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Mixtures of milk fat or milk fat fractions, produced by melt crystallization, and cocoa butter were studied using isothermal calorimetry. Crystallization of cocoa butter (at 15, 20 and 25‡C) was observed, and induction time for nucleation, peak time and amount of heat produced were recorded. Melting profiles and X-ray spectra were also obtained, yielding information about extent of crystallization and type of polymorph obtained. Induction time for nucleation generally increased with increasing temperature. Peak time increased at 15‡C, but decreased at 20‡C. Amount of crystallized fat decreased with increasing level of milk fat.

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structure and mechanical properties of milk fat. Food Res. Int. , 3 , 971–981. Marangoni A.G. Effect of cooling rate on the structure and mechanical properties of milk fat

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type equation, the effective activation energy ( E ), pre-exponential factor ( z ), and constant rate ( k ) are derived. Kinetic information of lipid oxidation has been reported in soybean/anhydrous milk fat blends [ 9 ], natural unsaturated fatty acids

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challenging issue. The traditional fats for sugar confectionaries are cocoa butter, milk fat and various vegetable oils such as coconut oil. Coconut fat is a complex mixture of triglycerides with carbon numbers 8 to 18 (C8–C18). It has a sharp melting profile

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. Huber , J. T. , Emery , R. S. , Bergen , W. G. , Liesman , J. S. , Kung , L. , Jr. , Gardner , R. W. and Checketts , M. ( 1984 ): Influences of methionine hydroxy analog on milk and milk fat production, blood serum lipids and plasma

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Abstract  

Chemical separation methods in conjunction with instrumental neutron activation analysis (INAA) were developed for measuring iodine levels in commercially available bovine milk with varying milk fat (MF) content. Samples of homogenized (3.25 % MF), partly skimmed (2 % MF), partly skimmed (1 % MF), partly skimmed calcium enriched (1 % MF + Ca), and skim (<0.05 %) milk were purchased from local supermarkets. Ion exchange chromatography, solvent extraction, and ammonium sulfate precipitation methods were applied to the separation of the inorganic, lipidic and proteic fractions of iodine in milk. The levels of iodine were measured by INAA in total reactor and epi-cadmium (EINAA) neutron flux in conjunction with conventional gamma-ray and Compton suppression spectrometry (CSS). A pseudo-cyclic INAA method coupled with CSS (PC-INAA-CSS) was also explored as an instrumental option to further lower the detection limit of iodine. The detection limits of 0.06, 0.06 and 0.02 μg mL−1 for iodine were obtained using INAA-CSS, EINAA-CSS, and PC-INAA-CSS methods, respectively. Although the PC-INAA-CSS method provided the lowest detection limit, the INAA-CSS method was sufficient for the determination of total iodine in almost all samples analyzed in this work. The total iodine concentrations (μg mL−1) were: 0.40 ± 0.01 (in 3.25 % MF), 0.40 ± 0.01 (2 % MF), 0.42 ± 0.01 (1 % MF), 0.42 ± 0.01 (<0.05 %), and 0.96 ± 0.01 (1 % MF + Ca) milk samples. Iodine bound to various fractions of the milk samples analyzed, in percent of total iodine content, ranged: (0.05–1.8), (1.9–4.8), (90–95) for the lipidic, proteic and anionic inorganic fractions respectively. Iodine recovery in all cases was higher than 96 %.

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Abstract  

We studied thermal transitions and physical stability of oil-in-water emulsions containing different milk fat compositions, arising from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a high melting temperature (AMF–HMT) or a low melting temperature (AMF–LMT) fraction. Changes in thermal transitions in bulk fat and emulsion samples were monitored by differential scanning calorimetry (DSC) under controlled cooling and reheating cycles performed between 50 and –45C (5C min–1). Comparison between bulk fat samples and emulsions indicated similar values of melting completion temperature, whereas initial temperature of fat crystallization (T onset) seemed to be differently affected by storage temperature depending on triacylglycerols (TAG) composition. After storage at 4C, T onset values were very similar for emulsified and non-emulsified AMF–HMT blend, whereas they were lower (by approx. 6C) for emulsions containing AMF or mixture of AMF–LMT fraction. After storage at –30C, T onset values of re-crystallization were higher in emulsion samples than in bulk fat blends, whatever the TAG fat composition. Light scattering measurements and fluorescence microscopic observations indicated differences in fat droplet aggregation-coalescence under freeze-thaw procedure, depending on emulsion fat composition. It appeared that under quiescent freezing, emulsion containing AMF–LMT fraction was much less resistant to fat droplet aggregation-coalescence than emulsions containing AMF or AMF–HMT fraction. Our results indicated the role of fat droplet liquid-solid content on emulsion stability.

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Acta Alimentaria
Authors: L. Darnay, A. Tóth, B. Salamon, K. Papik, G. Oros, G. Jónás, K. Horti, K. Koncz, and L. Friedrich

The aim of this study was to show how microbial transglutaminase (mTG) can be used as an effective texture-modifier for two popular Hungarian products: Trappist cheese and frankfurter. In both cases we investigated how components of these products, milkfat in cheese and phosphate in frankfurter, can be substituted by mTG. Therefore, Trappist cheese samples were produced from cow milk of 2.8%, 3.5%, and 5% milk fat. The effect of ripening was evaluated with Texture Profile Analysis (TPA) and sensory evaluation (scoring test, 10 trained panellists). Springiness and cohesiveness values were significantly higher by enzyme-treated semi-hard cheese samples at lower milk fat levels. Sensory evaluation showed that the enzyme-treatment led to higher scores by cheese samples made from cow milk of 3.5% and 5% milk fat. Frankfurter was made with 0.1%, 0.3%, 0.5%, and 0.7% tetrasodium pyrophosphate, and partly enzyme-treated with 0.2% commercial mTG enzyme preparation. Our results showed that mTG is able to significantly improve hardness and crunchiness by frankfurters made with 0.1% phosphate addition. Our sensory evaluation suggests that mTG and phosphate should be applied in combination in order to have a final product with recognisably more homogeneous texture.

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Investigation of the complex thermal behavior of fats

Combined DSC and X-ray diffraction techniques

Journal of Thermal Analysis and Calorimetry
Authors: G. Keller, F. Lavigne, C. Loisel, M. Ollivon, and C. Bourgaux

The thermal behavior of three ural fats (displaying very different composition), cocoa butter (CB)2, lard, and a stearin obtained from anhydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ray diffraction as a function of temperature (XRDT). To perform temperature explorations between −30‡C and +80‡C, at rates identical to those used for DSC and ranging from 0.1 K min−1 to 10 K min−1, a new set of X-ray sample-holders, temperature-controlled by Peltier effect, has been developed. It is shown that the three more stable polymorphic forms of CB were easily characterized by either X-ray diffraction or DSC, and existence of two Β-3L forms was confirmed. On the contrary, the more complex polymorphism of lard and AMF required combined examination by DSC and XRDT and the brightness of the synchrotron source for studies at the highest heating rates. Quantitative analysis of the long spacings of XRDT recordings is invaluable for interpretation of thermal events. For instance, it was found that the simultaneous formation of two polymorphic forms, of apparent long spacing of 34 and 42 å, at the onset of lard crystallization might explain the difficulty of its fractionation.

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Aimi, N. (2001): Effect of tempering on physical properties of shortenings based on binary blends of palm oil and anhydrous milk fat during storage. -in: Widlak, N., Hartel, R.W. & Narine, S

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