Hydrolysis of sorghum starch to glucose using organic acid catalyst from rosella flower extract (Hibiscus sabdariffa L.)

Abstract

Highly starch content in sorghum seed has a high potential raw material for the sorghum fluor to be a raw material of liquid sugar known as glucose syrup. The syrup is usually produced through enzymatically or chemically hydrolysis using a strong acid. In this study, sorghum starch is hydrolyzed chemically using a catalyst of organic acids extracted from roselle flower (Hibiscus sabdariffa L.). The goal of the study is to produce glucose syrup free from chemical agents so as generally recognized as safe (GRAS). Rosella flowers are known to contain high amounts of organic acids such as citric acid, malic acid, tartaric acid, oxalic acid, and hibiscus acid. Apart from having natural acid content, rosella flowers also contain vitamins (ascorbic acid) and are rich in natural red pigment dyes from the anthocyanins that can be an added value for the glucose syrup products. Organic acid extraction of dried rosella flowers was carried out at a temperature of 100°C for 30 minutes in a water bath and filtered. The resulting acid extract then determined the value of the total titrated acid (TTA) by the acid-base titration method. Sorghum starch is prepared by mixing sorghum flour with distilled water and then cooled at 4°C for 12 hours. Starch is obtained from the dried filtrate to obtain a water content of <14%. The starch hydrolysis process with rosella flower extract was carried out in several variations, namely the hydrolysis time of 1 - 4 hours, the TTA concentration of rosella 4 - 16%. Meanwhile, the temperature and stirring speed were fixed at 96°C and 200 rpm. The resulting glucose levels were analyzed by the spectrophotometric method. From this research, the result shows that the best sorghum starch hydrolysis condition was obtained at the addition of 16% acid extract for 180 minutes which gave 13.83% of glucose yield