Comparative production of glucose and high fructose syrup from cassava and sweet potato roots by direct conversion techniques

High fructose syrup (HFS) is a highly valued liquid sweetener for beverage, confectionery and processed food industry, owing to its special attributes like high solubility and non-crystalline nature. Even though 85% HFS production is from corn, increased food demand has necessitated the search for alternative substrates and starchy root crops like cassava and sweet potato are potential raw materials. However, the economic production needs direct use of the roots and simplification of the cost-intensive steps. This study aims at the direct enzymatic conversion of roots for HFS production. Glucose yield was compared from six treatment systems viz., liquezyme–dextrozyme (T1), Stargen (T2), Stargen in two split doses (T3), Spezyme–Stargen (T4), Stargen (60 °C;T5) and Spezyme–Stargen (60 °C; T6). Glucose was higher (22–25%) from cassava than sweet potato (14.0–15.7%), owing to the high starch content in cassava. Conversion to glucose was higher in T1–T4 (95–98%) compared to 88–92% for T5 and T6. Although the fructose yield was more from cassava (8.36–9.78%) than sweet potato (5.2–6.0%), percentage conversion was similar (37–38%) for both the roots. The cost of production of HFS could be reduced by the direct hydrolysis of root slurry using Stargen.Industrial relevanceThe conventional process for HFS production involved three cost-intensive enzyme steps such as liquefaction, saccharification and isomerization and the major raw material is starch. Economic production using cheaper raw materials and simplification of the process are the decisive factors for the widespread use of HFS in the developing and less developed countries. The present study aimed at the direct conversion of cassava and sweet potato root slurry (without conversion to starch) through the use of improved enzymes like Spezyme and Stargen and mild operating conditions of pH and temperature. The cost of production of HFS could be reduced by using the wet root slurry and performing the Stargen aided saccharification at room temperature, followed by isomerization at 60 °C using Sweetzyme T.