The baking quality and protein characteristics of a winter wheat grown at different levels of nitrogen fertilisation

Abstract

Three samples of field-grown winter wheat (Triticum arstivum 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 su1phur: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, w-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 noticeably affected.

Importance and Effect of Nitrogen on Crop Quality and Health

“…Byers and Bolton (1979) and Wrigley et al (1980) observed that high levels of nitrogen supply and marginal levels of sulfur supply resulted in marked reductions of the concentration of cysteine and methionine. Timms et al (1981) observed the similar reductions caused by a nitrogento-sulfur imbalance induced by late-season fertilization of wheat with urea. These changes in amino acid composition affected the quality of the gluten.…”

“…These changes in amino acid composition affected the quality of the gluten. im p o r t a n c e a n d ef f e c t o f n i t r o g e n o n cr o p Q u a l i t y a n d h e a l t h 55 Timms et al (1981) found in their study that bread baked with flour containing the highest protein concentration had a lower loaf volume and a lower texture score.…”

“…The composition of amino acids in wheat protein is affected by nitrogen fertilization. Poulsson (1973) and Timms et al (1981) found that nitrogen fertilization increased the proportion of glutamine, proline, and phenylalanine in wheat protein, while threonine, serine, glycine, alanine, valine, and sulfur amino acids decreased. The balance between nitrogen and sulfur nutrition of the wheat crop also had an effect on grain amino acid composition.…”

Preliminary investigation of concentrations of minerals and nitrogen in wheat grain, and their relationship with baking quality and grain weight

“…In addition, the downturn in the effect of grain N concentration on baking score as the N level rises suggests that other factors may be involved. Such decline in the baking quality of wheat at high N levels has been related to the changes in the solubility of the glutenin (Bushuk et al 1978) and to the S : N ratios (Timms et al 1981). The data base of this present study is not large enough to examine the high N results more intensively.…”

Responses of breadmaking quality to sulphur in three wheat varieties

“…Field experiments conducted in England before 1990 showed that breadmaking quality, as measured by loaf volume, was not affected signi®cantly by the applications of S fertilisers, 8,9 probably because S de®ciency was rare at that time. However, there was some evidence that when a large amount of nitrogen (N) was applied late to wheat, the quality of gluten proteins for breadmaking deteriorated owing to an imbalance of N and S. 10 Since S de®ciency in wheat has become more common in the 1990s in the UK and other European countries, it is important that the effects of S nutrition on the breadmaking quality of ®eld-grown wheat are fully understood.…”