Studies on physical, mechanical, and industrially relevant properties of spray-dried dairy systems

Engineering properties of food solids are highly dependent on their physical state, i.e. amorphous, crystalline, or liquid. Understanding glass transition-related relaxations and their coupling with engineering properties of food materials is highly essential. The present study investigated the physical and mechanical properties of two model dairy solids systems: (i) lactose/milk protein isolate (MPI) solids systems produced by a laboratory scale spray dryer and a pilot scale spray dryer, respectively; (ii) lactose/whey protein isolate (WPI) (4:1) mixtures pre-crystallised before spray drying. Dairy solids with smaller size particles showed lower glass transition temperatures (Tg) after equilibration at 0.11-0.33 aw. For lactose/WPI (4:1) mixtures with different crystallinity, increasing the amount of crystalline lactose had no significant influence on the glass transition temperatures and the initial crystallization temperatures at 0.11-0.44 aw. The present study also investigated the flow properties of two dairy-based solids systems: (i) lactose/MPI solids systems; (ii) lactose/WPI solids systems pre-crystallized before spray drying. Lactose/MPI mixtures with higher lactose contents showed better flowability at 0 and 44% relative humidity (RH). For pre-crystallization systems, flow function tests indicated that dairy solid with 11.2% crystallinity was more easy-flowing than lactose/WPI mixtures with 1.0, 29.2 and 46.8% crystallintiy. At last, the effect of formulation on encapsulation properties and flavor release of amorphous matrix was studied. Firstly, lactose/WPI (4:1, 1:1, and 1:4) mixtures, or WPI were used as wall systems. Wall material consisting of lactose/WPI (4:1) mixture had significantly (P < 0.05) higher encapsulation efficiency. Then, the encapsulation properties of dairy solids using lactose/WPI (4:1) or lactose/maltodextrin (MD)/WPI (3:1:1 or 1:3:1) mixtures as wall systems were determined. Wall systems consisting with lactose/MD (13-17)/WPI (1:3:1) mixtures and lactose/MD (23-27)/WPI mixtures had higher flavor retention than other wall systems after equilibration at high water activity (≥ 0.54 aw)