Mineral content of dairy products. II. Cheeses.

Twenty-one kinds of commercial cheese were analyzed for fat, solids, protein, and five major and four trace minerals. Calcium, magnesium, sodium, and potassium were determined by atomic absorption; phosphorus was determined colorimetrically. Flameless atomic absorption was used to determine iron, zinc, copper, and manganese. The data agreed in general with published values, although there were instances of wide variation. The data represent a comprehensive compilation of the mineral contents of popular cheeses that should be helpful to dietitians and nutritionists.

Mineral content of dairy products. I. Milk and milk products.

Sixteen kinds of dairy products were analyzed for five major minerals and four trace minerals. Commercial samples of fluid milk, cream, concentrated milks, cultured products, butter, and frozen desserts were also analyzed for fat, solids, protein, and minerals. Calcium, magnesium, sodium, and potassium were determined by atomic absorption, and phosphorus was determined colorimetrically. Flameless atomic absorption was used to determine iron, zinc, copper, and manganese. The data generally agreed with most recently published values. However, for the trace minerals, the data differed widely in some instances. Manufacturing practices and added ingredients produced considerable variations in mineral content of market samples. These variations, however, could be limited by selection of products, so that they would not preclude the use of dairy products in diets in which mineral composition must be controlled. The coefficients of variation, which indicate the variability that can be expected for each product, generally were high for sherbet and ice milk and low for low-fat milk and skim milk.

Inhibitory action of tetrathionate enrichment broth.

Tetrathionate enrichment broth is a complex mixture of salts including iodides and other polythionates, but only thiosulfate (0.0736 m) and tetrathionate (0.0236 m) in combination were toxic for Escherichia coli. Individually, these two salts were not lethal. The lethal action of this thiosulfate-tetrathionate mixture affected only growing cells. A possible relationship between the lethality of the thiosulfate-tetrathionate mixture for a culture and its ability to reduce tetrathionate is suggested.

Relationship of the frequency of isolation of Salmonellae to their resistance to drying and freezing.

The resistance of different Salmonella serotypes to drying and freezing has been shown to be related to their incidence in salmonellosis.

Inhibition of microbial lipases by fatty acids.

Addition of lard or sodium oleate to the medium used for lipase production by Pseudomonas fragi resulted in a decreased accumulation of lipase in the culture supernatant fluid without affecting cell growth. The production and activity of lipase was inhibited by lard, sodium oleate, and the salts of other unsaturated fatty acids. Some divalent cations, Tweens, lecithin, and bovine serum prevented oleate inhibition, but did not reverse it. Similar inhibitory actions were observed with Geotrichum candidum lipase, but not with a staphylococcal lipase or pancreatic lipase. A protective effect by protein in crude enzyme preparations is indicated. The ability of oleate to lower surface tension does not appear to be related to its ability to inhibit lipase.

Applicability of aeration and delayed addition of selenite to the isolation of salmonellae.

The effect of aeration combined with the delayed addition of selenite on the lag period of several strains of salmonellae and other enterobacteria is reported. A procedure has been developed involving shaking of the sample in a basal medium for 4 hr at 37 C, adding selenite and cystine, and continuing shaking for 20 hr. Confirmation by selective plating, biochemical tests, and serology gave results comparable to the standard lactose pre-enrichment method with the saving of 24 hr and elimination of one set of media. Confirmation by fluorescent-antibody tests showed that fewer positive fluorescent stains were obtained from the aerated procedure than from the lactose pre-enrichment procedure. Precautions in the application of this procedure are discussed.

Interaction of salt, pH, and temperature on the growth and survival of salmonellae in ground pork.

The interaction of temperature, pH, and NaCl concentration on the growth and survival of several strains of salmonellae has been determined in broth and ground pork. Growth of 23 strains occurred in broth at 30 C over a wide range of pH-NaCl combinations; at 10 C, growth was limited to only a few combinations. Cultures which would not grow at 10 C because of the pH-NaCl effect survived for long periods, however. In contrast, cultures which would not grow at 30 C remained viable for only a short time. Results in fresh ground pork were in close agreement with the broth studies. Salmonellae would not grow in ground pork stored at 4 C but would grow in pork containing 3.5% salt stored at 10 C. Salmonellae grew competitively with the natural background flora at 10 C even when the salmonellae constituted less than 5% of the initial flora, and the background flora would grow at a lower temperature than the salmonellae. The data show that, whereas decreasing temperatures increase the inhibitory effects of pH and NaCl, they decrease the lethal effects.

Growth response of weanling rats to heated, aged, fractionated, and chemically treated yogurts.

Significance of viable cultures in yogurt at time of ingestion on rate of growth of weaning rats was determined. Fresh yogurts were compared with those in which cultures were treated with heat, hydrogen peroxide, and ethylene oxide. They also were aged and freeze-dried. Fractions of yogurt prepared by ultrafiltration were recombined to determine which fraction gave the highest rate of gain in weight. Cultures were inactivated and growth in rats was depressed when yogurt was heated at 60 C and above for 2 min. Hydrogen peroxide reduced the viable yogurt count and rate of gain but not feed consumption. Yogurts treated with ethylene oxide were toxic. Aging did not effect culture viability or feed efficiency, but growth response was reduced. Fractionation of yogurt into components of high and low molecular weight and recombinations with control milk fractions indicated that the growth stimulant remained in the component of high molecular weight.

