Effect of partial hydrolysis with an immobilized proteinase on thermal gelation properties of beta-lactoglobulin B

We have investigated the influence of partial hydrolysis with an immobilize d proteinase from Bacillus licheniformis on the thermal gelation of isolate d beta -lactoglobulin B. Gelation behaviour was determined by dynamic rheol ogical measurements (small deformation) and the gels were characterized wit h respect to microstructure and water-holding properties. A fine-stranded g el with a complex modulus of similar to 2000 Pa was formed from beta -lacto globulin (50 g/l in 75 mM-Tris-HCl, pH 7.5). Limited hydrolysis prior to th ermal gelation resulted in coarser gels with thicker protein strands and la rger pores. Gel structure correlated with its permeability, proton mobility and water-holding capacity. Total gel stiffness increased with low degrees of hydrolysis, but decreased after prolonged hydrolysis. Maximal gel stiff ness was 1.5-fold that of gels made from unhydrolysed beta -lactoglobulin. This was much lower than the stiffening effect obtained after partial hydro lysis of whey protein isolate, showing that the gel strengthening effect of partial hydrolysis was dependent on the protein composition and/or the hyd rolysis and gelation and gel properties is presented.