Rheological Properties of Rennet Gels Containing Milk Protein Concentrates

Schematic of treatments applied during the dispersability test for milk protein concentrate.

Particle size distribution (volume % vs. diameter) of a commercial milk protein concentrate (MPC90) dispersed under selected treatment combinations. Powders dispersed at 20°C (A) for 1h; 3h; 1h and 5min of shear (1h + s); 1h and 5min of shear and overnight storage at 4°C (1h + s + o); or (B) dispersed for 1h at 20°C and then heated at 40°C for 30min (1h + 40°C); 1h at 20°C and then heated at 60°C for 30min (1h + 60°C); 3h at 20°C and then heated at 60°C for 30min (3h + 60°C); 1h at 20°C, heated at 60°C for 30min, and then sheared for 5min (1h + 60°C + s). Distributions shown are the average of 2 replicate experiments.

Elution profiles of centrifuged supernatant of reconstituted skim milk powder (SM) or commercial milk protein concentrates (MPC56, MPC70, MPC90; 5% protein) dissolved in water for 1h and then heated at 60°C for 30min and sheared for 5min.

Storage modulus, G′ (right axis, solid symbols), and CN macropeptide (CMP) release (left axis, open symbols) as a function of time for rennet gels made from commercial milk protein concentrates MPC90 (▴▵), MPC70 (■□), and MPC56 (●○) reconstituted in water (5% protein). Values are the average of 3 replicate experiments. The CMP values are shown as percentages of CMP (CMP_t/CMP_∞, where CMP_∞ is the amount of CMP released at plateau from skim milk powder reconstituted at 5% protein). Dotted lines denote gelling points.

Sodium dodecyl sulfate-PAGE of centrifugal supernatants under reducing (lanes 1 to 6) and nonreducing (lanes 7 to 10) conditions for dispersions of commercial milk protein concentrates MPC56 (lanes 1 and 7), MPC70 (lanes 2 and 8), and MPC90 (lanes 3 and 9), and skim milk powder (lanes 4 and 10). Lanes 5 and 6 are sodium caseinate and whey protein isolate standards.

Effect of the reequilibration by dialysis of milk protein concentrate (MPC) dispersions against reconstituted skim milk (5% protein). Sodium dodecyl sulfate-PAGE of centrifugal supernatants of MPC56 (lanes 1 and 7), MPC70 (lanes 2 and 8), and MPC90 (lanes 3 and 9) before (lanes 1 to 3) and after (lanes 7 to 9) dialysis conditions. Lane 4: centrifugal supernatant of reconstituted skim milk powder; lanes 5 and 6: sodium caseinate and whey protein isolate standards, respectively.

Storage modulus, G′, as a function of time for rennet gels made from milk protein concentrate (MPC) or skim milk powder in water (5% protein solutions) that had been given heat treatment 60°C and shear (A) and dialyzed (B). Values are taken from representative master curves of 3 replicates.