Textural Properties of Acid Milk Gels: Effects of Dairy Protein Powder Rehydration State

International audienceIn this study, the effect of dried dairy ingredient rehydration state on the textural properties and microstructure of acid milk gels was investigated. The control acid gel samples were made with 12% w/w of reconstituted skim milk powder. Milk base was enriched with whey protein isolates and/or micellar casein powders. Different rehydration times (5, 120, 240, 1,440 min) were considered before studying gel textural properties. This study showed that acid milk gels made with whey instead of casein resulted in an increase in firmness, gel strength, graininess but a decrease in syneresis susceptibility. Nevertheless, rehydration duration of casein powder in contrast to that of whey powder strongly altered the physical properties of the obtained acid milk gels. Moreover, prolonged hydration resulted in enhanced textural properties and decreased syneresis. PRACTICAL APPLICATIONS Commercial preparation of yogurt involves different processing steps. Among them, protein fortification of the milk appears as a crucial step that attributes toward the change in textural properties. Milk protein powders are frequently dried in order to stabilize and transport. This is the reason why rehydration is an essential quality attribute of the powder. Consequently, rehydration is often realized by the industry before use and for a long time. This study showed that acid milk gels made with whey instead of casein resulted in an increase in firmness, gel strength, graininess but a decrease in syneresis susceptibility. Rehydration duration of casein powder in contrast to that of whey powder strongly altered the physical properties of the obtained acid milk gels. Prolonged hydration resulted in enhanced textural properties and decreased syneresis. These aspects are of high significance in the preparation of dairy products, i.e., different types of set and stirred yogurts