Rheological properties of milk gels made with coagulants of plant origin and chymosin

The rheological properties of milk gels made using coagulants obtained from the plants Cynara cardunculus L. and Cynara humilis L. were compared with those of fermentation-produced chymosin, using dynamic low amplitude oscillation as well as large strain (yield) testing. Gelation experiments were performed at 32°C using skim milk powder that had been reconstituted for 2 or 16 h at 32°C. The storage modulus (G′), loss tangent (
tanδ
) at low frequency (0.002 Hz) and yield stress were higher for chymosin-induced gels than those of plant coagulants, when tested ∼6 h after coagulant addition. Plant coagulants were slightly more proteolytic than chymosin, and casein hydrolysis may have resulted in lower gel firmness. Most of the rheological properties were similar for the two plant coagulants, in agreement with their similar enzyme contents. Gelation properties were different in milk reconstituted for 2 or 16 h. This behaviour was probably due to casein hydrolysis by plasmin, as milk reconstituted for 16 h at 32°C had significant levels of degradation of both αs- and β-caseins. The addition of soybean trypsin inhibitor which inhibits plasmin activity resulted in similar gelation profiles for gels made from milk reconstituted for 16 and 2 h