Influence of α-Amylase on the Physical Properties and Consumer Acceptability of Sweetpotato Starch Syrup

The sweetpotato (Ipomoea batatas [L.] Lam) is a candidate crop for future space missions. However, sweetpotatoes are highly perishable and difficult to store, therefore, novel avenues for processing the surplus roots into value-added products that are commercially viable are needed. Technology was developed on a laboratory scale for the production of sweetpotato syrup and: i) the effect of varying levels of α-amylase on syrup quality determined; and ii) the storage stability and consumer acceptance of the syrup evaluated. Three levels of thermostable bacterial α-amylases (1.5, 3.0, 4.5 mL) were used for conversion of sweetpotato starch (SPS) into glucose syrup. The 1.5 mL α-amylase-treated was dropped from the experiment because there was no hydrolysis. The enzymatic conversion of SPS into glucose was significantly higher (P<0.05) for the 4.5 mL α-amylase-treated compared to the 1.5 and 3.0 mL levels. The refractive index (RI) was 1.5 and 1.4 for the 4.5 and 3.0 α-amylase-treated syrups, respectively, while moisture content (16.7 vs 12.5) and °Brix (65.0 vs 57.0) were higher for the 4.5 mL α-amylase-treated syrup. Syrups were stored at room (RSPSS) and refrigerated (RESPSS) temperatures. During storage, the L^* color value for RESPSS was significantly higher (P<0.05) than that of RSPSS. Similarly, the °Brix was 64.1±1.1 and 66.0±1.7 for the RSPSS and RESPSS, respectively. The RSPSS was stable for 12 weeks. The SPSS and two commercial syrups (maple and ginger) were evaluated by 112 children between the ages of 12 and 13 years on a 9-point hedonic scale. For the younger children, there were no significant differences in liking between the SPSS (6.1) and maple syrup (5.8). However, the mean preference for the ginger syrup was significantly less (P<0.001). Overall, the SPSS had acceptable physical and consumer properties, indicating the need for further evaluation of a potential commercial SPSS.