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Whole native caseinate (WNC) and casein (CN) fractions from preparative DE-52 cellulose urea columns were chromatographed using C-8 reverse-phase (RP) and DEAE-type anion-exchange (AEx) HPLC systems. With RP, (us2-CN and K-CN eluted first as several small peaks; as&N eluted later as two peaks, followed by P-CN peaks. With AEx, K-CN eluted early as a group of peaks, P-CN eluted next, and a&N and cxsZ-CN coeluted last. Standard curves were prepared for a&N and &cN using RP-PHLC and showed correlation coefficients of 0.99 and 0.98. resuectivelv. The caseins in WNC. nonfat dry milk casein, commercial 'casein(ates) and caseins from milks of individual cows were determined.

No abstract

Thermal preservation is used by the egg industry to ensure the microbiological safety of liquid egg white (LEW); however, it does not eliminate all microorganisms and impairs some of the delicate functional properties of LEW. In this study, a pilot-scale cross-flow microfiltration (MF) process was designed to remove the natural microflora present in commercial LEW, obtained from a local egg-breaking plant, while maintaining the nutritional and functional properties of the LEW. LEW, containing approximately 10(6 +/- 1.7) colony forming units (CFU) per milliliter of total aerobic bacteria, was microfiltered using a ceramic membrane with a nominal pore size of 1.4 microm, at a cross-flow velocity of 6 m/s. To facilitate MF, LEW was screened, homogenized, and then diluted (1 : 2, w/w) with distilled water containing 0.5% sodium chloride. Homogenized LEW was found to have a threefold lower viscosity than unhomogenized LEW. Influence of MF temperature (25 and 40 degrees C) and pH (6 and 9) on permeate flux, transmission of egg white nutrients across the membrane, and microbial removal efficiency were evaluated. The pH had a significantly greater influence on permeate flux than temperature. Permeate flux increased by almost 148% when pH of LEW was adjusted from pH 9 to pH 6 at 40 degrees C. Influence of temperature on permeate flux, at a constant pH, however, was found to be inconclusive. Microbial removal efficiency was at least 5 log(10) CFU/mL. Total protein and SDS-PAGE analysis indicated that this MF process did not alter the protein composition of the permeate, compared to that of the feed LEW, and that the foaming properties of LEW were retained in the postfiltered samples.

Six cheese varieties encompassing a wide compositional and age range were analyzed fresh and after aging to determine correlations between casein proteolysis products, fat content, moisture content, and torsion results. Shear stress, a measure of the strength of the casein matrix, was dependent on the amount of intact αsl‐casein. Shear strain, a measure of the cohesiveness of a structure, exhibited a negative correlation with fat content and a positive correlation with moisture content. Shear strain was also correlated with the ratio of moisture to protein, an indication of the interaction between casein particles. Torsion tests provide information on the level of degradation of the casein network in cheese, which can be used by manufacturers to alter storage conditions to optimize the quality of their aged cheese., April 10, 2003