Seasonal variation in the rheological properties of acid and heat-induced gels made from reconstituted concentrated milk

The rheological properties of chemically acidified concentrated milks (20% milk solids non-fat, MSNF) reconstituted from high-heat milk skim milk powder (SMP) manufactured over a three-year period were studied using small strain oscillatory measurements and compression testing. Milk gels (pH 5.3-5.4) were made by addition of glucono-delta-lactone (GDL) to reconstituted concentrated milks (20% MSNF) at a level of 0.05 g GDL/g MSNF and heating the mixture under quiescent conditions at 60 degrees C. There were differences in the rate of gelling, gel strength and viscoelastic properties of gels made from SMP produced at different times of the year. Gels made from SMP manufactured during late lactation had lower gel strength and took longer to gel compared to those made from SMP produced at other stages of lactation. Gels made from SMP produced in mid-lactation were more elastic than those made from SMP produced in late lactation.