Effect of alpha-amylase hydrolysis on reducing sugar and viscosity of two brown rice flours

Abstract

Brown rice flour is very attractive as an ingredient for functional food. The high viscosity of starch component can be reduced by enzymatic hydrolysis. However, there is limited information about enzyme treatment on brown rice flour. The objective was to investigate the effect of alpha-amylase hydrolysis on two varieties of brown rice flours (Sinlek rice and Jasmine rice). Both of them contain the same level of amylose content. In addition, Sinlek rice (a crossbred of Jasmine rice and Hom Nil rice) is nutritious and presents high amount of iron. Brown rice flour was prepared by milling with pin mill and then sieving (14 mesh sieve). Proximate composition and pasting profile measured by Rapid Visco Analyzer were determined to characterize the material. Alpha-amylase (Termamyl SC, 1.80 U/g and 4.40 U/g) was introduced in 20% (w/v) brown rice flour at a temperature of 90±2 ºC and hold for 90 minutes. Reducing sugar and Brookfield viscosity of the hydrolyzed products were measured. The results showed that the unhydrolyzed Jasmine brown rice flour presented higher peak, breakdown and final viscosity than another sample. On the contrary, the hydrolyzed brown Jasmine rice exhibited less viscous when comparing at the same level of α-amylase. The viscosity of the hydrolyzed product was found to have a statistically significant difference between a couple of rice varieties as well as two levels of enzyme activity. In term of reducing sugar, it was only found a significant difference in enzyme level. The present study could provide guidance for food applications i.e. beverage and instant mixes.