Modelling the contribution of alpha-amylase, beta-amylase and limit dextrinase to starch degradation during mashing

Response surface methodology was used to determine the levels of alpha-amyl ase, beta-amylase and limit dextrinase enzymes required for efficient conve rsion of starch to fermentable sugars during mashing. Micro-scale mashes wi th purified barley starch and malt enzymes were performed in a Brewing Rese arch Foundation mash bath, and mash liquors were analysed for solubilised s tarch, reducing sugars (neocuproine assay) and fementable sugars (anion exc hange HPLC). Fermentable sugars in the mash liquor were positively correlat ed with reducing sugars (R-2=0.94) and the percentage of starch solubilised during mashing (R-2 = 0.68). A multiple regression equation relating the l evels of the three starch degrading enzymes to the percentage of starch hyd rolysed to fermentable sugars gave a good fit to the second order response surface (R-2 = 1.00, RMSE = 1.37%). Addition of limit dextrinase to the mas hes resulted in a substantial increase in levels of fermentable sugars, and limit dextrinase showed a synergistic effect in increasing levels of malto se in the mash liquor when combined with high levels of beta-amylase. The e fficiency of any one starch degrading enzyme in a mash is influenced by the presence of other starch degrading enzymes. Commercial malts contain exces s levels of beta-amylase and below optimal levels of limit dextrinase. Malt extract may not be a good indicator of the level of fermentable carbohydra tes produced during mashing. (C) 1999 Academic Press.