Rennet paste

Semi-purified preparations of PGE from calf, kid and lamb are commercially available and give satisfactory results slight differences in specificity renders one or other more suitable for particular applications. Connoisseurs of Italian cheese claim that rennet paste gives superior results to semipuri-fied PGE, and it is cheaper. 

A good-quality rennet extract is free of lipolytic activity but a rennet paste is used in the manufacture of some Italian varieties, e.g. Romano and Provolone. Rennet paste contains a lipase, referred to as pre-gastric esterase (PGE), which makes a major contribution to lipolysis in, and to the characteristic flavour of, these cheeses. Rennet paste is considered unhygienic and therefore semi-purified PGE may be added to rennet extract for such cheeses (Chapter 8). 

Extensive lipolysis occurs in two families of cheese in which fatty acids and/or their degradation products are major contributors to flavour, i.e. certain Italian varieties (e.g. Romano and Provolone) and the Blue cheeses. Rennet paste, which contains pre-gastric esterase (PGE) rather than rennet extract, is used in the manufacture of these Italian cheeses. PGE is highly specific for the fatty acids on the sn-3 position of glycerol, which, in the case of milk lipids, are predominantly highly flavoured short-chain fatty acids (butanoic to decanoic). These acids are principally responsible for the characteristic piquant flavour of these Italian cheeses. 

Rennet extract should contain no lipolytic activity. Rennet pastes used in the manufacture of hard Italian varieties (e.g., Romano, Provolone) contain a potent lipase, pregastric esterase (PGE), which is responsible for the extensive lipolysis and the characteristic piccante flavor in such varieties. The literature on PGE was comprehensively reviewed by Nelson et al. (1977). 

Pirisi, A., Pinna, G., Addis, M., Piredda, G., MaurieUo, R., De Pascale, S., Caira, S., Mamone, G., Ferranti, R, Addeo, R, and Chianese, L., Relationship between the enzymatic composition of lamb rennet paste and proteolytic, hpolytic pattern and texture of PDO Fiore Sardo ovine cheese, Int. Dairy J.,11, 143, 2007. 

Whole milk (2 litres) is diluted with an equal volume of water at 30°-40° and commercial rennet (0-1 g.), dissolved in a few cubic centimetres of water, is added. The mixture is then left at the same temperature until separation of the casein is complete (about two hours). The whey is filtered through a filter cloth, and after the liquid has run off the residue is pressed down well. The casein, which contains a great deal of fat, is ground in a mortar with a little 1 per cent sodium hydroxide solution 1 to 1-5 litres of sodium hydroxide solution of the same concentration are then poured on to the resulting paste, and the mixture is gently warmed in a porcelain basin until all but the fat dissolves. 

Pepsin Obtained from the glandular layer of hog stomach. Produced as a white to light tan, water-soluble powder amber paste or clear, amber to brown, aqueous liquids. Major active principle pepsin. Typical applications used in the preparation of fishmeal and other protein hydrolysates and in the clotting of milk in manufacture of cheese (in combination with rennet). 

In the past, there have been concerns over the transmissible spongiform encephalopathies (TSE) contamination of animal-derived products. However, in the light of current scientific knowledge, and irrespective of geographical origin, milk and milk derivatives are reported as unlikely to present any risk of TSE contamination TSE risk is negligible if the calf rennet is produced in accordance with regulations. ... 

Owing to increasing world cheese production ( 4% p.a. over the past 30 years), concomitant with a reduced supply of calf rennet (due to a... 

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