Postharvest changes along supply chains of Solanum aethiopicum (Shum) (nakati) and Amaranthus lividus (Linn) (bugga) leafy vegetables

Abstract

Objectives: The objectives were three; document postharvest handling practices along supply chains of Solanum aethiopicum (Shum) and Amaranthus lividus (Linn) leafy vegetables; assess changes in sensory attributes of S. aethiopicum and A. lividus leafy vegetables along the supply chain and thirdly, assess the effect of postharvest practices on vitamin C and beta carotene content of the respective vegetables. Methods: A cross sectional study design was employed for the purpose of understanding the postharvest practices and their impact on sensory and nutritive quality of the leafy vegetables. The target population included supply chain actors (farmers, transporters and traders) who were selected purposively for interviews. Quantitative descriptive sensory analysis was used to profile and investigate changes in sensory attributes of vegetables with time after harvest. Beta carotene was analyzed using reverse High Performance Liquid Chromatography, vitamin C by titration method and moisture content by oven drying. Correlation and regression analyses were carried out to establish relationships amongst variables of interest (p<0.05). Results and discussion: Harvesting was mainly done in the evening hours and by hand. The main transport means used was truck (100%), commonly hired by one or more farmers. However, a key informant interview revealed that other alternative transportation means included motorcycles and bicycles. There was no proper storage and packaging observed both on farm and in the market. Moreover, inappropriate packaging and improper storage have been reported as major causes of postharvest loss in vegetables. Only 16.6% of traders sorted and graded the vegetables as compared to 83.4% who did not. There was complete lack of recommended handling, storage and packaging practices along the supply chains. Sensory profiles of eight (8) and nine (9) descriptors were developed for S. aethiopicum and A. lividus respectively. Descriptive Sensory Analysis (DSA) results showed that all 9:00hrs samples were rated highly for each attribute compared to the 12:00hrs and 15:00hrs samples. Results for S. aethiopicum showed statistically significant (p<0.05) difference for all the sensory attributes except for light green colour of leaf stalk. For A.lividus, significant (p<0.05) differences were observed for moist appearance, well spread appearance, smoothness and overall quality. This result shows that sensory attributes of S. aethiopicum deteriorate faster than those of A. lividus under same handling conditions. Correlation results showed significant (p<0.05) positive relationship among attributes, indicating that deterioration in one attribute may lead to deterioration of the other. Beta carotene had a significant (p<0.05) negative regressive association with trimming-off roots in both types of vegetables. This indicates that increase in the practice may lead to losses in beta carotene, keeping all other factors constant. However, trimming-off roots and sprinkling with water had a negative significant (p<0.05) association with vitamin C content whereas harvesting by hand had a positive significant (p<0.05) association with vitamin C for both types of vegetables. Harvesting by hand may seem to retain vitamin C in vegetables compared to other methods such as mechanical/machine given the positive association. Conclusion: Postharvest handling practices; harvesting by hand, improper storage and packaging, use of trucks for transporting vegetables to the market, lack of sorting and grading characterized the supply chains in this study. These practices are generally poor and have a negative impact on sensory attributes, beta carotene and vitamin C contents of S. aethiopicum and A. lividus leafy vegetables.