The dependence of wheat quality tests on protein level — a comparative study of some Australian varieties

Abstract

Six commonly used wheat quality tests – baking performance, water absorption, dough development time, Valorimeter number, extensibility, and resistance to extension – have been examined for their abilities to characterise and discriminate among wheat varieties. Twelve Australian varieties are considered over a wheat protein range of 7.5–14.5 per cent. The recovery of wheat protein in the flour was also examined for their of the varieties. Except for resistance to extension, the tests showed a positive linear relationship of test measurement to log protein per cent, so that varieties were characterised for each of these tests by a pair of constants, a and b, where a is the average varietal value of the test property at 11.0 per cent wheat protein and b the average change in its value 46 per unit change in log protein per cent. The tests differ markedly in the extent and manner in which varieties are discriminated, baking performance being the most striking, in that the varieties are separated in two dimensions-level of performance (a) and sensitivity of performance to changes of protein content (b). Farinograph measurements discriminate primarily in the dimension of level performance for water absorption most of the varieties have approximate the same b values, while for dough development time and Valorimeter number the b values are positive and linearly related to the a values. For extensibility, varieties differ widely in both their a and b values but no clear pattern emerges, while for resistance to extension only differences in level of response occur. In most cases, the tests clearly distinguish between the hard and so) varieties, and within these groups suggestions are made and specifications are described for variety quality standards.