Heat-induced gelation of pea legumin: comparison with soybean glycinin

Gel network formation of pea legumin (8.4% on a protein basis, pH 7.6) was monitored via dynamic rheological measurements. Gelation was performed in the absence and presence of the thiol-blocking reagent N-ethylmaleimide, at different rates of heating and cooling. Overall, it was shown that pea legumin gel formation was not effected by changes in the heating rate, and the two differently heated samples were unaffected by the addition of 20 mM NEM, which indicated that disulfide bonds were not essential within the network strands of these legumin gels. However, slowly cooling the legumin samples caused disulfide bonds to become involved within the network; this was observed by a large increase in gel strength that was then substantially reduced when repeating the sample in the presence of NEM. These experiments were repeated with soybean glycinin in order to determine whether a common model for gel formation of legumin-like proteins could be built, based upon molecular reasoning. The two proteins were affected in the same way by changes in the conditions used, but when applying a procedure of reheating and recooling the gel networks responded differently. Pea legumin gel networks were susceptible to rearrangements that caused the gels to become stronger after reheating/recooling, yet glycinin gel networks were not. It was concluded that the same physical and chemical forces drove the processes of denaturation, aggregation, and network formation. Each process can therefore be readily targeted for modification based upon molecular reasoning. Pea legumin and soybean glycinin gel networks had structurally different building blocks, however. A model of gelation aimed at texture control therefore requires additional information.