# Study of the Properties of Human Milk Fat Substitutes Using DSC and GC Methods
## 1 Introduction  
Mother's milk is the major source of nutrients for infants. The ingredient that provides the largest part of the infant's required nutritional energy is human milk fat (HMF) [1]. Therefore, fat in breast milk is the main source of energy for infants, especially in the first period of their life. Additionally, HMF delivers important structural components for neonatal cell membranes [2]. The structure of HMF and its fatty acid (FA) composition are unique. It is characterized by a high content of palmitic acid (20-25%) belonging to saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA) [3]. Among the PUFA in human milk, there are both essential FAs precursors, linoleic acid (18:2 n-6) and \(\alpha\)-linolenic acid (18:3 n-3), and a very long chain of bioactive PUFA of both the n-6 and the n-3 families [4, 5]. Triacylglycerblycerols (TAG) are the main component of HMF (98% of HMF). The structure of human milk TAG is special, as 60-70% of palmitic acid (16:0) is found in the internal position of TAG, and unsaturated FAs are positioned externally. The positionof palmitic acid in TAG affects digestion and absorption of fats and minerals from the infant's intestines [1; 6]. The World Health Organization and other important health organizations recommend breastfeeding as the best method that provides distinctive benefits for the child and mother. In order to assess the suitability of a given infant formula for feeding, its ability to promote growth and development comparable to that of human milk was determined. The biochemical, functional, and metabolic responses of modified formula-fed infants are compared to those of breast-fed infants [7]. Vegetable oils, which are typically used in infant formulas, contain palmitic acid in the external positions of TAG. The use of vegetable oils as a substitute of HMF in infant formulas may cause calcium deficiency due to the formation of insoluble calcium soaps with saturated FA released by the action of the specific pancreatic lipase [6; 8; 9]. Recently, many scientific studies have been carried out and attempts have been made to obtain structured lipids (SL) with FA content and TAG structure similar to HMF. SL are often called nutraceuticals or next generation fats. Nutraceuticals are foods or parts of foods that not only provide basic nutrition but also medical and health benefits and prevent and even treat certain diseases. SL are produced by enzymatic or chemical modification of the TAG [10; 11]. Due to the numerous advantages of using enzyme catalysts in order to obtain SL with specific functional properties, the number of studies on this type of modification is constantly increasing [6; 8]. Enzymatic modification has many advantages compared to chemical methods used during fat modification. Lipases (triacylglycerol acylhydrolases, EC. 3.1.1.3) hydrolyze esters in an aqueous medium. However, if access to water is restricted, intereesterification reactions can also be catalyzed with lipases. Lipase catalyzed reactions are performed under milder circumstances and with greater selectivity than chemically catalyzed reactions. Additionally, the use of regioselective lipases allows the FA to be kept in the internal position of the acylglycerols. This is desirable for nutritional reasons and impossible to achieve via chemical catalysis [12]. Several studies were carried out by means of immobilized lipases as catalysts to produce HMFS which mimics HMF. In most of them, SL reminiscent of HMF were obtained via enzymatic acidosis or intereesterification of lard or tripalmitin with free FA from various sources. Lard is the only fat resembling HMF in terms of FA composition and their distribution in glycerol backbone. Compared to HMF, lard is characterized by a similar palmitic and oleic acids content, but it is a worse source of essential FAs. Vegetable oils are rich in polyunsaturated fatty acid.