Cheese curd

The absorption of vitamins K2, which are found mainly in cheese, curd cheese, and natto, is much higher and may be almost complete. Thus the nutritional importance of menaquinones is often underestimated. The vitamin K activity is related to the activation of specific proteins involved in blood clotting and bone metabolism. Clinical vitamin deficiency due to dietary inadequacy is rare or nonexistent in healthy adults, thanks to the widespread distribution of the vitamin K in foodstuffs and the microbiological flora of the gut, which synthesizes menaquinones. Only infants up to 6 months are at risk of bleeding due to a vitamin K deficiency. No data on negative effects of an overdose of vitamin K are found [417]. 

Cathepsin D (EC3.4.23.5). It has been known for more than 20 years that milk also contains an acid proteinase, (optimum pH ss 4.0) which is now known to be cathepsin D, a lysozomal enzyme. It is relatively heat labile (inactivated by 70°C x 10 min). Its activity in milk has not been studied extensively and its significance is unknown. At least some of the indigenous acid proteinase is incorporated into cheese curd its specificity on asl- and / -caseins is quite similar to that of chymosin but it has very poor milk-clotting activity (McSweeney, Fox and Olson, 1995). It may contribute to proteolysis in cheese but its activity is probably normally overshadowed by chymosin, which is present at a much higher level. 

Extensive lipolysis also occurs in Blue cheese varieties in which the principal lipase is secreted by P. roqueforti (Chapter 10). It is claimed that treatment of Blue cheese curd with PGE improves and intensifies its flavour but this practice is not widespread. Several techniques have been developed... 

Typically, five steps, or groups of steps, are involved in the conversion of milk to cheese curd coagulation, acidification, syneresis (expulsion of whey), moulding/shaping and salting. These steps, which partly overlap, enable the cheesemaker to control the composition of cheese, which, in turn, has a major influence on cheese ripening and quality. 

Syneresis. Renneted milk gels are quite stable if undisturbed but synerese (contract), following first-order kinetics, when cut or broken. By controlling the extent of syneresis, the cheesemaker can control the moisture content of cheese curd and hence the rate and extent of ripening and the stability of the cheese - the higher the moisture content, the faster the cheese will ripen... 

While rennet-coagulated cheese curd may be consumed immediately after manufacture (and a little is), it is rather flavourless and rubbery. Consequently, rennet-coagulated cheeses are ripened (matured) for a period ranging from about 3 weeks for Mozzarella to more than 2 years for Parmesan and extra-mature Cheddar. During this period, a very complex series of biological, biochemical and chemical reactions occur through which the characteristic flavour compounds are produced and the texture altered. 

Glycolysis. Most (about 98%) of the lactose in cheese-milk is removed in the whey as lactose or lactic acid. However, fresh cheese curd contains 1-2%... 

Gervais, A. and Vermeire, D. 1983. A critical study and improvement of the cheese curd torsiometer. J. Texture Stud. 14, 31-45. 

The physical and chemical characteristics of cheese curd depend on the method used to form the curd matrix. The curd is formed in basically one of two ways acid or enzymatic coagulation. In acid curd cheeses (cottage, baker s, cream), the curd is formed by direct addition of acid to the milk or by lactic acid produced by the fermentation of lactose. As the pH of the milk approaches the isoelectric point of casein (pH... 

Most varieties of cheese are cooked by applying heat to the outside of the vessel containing the curd and whey slurry. Gouda cheese curd is heated by first draining a portion of the whey and then adding hot water. The proportion of whey removed and water added is varied to control the amount of residual lactose in the curd. Washing of the curd is also used in cottage and brick cheese manufacture to remove lactic acid and lactose, but in these cases the cheese curds have first been heated. 

High mineral content of cheese curd at draining promotes the development of elastic texture. Minimum mineral loss from the curd occurs after draining. Cheese varieties with eyes (Swiss, Gouda) require elastic curds to permit round eye formation. These cheeses are drained... 

The other major casein in cheese is /3-casein, but it is generally not hydrolyzed by rennet in low-pH cheeses. Alkaline milk protease (plas-min) plays the major role in the hydrolysis of /3-casein (Richardson and Pearce 1981). The plasmin level in cheese is related to the pH of the curd at whey drainage, since plasmin dissociates from casein micelles as the pH is decreased. Richardson and Pearce (1981) found two or three times more plasmin activity in Swiss cheese than in Cheddar cheese. Swiss cheese curds are drained at pH 6.4 or higher, while Cheddar cheese curds are drained at pH 6.3 or lower. Proteolysis of /3-casein is significantly inhibited by 5% sodium chloride. The inhibitory influence of sodium chloride is most likely due to alteration of /3-casein or a reduction in the attractive forces between enzyme and substrate (Fox and Walley 1971). 

The cheddared cheese curd is milled into thin strips, salted, placed in cheese hoops, and pressed overnight to expel additional whey and fuse and curd strips together. The pressed cheese is then removed from the hoops and coated with wax or wrapped in a plastic film. 

Fat is a major component in most cheese types, but its level and importance differ markedly with variety. Inter- and intra-variety differences in fat content are affected by a number of factors, including milk composition (particularly ratio of protein to fat), and the cheesemaking process (recipe, manufacturing procedure and technology), which control the levels of milk fat and moisture retained in the cheese curd and the moisture content of the cheese. The ratio of protein-to-fat in the cheese milk is probably the principal factor influencing fat content, as it controls the relative proportions of two of the three major compositional components in cheese, namely protein and fat the third major component is moisture. Owing to the inverse relationship between the percentage of moisture and fat in cheese, as discussed in Section... 

Shakeel-Ur-Rehman, Waldron D., Fox P.F. 2004. Effect of modifying lactose concentration in cheese curd on proteolysis and in quality of Cheddar cheese. Int. Dairy J. 14, 591-597. 

This liposome enzyme system is a combination of an endopeptidase and an exopeptidase. The enzymes are slowly released after the cheese is put into the aging chamber. Using these liposomes for cheddar cheese production showed that the liposomes were evenly distributed and 90% of the added enzyme was retained in the cheese curd. The resulting cheese ripened in half the normal time with excellent flavor and textural properties. 

Enterococci occur in a variety of cheeses, especially artisan cheeses produced in mostly Mediterranean countries from raw or pasteurized goat s, ewe s, water-buffalo s or bovine milk. Numbers of enterococci in different cheese curd range from l(f to 10 CPU g", and in the fully ripened cheeses their range is from 10 to 10 CPU g" (Franz et al. 2003). The most frequently isolated species are E. faecalis and E. faecium (Gelsomino et al. 2001), followed by E. durans (Cosentino et al. 2004 Suzzi et al. 2000). The European cheeses in which enterococci have been studied are in Table 3. 

Huppertz, T., Fox, P.F., and Kelly, A.L. 2004. Effects of high pressure treatment on the yield of cheese curd from bovine milk. Innovative Food Science and Emerging Technologies 5 1-8. 

Effective Diffusion Coefficients for Total Solids During Washing of Cheese Curd, J. Food Sci.. 

Only about 7% of the coagulating enzyme activity is retained in the cheese curd (200) the remaining activity is expelled in the whey. Recently, Dulley (200) observed that cheeses containing normal and double normal amounts of rennet showed very little difference in peptides soluble in dilute trichloroacetic acid after 10 months maturation this suggests that the amount of rennet did not significantly affect proteolytic breakdown of the cheese proteins. Furthermore, Dulley (200) did not observe a significant difference in starch gel electrophoretic patterns of cheese proteins from cheese containing normal and double normal... 

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