ICE RECRYSTALLIZATION IN ICE CREAM: THE ROLES OF MILK FAT AND PROTEIN, AND THE INHIBITION EFFECT OF CHITIN NANOCRYSTALS

Ice recrystallization is one of the most relevant events that define the shelf life in frozen desserts. The functions of all the ingredients in the ice cream mix have been studied, but there is still a gap in understanding the roles of milk fat and milk protein on ice recrystallization. The first part of the present dissertation is focused on unveiling the role of both. After purification, milk fat with concentrations from 0.5% to 15% was studied for ice recrystallization inhibition (IRI) in 25% sucrose by sandwich assay in the presence of 0.2% mono-diglycerides (MDG). The results indicated that higher milk fat levels, especially above 6.5%, significantly reduced ice recrystallization, suggesting an inhibitory role of milk fat. Partial coalescence of milk fat did not consistently impact the ice recrystallization. Vegetable emulsions at 2.9, 10, and 15% fat did not inhibit ice recrystallization. The role of milk protein on ice recrystallization was studied with dialyzed nonfat milk protein (MP) at concentrations up to 5% and milk protein isolate (MPI) at concentrations up to 10% in 20% sucrose solutions. The highest level of milk protein (10% MPI) was necessary to achieve smaller ice crystals. Ice cream mixes at different milk fat levels were evaluated at two milk protein levels to determine the joint effect on ice recrystallization. Systems with the same milk fat amount and different protein content had smaller ice crystals at the highest milk protein level (5% for dialyzed MP and 10% for MPI), especially with milk fat concentrations below 10%. The second part of this dissertation discovered new materials - chitin nanocrystals (ChNCs) with outstanding IRI activity and studied their effects on the properties of ice cream. ChNCs synthesized by hydrochloride acid hydrolysis were also found to have ice shaping activity. The performance of ChNCs in an ice cream model system was compared against typical stabilizers: locust bean gum (LBG) and guar gum. ChNCs inhibited the ice crystal growth at the same level as LBG and guar gum without significant negative impacts on the physical properties of ice cream demonstrating the potential of ChNCs as a promising stabilizer.