Rennet coagulation properties of heated milk

Authors

• J. A. Lucey Department of Food Chemistry, National Food Biotechnology Centre, University College, Cork, Ireland and Teagasc, National Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Ireland
• C. Gorry Teagasc, National Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Ireland
• P. F. Fox Department of Food Chemistry, National Food Biotechnology Centre, University College, Cork, Ireland

DOI: https://doi.org/10.23986/afsci.72659

Abstract

Heating impaired the rennet coagulation properties of milk which deteriorated further during storage, i.e. rennet hysteresis occurred. Acidification to pH values ≤ 6.2 or addition of low concentrations of CaCl2 greatly improved the rennet coagulation properties of heated milk. Acidification of heated milk to pH values < 5.5 followed by neutralization to pH 6.6 to produce reformed micelles, resulted in greatly improved rennet coagulation properties except for severely heated milks (120°C for 10 min) which were not coagulable even after acidification/neutralization. Acidification of heated milk to pH values < 5.5 and storage at the low pH for 24 h before neutralization resulted in a further improvement in the rennet coagulation properties. Dialysis of heated milk that had been acidified and reneutralized against an excess of normal milk resulted in a dramatic deterioration of its rennet coagulability. Reheating milk that had been heated, acidified and reneutralized resulted in little change in RCT or gel firmness. Addition of heated milk to raw milk resulted in an increase in RCT of the latter and a reduction in gel firmness.