Characterization of curd formation during the rennet coagulation of milk by an optical microscopic method

Abstract

Optical microscopic observation of the coagulation of rennet-treated milk was performed using a conventional light microscope under standardized conditions. The microscopic images, i.e., number and average area of milk aggregates, were analyzed using Optiscan software. The evolution of the latter parameters was followed as a function of the rennet coagulation time of milk. The curves presented two inflection points which correlated with the rennet flocculation time and the rennet clotting time values, as determined by reference methods. These relationships were validated on milk supplemented with different concentrations of calcium (5.0-7.5mM) and subjected to varying temperatures for rennet coagulation (22.5-40°C). This optical microscopic method with associated image analysis software allowed (i) the observation of structural changes occurring during gel formation, even at low magnification (200X) and (ii) the determination of the rennet flocculation and clotting times. © 2004 Elsevier Ltd. All rights reserved.