ABSTRACT

Orange-fleshed sweet potato flour was processed from UMUSPO1, a well-known orange- fleshed sweet potato varieties from National root crop research institute Umudike. The effect of processing pretreatments and storage on total carotenoid content, proximate composition, functional properties and microbial quality of the flour samples were investigated. Three pretreatment methods; blanching, boiling and treating with 0.5% metabisulphite solution for 10mins were employed and the flour samples were either sun dried or oven dried. Significant percentage decreases (P<0.05) were observed in the total carotenoid content of the samples after storage which ranged from 5.47% - 27.3%, however blanched oven dried flour samples retained higher percentage total carotenoid content of53.83% while the untreated sun dried sample had 15% retention which is the lowest after 3months of storage. There were significant differences (P<0.05) in the proximate composition of the samples during storage and this varied among pretreatment methods. Moisture content of the flour samples ranged from 8.23% - 12.01% which is within the acceptable limit. There were significant differences (P<0.05) in carbohydrate (75.36%-83.62%), crude fiber (1.7% -2.65%), protein (6.50% - 8.00%), fat (0.47% -1.7%) and ash (1.63% - 1.89) content of the flour samples. The functional properties of the flour samples showed significant differences (P<0.05) in their values with Swelling power ranging from 13.12% - 15.54ml/g, OAC 1.45-3.55g/ml, WAC 2.40-3.05%, Gelatinization temperature 76.500C-830C and Bulk density 0.61g/ml – 0.70g/ml. There were significant increases (P<0.05) in the bacterial load of the samples during storage with boiled sundried sample having the highest increase from 10.00 - 14.00 × 104CFU/g while metabisulphite treated oven dried maintained the lowest values from 5.50-8.50 × 104CFU/g from 0 month to 3rd month. However, there was no significant difference (P>0.05) in the fungal load of the flour samples.