Fat-free

While free fat remains a controversial concept in liquid dairy products, it undoubtedly has an important role in whole milk powder (WMP) for certain applications (e.g., chocolate manufacture) high-free fat WMP is favored. Keogh et al, (2003) reported that the particle size in chocolate mixes after refining and the viscosity of the molten chocolate decreases as the free fat content of the WMP increased such changes have significant implications for the mouthfeel and smoothness of chocolate. For more information on the role of fat in milk powder, see Chapter 13 

Influence of Fat Globules on Rheological Properties of Milk and Cream 

If fat globules are present as separate particles, the fat content is 40% and the milk fat completely molten, milk and cream behave as Newtonian fluids at intermediate and high shear rates (Phipps, 1969 McCarthy, 2003), i.e., its viscosity is not influenced by shear rate (t = rj / y, where r is the shear stress [Pa], 17 is the viscosity [Pa s] and y is the shear rate[l/s]). For a Newtonian fluid, Eilers equation (Eilers, 1941) is generally obeyed (Walstra, 1995)  

At a temperature 40°C, milk does not behave as a Newtonion fluid the deviation from Newtonian flow becomes larger as the temperature decreases (Randhahn, 1973 Wayne and Shoemaker, 1988 Kristensen et ah, 1997). Viscosity of milk decreases with increasing shear rate at a temperature below 40°C (Randhahn, 1973), which Mulder and Walstra (1974) suggested may be due to disruption of clusters of milk fat globules, which were formed as a result of cold agglutination. 

Rheological properties of milk and cream are influenced by various processes (e.g., heat treatment, cooling or homogenization). McClements (1999) reported that the main factors that determine the rheological properties of emulsions can be divided into five groups  

Other methods used to quantify free fat include centrifugation in Babcock or Gerber butyrometers at 40-60°C (the free fat is read off directly on the graduated scale) release of membrane-bound enzymes, especially xanthine oxidase or alkaline phosphatase, or the susceptibility of milk fat to hydrolysis by added lipase (e.g. from Geotrichum candidum). 

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The Food and Drug Administration permits the use of diethanolamine as a component of adhesives in food packaging, as an indirect food additive, as a component of the uncoated or coated food contact surface of paper and paperboard for use with dry solid foods with no free fat or oil on the surface, and for use only as an adjuvant to control pulp absorbance and pitch content in the manufacture of paper and paperboard or for use only in paper mill boilers in the United States (Food and Drug Administration, 1999). 

Severe heat treatment, as is encountered during roller drying and to a lesser extent spray drying, results in at least some demulsification of milk fat, with the formation of free fat, which causes (Chapter 3) ... 

Homogenization of raw whole milk or cream stimulates lipolysis and thus leads to a decrease in surface tension, but if the product has been previously pasteurized, the effect of homogenization is an increase in surface tension (Trout et aL 1935 Watson 1958 Webb 1933). The reason for such an increase is not known, but suggestions have been made that it results from denaturation or other changes in the lipoprotein complex or from a reduction in the amount of protein available to the milk-air interface because of adsorption on the extended fat surface. The latter explanation seems unlikely in view of the very slight effect of fivefold dilution on the surface tension of skim milk. Another possible suggestion is that homogenization reduces the amount of free fat in the product. 

Monobasic Acids. The overwhelming majority of monobasic acids used in alkyd resins are long-chain fatty acids of natural occurrence. They may be used in the form of oil or free fatly acid. Free laity acids arc usually available and classified by dieir origin, viz, soya fatly acids, linseed fatty acids, coconut fatty acids, etc. Fats and oils commonly used in alkyd resins include castor oil. coconut oil, eotlonseed oil. linseed oil, oilicica oil, peanut oil. rapeseed oil, safflower oil, soyabean oil, sunflowerseed oil. and tung oil. 

The fatty acid composition of the trans-free reference fat plays a critical role. If the selected trans-free fat is significantly different from the matrix of the fat investigated, it may have an adverse impact on accuracy, particularly near the official method s lowest trans level of quantitation, 5% (AOAC International, 2000) or 1% (AOCS, 1999a). This trans-free reference fat must be carefully selected and should represent as much as possible t e composition of the unknown trans fat or oil being determined. 

Single-beam spectra for neat (without solvent) frans-free fat (background) and trans fat (test samples). Reprinted from Adam et al. (2000) with permission from the American Oil Chemists Society. 

As a result, the depth of penetration, or effective pathlength, will be higher the greater X or the smaller the frequency. Therefore, an interferogram (raw infrared spectrum) is a measure of the attenuation of a trans fat test sample of the totally internally reflected infrared light. The interferogram of a reference background material (trans-free fat) is similarly measured. These are subsequently used to obtain an absorption spectrum. 

VIII. Dry solids with surface containing no free fat or oil, e.g. macaroni, shreaded wheat, com meal, coffee. 

Evers, J.M., Crawford, R.A., Robinson, N.P., Harding, D.R.K., McCarthy, O.J. 2001. Free fat solvent extraction methods damage milkfat globules. Milchwissenschaft. 56, 504-508. 

Fink, A., Kessler, H.G. 1983. Determination of free fat in cream for the assessment of damage caused to fat globules by processing. Milchwissenschaft. 38, 330-334. 

Keen, A.R. 1991. Method for production of a substantially sterol free fat or oil. United States Patent, No. 5,039,541. 

Fat in dried milk is present in a finely emulsified state or in a coalesced de-emulsified state (Buma, 1971). Damage or removal of the fat globule membrane causes the fat globules to flow together as pools (Buma, 1971). Free fat is defined as the fraction of fat that is not protected by protein film but is present as fat pools or patches instead of globules on the surface of whole milk powders (Pisecky, 1997). It is the fraction of milk fat that is on the surface of the powder particle, or in vacuoles, pores, or cracks, and is extractable under defined conditions, (i.e., solvent type, extraction time and temperature) (Buma, 1971). Pisecky (1997) summarized the work of Buma (1971), which describes four types of extractible fat as ... 

Total fat content—free fat content increases with fat content above 26%. 

Product composition—a high lactose content gives low free fat a high protein content gives high free fat. 

Physical state of lactose—amorphous lactose protects free fat from being extracted while crystalline lactose promotes extraction. 

Drying conditions gentle drying results in powder particles with a smooth surface and hence a lower level of free fat. High-temperature drying results in cracks and micropores. 

Powder handling—gentle treatment reduces the level of free fat hence, avoid pneumatic transport, use a type of dryer with a low cyclone fraction, operate with a low pressure drop over cyclones, allow adequate powder cooling in fluid bed, and avoid high powder moisture from first drying stage. 

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