SDS-protein gel test for prediction of bread loaf volume

Flour dispersed in aqueous solutions of sodium dodecyl sulfate (SDS) forms a proteinaceous gel when centrifuged at high speed. The conventional methodology for SDS gel testing was modified to develop a small-scale (<1 g of flour or wheat meal) screening test for evaluation of the protein quality of wheat for breadmaking. The principal modification involved centrifugation with a swinging-bucket rotor to facilitate direct measurement of gel height, which is the primary test parameter. The effects of suspension temperature and time, centrifugation speed, sample size, and sieving of ground wheat or flour on the efficacy of the test were examined. Gel height, wet weight, and protein content were assessed as test parameters. In the standard test procedure that was developed, 0.67 g of flour or ground whole wheat was dispersed in 13.5 mL of 1.5% SDS solution for 15 min at 20 degrees C, followed by centrifugation at 80,000 x g for 30 min. The test was evaluated using seven Canadian commercial wheat flours with diverse breadmaking quality. For the samples, gel height was strongly related to loaf volume (R-2 = 0.89 and 0.95 for flour and ground wheat, respectively). Sieving flour through a 75-mu m sieve slightly increased the predictive power of the test (R-2 = 0.94). SDS gel height gave better discrimination of samples for prediction of loaf volume than did the traditional SDS sedimentation test. The performance of the sedimentation test improved when sieved ground wheat was used. The relationship between gel height or protein content and flour protein content was comparatively poor (R-2 = 0.25). The SDS gel test appears to primarily measure the effects of flour protein quality.