Physical Modification of Milk Fat

Physical modification of milk fat by fractionating milk fat or by blending milk fat or milk fat fractions with other oils and fats results in products with an altered triacylglycerol composition, but one in which the fatty acids in milk fat maintain their original position in the triacylglycerol molecules (Kaylegian, 1999). 

Dry fractionation involves melting the milk fat, controlled cooling and crystallization of molten milk fat while cooling to or at a desired temperature and separation of the crystals from the liquid phase. The process is attractive because of its simplicity, relatively low costs and ability to select between fractions based on the melting or functional properties of the fats, which is usually the reason for fractionation. It does not involve the use of solvents, detergents or other additives and furthermore, the desirable flavor notes are not lost although they are partitioned differently between the various fractions. 

Dry fractionation is the most commonly used method in industry for fractionation of milk fat. After a decade of rapid growth to an installed capacity of over 800 tonnes/day in 1990 (Versteeg et al., 1994), with plants in Belgium and several other European countries, growth to 2005 has been 

The main commercial fractionation process for milk fat is the Tirtiaux process, followed by the De Smet process. There are also some proprietary variations of the dry fractionation process which enable the production of various milk fat fractions. The characteristics of the fractions obtained are affected by many factors, including the equipment design, the associated process, the initial temperature of the molten fat, the crystallization conditions (e.g., degree of initial supercooling), the rate of subsequent cooling and agitation after crystallization commences, the final temperature of fractionation and the method used to separate the fractions. 

The observations of Campos etal. (2002) showed that in non-isothermal crystallization, the slow reduction of temperature results in a lower crystal volume containing larger crystals and a more heterogeneous spatial distribution of the mass. This gives a softer fat compared to when milk fat is crystallized at a faster rate. In laboratory experiments using a Bohlin rheometer as a crystallizer, Breitschuh and Windhab (1998) demonstrated that compound crystals were formed during supercooling and that less compositionally differentiated fractions were produced. 

---

Milk fat may be chemically modified to obtain products with altered functionality. In contrast to physical modification of milk fat where the position and nature of the fatty acid chains of the triacylglycerols are maintained, the use of chemical processes results in modification of the composition of the fatty acid chains or their positions in the triacylglycerol molecule. 

---