Effects of different pre-treatments of granular rice starch using ethanol (ET) and maltogenic α-amylase (MA), separately or combined sequentially ET→MA, were performed to enable efficient subsequent modification with branching enzyme (BE). The pre-treated samples were characterized with respect to morphology, molecular structure, physicochemical properties and the rate of digestion to amylolytic enzymes. MA produced pores and also eroded the granular surface whereas ET caused coapted granules, noticeable swelling but no pores. Crystallinity and enthalpy of gelatinization dramatically decreased with ET and ET→MA. Subsequent BE catalysis increased the specific surface area, crystallinity, α-1,6-glucosidic linkage ratio and enthalpy. BE catalyzed branching resulted in more intact granules, less swelling capacity, solubility and granular separation as compared to their control. These effects were related to reduced amylolytic susceptibility. Pre-treatment prior to BE catalysis offers an efficient alternative way to modify granular starch with different structure and properties depending on the pre-treatment protocol.
Keywords: Branching enzyme; Enzymatic modification; Ethanol-treated starch; Rice starch.
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