Production of high‐fructose rice syrup and high‐protein rice flour from broken rice

Abstract

AbstractThe objective of this study was to develop a process for the production of both high‐fructose rice syrup and high‐protein rice flour from broken rice. The rice flour was obtained from broken rice by using either a dry or wet milling method. The glucose produced from the slurry of various raw materials by treating with α‐amylase and glucoamylase was compared. Results indicated that cassava and corn starch were better raw materials than rice flour. However, the filtered residue of liquefied rice slurry could be recovered as high‐protein rice flour. The particle size of rice flour had a small effect on the glucose yield. The orthogonal‐array table (L27) method of experimental design was employed to determine optimum conditions for liquefaction. The glucose yield based on starch was 90.8±3.6% under the following optimum conditions α‐amylase, 0.12%; rice flour, 20%; temperature, 96°C; time, 90 min. The filtrate from liquefied rice slurry was saccharified at 60°C with three different concentrations of glucoamylase. The higher the enzyme concentration, the shorter the time required to reach the maximum yield. After saccharification, the glucose solution was decolourised, desalted and concentrated to 40% d.s. and then isomerised to fructose at 60°C under continuous operation by using immobilised glucose isomerase packed in a column. The isomerised syrup was then purified and concentrated to 71% d.s. The final high‐fructose rice syrup contained 50% glucose, 42% fructose and 3% maltose. After liquefaction, the rice slurry was centrifuged and the precipitate was dried by either spray or drum drying. The composition of these two high‐protein rice flours was almost the same and the protein content was about three times as high as the raw material. There were significant differences in surface structure of rice flour and high‐protein rice flours, as observed by the scanning electron microscope.