Abstract:

Ultrasound-assisted enzymatic hydrolysis was utilized for the pretreatment of brown rice. The 3-factor 3-level
response surface analysis was designed using temperature, ultrasound processing time and enzyme concentration as the
independent variables, and using total sugar content after brown rice pretreatment, brown rice germination percentage,
and γ-amiobutyric acid (GABA) content of germinated brown rice as the response values through central composite
design model. At the same time, the effect of pretreatment on the physicochemical properties of germinated brown rice
such as GABA content, total content of phenols, amylase activity, gelatinization viscosity and texture characteristics of
cooked rice was investigated. Results indicated that both processing temperature and time had significant effects on rice
germination percentage and GABA content. Treatment time of 0.71 h, temperature of 31.21 ℃, and enzyme concentration
of 0.28 g/L could result in the optimal germination percentage with the predicted maximal germination rate of 91.98%. The
predicted maximal GABA content could be up to 38.25 mg/100 g after pretreatment for 0.5 h at 35.65 ℃ with an enzyme
concentration of 0.22 g/L. Based on physical and chemical properties of germinated brown rice, the ultrasound-assisted
enzymatic pretreatment is beneficial to the enrichment of GABA, but unfavorable to the accumulation of total phenols. This
pretreatment could effectively enhance the activity of endogenous amylase, accordingly reducing the pasting viscosity of
germinated brown rice and its hardness after cooking.

Key words: ultrasound, enzyme, germinated brown rice, physicochemical property