Properties of acid casein gels made by acidification with glucono-δ-lactone.: 1.: Rheological properties

The effects of gelation temperature (20, 30 or 40 degrees C), assay temperature, concentration of glucono-delta-lactone (GDL) added, and NaCl concentration on the rheological properties of acid casein gels were studied at small and large deformations. Gels prepared at a high incubation temperature had very low storage moduli (G'), whereas those made at a low incubation temperature had extremely high G' values. A higher 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 formed 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 frequency; 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 increased. Fracture stress (sigma(fr)) of gels formed at 20 degrees C was much 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.