ABSTRACT
Molecular weight distribution of wheat proteins is primarily responsible for the viscoelastic properties of flour dough. Furthermore, the amount of SDS insoluble proteins (mainly high molecular weight glutenin) plays the major role. We have developed a simple test to determine the swelling power of glutenin (swelling index of glutenin or SIG) for predicting dough properties and end-use quality. Flour samples (40 mg) were hydrated in distilled water and then allowed to swell in nonreducing solvents (SDS, lactic acid, or mixtures of the two) followed by low speed centrifugation. The SIG was calculated as the weight of the residue divided by the original sample weight. The SIG test was compared with the results from other small-scale tests for 20 flour samples. SIG tests showed highly significant correlations with the gel protein and insoluble glutenin test (r ≥ 0.85, r ≥ 0.93, P < 0.001, respectively) and significant correlations with SDS and Zeleny sedimentation tests (r ≥ 0.74, r ≥ 0.72, P < 0.001, respectively). The swelling capacity of glutenin depended on swelling time and mixing intensity in nonreducing solvents. Swelling curves obtained from SIG values versus different swelling time can be divided into three distinct stages: swelling, swollen, and breakdown. These stages may reflect soluble and insoluble glutenin contents and quality among different cultivars. SIG test values for short swelling time and low mixing intensity were significantly correlated to gel protein content and SDS-sedimentation values (r = 0.96, r = 0.90, P < 0.001, respectively). SIG test values for long swelling time and high mixing intensity were significantly correlated to insoluble glutenin content (r = 0.96, P < 0.001). The difference of swelling condition (time and mixing intensity) among these small-scale methods is the reason for their different correlations with insoluble glutenin content. Because large numbers of samples can be analyzed in a short time with excellent reproducibility, the SIG test may be a useful screening test in a breeding program, predicting the quantity and quality of insoluble glutenin.
