Effect of Calcium and High Pressure Treatment on Soy Protein Gelation Properties

FRANCISCO SPERONI; STEPHANIE JUNG; MARIE DE LAMBALLERIE

Le Mans Francia

Congreso; Twelfth Food Colloids Conference; 2008

Gelation is a very important functional property of soy storage proteins (b-conglycinin and glycinin). High pressure treatment (HPT) is an emerging non thermal technology which stabilizes food, but modifies the structure of proteins, thus their behaviour in foods. Calcium addition to soy protein is an important topic for increasing the nutritional value and for changing protein properties due to specific interactions. In this work the effect of calcium addition, HPT and their combination on soy protein thermal gelation were studied by rheology, gel filtration chromatography and DSC. Experiments were carried out on soy protein isolates (SPI), a b-conglycinin enriched fraction (7SEF) and a glycinin enriched fraction (11SEF). It was found that calcium addition increased the temperature of denaturation (Td) while decreased the temperature of gelation (Tg), suggesting that calcium allowed interactions between polypeptides whit a minor degree of denaturation. The magnitude of changes in Tg and Td were different in the three products, indicating that the effect of calcium was dependent on the proportion of b-conglycinin and glycinin. The value of elastic modulus at the end of the thermal cycle (G’e) was evaluated, revealing that calcium enhanced this parameter in the three analyzed products. The HPT previous to thermal cycle strongly diminished Tg of the three dispersions without or with calcium, suggesting that a three dimensional network began to be formed from the partially high-pressure-denatured proteins. G’e exhibited different behaviours depending on the nature of proteins and presence of calcium: G’e decreased if HPT was carried out in calcium absence; while in calcium presence, G’e was enhanced for the products that contained b-conglycinin (SPI and 7SEF), but not for the 11SEF. Glycinin has a different mechanism of high pressure denaturation that b-conglycinin in the presence of calcium due to its higher affinity for this ion. The results of gel filtration chromatography shown that in the calcium added SPI and 7SEF the HPT produced aggregates with a very broad distribution of molecular weights. It is likely that these aggregates were able to re-arrange and form a stronger network conducting to higher values of G’e. These results indicate that calcium and HPT strongly affected aggregation, thermal and rheological properties of soy proteins. The effects of high pressure on calcium added proteins were different for the two soy globulins and the three studied products SPI, 7SEF and 11 SEF, reflecting differences in structure and calcium affinity.