42 Characterization of the strength of doughs using small strain rheological measurements.

S. J. MULVANEY (1), C. Lee (1), V. K. Rao (1), D. Peressini (2), N. M. Edwards (3), and J. E. Dexter (3). (1) Cornell University, Dept. of Food Science, Ithaca, NY 14853; (2) Udine University, Dept. of Food Science, via Marangoni 97, 33100 Udine, Italy; (3) Grain Research Laboratory, Canadian Grain Commission, Winnipeg, Manitoba R3C 3G8.

Doughs from four varieties of Canadian bread wheats of differing strength were evaluated using stress relaxation (SR) and creep testing. Cultivars represented the following Canadian grain classifications: CWES (ES12), CWRS (Neepawa), CPS-R (HY 443) and CPS-W (SWS238). For SR, doughs were mixed in a 35g mixograph, rested and evaluated in a Bohlin VOR-M rheometer. For creep, a Rheometrics SR500 rheometer was used. Creep tests were characterized by the steady state viscosity and compliance, J(o). The most significant SR parameter for the stronger doughs appeared to be the 75% relaxation time t(75), which was about 50s, 13.4s and 5s for ES12, Neepawa and HY443, respectively. This parameter was highly correlated with mixing time and positively correlated with extensigraph and alveograph measurements. The same trend was found for t(75) for hydrated glutens (60% MC) obtained from these three cultivars. These results were generally consistent with the viscosities obtained from creep testing, where the viscosity of the ES12 dough was about twice that of HY443 at the same absorption (60%). Both ES12 and Neepawa glutens showed a prominent second maximum at longer times in the SR spectrum, which was reduced to a shoulder for the HY443 and SWS238 cultivars. Proximate analysis and SE-HPLC indicated differences in both the total protein and proportions of gluten proteins for these cultivars, which may help explain differences in strength.