# The Effect of Storage on Potentially Synbiotic Emulsion Spread Based on Milk Fat and Inulin
## 1 Introduction  
Among products designed for spreading, there is butter, various types of margarines, and several other products available on the market, the offer of which is changing quite dynamically. For many years, the use of butter has been controversial due to the content of cholesterol and saturated fatty acids. Until the 1990s, margarines seemed to be an alternative; however, usually they contained high levels of trans fatty acids, which turned out to be no less harmful than saturated fatty acids. Currently, margarines in most countries are free from trans fatty acids. Changes in technology in margarine production resulted in the use of palm oil. The use of palm oil is controversial because the cultivation of palm trees is often carried out at the expense of tropical forests, which contributes to an increase in the greenhouse effect. Due to the recent reports about relatively small or neutral associations of milk fat consumption with mortality, diabetes, and cardiovascular disease [1, 2], the idea was born [3] of obtaining emulsions for spreading containing milk fat and inulin--indigestible carbohydrates which have fat-mimetic properties [4]. Dairy production still takes place, and there is a surplus of milk fat on the market. Production of the milk fat-inulin emulsion will, on the one hand, use up some of the milk fat, and, on the other hand, reduce the use of palm oil. In addition, when compared with butter or traditional margarine, replacing part of the fat with inulin allows producers to reduce the caloric value of such a product and decrease the amount of saturated fatty acids in the diet, simultaneously increasing the amount of fibre. Inulin, from a chemical perspective is a group of fructans with a 2-60 degree of polymerization (DP) [5]. Hundreds of thousands of tons of inulin, in the form of white powder, are produced in the world every year. As a fat substitute (high polymerized inulin with a DP of at least 23), sugar substitute (native inulin with a DP of 12, or short chain inulin with DP of 4), and being a fibre and bifidogenic agent, inulin is widely applied in many food products present in the market. Many of these products were previously studied in laboratories, such as dairy products [6; 7; 8; 9], meat products [10; 11; 12], bakery products [13; 14], mayonnaise [15; 16], as well as prebiotic beverages [17]. So far, several attempts have been made to obtain spreads based on inulin. After preliminary studies showing that inulin gels have the potential to be used as fat mimetics [18], [PERSON] et al. [19] conducted research demonstrating the possibility of obtaining a spread based on inulin (20% \(w/w\)) and rapeseed oil (20% \(w/w\)) with the addition of polyglycerol polyricinoleate (1% \(w/w\)) or whey protein isolate (3% \(w/w\)) as an emulsifier. Although the analysis of rheological properties showed the stability of the tested emulsion during storage and in the sensory and instrumental analysis, the spreadability did not differ significantly from the margarines available on the market; however, the assessment of flavour, meltability in mouth, and general acceptance recorded significantly worse results than commercial margarines. Another attempt showed that it is possible to manufacture emulsions based on milk fat (15%, 20%) and inulin (15%, 18%, 21%, and 24%) with soya lecithin (2%) as an emulsifier; however, under the condition that during production the temperature will not exceed 65 \({}^{\circ}\)C to keep the predictable textural and rheological properties of the final product [3]. Recently, [PERSON] et al. [20] optimised the composition of emulsion spreads, based on milk fat and inulin with lecithin or whey protein concentrate (WPC) as emulsifiers, with the addition of probiotics: _Bifidobacterium animals_ BB-12, _Streptococcus thermophilus_, and _Lactobacillus acidophilus_ La-5. The optimal concentration of milk fat and of inulin was 20%, and only the emulsion spreads with WPC contained live probiotic bacteria.