Determination of the Effect of Steeping and Blanching Pretreatments and Drying Temperatures on the Proximate Properties of White-Fleshed Sweet Potato Variety

Abstract— Agricultural products require suitable preservation methods for retention of their nutritional qualities and attributes. Sweet potatoes are underutilized due to cost implications of their preservation using modern storage techniques. Enzymatic discoloration of freshly cut potato flesh surfaces from exposure to air affects processed potato qualities adversely. While steeping/blanching pretreatment is deployed in curbing this challenge, varying the steeping/blanching and drying treatments can assist in arriving at the optimum process conditions for white-fleshed sweet potatoes. 4 kg of similarly sized and healthy white-fleshed sweet potato tubers obtained from Eke Awka market (Latitude 6.210528 °N and Longitude 7.072277 °E) in Anambra state, Nigeria, was washed with clean tap water, peeled and cut into 4 mm by 10 mm by 10 mm slices. The experiment was designed using the Response Surface Methodology (RSM) software. The chipped potatoes were divided into 24 samples of 100g each for the analysis. 19 samples were pretreated in water at temperature range of 11oC to 100oC and 5 samples were not pretreated (served as control). All the pretreated samples were held in the fluid for period of 2 mins to 18 mins as contained in the design matrix. Both the pretreated and control samples were grouped and dried in convective oven at set temperatures of 53 °C, 60 °C, 70 °C, 80 °C and 87 °C and weighed every 30 mins until there was no further weight loss at three consecutive readings. The dried sweet potato chips were grated into flour, for the determination of the proximate composition of the chips. Optimized drying and pretreatment conditions were analyzed from the results using RSM software. Result of the analysis showed significant increase in proximate composition of the samples with increase in both the steeping and drying temperatures and indicated significance of the model terms. The error analysis showed a high degree of correlation between the observed and the predicted values. From this work the optimal conditions predicted by the RSM model were blanching temperature of 70 oC, blanching time of 5 mins and drying temperature of 80 oC for 4 mm-thick 100g of sliced white-fleshed sweet potato chips to yield 2.40% Crude protein, 73.95% Carbohydrate, 2.54% Fiber, 4.31% Ash, 3.24% Fat and 9.86% Moisture content which served as a guide for high quality sweet potato chips production from freshly harvested white- fleshed sweet potato tubers. The dried potato chips can be grated into flour and used as the major ingredient for bread, noodles and cake making. The application of the outcome of the work will help in reduction of post-harvest losses of the crop.