Effects of reverse CO2 acidification cycles,calcium supplementation,pH adjustment and chilled storage on physico-chemical and rennet coagulation properties of reconstituted low- and medium-heat skim milk powders

The reversibility extent of one and two reverse CO₂ acidification cycles on the physico-chemical and rennet coagulation properties of milks reconstituted from low- (LH) or medium- (MH) heat skim powder, enriched or not with calcium and pH adjusted or not was investigated. The ionized calcium concentration, buffering properties and average casein micelle size of untreated and CO₂-treated milks were evaluated before and after a chilled storage for 2 days. The ionized calcium concentration and buffering properties have been modified by the CO₂-treatment, particularly after a second CO₂-cycle. These modifications were highly dependent on the initial milk properties and chilled storage. Inversely, the average casein micelle size was not significantly changed. In addition, the rennet-clotting behaviour checked by near infrared spectroscopy (NIR-S) and rheology (SAOR) indicated the main factors responsible for changes in the casein micelles environment and dynamic casein micellar calcium phosphate reorganization, especially after two CO₂-cycles. A single CO₂-cycle induced a better rennetability for non Ca-enriched milk reconstituted from MH-powder. A second CO₂-cycle was particularly efficient to improve Ca-enriched pH-adjusted milks.