Conjugated linoleic acid (CLA) is a potent cancer preventive agent in animal models. To date, all of the in vivo work with CLA has been done with a commercial free fatty acid preparation containing a mixture of c9,t11-, t10,c12- and c11,t13-isomers, although CLA in food is predominantly (80-90%) the c9,t11-isomer present in triacylglycerols. The objective of this study was to determine whether a high CLA butter fat has biological activities similar to those of the mixture of free fatty acid CLA isomers. The following four different endpoints were evaluated in rat mammary gland: 1) digitized image analysis of epithelial mass in mammary whole mount; 2) terminal end bud (TEB) density; 3) proliferative activity of TEB cells as determined by proliferating cell nuclear antigen immunohistochemistry; and 4) mammary cancer prevention bioassay in the methylnitrosourea model. It should be noted that TEB cells are the target cells for mammary chemical carcinogenesis. Feeding butter fat CLA to rats during the time of pubescent mammary gland development reduced mammary epithelial mass by 22%, decreased the size of the TEB population by 30%, suppressed the proliferation of TEB cells by 30% and inhibited mammary tumor yield by 53% (P < 0.05). Furthermore, all of the above variables responded with the same magnitude of change to both butter fat CLA and the mixture of CLA isomers at the level of CLA (0.8%) present in the diet. Interestingly, there appeared to be some selectivity in the uptake or incorporation of c9,t11-CLA over t10,c12-CLA in the tissues of rats given the mixture of CLA isomers. Rats consuming the CLA-enriched butter fat also consistently accumulated more total CLA in the mammary gland and other tissues (four- to sixfold increases) compared with those consuming free fatty acid CLA (threefold increases) at the same dietary level of intake. We hypothesize that the availability of vaccenic acid (t11-18:1) in butter fat may serve as the precursor for the endogenous synthesis of CLA via the Delta9-desaturase reaction. Further studies will be conducted to investigate other attributes of this novel dairy product.

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The protein uptake equilibrium and kinetics and the breakthrough behavior of recently developed commercial chromatography media are evaluated using lysozyme as a model solute. One of the adsorbents, known by the trade name POROS 50, is a macroporous matrix based on a styrene-divinylbenzene copolymer. The other adsorbent, known by the trade name HyperD, is a composite obtained by filling the pores of high-porosity polystyrene-coated silica particles with a polyacrylamide-based hydrogel. Both materials are designed for preparative and process ion-exchange chromatography of proteins at high speed and have a strong cation exchange functionality. The equilibrium and transport properties of lysozyme in each adsorbent are studied in batch experiments. The maximum equilibrium uptake capacity in a 10 mM sodium phosphate buffer at pH 6.5 is 160 ( 5 mg/cm 3 of particle volume for the macroporous adsorbent and 260 ( 10 mg/cm 3 for the gel-composite material. With the macroporous adsorbent mass transfer appears to be dominated by macropore diffusion with an effective pore diffusivity of 1.1 × 10 -7 cm 2 /s, except during the initial saturation of the outermost layer of the particle, when external film mass transfer is controlling. An idealized two-step model of this process is found to be consistent with the experimental data. With the gel-composite adsorbent, however, mass transfer appears to be dominated by homogeneous gel diffusion with an effective pseudo-homogeneous diffusivity of 7.5 × 10 -9 cm 2 /s at high protein concentrations and by the external film resistance at low protein concentrations. For both adsorbents, breakthrough profiles obtained experimentally at elevated flow rates in packed columns are in good agreement with predictions based on the batch measurements and external film coefficients predicted from literature correlations. In spite of the fact that it possesses a larger particle size, the gel-composite adsorbent appears to be superior to the macroporous medium, exhibiting a dynamic capacity at 10% breakthrough more than a factor of 2 larger at mobile phase velocities in the range 0-5000 cm/h.

The paper gives a summary of successful methods for measuring protein mass transfer kinetics in ion exchange matrices along with models needed to interpret experimental results. Both macroscopic methods (isocratic elution, gradient elution, batch adsorption, frontal analysis) and microscopic methods are considered. In all cases the main focus is the determination of the effective intraparticle diffusivity in order to permit a comparison of different stationary phases and provide a basis for predicting chromatographic process performance. Experimental results for representative systems are evaluated alongside the experimental and modeling aspects. Practical criteria for the selection of experimental conditions and the application of different models are discussed along with the advantages and disadvantages of the various approaches.