Encapsulation and oxidation of fat in recombined milk powder

Sammanfattning: Fat-filled milk powders are manufactured by blending skim milk powder with vegetable oil and these powders have gained a great economic importance. Sensible selection of vegetable oil can help in satisfying both nutritional features and functional characteristics of fat for dairy application. The stability of milk powders can be affected by its composition, mainly the composition of fats which can lead to lipid oxidation. The stability of fats depends on various parameters, some of which are, the composition of the fat, crystal form of fat, the composition of powder etc. The parameter which was mainly focused in this study was the crystal form of the fat. The rate of oxidation to some extent depends directly on the fraction of unsaturated lipids and hence this parameter was also used to calculate the measurable oxidation rate. The primary goal of this thesis was to encapsulate vegetable oil in skim milk powder and determine the influence of different crystal forms of fats on the stability of milk powder. The different fats selected were based on the form in which they crystallize. These fats also varied in the fraction of unsaturation. Milk powder was encapsulated with highly unsaturated fat (liquid fat), fat with a very low fraction of unsaturation (hard fat) and in combination of both the kinds of fat, keeping in mind the objective to investigate the effect on the properties of milk powder by the addition of hard fat to liquid fat. Numerous techniques such as DSC, particle size determination, surface free-fat extraction, quantifying the extent of oxidation, X-ray crystallography and SEM were carried out. The results obtained shows that the addition of hard fat to liquid fat brings about changes in the properties and the stability of the fat-filled milk powder. With respect to oxidation, the addition of hard fat reduces the rate of oxidation compared to the rate of oxidation of just the liquid fat in milk powder. But varying the concentration of hard fat did not show a significant difference.