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Mozzarella cheese was manufactured from milk containing either a low (olein) or a high (stearin) melting point fraction of milk fat or anhydrous milk fat. The fat was dispersed into skim milk by homogenization at 2.6 MPa before being manufactured into cheese. The melting point of the milk fat did not affect the size or shape of the fat globules, nor was there any effect of homogenization on the polymorphic state of the milk fat. There were no changes in milk fat globule size and shape concomitant with the amount of free oil formed. The polymorphic state of the milk fat did affect the amount of free oil formed and the apparent viscosity of the cheese. The lower melting point fraction yielded a larger amount of free oil. The higher melting point fraction yielded a higher viscosity of melted cheese at 60 degrees C. Mozzarella cheese was also manufactured from homogenized milk, nonhomogenized milk, and a 1:1 ratio of the two, without altering the milk fat composition. Increasing the proportion of homogenized milk yielded a lower free oil content and higher viscosity of the cheese.

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The effect of the extent and rate of compression and stretching on free oil formation in Mozzarella cheese curd was investigated at 55, 65, and 75 degrees C. Confocal laser scanning microscopy was used to determine the maximum cross-sectional diameter, cross-sectional area, elongation factor (maximum divided by minimum cross-sectional diameter), and circularity of fat globules in the cheese curd at the different temperatures, and after stretching or compression. Free oil was not significantly affected by the rate of biaxial compression from 50 to 2000 mm/min at 65 degrees C, the rate of tensile stretching from 1000 to 2500 mm/min at 60 degrees C, or the extent of biaxial compression from 40 to 80% of the original height at 1000 mm/min and 65 degrees C. Increasing the rate of stretching from 1000 to 2500 mm/min increased the elongation factor from 1.91 to 2.61. Cross-sectional area, maximum diameter, and circularity were not affected by the rate of biaxial compression. The extent of curd compression had no effect on the milk fat globule size and shape. Increasing the extent of stretching at 60 degrees C and at 1000 mm/min increased the free oil content (on a fat basis) from 23.8% (curd stretched by 1.4x) to 32.3% (stretched by 4.6x) and the elongation factor of the globules, but did not affect any of the other globule parameters. Increasing the temperature of the cooking-stretching water increased the cross-sectional area, diameter of the globules, and free oil content from 24.1% at 55 degrees C to 34.5% at 75 degrees C for curd compressed to 50% height at 1000 mm/min.

Mozzarella cheese was manufactured to different salt levels by a combination of dryand brine-salting. Free oil formation was lower, apparent viscosity of melted cheese was higher, and expressible serum was lower for cheese at the higher salt levels. Salt had no effect on the extent of primary proteolysis as measured by pH 4.6 sodium acetate buffer or 120 g•L-1 trichloroacetic acid soluble peptides. Fat globule size decreased in the cheese after 20 d of ripening. Additional Mozzarella curd was salted separately in a brine bath without additional dry-salting. At the centre of the brined block of curd where the salt content was lowest, free oil was highest and apparent viscosity was lowest. These results are discussed in relation to how salt affects free oil formation by altering the protein and water phases during ripening. Salt / mozzarella / cheese / fat globule / free oil Résumé-Modifications structurelles de la Mozzarella induites par le sel, et impact sur la formation d'huile au cours de la maturation du fromage. De la Mozzarella a été fabriquée avec différentes concentrations de sel, par une combinaison de salage à sec et par saumure. À niveau de sel élevé, la formation d'huile et la libération de sérum étaient faibles tandis que la viscosité apparente de fusion était élevée. Le sel n'avait aucun effet sur la protéolyse primaire, basée sur les peptides solubles mesurés soit dans un tampon acétate de sodium (pH 4,6) ou dans 120 g•L-1 d'acide trichloroacétique. La taille des globules gras dans le fromage diminuait après 20 j de maturation. Du caillé de Mozzarella a été également salé à différents degrés dans des bains de saumure. Au centre de ce caillé, là où la quantité du sel était la plus faible, la concentration en huile libre était la plus élevée et la viscosité apparente la plus faible. Les effets du sel sur la formation d'huile libre au cours de la maturation sont discutés en relation avec les effets du sel sur les protéines et la phase aqueuse.

Regulation of c-myc expression is known to occur at the level of transcription initiation. However, the participating promoter elements and their cognate binding proteins have not been fully characterized. c-myc transcription can be stimulated by a number of cytokines including interleukin-2 (IL-2). We have identified a novel IL-2-responsive element, located in the 5-flanking region of the c-myc gene, between nucleotides ؊1406 and ؊1387 (relative to the P2 promoter). This element belongs to the family of interferon-␥ activation site-like responsive elements and has the core sequence TTC-CAATAA. We confirmed that IL-2-mediated signaling involves activation by phosphorylation of Jak2 tyrosine kinase and subsequently STAT4. The transcription factor STAT4 binds the TTCCAATAA motif within this responsive element and, therefore, is probably involved in enhancing c-myc transcription upon IL-2 stimulation. Our results propose participation of Jak2 and STAT4 in IL-2-induced up-regulation of c-myc.

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