Physicochemical Properties of Fungal Detoxified Cassava Mash and Sensory Attributes of Wheat-Detoxified Cassava Composite Doughnuts

摘要

The physicochemical properties of fungal detoxified cassava mash and sensory characteristics of wheat-detoxified cassava composite doughnuts were investigated. Fungal isolates from soils collected at cassava processing sites were isolated, quantifiedand identified. Cassava mash from grated tuber was partially dewatered and inoculated separately with Candida utilis and Rhizopus stolonifer isolates at 1:100 (w/v) level, then allowed to ferment at ambient temperature (30 ± 1°C,RH 80%) for 48hr. Fermenting samples were withdrawn at 12hr intervals and analysed for changes in pH, cyanide, moisture and protein contents. Detoxified cassava mash was toasted, blended with wheat flour in a ratio of 1:10 (w/w) and used in the preparation of four composite doughnuts that were assessed for their sensory characteristics. Soil samples from cassava grating site had 103 cfu/g moulds and no yeast while clayey moist soils at the dewatering sites had 104 cfu/g and 105 cfu/g moulds and yeasts cells, respectively. Candida fermented cassava mash was completely detoxified in 24hr while the un-inoculated control and Rhizopus-fermented mash had cyanide content reductions of 91.6 and 97.2%, respectively. Candida-fermented cassava mash yielded an initial pH increase, reaching up to pH 7.27 in 48hr while the Rhizopus-fermented samples showed an initial drop in pH followed by a steady increase after 12hr of fermentation to pH 6.8. There was proteolysis with perceived ammonical odour development in Candida-fermented mashes while the control and Rhizopusfermented mashes had increased protein contents ranging from 4.6-7.6% and 4.6-7.1%, respectively, after 48hrs. Composite doughnuts containing 24hr Rhizopus-fermented flour compared favourably with wheat doughnuts and was rated significantly (P = 0.05) higher than other composite doughnuts for taste, flavour/aroma and overall acceptability characteristics.