Effect of heat treatment of rennet skim milk induced coagulation on the rheological properties and molecular structure determined by synchronous fluorescence spectroscopy and turbiscan

Heat treatment applied to milk induces denaturation of whey proteins, leading to a complex mixture of whey protein and whey protein coated casein micelles. The present paper investigates the effects of heat treatment (60 and 80 °C during 20 min) and rennet-induced coagulation temperature (30 and 40 °C) determined by rheology, synchronous fluorescence spectroscopy (SFS) and turbiscan measurements. The gelation times determined by rheology and SFS increased with the increase of heat treatment applied to milk. The rise in temperature induced a decrease in the maximum curd firming rate and an increase in the viscosity of the investigated milk samples. The principal component analysis (PCA) applied, sepa- rately, to the SF and turbiscan spectra showed a clear discrimination between: (i) raw milks and heated milks; and (ii) milks renneted at 30 °C from those renneted at 40 °C. The results showed the ability of SFS as a rapid and non-destructive technique for the: (i) monitoring network structure and molecular inter- action during the coagulation process; and (ii) determination of gelation time of rennet-induced coagu- lation of studied milk samples.