Effects of calcium and pressure treatment on thermal gelation of soybean protein.

The effect of calcium and high-pressure (HP) treatment on the heat gelation of soybean proteins was investigated. In the presence of calcium (2 to 25 mM), the gelation of dispersions of soybean protein isolate (SPI), a beta-conglycinin-enriched fraction (7SEF), and a glycinin-enriched fraction (11SEF) started with protein having a lower degree of denaturation. The gels from these dispersions had greater stiffness than the samples without added calcium. HP treatment had different effects on heat-induced gelation depending on the presence of calcium and on the nature of the proteins. In the absence of calcium, gels with low stiffness were formed after HP treatment, compared with untreated samples, and regardless of the sample type (SPI, 7SEF, 11SEF). In the presence of calcium, gel stiffness was increased after HP treatment of dispersions containing beta-conglycinin (SPI and 7SEF), while the opposite effect was observed for 11SEF. In the presence of calcium, HP treatment promoted a greater contribution of hydrophobic interactions in SPI and 7SEF. In the dispersions containing beta-conglycinin, these conditions also promoted the appearance of a heterogeneous distribution of molecular sizes, from enormous aggregates to dissociated species. Our results suggest that, in the presence of calcium, HP treatment has an opposite effect on the ability of glycinin and beta-conglycinin to participate in the formation of a 3-dimensional network upon heating.

Optimization of gluten-free formulations for French-style breads.

The formulation of gluten-free bread, which will be suitable for patients with coeliac disease, was optimized to provide bread similar to French bread. The effects of the presence of hydrocolloids and the substitution of the flour basis by flour or proteins from different sources were studied. The added ingredients were (1) hydrocolloids (carboxymethylcellulose [CMC], guar gum, hydroxypropylmethylcellulose [HPMC], and xanthan gum), and (2) substitutes (buckwheat flour, whole egg powder, and whey proteins). The bread quality parameters measured were specific volume, dry matter of bread, crust color, crumb hardness, and gas cell size distribution. Specific volume was increased by guar gum and HPMC. Breads with guar gum had color characteristics similar to French bread. Hardness decreased with the addition of hydrocolloids, especially HPMC and guar. Breads with guar gum had the most heterogeneous cell size distribution, and guar gum was therefore selected for further formulations. Bread prepared with buckwheat flour had improved quality: an increased specific volume, a softer texture, color characteristics, and gas-cell size distribution similar to French bread. Bread with 1.9% guar gum (w/w, total flour basis) and 5% buckwheat flour (of all flours and substitutes) mimicked French bread quality attributes.