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R W Hartel

Publications and source records attributed to R W Hartel.

6 recordsLinked to original sources
PubMed2001

Effect of cooling rate on nucleation behavior of milk fat--sunflower oil blends.

The effect of cooling rate on the crystallization behavior of mixes of high-melting milk fat fraction (HMF) and sunflower oil (SFO) was studied by following nucleation with laser-polarized turbidimetry. The initial crystals were photographed, and their thermal and polymorphic behaviors, as well as chemical composition, were investigated by calorimetry, X-ray diffraction, and capillary gas chromatography. Activation energies of nucleation were calculated using the Fisher-Turnbull equation. Despite small differences in Mettler dropping points for different ratios of SFO to HMF, induction times were significantly different between samples and were shorter at a slow cooling rate for the same supercooling. Rapidly cooled samples required more time at crystallization temperature to crystallize than slowly cooled samples because molecular organization prior to nuclei formation took place under different conditions. Regardless of cooling rate or composition, all crystals were in the beta' polymorph. However, morphology, thermal behavior, and chemical composition showed differences with cooling rate. Activation free energies of nucleation were of the same order of magnitude as those published for hydrogenated SFO.

Crystallization↗
PubMed2001

Interactions of milk fat and milk fat fractions with confectionery fats.

The objectives of this study were to provide a better understanding of the effects of triacylglycerol (TAG) and non-TAG components (minor lipids) of milk fat on phase and crystallization behavior of binary mixtures of palm kernel oil (PKO) and the physical properties of corresponding compound coatings. Binary mixtures of a fractionated PKO with the different milk fats were examined for melting profiles, crystallization kinetics, and crystalline microstructures, and polymorphic changes during storage. Compound coatings were made with equivalent binary fat mixtures and measured for hardness and bloom formation. Milk fat and milk fat fractions affected crystallization rates of fractionated PKO, depending on the melting point of the fat. High-melting components resulted in more rapid crystallization, whereas the original milk fat and low-melting components inhibited crystallization. The crystal structure (e.g., number, size, shape) of the PKO crystals was influenced significantly by the addition of milk fat fractions and was influenced by the presence or absence of the minor lipids in milk fat. Milk fat and milk fat fractions had a softening effect on fractionated PKO, which was apparent in the binary mixtures as well as the compound coatings. In general, as the solid fat content (at 25 degrees C) of the binary mixtures increased, the hardness of the respective coatings increased. This also was related to an increased rate of bloom formation during storage.

Animals↗
PubMed2001

Compositional effects on milk fat crystallization.

Seasonal and regional variability in milk fat composition causes differences in crystallization behavior, which can, for example, result in variability in fractionation efficiency and physical properties of butter. However, the specific compositional causes of variability in milk fat crystallization behavior are still only poorly understood. In this work, the seasonal and regional variations in composition of anhydrous milk fat were analyzed and related to crystallization behavior. Although there were no clear-cut trends in chemical composition (triacylglycerol, fatty acid, and minor lipid profiles) among the milk fats, significant differences in crystallization behavior were observed. For anhydrous milk fat samples made from sweet cream and obtained from the same milk supply through a period of 14 mo, no significant trends in either composition or crystallization behavior were observed. This suggests that seasonal variability of milk fat may be reduced by current feeding strategies in the United States. More detailed examination of the triacylglycerol profiles led to the conclusion that the relative contents of certain triacylglycerol combinations correlated well with crystallization behavior. In particular, the ratio of higher-melting to lower-melting triacylglycerols could be used to predict crystallization behavior. Higher ratios of higher-melting triacylglycerols led to higher crystallization rate.

Animals↗
PubMed1991

Sugar crystallization in food products.

A review of the recent literature on crystallization of the commercial sugars (fructose, glucose, lactose, and sucrose) is presented. Topics include: NUCLEATION--The formation of the crystalline phase from supersaturated solutions can occur by either a spontaneous or a forced nucleation mechanism. Recent work on the mechanisms, kinetics, and impact of both heterogeneous and secondary (contact) nucleation is discussed. GROWTH--Recent studies on the mechanisms and kinetics of crystal growth will be reviewed. This discussion includes work on the growth rate dispersion exhibited by these sugars. EFFECTS OF IMPURITIES AND ADDITIVES--The presence of impurities and additives (including mixed sugar systems) affects both the nucleation and growth steps. A discussion of the recent work in this area is included. Emphasis is placed on the relationship between these crystallization phenomena and the solution structure for comparison purposes.

Carbohydrates↗