Optimisation of some technological factors of pretreatment by pullulanase enzymatic hydrolysis combined with hydrothermal process to produce resistant starch (RS3) from rice flour ingredients

Abstract

The purpose of the study was to conduct a multi-factor experiment and optimise some technological factors of pretreatment by pullulanase enzymatic hydrolysis combined with hydrothermal process to produce resistant starch (RS3) from rice flour of IR50404 paddy variety. The multi-factor experimental plan used the Box-Behnken planning model with 3 independent variables corresponding to the variation range: pullulanase enzyme concentration (1.5-2.5%); hydrolysis temperature (52-58^oC), hydrolysis time (8-12 hours). The objective functions include: RS3-resistant starch content (%), reducing sugar content (%), and solubility (%). The experiments were conducted under the same conditions with the parameters determined from single-factor experiments: Prepare enzymatic hydrolysis solution with rice starch/water concentration of 15% at pH 5.5; hydrothermal mode includes 3 heat treatment/cooling cycles: autoclaving (130^oC, 60 minutes) → cooling and storage time (4^oC, 18 hours). Experimental data processing and optimisation used Design - Expert 7.1 software with expected function algorithm with the desire that the RS3-resistant starch content, reducing sugar content and solubility reach their maximum values, corresponding to the important coefficients of 5/5, 4/5, and 4/5. The results were the determination of the optimal enzymatic hydrolysis pretreatment regime with pullulanase enzyme concentration of 2.2%, hydrolysis temperature of 54.4^oC for 10.4 hours, corresponding to RS3 resistant starch content reached 47.58±0.22%, reducing sugar content reached 14.12±0.08%, and solubility reached 68.52±0.18% after hydrothermal process.