The baking quality and protein characteristics of a winter wheat triticum aestivum cultivar atou grown at different levels of nitrogen fertilization

Timms, M.F.; Bottomley, R.C.; Ellis, J.R.S.; Schofield, J.D.

Journal of the Science of Food and Agriculture 32(7): 684-698


ISSN/ISBN: 0022-5142
Accession: 006605030

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Three samples of field-grown winter wheat (T. aestivum cv. Atou) with different protein contents were produced by late application of urea as a nitrogenous fertilizer. 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 N and S available to the plants grown on this particular soil. Analysis of the flours and glutens indicated that the ratio of S:N fell as grain protein content increased; this correlated with a lower proportion of the S amino acids cyst(e)ine and methionine. Gel electrophoresis studies revealed an increase in the proportion of the S-deficient, .omega.-gliadin species as grain protein content increased. Agarose gel filtration chromatography of the flour and gluten proteins suggested a correlation between the extent of aggregation of their glutenin components (mediated by disulfide 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 fertilizer in the absence of S fertilization led to a change in the balance between available N and available S, such that the available S levels became insufficient for normal grain development. Considerable alteration in the biochemical characteristics of the flour proteins occurred before gluten baking quality was noticeably affected.