Paper Title
Effect of Drying Temperature on Functional and Digestive Properties of Sweet Potato Flour

Proper drying of food products helps in extending shelf life and either maintaining or improving their quality. In this study, the effect of hot air drying temperature (at 55, 70 and 85 0 C) in comparison to freeze drying on the functional and digestive properties of flours from sweet potato roots with orange flesh (OFSP) and purple flesh (PFSP) were investigated. The proximate compositions and amylose content (AC) were also analyzed. Results showed that flours obtained from hot air dried sweet potatoes had higher AC (12.36 to 18.95%db for OFSP and 16.45 to 19.31%db for PFSP) than that from freeze dried ones (11.44%db for OFSP and 13.09%db for PFSP). Drying possibly modified the structure of starch granules and consequently changes in pasting viscosity based on Rapid Visco Analyzer (RVA). Overall pasting viscosities ranges include Peak viscosity (PV) 831.33 (freeze OFSP) to 2996 (85 PFSP), Trough viscosity (TV) 124.67 (55 OFSP) to 1398 (85 PFSP), Breakdown viscosity (BDV) 476.33 (freeze OFSP) to 1598 (85 PFSP), Final viscosity (FV) 167.33 (55 OFSP) to 1825 (85 PFSP) and Setbak viscosity (SBV) 42.67 (55 OFSP) to 427 (85 PFSP) all increased with increasing drying temperature. The exception was for freeze dried OFSP since it showed high swelling index, resulting in the high pasting viscosities. Drying showed less apparent effect on gelatinization temperatures at onset (To) range 77.35 0 C (70 OFSP) to 78.24 0 C (freeze OFSP), peak (Tp) range 80.92 0 C (70 OFSP) to 82.21 0 C (freeze PFSP) and conclusion (Tc) range 85.31 0 C (70.OFSP) to 86.76 0 C (freeze PFSP) based on Differential Scanning Calorimetry (DSC) test results. However, positive correlations were observed between gelatinization enthalpy and AC (p<0.05). Drying under the temperature range of this study affected starch fractions including resistant starch (RS), non-resistant starch (NRS) and total starch (TS) only slightly. Results of this study suggested that high temperature drying could be applicable in modifying paste viscosities of sweet potato for use as thickening or stabilizing in food product. Keywords: Flour functional properties, Freeze drying, Hot air drying, Starch, Sweet potato