Effects of meat-curing salts and temperature on production of staphylococcal enterotoxin B.

We investigated the effect of time, temperature, and the presence of sodium chloride, nitrates, and nitrites in the medium on the growth and production of enterotoxin B by Staphylococcus aureus. Assays by the double gel-diffusion method showed that maximal enterotoxin B production occurs at the beginning of the stationary phase of growth. Lowering the temperature of incubation decreased the amount of toxin produced without affecting the total amount of growth. Increases in concentration of curing salts reduced toxin production more rapidly than cell growth. The relationship of these observations to food-poisoning outbreaks is briefly discussed.

Composition of cheddar cheese made with different milk clotting enzymes.

Six commercial milk clotting preparations from animal and fungal sources were used to make cheddar cheese. The cheeses were analyzed initially and over 6-mo ripening for proximate composition, minerals, amino acids, soluble protein, nonprotein nitrogen, free fatty acids, lactones, and flavor development. No significant differences in the composition of the cheeses could be attributed to the type of clotting enzyme. One lot of one enzyme showed increased lipolytic activity which indicated contamination and suggested that the purity of the enzyme preparation should be checked.

Biological and physicochemical characteristics of four serotypes of Salmonella enteritidis.

Four serotypes of Salmonella enteritidis, Anatum ATCC 9270, Newbrunswick ATCC 1608, Oranienburg 200 E, and Pullorum RM, were studied to determine biological, chemical, or physical differences which might explain variations in Salmonella virulence as previously reported by McCullough and Eisele (J. Infect. Dis. 88:278-289, 1951; 89:259-265, 1951). These investigators found that serotype Pullorum was significantly less virulent than serotypes Newport, Derby, Barielly, Meleagridis and Anatum when fed to healthy humans. Results of our own experiments showed that serotype Pullorum RM had a generation time approximately twice that of serotype Anatum 9270. The volume of serotype Pullorum was approximately one-half the volume of the other serotypes used (Anatum 9270, Newbrunswick 1608, Oranienburg 200 E, Cubana 12007, and Meleagridis DR). The number of cells required to yield 1 g dry weight was substantially higher for serotype Pullorum RM than for serotypes Anatum 9270, Newbrunswick 1608, and Oranienburg 200 E. The yield of endotoxin per gram dry weight for serotype Pullorum RM averaged 22 mg/g, whereas yields of endotoxin for serotypes Anatum 9270, Newbrunswick 1608, and Oranienburg 200 E averaged 32 to 35 mg/g. The relative abundance of the four major fatty acids (measured by gas chromatography) also showed distinct differences among the serotypes. Pullorum RM contained less lauric and 3-hydroxymyristic acids and more myristic and palmitic acids than the other three serotypes. The identity of 3-hydroxymyristate was confirmed by mass spectroscopy. Serotype Pullorum RM required 10 times more lipopolysaccharides (endotoxin) to obtain a 50% lethal dose in mice than the other three serotypes. When the lipid part was separated from the polysaccharide and solubilized with bovine serum, the 50% lethal dose of serotype Pullorum RM was equal to that of the other three.

Expression of the alpha(1,3)fucosyltransferase Fuc-TVII in lymphoid aggregate high endothelial venules correlates with expression of L-selectin ligands.

Lymphocyte homing to lymph nodes and Peyer's patches is mediated, in part, by adhesive interactions between L-selectin expressed by lymphocytes and L-selectin ligands displayed at the surface of the cuboidal endothelial cells lining the post-capillary venules within lymphoid aggregates. Candidate terminal oligosaccharide structures thought to be essential for effective L-selectin ligand activity include a sulfated derivative of the sialyl Lewis x tetrasaccharide. Cell type-specific synthesis of this oligosaccharide is presumed to require one or more alpha(1,3)fucosyltransferases, operating upon common 3'-sialylated and/or sulfated N-acetyllactosamine-type precursors. The identity of the alpha(1,3)fucosyltransferase(s) expressed in cells that bear L-selectin ligands has not been defined. We report here the molecular cloning and characterization of a murine alpha(1,3)fucosyltransferase locus whose expression pattern correlates with expression of high affinity ligands for L-selectin. In situ hybridization and immunohistochemical analyses demonstrate that this cDNA and its cognate alpha(1,3)fucosyltransferase are expressed in endothelial cells lining the high endothelial venules of peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. These expression patterns correlate precisely with the expression pattern of L-selectin ligands identified with a chimeric L-selectin/IgM immunohistochemical probe and by the high endothelial venule-reactive monoclonal antibody MECA-79. Transcripts corresponding to this cDNA are also detected in isolated bone marrow cells, a source rich in the surface-localized ligands for E- and P-selectins. Sequence and functional analyses indicate that this murine enzyme corresponds to the human Fuc-TVII locus. These observations suggest that Fuc-TVII participates in the generation of alpha(1,3)fucosylated ligands for L-selectin and provide further evidence for a role for this enzyme in E- and P-selectin ligand expression in leukocytes.