Rheological Aspects of the Renneting of Milk Concentrated by Ultrafiltration

Abstract

The kinetics o f clotting by rennet o f ultrafiltrated milk were studied by determining induction and clotting times, and development o f the rigidity modulus as a function o f rennet concentration and protein content in the sample. Creep compliance-time studies were conducted on the resultant gels at three different stresses. Clotting time increased with protein content and decreased with rennet concentration. The protein effect on clotting time decreased with increasing rennet concentration and was practically nil at 200 mg enzymelkg sample. The ultimate rigidity and the viscoelastic parameters o f gels depended on the protein concentration in a double logarithmic relationship. The calculated values o f the constants indicated that the viscosities were influenced to a greater degree by the protein concentration than were the elastic moduli. The renneted milk gels exhibited creep compliancetime response at low shear stresses indicative of the viscoelastic behaviour o f an interlinked three-dimensional network. Gelation followed a second order reaction in its initial stages and an approximately third order reaction in the final stage. The results are discussed in terms o f potential mechanism and type o f bonds involved. 'Now at I.N.R.A., Station de Recherches Sur La Viande, Theix, 63110

Characterization of rennet coagulation of milk concentrated by vacuum condensing and ultrafiltration

“…Also, treatments with higher protein level (C vs. CM1 or UF1 vs. CM2 or UF2) had shorter (P<0.05) T 0 . Similar results have been reported previously (Culioli and Sherman 1978). Culioli and Sherman (Culioli and Sherman 1978) also observed that the effect of protein on clotting time could be reduced to nil by changing rennet concentration.…”

“…Similar results have been reported previously (Culioli and Sherman 1978). Culioli and Sherman (Culioli and Sherman 1978) also observed that the effect of protein on clotting time could be reduced to nil by changing rennet concentration. Considering the high Mean Square value of rennet (Table 4), a similar conclusion can be deduced that the time of onset of increase in apparent viscosity (T 0 ) can be significantly modified based on rennet concentration.…”

“…A number of studies have been reported which discuss various aspects of coagulation in ultrafiltered milk (Culioli and Sherman 1978;Kameswaran and Smith 1999;Mehaia and ElKhadragy 1998). In spite of the interest of cheese manufacturers in using vacuumcondensed milk concentrates (Sandfort 1983), a little has been studied evaluating rennet coagulation behavior of vacuum-condensed and its comparison to ultrafiltered milk.…”

“…These phenomena are affected by a number of factors, such as, temperature (Kowalchyk and Olson 1977), pH (Cheryan et al 1975), heat treatment of milk (Wilson and Wheelock 1972), presence of divalent cations (Lucey and Fox 1993), protein concentration of milk (Garnot and Corre 1980), and milk concentration (Culioli and Sherman 1978;Kameswaran and Smith 1999;Mehaia and El-Khadragy 1998).…”

Computerized rheometric method for studying rennet coagulation of milk

“…TSOULIet al (1975) applied conductimetry andPARKER andDALGLEISH (1977 a, b) used the light scattering method to detect early stages of rennet coagulation of milk. CULIOLIand SHERMAN (1978) used ScoTT-BLAIRand BURNETT(1958 a) V-tube gelometer to establish the rheological properties of gelifying milk and renneted milk gels. BACHMAN et al (1978BACHMAN et al ( , 1980 used an ultrasonic viscometer to measure milk clotting activity of proteolytic enzymes.…”