Fractional crystallization, of milk-fats

De Man (1983) has reviewed this property of fats. Consistency is defined as (1) an ill-defined and subjectively assessable characteristic of a material that depends on the complex stress-flow relation or as (2) the property by which a material resists change of shape. Spreadabil-ity, a term used in relation to consistency, is the force required to spread the fat with a knife. The definition is similar to that for hardness the resistance of the surface of a body to deformation. The most widely used simple compression test in North America is the cone penetrometer method (AOCS Method Cc 16-60, 1960). More sophisticated rheological procedures are also available. Efforts have been made to calibrate instrumental tests with sensory response. With the cone penetrometer method, penetration depth is used as a measure of firmness. Hayakawa and De Man (1982) studied the hardness of fractions obtained by crystallization of milk fat. Hardness values obtained with a constant speed penetrometer reflected trends in their TG composition and solid fat content. 

Milk fat can be separated into fractions with different melting points by crystallization in an organic solvent. Many studies have examined crystallization of milk fat in solvents such as acetone or ethanol other solvents including hexane, pentane, ethylacetate and isopropanal have been studied also. The properties of fractions crystallized from solvents have been summarized by Kaylegian and Lindsay (1995). 

Despite the benefits of faster crystallization rates and better efficiency compared to dry fractionation (Schaap and van Beresteyen, 1970 Wright et al., 2000b Illingworth, 2002), crystallization of milk fat from a solvent has not been carried out on an industrial scale. Some of the hurdles to the uptake of solvent fractionation technology are the impaired flavor of the milk fat fractions, the cost of the operation, and toxicological and environmental concerns. 

Breitschuh, B. 1998. Continuous Dry Fractionation of Milk Fat - Application of High Shear Fields in Crystallization and Solid - Liquid Separation. Ph.D. Thesis. Swiss Federal Institute of Technology, Zurich. 

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 phase behavior and crystallization kinetics of the milk fat are dependent on the choice of solvent used for fractionation. Larsen and Samuelson (1979) examined the use of acetone for fractionation of milk fat. These authors suggest that the use of polar solvents has advantages over the use of non-polar solvents. The polarity of the solvent used affects the phase behavior and crystallization kinetics of milk fat. In polar solvents,... 

There is a potential for the commercial application of supercritical CO2 fluid extraction for fractionation of milk fat. However, the differences between the melting properties are not as pronounced as with melt crystallization, thereby limiting the application range of these fractions. Moreover, this process is more expensive than melt crystallization (Bhaskar et al., 1998). Nevertheless, niche applications could be developed if fractions rich... 

The crystallization behavior of milk fat (which contains minor lipids) and a pure triacylglycerol fraction of milk fat were compared by Herrera et al. (1999). The results suggested that minor lipids delay nucleation but promote crystal growth. Other workers who examined the effects of added phospholipids on palm oil, suggested that some phospholipids delayed nucleation while others had more significant effects on the rate of growth of fat crystals (Smith, 2000),... 

Dimick, P.S., Reddy, S.Y., Ziegler, G.R. 1996a. Chemical and thermal characteristics of milk-fat fractions isolated by a melt crystallization. J. Am. Oil. Chem. Soc. 73, 1647-1651. 

Vanhoutte, B., Foubert, I., Duplacie, F., Huyghebaert, A., Dewettinck, K. 2002b. Effect of phospholipids on isothermal crystallization and fractionation of milk fat. Eur. J. Lipid Sci. Technol. 104, 738-744. 

Wright, A.J, McGauley, S.E., Narine, S.S., Willis, W.M., Lencki, R.W., Marangoni, A.G. 2000b. Solvent effects on the crystallization behavior of milk fat fractions. J. Agric. Food Chem. 48, 1033-1040. 

The sensory properties, especially texture and appearance, of milk fat-based products such as butter, cream, cheese, ice cream and milk chocolate are largely dependent on the physical properties of the product, especially properties governed by the phase change behavior of the fat, used here to mean melting and crystallisation behavior, crystal polymorphism and microstructure (Birker and Padley, 1987 O Brien, 2003). The same may be said of the functional properties of milk fat, milk fat fractions and milk fat-based products when these are used as food ingredients. 

Breitschuh and Windhab (1996) described a novel use of DSC for directly investigating or monitoring crystallization processes such as those used in the fractionation of milk fat. In their technique, called DSC direct, a small sample of fat is taken from the process line, placed immediately in the sample pan of the DSC instrument, and within seconds, subjected to a heating scan. In this way, the melting characteristics of the fat at that particular stage of the process, as determined by processing conditions up to that stage, can be determined directly. 

Confectionery-Liquors and Liqueur. In chocolate confectionery and for pastry creams, it is the physical properties linked to the fusion and the crystallization of the fat that are essential. For milk chocolate, for coating or in bars, AMF can be used in proportions that depend on its compatibility with cocoa butter, whose properties of hardness and rapid fusion at 35°C cannot be altered. Thus it is currently accepted that AMF with high fusion levels obtained by the fractionation technique can be used. In general, milkfat has an interesting characteristic it inhibits the appearance of fat bloom (133). 

Fig. 4. Fractional crystallization of anhydrous milk-fat (AMF) (A), MF-TAC (B), and milk-fat MF-TAC with 0.1% milk-fat diacylglycerol (MF-DAC) (Q determined by pNMR measurements of solid fat content, turbidity measurements, and polarized light microscopy coupled to image analysis at 22.5°C. Symbols in (A) and (B) represent the average and standard errors of three replicates. See Figures 2 and 3 for other abbreviations.

The technology of milk fat fractionation does not use solvents, but rather crystallization from melted fat. Crystalline fractions of different chemical compositions and different physical properties are formed at conteolled temperatures (Bhaskar et al., 1998). The results of fractionating are solid and liquid fractions with their melting points of 48°C and 25°C, respectively. The melting point of unfractionated fat was 41.6°C. The liquid fraction in comparison with the solid fraction had 17% more Cg g - C,o o FA, 11% less C,2.o - Ci6.o FA, 32% less Cjs-o FA, but 41% more Cig. , C,g.2 ... 

Wright, AJ, SE McGauley, SS Narine, WM WUhs, RW Lencki, AG Marangoni. (1999). Solvent effects on the crystallization behaviour of milk fat fractions. J Agric Food Chem 48(4) 1033-1040. 

B Breitschuh. Continuous dry fractionation of milk fat—Application of high shear fields in crystallization and solid-hquid separation. Doctor of Tech Sci Dissertation, Swiss Fed Inst Technol, Zurich, 1998. 

Wahba, A., El-Hagarawy, I.S., Zeidan, I.A. 1977. The effect of addition of globulin protein fractions on the creaming of buffaloes and cow s milk. Egypt. J. Dairy Sci. 5, 43—46. Walstra, P. 1967. On the crystallization habit in milk fat globules. Neth. Milk Dairy J. 21, 166-191. 

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