Chemical analysis to promote the use of wild fruits from Mozambique

Abstract

Wild fruit trees have significant cultural and socio-economic value in rural areas of Mozambique. Most of the wild fruits are seasonal and are available mainly in the wet season. Generally they have a short shelf-life and are eaten fresh or after minimal processing; the most common method of preservation is sun-drying. The fruits of Adansonia digitata, Landolphia kirkii, Salacia kraussii, Sclerocarya birrea, and Vangueria infausta were selected for this study. These fruits are the most popular, and are consumed in different districts of Mozambique, especially by children, and form part of their normal diet. Besides from eaten fresh, the fruits are mixed with sugar, pressed to make juice, as jam or a kind of dessert, and the pulp and sometimes the kernels are dried and used as flour to make porridge or a sauce. New data on nutritional components and other characteristics have been obtained. The pH, titratable acidity and the content of soluble solids in the fruit pulps were determined as these are of importance for the fruit processing industry. The pulp of all the fruits except S. kraussii had an acidic character. The organic acids citric, malic and succinic acids were found at various amounts in all pulps. The highest amounts of citric acid were found in A. digitata and L. kirkii; above 20 g/kg. Organic acids are responsible for many characteristic fruity tastes and may enhance the absorption of minerals. The contents of different mono- and disaccharides were also analysed in the pulps. The highest amounts of glucose (7.5%) and fructose (5.7%) were found in L. kirkii, while A. digitata contained the highest amount of sucrose (4.3%). The protein content was low in all the fruit pulps, as is the case in fruits in general. However, the protein content was high in the kernels of A. digitata and S. birrea, about 30 to 40% on dry matter basis. For children aged 4 to 8 years, around 80 and 67% of the adequate intake (AI) (defined by the Food and Nutrition Board of the US Institute of Medicine) could be covered by the consumption of 40 g A. digitata kernels or S. birrea kernels, respectively. The total content and relative amounts of the different essential amino acids are with a few exceptions similar to or above that recommended by the WHO for children aged 3 to10 years. The fat content was below 2% in the fruit pulps, while the fat content in A. digitata kernels was almost 40%, and S. birrea kernels about 60%. The kernels of A. digitata and S. birrea are rich in unsaturated fatty acids, and constituted about 68 and 80%, respectively, of the total fat. The A. digitata kernels contained appreciable amounts of essential fatty acids; the amount of linoleic was about 30% and linolenic acid 2%. S. birrea kernels contained about 7% linoleic acid. Estimations showed that 40 g A. digitata kernels can cover the daily intake of omega-6 fatty acids for those aged 4 to 13 years, and about 90% of the requirement for pregnant women. The i same quantity of A. digitata kernels can provide 60 to 93% of the daily requirement of omega-3 fatty acids for the same groups. The fruits contained both insoluble and soluble dietary fibre. The pulp of A. digitata had the highest amount of soluble dietary fibre, around 60% (on dry matter basis), while V. infausta pulp had the highest amount of insoluble dietary fibre, around 40%. The kernels contained 3 to 5% phytic acid which may decrease the absorption of minerals. Treatment with phytase reduced the phytic acid content by 20 to 30% after only 15 minutes enzymatic incubation. Interestingly, almost 50% of the estimated original content of minerals was found in the supernatant after a few minutes’ enzyme incubation. The amount of iron in the pulps ranged from 1 to 9 mg/100 g (on dry matter basis); the highest amount being observed in S. kraussii. The highest iron content, 29 g/100 g DM, was found in whole seeds of A. digitata, 29 mg iron/100 g, and consumption of 40 g could provide more than 100% of the AI for children and 43% for pregnant women. The A. digitata pulp contained an appreciable amount of calcium, and the kernel also had high content of calcium. Consumption of 100 g of A. digitata pulp would give about 23 to 29% of the AI for children and about 37% for pregnant women. In conclusion, data from this study can be used to encourage the increased consumption of these wild fruits and kernels. In addition, the results of the analysis of the investigated fruits can form the basis for the selection of fruits for wider use, domestication, and processing to extend their shelf-life and for the manufacture of other food products