The properties of spray -dried milk fat emulsions as affected by types of wall materials and processing and storage conditions
Encapsulation of lipids and other oxidizable compounds provides a means of protecting these compounds against their environment, including such factors as oxygen and humidity. The physical properties of wall matrices have a major influence on the oxidative stability of encapsulated lipids. This study investigated the effects of composition and processing conditions on physical and chemical stability of encapsulated milk fat powder (dairy creamer). Achieving a stable liquid emulsion is a necessary first step. Emulsifier type and concentration as well as processing conditions affected oil droplet size distribution. Larger oil droplet size led to an unstable emulsion and a consequential increase in surface fat of spray dried powder. At best, about 98% of the milk fat was encapsulated (average oil droplet size ∼0.5 μm, 2.0% lecithin, 36 DE corn syrup solids). The physical properties of spray dried powders that were studied include internal and external morphology, water sorption isotherm, surface fat, true density, and melting and crystallization. Upon storage, physical changes led to a complex change in surface fat with storage humidity, crystallization of carbohydrates (at higher %RH), and caking. These were dependent on maltodextrin dextrose equivalent (DE) and storage humidity.
Oxidative stability of milk fat encapsulated in powder with DE-36 corn syrup solids was studied at 14–52%RH and 25°C (Collaborative work with two other investigators; Dr. Nitin Hardas and John L. Foley). Oxidation was negligible for powders stored in the dark at all relative humidities. Under UV light, the encapsulated fat significantly increased in peroxide value (PV) and decreased in 18:2 and 18:3 fatty acids over time. The highest rate of oxidation was found at 52% RH, indicating increased diffusivity of oxygen and other components under this condition. In contrast, surface fat oxidative rate was slower at 52% than at 14% and 44% RH. Overall oxidative stability was dominated by the encapsulated fraction although in general the surface fat fraction was oxidized more rapidly.