AbstractThree samples of field‐grown winter wheat (Triticum aestivum cv. Atou) with different protein contents were produced by late application of urea as a nitrogenous fertiliser. Baking tests (a conventional fermentation procedure) indicated that the breadmaking quality of the flours increased as protein content was raised from the lowest to the intermediate level, but that the flours of intermediate and highest protein content were of equivalent breadmaking quality. To compare gluten baking quality independently of protein quantity, loaves were also baked from ‘flours’ reconstituted to equivalent protein levels using the isolated glutens. The flours of low and intermediate protein content yielded glutens of similar baking quality. The gluten derived from the flour of highest protein content gave a lower loaf volume and texture score: subsequent biochemical investigations suggested that this was due to an effect of the relative levels of nitrogen and sulphur available to the plants grown on this particular soil. Analysis of the flours and glutens indicated that the ratio of sulphur:nitrogen fell as grain protein content increased and this correlated with a lower proportion of the sulphur amino acids cyst(e)ine and methionine. Gel electrophoresis studies revealed, in particular, an increase in the proportion of the sulphur‐deficient, ω‐gliadin species as grain protein content increased. Agarose gel filtration chromatography of the flour and gluten proteins also suggested a correlation between the extent of aggregation of their glutenin components (mediated by disulphide bonds involving cystine residues) and their functional properties. The results of this study suggest that for wheat grown on this particular soil late application of high levels of a nitrogenous fertiliser in the absence of sulphur fertilisation led to a change in the balance between available nitrogen and available sulphur, such that the available sulphur levels became insufficient for ‘normal’ grain development. Nevertheless, the results indicated that considerable alteration in the biochemical characteristics of the flour proteins occurred before gluten baking quality was notic
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