The objective of the research was to characterise the quality of shea kernel that is whole and intact (WSK), bruised (BSK), and microbial and pest (MPSK) and, to evaluate the physico-chemical properties of the extracted butter in order to partition the contributions of the spoilt kernels to the overall butter quality. The study was performed using shea nuts from Kutigi, Bida, Nigeria. Proximate composition, physico-chemical and fatty acid composition were determined using standard methods of analysis on the whole kernel and the extracted butter. The lipid content was significantly (p < 0.05) higher in WSK (52.44%) relative to BSK (41.99%) and MPSK (39.80%). The study indicated that MSPK made the highest contribution in lowering the shea butter quality by 30%–50%. There was no significant difference in the fatty acid composition of the three sample categories. The free fatty acid, acid value, peroxide value and anisidine value were 3.4, 3.4, 5 and 3 times higher in MPSK than in BSK respectively. This study recommends that the shea kernel processors should sort the shea kernels into three categories and process them correspondingly to yield three different grades and markets depending on period of storage. Overall, the spoilage process in stored shea kernel significantly affects the chemical quality of butter and this study has revealed numerically the degree.
Keywords: shea kernel, proximate composition, fatty acids, microbial, butter, quality, Nigeria, postharvest