EFFECT OF PRETREATMENTS AND DRYING METHODS ON QUALITY ATTRIBUTES OF ORANGE FLESHED SWEET POTATO (Ipomoea Batatas) SLICES AND FLOUR

Abstract

Sweet potato roots are classified as perishable since they cannot be kept for an extended period once they have been removed from the plant. Therefore, this study was initiated to assess the effect of pretreatments and drying methods on quality attributes of orange-fleshed sweet potato slices and flour. The experiment was planned with two factors; drying methods (microwave, oven, and Sun) and pretreatments (blanching, sodium metabisulfite, citric acid, and control). It consisted of twelve combinations of treatments executed in a factorial design with two factors and levels. The drying characteristics such as coefficient of regression (R2 ) and chi-square (χ 2 ), resulted in values within the range of 0.962 to 0.998 and 0.000000172 to 0.27119, respectively. As a result of R2 (0.96875 to 0.99889), the Lewis model was the best fit that could adequately describe the drying characteristics of the sliced orange-fleshed sweet potato in thin layers. Nonlinear regression was used to evaluate the data for the drying characteristics and properties of the flour using Excel (2019) and SAS (version 9.1), respectively. The proximate analysis showed that the flour had respective ranges for moisture, protein, fat, fiber, ash, utilizable carbohydrate, and energy contents were ranged from (6.96-7.84, 6.10-7.28%, 0.98-1.17, 2.82-3.43, 3.25-4.12, 77.54-78.11%, and 345.17-351.12 kcal/100, respectively). The Iron, Zinc, Calcium, carotenoid, and vitamin C of the dried orange fleshed sweet potato, were 7.89-8.20, 2.96-3.27, 22.37-24.16, 9.96-10.19, and 6.33-7.69 mg/100 g. Similarly, the engineering properties such as particle size distribution range 13.16-39.91% of 250 μm, 40.37-52.79% of 150 μm, 6.16-14.95% of 106 μm, and 6.45-14.54% of 75 μm, bulk density and angle of repose 0.66-0.69gm/mL, and 35.41o -37.88o , respectively were also determined. Likewise, the color values of dried orange fleshed sweet potato flour ranged from 70.63-81.55, 9.82-10.17, 21.56-32.56, 64.70-73.07o , and 23.85-34.04 for L*, a*, b*, hue, and chroma, respectively, and was significantly affected by the treatments. The values of functional properties of dried flour, which included WAC and OAC, WSI and SP, and dispersibility ranged from 2.73-3.01 and 1.73-2.01g/g, 26.75-27.58%, and 4.07-4.82g/g and 50.16-53.91%, respectively. The result of this study demonstrates that pretreatments and drying methods had different effects on the quality attributes of dried OFSP slices and flour. However, for optimum preservation of quality, pretreatment by dipping in sodium metabisulfite combined with the microwave drying method is recommended.