Tanzania Journal of Agricultural Sciences 2003, Vol 6(1) : 19:27
Sweet potato is an important food security crop in, many parts of Tanzania. Despite this potential, research into its post-harvest handling for maximum utilisation hass been low. The objective of this study was therefore, to assess slicing performance of a fabricated hand operated slicing machine against the traditional knife slicing by hand in the production of michemhe. It also assessed how slice thickness, the drying surfaces, and packaging of the slices influenced quality during storage. The slicing machine was set to produce slices of 4.8 12 and 16 mm thickness. Together with the traditionally obtained slices the samples were dried on three surfaces (perforated surface, thatched roof and on the ground) for three days. Dry samples were then packaged in polypropylene bags, perforated polyethylene bags and sealed plastic containers and stored for nine months with observation carried in three months intervals. The investigations included moisture content, fungal count and mycotoxin detection discoloration and insect infestation aa quality attributes. Results showed that the slicer throughput ranged between 16 and 46 kg/h of fresh peeled roots in the thickness range of 4-16 mm, against 17 kg/h for traditionally sliced (75 mm) sweet potatoes. During drying, weight of slices decreased exponentially with time. In terms of drying effectiveness, the three drying surfaces used displayed almost the same final mean moisture content in the lower slice thickness range (4-8 mm). With increased slice thickness to 12 and 16 mm: the perforated surface was the most effective (10. 63-18. 03%) followed by the ground floor- (15.67-18.65%) and thatched roof the least (16.5-19.36%) Quality of dried michembe decreased with storage time and the best performance was obtained in polypropylene bags for the nine months storage. Packaging in sealed plastic containers produced the worst results. Quality was also influenced by the drying surfaces used with ground floor resulting in poor product and perforated surface the best. Increasing the slice thickness affected the quality of the dry product except in the range of 4 to 8 mm. Slicing of the roots to 4-8 mm drying on perforated surface and packging in polypropylene bags for room temperature storage of up to six months produced michembe of acceptaple quality. Use of improved slicing machines including mechanically powered machines requires further investigation. Studies on more drying surfaces more packaging materials, and nutrition of michembe are also recommended