PROPERTIES OF ACID CASEIN GELS MADE BY ACIDIFICATION WITH GLUCONO-DELTA-LACTONE - 1 - RHEOLOGICAL PROPERTIES

The effects of gelation temperature (20, 30 or 40 degrees C), assay te mperature, concentration of glucono-delta-lactone (GDL) added, and NaC l concentration on the rheological properties of acid casein gels were studied at small and large deformations. Gels prepared at a high incu bation temperature had very low storage moduli (G'), whereas those mad e at a low incubation temperature had extremely high G' values. A high er concentration of GDL resulted in faster gelation but slightly lower G' values of aged gels. Addition of NaCl resulted in longer gelation times and a slower rate of increase of G'. Cooling of gels prepared at 30 or 40 degrees C resulted in an increase in G'. However, for gels f ormed at 20 degrees C, G' decreased initially on cooling but returned to its original value on holding at 5 degrees C. The loss tangent (tan delta) of gels formed at 20 or 30 degrees C was independent of freque ncy; however, for gels formed at 40 degrees C, tan delta was lower at low frequencies. As gels were cooled to 5 degrees C, tan delta increas ed. Fracture stress (sigma(fr)) of gels formed at 20 degrees C was muc h greater than that of the gels formed at higher temperatures. Heating gels to temperatures higher than the gelation temperature resulted in a decrease in sigma(fr). At low gelation temperatures, young gels had very high sigma(fr) values. (C) 1997 Elsevier Science Ltd. All rights reserved.