 to 71%. Tempe processing reduced the tannin and hydrogen cyanide content by 55.2 to 75.7, and 71.0 to 86.2%, respectively. It increased the content of reducing sugars, amino nitrogen, total acidity by 4 to 15, 3 to 6.9, and 4.3 to 12-fold, respectively. The in vitro protein digestibility was also improved. The developed tempe had protein quality and energy content recommended for weaning foods. The deep-fried tempe snacks were fairly organoleptically acceptable.

Production and storage stability of non-alcoholic pawpaw beverage powder

Powder for instant non-alcoholic pawpaw beverage formulation was manufactured by traditional sundrying and controlled ovendrying. The reconstituted beverage was organoleptically acceptable. The effect of sundrying on mats and ovendrying on product quality was investigated. Sundrying resulted into losses of vitamins A and C, and total sugar by 97, 98 and 87 percent; while, oven drying losses were 92, 98 and 87 percent, respectively. Nutrient losses during storage in transparent polythene bags at ambient conditions reached 98, 98 and 82 percent in sundried samples and; 87, 99 and 67 percent in ovendried samples respectively. The moisture content of sundried and oven dried samples increased by 14 percent during storage. The increase in microbial load during storage was higher in sundried samples.

Production and storage stability of non alcoholic banana beverage powder

Powder for an instant, non-alcoholic beverage formulation was manufactured by sundrying and ovendrying of a popular dessert ('silk') banana variety. The reconstituted beverage was organoleptically acceptable. The effect of traditional sundrying on mats and ovendrying methods on product quality was investigated. Sundrying resulted in losses of Vitamin A, C and total sugar contents by 74, 91 and 63%, while ovendrying losses were 73, 90 and 62%, respectively. Nutrient losses during storage for three months in transparent polythene bags reached 93, 93 and 70% in sundried samples and 84, 99 and 55% in ovendried samples, respectively. The moisture content of sundried and ovendried samples increased by 12 and 17%, respectively, during storage. The increase in microbial load in this period was higher in sundried samples.

Bacteriological quality of potable water sources supplying Morogoro municipality and its outskirts: a case study in Tanzania

Bacteriological quality of potable water supplying Morogoro municipality and its outskirts (population 135,000 people) was assessed by the determination of the most probable number (MPN) of faecal coliforms, Escherichia coli, faecal streptococci and Clostridium perfringens for a period of 6 months. River water and chlorinated pipeborne water were found contaminated with microorganisms in the order of 3.8 x 10(1) to 4.95 x 10(3); 3.2 x 10(1) to 4.5 x 10(3); 10(1) to 6.4 x 10(1) and 1.2 x 10(1) to 2.5 x 10(2)/100 ml of water respectively. Injured coliforms in treated water averaged 87%. Pollution of river water by organic matter was much above acceptable standard. These findings indicate that there is a need for further treatment of water before consumption in order to avoid potential health hazards.