# Study of the Properties of Human Milk Fat Substitutes Using DSC and GC Methods
## 4 Discussion
The selective pancreatic lipase plays an significant role in the digestion of fat; it hydrolyzes TAG molecules in the external positions to free FAs and 2-monoglyceride. Therefore, the products of human fat digestion will be 2-monopalmitin that is effectively absorbed and unsaturated free FAs. However, if free palmitic acid is present after hydrolysis, insoluble calcium soaps may form in the intestine. This reduces the absorption of both calcium and fat. Therefore, the position of palmitic acid in TAG is important for the absorption of minerals and fat in infants [2; 5]. Given the results on the distribution of FAs in the TAG molecules of investigated SL, it can be stated that this distribution is very similar to that of HMF. The percentage of palmitic acids in internal position of TAG in all SL exceeded 33%, which means that it is mostly in the sn-2 TAG position. Considering the percentage of unsaturated FAs in the internal TAG position in SL, it can be deduced that they are mainly in the external TAG positions. These are especially linoleic acid and oleic acid. Similar results were obtained in the work related to enzymatic modification of lard with milk thistle oil [4]. Taking into account the obtained results, it can be concluded that the time of intresetrization affects the distribution of FAs in the TAG both in the middle and in the outer position. The modification of fats with the use of Lipozyme RM IM occurred predominantly in the outer positions of the TAG. Because intresetrization in the presence of regiospecific enzymes only occurs at the external positions, the sn-2 position of the TAG remains unchanged [33]. Changes in internal position of TAG may be caused by possible acyl migrations within and between TAG molecules during a longer intresetrization period, as evidenced by [PERSON] et al. [38]. Literature data indicate that fats after intresetrization are characterized by a reduced oxidative stability compared to the starting blends [19; 20; 23]. The obtained results confirm that the enzymatic modification of fats reduces their oxidative stability. The induction time for samples intresetrified for a long time (24 h) is higher than for those intresetrified for short time (4 h). The results obtained by DSC are consistent with tests of peroxide value (PV) determination. The high PV is a measure of the content of primary oxidation products from which secondary oxidation products can be formed very quickly. [PERSON] et al. [23] report that there is an inverse relationship between PV and induction time. An increased index of PV in the blends after intresetrization may reduce its oxidative stability. This parameter is a very important factor that affects the quality of oils, fats, and foods. Usually, foods containing high amounts of unsaturated FAs are characterized by a low oxidative stability. Within the FA family, PUFA are highly unstable molecules and are susceptible to oxidation processes, which results in the formation of free radicals,polymers and hydroperoxides which may lead to quality loss, both in terms of technology and health [20]. The presence of free FAs in the oils can induce oxidation due to the catalytic effect of FAs carboxyl groups on the formation of free radicals. [PERSON] et al. [39] investigated the effect of free FA content on the oxidative stability of vegetable oils. The scientists observed the pro-oxidative effect of free FAs with all filtered oils. A higher reduction in oxidative stability was also observed in the case of modified oils and fats, when the product after intereesterification contained a higher level of free FAs, monoacylglycerolglycerols and diacylglycerols [20]. Triacylglycerols are the core components of fats. Fats also include certain quantities of incomplete acylglycerols and free FAs. As a result of the hydrolysis process in the presence of lipases free FAs, partial acylglycerols and glycerol are obtained. The hydrolysis reaction is reversible and, if the water level is lowered, the formation of new acylglycerols will dominate the hydrolysis [40].