Optimizing traditional processing and preservation techniques of cowpea leaves

Abstract

Cowpea (Vigna unguiculata) leaves are have the potential of reducing malnutrition among the populations in sub-Saharan Africa and Uganda specifically. The leaves are rich in proteins, micronutrients such as vitamin A, vitamin C, and iron whose deficiencies are prominent in Uganda especially among children below 5 years. However, due to it is seasonality and high post-harvest losses, utilization is limited among the local populations. Aim and objectives of the study The main aim of the study was to enhance the nutrient and bioactive compounds retention and utilization of cowpea leaves. Four specific objectives were generated to achieve the above aim and these include; (1) To determine utilization and the processing and preservation techniques of cowpea leaves in Jinja district; (2) To establish the effect of traditional processing and preservation techniques on nutrient retention and storage stability of cowpea leaves; 3) To determine the optimal processing conditions for enhanced nutrient retention in cowpea leaf product and (4) To evaluate the sensory and nutritive composition of optimally processed cowpea leaf based composite products. Methodology To realize objective one, focus group discussions (FGDs) and key informant interviews (KIIs) were conducted among the cowpea growing communities in Budondo subcounty Jinja district. Objective two was achieved by carrying out nutrient analysis of the cowpea leaves for the two traditional processing and preservation techniques to determine the nutrient retention of the leafy vegetables. Objective three was realised by using design expert software to determine the optimum drying conditions that were achieved using refractance window drying technology for maximum nutrient retention. Objective four was achieved by carrying out sensory analysis of the porridge products developed from cowpea leaves among the population in Kayunga district with the help of a structured questionnaire. Results and discussion Three varieties of cowpeas are grown in Budondo sub-county including; Empindi, Ngogodi and Choloko. The leaves of Empindi variety mature faster (harvested between three to four weeks) and have tender leaves as compared to other varieties of Ngogodi and Choloko. The tender leaves of Empindi are easy to cook and save the fuel hence economical. Men are more dominant than women in the production of Empindi cowpeas since their cultivation of is labour intensive, time consuming and women lack capital in terms of land and irrigation equipment, making it unfavourable for the women especially during the dry season. Findings also revealed that among the traditionally processed and preserved cowpea leaves, the sundried samples a significantly (p<0.05) higher retention of carbohydrates (92.72%), proteins (97.41%) and ash (92.39%) than the samples subjected to a combination of boiled and sundried technique of processing. Considerable reduction in lipids content of sun-dried samples (20.24%) and boiled and sundried samples (17.16%) were registered. Optimum drying of cowpea leaves using refractance window drying (RWD) resulted into substantially high retention of vitamin A (12.41 µgRAE/100g), vitamin C (261.00 mg/100g) and proteins (31.29 g/100g).. The two composite porridge blends of cowpea-millet and cowpea-maize had significantly (p>0.05) higher proteins contents (43.70 g/100g and 30.03 g/100g), carbohydrates (94.81 g/100g and 133.25 g/100g) and dietary fibre (20.05 g/100g and 12.51 g/100g) as compared to the controls. The two composites of flours can contribute 100% RDAs proteins, carbohydrates requirements, and more than 30% RDAs for fats to infants (0-12 months) and children (1-8years). Conclusions and recommendation Processing and preservation of cowpea leaves using optimally designed methods and technologies that are relatively cheap and reliable can lead to enhanced retention of nutrients and bioactive compounds. This can ensure availability of nutrients to the vulnerable populations, contributing to ongoing efforts of eradicating malnutrition in Uganda. It is recommended that adopting of improved processing and preservation techniques such as refractance window drying will scale up production of cowpea leaves and scale up the economic status of the farmers.