Assessing Malted and Adjunct Rice Potential in Diverse Rice Germplasm through Simulated Enzymatic Hydrolysis

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Abstract To elucidate the relationship between rice starch structure and amylolytic hydrolysis during brewing, five enzymes (α-amylase, β-amylase, glucoamylase, pullulanase, and isoamylase) were evaluated individually and in blends on ungelatinized and pregelatinized rice starches varying in amylose content and gelatinization temperature (GT). The resulting starch hydrolysate fraction distribution was measured by high-performance anion-exchange chromatography with pulsed amperometric detection. Under malt-like (ungelatinized) conditions, low-GT starches produced lower overall starch solubilization but higher fermentable sugars (FS), whereas high-GT starches generated greater proportions of residual dextrins and lower FS production. β-Amylase and glucoamylase drove FS production. In adjunct simulations (pregelatinized), most starch conversion generally exceeded 80%, and complete enzyme blends increased FS conversion to as high as 87%. Starch hydrolysis and FS production depended strictly on matching enzyme blends to starch structure: waxy varieties (zero-to-very low amylose) required glucoamylase-inclusive blends, whereas high-amylose (∼35–37%) starches required β-amylase. Ultimately, tailoring enzyme blends to the malt or adjunct starch chemistry may improve starch conversion and FS production while informing targeted breeding of rice varieties for brewing applications.

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