The Effect Of Postharvest Handling Practices On The Quality Of Selected Kenyan Sweetpotato Varieties

Abstract

Sweetpotato (Ipomea batatas) is a versatile crop that serves the roles of food and nutrition security, cash crop, feed for livestock and can provide raw materials for processing in the commercial industry. The hidden commercial potential of the sweetpotato in Kenya is yet to be exploited since little attention has been paid to postharvest harvest practices thus, little documented information exists on postharvest practices. Maximum utilization of sweetpotato roots is also hindered by lack of adequate information documented on current varieties. This study aimed at assessing the effect of sweetpotato postharvest handling practices on the physicochemical properties of roots of selected varieties in Kenya. A survey was carried out in Homabay and Bungoma counties to assess the postharvest handling practices. Structured questionnaires were administered to a total of 165 respondents comprising 96 farmers, 64 traders and 5 processors. Eight selected sweetpotato varieties were then evaluated for their physicochemical properties and for the pasting profiles of their flours. To establish the effect of storage conditions on the quality of the roots, Kabode (orange fleshed) and Kenspot 2 (white fleshed) varieties of sweetpotato were harvested and subjected to similar storage conditions in an experiment with factorial arrangement of 24 treatment combinations. Half of the samples were washed while the similar half unwashed before storage. Half of the samples were stored under room temperature 22-24oC, relative humidity of 60-70% and the other half stored at temperature of 12-13oC, relative humidity of 80-90% for three weeks. Changes in moisture content, starch, reducing sugars, beta carotene and vitamin C were monitored during the three-week period. The survey results showed that 68%, 87% and 40% of sweetpotato farmers, traders and processors respectively, were women. Marketing systems that quantified roots using bags, buckets and heaps were prevalent. Motorcycles, donkeys and bicycles, were used by 26%, 21% and 11% respectively xxii to transport roots to the markets. Storage was rarely practiced by 43% of farmers and 45% of traders. Processed products included flour, puree and dried chips. High perishability and unreliable supply of roots were major challenges indicated. There were significant (p< 0.01) variations in the physichochemical attributes of the eight varieties. Orange fleshed varieties had comparatively higher moisture, beta carotene, fat, reducing sugars and mineral contents but lower pasting profiles compared to the non-orange fleshed varieties. Flour from the orange fleshed varieties showed lower Peak viscosities (124-590cP) and lower cold paste viscosities (89.5-319cP) compared to that of the non-orange fleshed varieties. During the storage experiment, significantly (p≤0.05) more changes in physicochemical attributes of the roots were recorded in samples stored at room temperature (22-24oC) with relative humidity 60-70% compared to samples stored at 12-13oC with relative humidity ranging 80-90% at the end of three-week storage. Loss of over 50% in moisture content, beta carotene, vitamin C, about 30% starch and increase in reducing sugars by more than 50% were noted after three-week storage. Washed samples experienced higher deteroriation in quality compared to unwashed samples irrespective of variety. Sisal and gunny bag packaging showed slower deterioration of quality of the roots compard to the roots that were not packaged prior to storage. In conclusion, postharvest handling practices and challenges were similar in both Bungoma and Homabay counties. Inadequate knowledge on storage and lack of storage facilities and infrastructure were major challenges cited by the respondents. Sweetpotato varieties differ significantly in their physichochemical properties and hence can have diverse uses in both food and non-food applications. Washing, packaging and storage conditions significantly affect the physicochemical properties of sweetpotato roots during storage. The findings of this study will inform actors on postharvest handling and management of sweetpotato in order to tap in to the unexploited commercial opportunities in the sweetpotato value chain. A comprehensive xxiii sweetpotato policy in Kenya is required to address identified challenges on sweetpotato handling practies along the value chain in order to promote utilization and minimize postharvest loses.