The crystallization behavior of milk fat was investigated by varying the cooling rate and by isothermal solidification at various temperatures while monitoring the formation of crystals by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). Three different polymorphic crystal forms were observed in milk fat: γ, α, and β′. The β-form, occasionally observed in previous studies, was not found. The kind of polymorph formed during crystallization of milk fat from its melted state was dependent on the cooling rate and the final temperature. Moreover, transitions between the different polymorphic forms were shown to occur upon storing or heating the milk fat. The characteristic DSC heating curve of milk fat is interpreted on the basis of the XRD measurements, and appears to be a combined effect of selective crystallization of triglycerides and polymorphism.Milk fat is one of the main constituents of milk and determines the specific properties of butter and cream. It is also an important ingredient in many bakery and confectionery industry applications. The various applications require different properties of milk fat, which in turn requires improved functionality control. The functional properties of milk fat are strongly related to the amount and type of milk-fat crystals at the temperature of application. The crystalline part of the fat determines to a large extent the firmness of products in which fat is present as the continuous phase, such as butter and butter oil, and the stability of products containing an emulsion of milk fat, such as cream. Milk fat has a broad melting range due to a large number of triglycerides with a wide range of chain lengths and degrees of saturation. Moreover, the phase behavior is complicated because of the polymorphism of the solid phase.Polymorphism of the crystallized phase is a general feature of triglycerides. The different polymorphic forms can be identified by X-ray diffraction (XRD). The polymorphic forms are characterized by the d-spacings (short-spacings) of the crystal lattices (typically between 3 and 6 Å) as observed in XRD patterns, which correspond to the distances associated with the lateral packing of the fatty acid hydrocarbon chains. Polymorphs with similar packing of the fatty acid hydrocarbon chains were found for pure tristearin (1), and for natural oils and fats (2), including milk fat (3). The d-spacings are characteristic for the type of polymorph, and this has led to the nomenclature given by Larsson (4) that is now widely accepted. Table 1 lists the d-spacings of the polymorphs of triglycerides (2). In general, the stable polymorph of triglycerides is either a β′-or a β-crystal form. The density of the β-crystal form is higher than that of the β′-crystal form, and this leads to more severe packing constraints for the first form as compared with the latter (5). As a result, asymmetrical triglycerides, i.e., triglycerides of the SSU or UUS type, in which the single unsaturated (U) or saturated (S) fatty acid resides in either the sn-1 or ...

The lipids found in the bilayers of the stratum corneum fulfill the vital barrier role of mammalian bodies. The main classes of lipids found in stratum corneum are ceramides, cholesterol, and free fatty acids. For an investigation of their phase behavior, mixed Langmuir-Blodgett monolayers of these lipids were prepared. Atomic force microscopy was used to investigate the structure of the monolayers as a function of the monolayer composition. Three different types of ceramide were used: ceramide extracted from pigskin, a commercially available ceramide with several fatty acid chain lengths, and two synthetic ceramides that have only one fatty acid chain length. In pigskin ceramide-cholesterol mixed monolayers phase separation was observed. This phase separation was also found for the commercially available type III Sigma ceramide-cholesterol mixed monolayers with molar ratios ranging from 1:0.1 to 1:1. These monolayers separated into two phases, one composed of the long fatty acid chain fraction of Sigma ceramide III and the other of the short fatty acid chain fraction of Sigma ceramide III mixed with cholesterol. Mixtures with a higher cholesterol content consisted of only one phase. These observations were confirmed by the results obtained with synthetic ceramides, which have only one fatty acid chain length. The synthetic ceramide with a palmitic acid (16:0) chain mixed with cholesterol, and the synthetic ceramide with a lignoceric acid (24:0) chain did not. Free fatty acids showed a preference to mix with one of these phases, depending on their fatty acid chain lengths. The results of this investigation suggest that the model system used in this study is in good agreement with those of other studies concerning the phase behavior of the stratum corneum lipids. By varying the composition of the monolayers one can study the role of each lipid class in detail.

Milk fat was fractionated by solvent (acetone) fractionation and dry fractionation. Based on their fatty acid and acyl-carbon profiles, the fractions could be divided into three main groups: high-melting triglycerides (HMT), middle-melting triglycerides (MMT), and low-melting triglycerides (LMT). HMT fractions were enriched in long-chain fatty acids, and reduced in short-chain fatty acids and unsaturated fatty acids. The MMT fractions were enriched in long-chain fatty acids, and reduced in unsaturated fatty acids. The LMT fractions were reduced in long-chain fatty acids, and enriched in short-chain fatty acids and unsaturated fatty acids. Crystallization of these fractions was studied by differential scanning calorimetry and X-ray diffraction techniques. In this study, the stable crystal form appeared to be the β′-form for all fractions. At sufficiently low temperature (different for each fraction), the β′-form is preceded by crystallization in the metastable α-form. An important difference between the fractions is the rate of crystallization in the β′-form, which proceeds at a much lower rate for the lowermelting fat fractions than for the higher-melting fat fractions. This may be due to the much lower affinity for crystallization of the lower-melting fractions, due to the less favorable molecular geometry for packing in the β′-crystal lattice.Milk fat is a natural product obtained from cream, and it forms the main constituent of butter. It has excellent organoleptic properties, which makes it an important ingredient in the bakery and confectionery industry. Despite these good qualifications, the market for milk fat has tended to decline in recent years due to its high price and limited functional properties. Melting characteristics and firmness vary with the season, breed of cow, stage of lactation, and the feed given to the cows. Moreover, the product diversity of milk fat is limited compared to that of margarine, for which a whole range of products exists for applications such as puff pastry, cookies, and cold-spreadable products.The physical properties of milk fat are determined by triglycerides, which are its main components. These triglycerides are composed of a large number of different fatty acids. This leads to a heterogeneous composition of triglycerides and a very broad melting range, which varies between approximately −40 and 35°C. Characteristic for milk fat is the occurrence of large amounts (approximately 25% on a molar basis) of short-chain fatty acids, of which butyric acid is the most important.Polymorphism is a common property of all triglycerides (1,2), including milk fat. The main types of polymorphic crystal forms in triglycerides are the γ-, α-, β′-, and β-forms (3-5). Of these main types, either the β′-or β-form is the stable form, depending on the molecular geometry of the triglyceride (6). The other forms are metastable, although they may persist for a long time. For milk fat, the β′-form is the most stable.The utilization range of milk fat can be broadened by separating it into fractio...

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