The factors responsible for the poor breadmaking quality of the high yielding wheat cultivar, Maris Huntsman, have been studied by fractionation of its flour, followed by reconstitution and small scale test baking. Interchange of components with those from quality Canadian Western Red Spring (CWRS) wheat demonstrated the unique importance of the gluten component. Further fractionation revealed that the proportion of 'residue protein', i.e. protein insoluble in lactic acid solution, was much lower in Maris Huntsman than the CWRS. However, no improvement in quality resulted when this deficiency was overcome by the addition of extra residue protein derived from Maris Huntsman. Other studies involving interchange of Maris Huntsman and CWRS gluten components showed that there is a lack of quality in both the lactic acid-soluble and -insoluble components of Maris Huntsman gluten.
Wheat gliadin has been y-irradiated under nitrogen with a dose of 20 Mrad. No significant changes were observed in the amino acid analysis, chymotryptic fingerprints, or elution curves from Sephadex G-200. Discrete bands had been largely replaced by tailing in the starch-gel electrophoretic pattern. It is concluded that random bond scission has occurred, chiefly altering the side chains, and to some degree protein fragments have been grafted on to other sites. There is no definite evidence for the formation of macromolecular structures by inter-protein crosslinks. On average it is likely that of the order of only one or two bonds per molecule were affected.
IlltrOdUCtiOnThe production of free radicals is one of the effects of substantial doses of y-radiation on dry proteins. According to Singh & Ormerod the radicals are locaiised on certain preferred sites, probably glycine or cystine.1 The possibility of polymerisation of flour proteins by y-rays was suggested by Maes.2 Lee reported protein and starch breakdown and a deterioration in dough properties when flour was y-irradiated.3-5 The results of Deschreider6 indicated a decrease in the glutenin fraction and an increase in starch solubility on y-irradiation.This paper describes attempts to deduce the nature of changes in gliadin proteins induced by y-rays.
Experimental Preparation of gliadinPurified Wichita gliadin, prepared as described earlier,7 was run for 16.5 h in an LKB 3340C column electrophoresis apparatus. The column was packed with Pevikon C-870 powders as a supporting medium. Dilute sodium lactate (pH 3 '3) was the buffer used, and a potential of 300 V was applied between the electrodes. The eluted fractions were dialysed vs. 0.01 N acetic acid and freeze-dried. Fractions showing no sign of glutenin on starch-gel electrophoresis were combined.
IrradiationThe glutenin-free gliadin (200 mg), contained in a specimen tube which had been closed with a rubber bung after evacuation and flushing with nitrogen (< 10 ppm OZ), was irradiated to a level of 20 Mrad over 154 h from a SOCo source at Leicester University.
Starch-gel electrophoresisThis was carried out as described previo~sly.~ Proteins were reduced as follows: 0.5 ml of 0.067 M phosphate buffer pH 7.4,2.5 % in mercaptoethanol and 6 M in urea was added to > 9 mg of protein in a tube, which was flushed with nitrogen, closed and allowed to stand for 24 h. The pH of the solution was changed by dialysing overnight against dilute sodium lactate buffer9 containing similar levels of urea and mercaptoethanol. To make gels suitable for electrophoresis under reducing conditions, 70 g of starch, suspended in 500 ml of dilute sodium lactate buffer 6 M in urea, were heated with stirring for 4.5 min and a further 50 ml of solution containing 15 ml of mercaptoethanol were added just before the liquid was poured. Electrophoresis was carried out for 20 h at N 7V/cm.
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