COMPARATIVE-STUDIES OF HIGH M(R) SUBUNITS OF RYE AND WHEAT .1. ISOLATION AND BIOCHEMICAL-CHARACTERIZATION AND EFFECTS ON GLUTEN EXTENSIBILITY

The structural features of high M(r) glutenin subunits of wheat were c ompared with those of analogous proteins from rye. Subunits of two rye cultivars (Danko and Halo) and of the wheat cultivar Rektor were isol ated from defatted flours by extraction with 50% (v/v) aqueous propan- 1-ol under reducing conditions at 60 degrees C followed by precipitati on using a 60% concentration of propan-1-ol. The yields of dialysed an d freeze-dried subunits were 0.33% and 0.32% (w/w of flour), respectiv ely (rye cultivars), and 0.91% (Rektor). SDS-PAGE revealed that the ry e cultivars contained at least five subunits with mobilities correspon ding to the x-type subunits of wheat. Separation by RP-HPLC indicated that the rye cultivars did not differ in the qualitative composition o f subunits, but in their quantitative proportions. The surface hydroph obicities of the rye subunits were significantly lower than those of w heat subunits. The amino acid compositions of single rye subunits were characterised by high contents of Glx, Gly and Pro, and they were clo sely related to those of wheat subunits, except that the Glx content w as generally lower and the Cys content higher. Notable differences bet ween rye and wheat subunits were found in their contributions to glute n strength. Whereas wheat subunits, reoxidised with potassium bromate and mixed with a standard wheat flour, caused a significant increase i n gluten strength, reoxidised rye subunits had the opposite effect. (C ) 1996 Academic Press Limited