Amylase, falling number, polysaccharide, protein and ash relationships in wheat millstreams

Abstract

Wheat of two strong high-protein and two weak low-protein cultivars from New Zealand and Australia were milled to commercial specifications. All millstreams were tested for α-amylase, β-amylase, falling number, protein, starch, damaged starch, amylose, amylopectin, pentosan and ash. The distribution of β-amylase in millstream flours was more variable among cultivars than α-amylase. Generally, both enzymes had lowest activity in sizing and early reduction flours. α-Amylase was very high in the bran, pollard and germ fractions, in which ash content was very high, whereas β-amylase was low in these fractions. These observations, together with the moderate correlation of α-amylase and poor correlation of β-amylase to ash content, suggest that most α-amylasein flour derives from contamination with bran, pollard and germ, whereas most β-amylase derives from the endosperm. Falling numbers varied between the cultivars, but variation amongst millstreams for each cultivar was low, except for cv. Frame, which had particularly high falling number values (834 and 1197) in second and third break flours. These two flours had some of the highest α-amylase levels and lowest starch levels. However, they also had very high protein content (22 and 26%) and very low starch damage (3.2 and 4.5%), which may contribute to the high falling numbers. When endogenous α-amylase in the flour with the highest falling number was supplemented with high levels of barleyα-amylase, the flour withstood the detrimental effects of α-amylasein baking (sticky crumb, poor crumb texture and loaf volume) better than flours of lower falling number, but did not withstand the effects ofα-amylase on falling number.