Rheological characterisation of long- and short-mixing flours based on stress-relaxation

Mixing characteristics, descriptive rheological measurements, and stress re laxation behaviour of flour water doughs from a diverse range of Canadian h ard common wheat cultivars were investigated. When mixed in a mixograph, fl ours from two varieties and two breeding lines in the Canada Western Extra Strong (ES) breeding trials required longer rime (6-8 min) and higher work input (270 350 Arbitrary Units) to mis to peak dough resistance PDR than mo derately strung to strong bread wheats (MS) (2.5 min and 110 120 AU). Exten sigraph maximum resistance to extension (R-max/E ratio) and alveograph P/L (tenacity to length ratio) values were higher for doughs from ES cultivars than for MS cultivars. Flour-water doughs from ES cultivars exhibited highe r G' and G ", and lower tan delta values than those from MS cultivars at al l frequencies. Doughs from ES cultivars exhibited slower relaxation rates t han exhibited by MS. Doughs from ES cultivars exhibited characteristic bimo dal relaxation spectra, which appeared to represent two discrete spectra se parated by time. In contrast, doughs from MS cultivars exhibited only one p rominent peak at about 0.1 s, with the second peak reduced it, a shoulder. Adding cysteine (30 ppm) to flour-water mixtures of two ES cultivars reduce d mixograph mixing times to 2.5 min. The ES doughs with added cysteine exhi bited relaxation behaviour similar to that of MS doughs without added cyste ine. This suggests that high molecular weight glutenins are primarily respo nsible for the longer mixing times of ES cultivars, and the characteristic second peak in their relaxation spectra. Relaxation behaviour of all doughs examined was positively correlated with mixograph mixing time. extensigrap h R-max/E, alveograph P/L, and mixing energy and mixing time obtained by a long and a short bread-making process. However, the stress relaxation data demonstrated Ilo simple correlation to loaf volume, because all of the cult ivars had sufficient strength to produce high quality bread when dough was optimally developed. The stress relaxation measurements differentiated betw een overly strong (ES) cultivars, and cultivars that have mixing requiremen ts that are more suitable for overall bread-making performance (MS). Stress relaxation results also appeared to reflect expected qualitative differenc es in the underlying molecular weight distribution of glutenin polymers whi ch relate to dough strength. (C) 2000 Academic Press.