Coagulation rennet action

Thus, at the end of 24 hours, the milk coagulates less easily than an hour after the treatment. On the contrary, if the same milk is kept at ordinary temperature, it is found that at the end of ten hours it shows no notable modifications in its resistance to rennet-action. The difference in these results comes from the fact that, in the preservation at ordinary temperature, the lactic microbes have been able to develop and the activating action of the acid formed counterbalances the increasing resistance of the pure milk with age. The proof of this hypothesis is that if the lactic bacteria are prevented from developing, either by the use of formaldehyde, of mercury bichromate, or chloride, added to the milk at the temperature of the sunounding air, or quite simply by maintaining the milk at a temperature of 58 , we see that this milk acts like that kept in the refrigerator. This observation shows the precautions necessary to cany on experiments results of which shall be comparative. 

Destruction of the casein micelles in the milk with subsequent precipitation of the casein can be accomplished in a number of ways. The action of heat or the action of alcohols, acids, salts and the enzyme rennet all bring about precipitation. In commercial practise the two techniques used employ either acid coagulation or rennet coagulation mechanisms. 

Microbial coagulants are now useful and are responsible for about one third of all the cheese produced worldwide, but suffer from the disadvantage of being too stable and so are threatened commercially by improved methods of produdng chymosin by recombinant DNA technology. The use of thermally destabilized microbial rennets results in residual enzyme levels in the milk product similar to or below those encountered when calf rennet is use (55). An unexpected benefit has been an increase on some occasions of the specificity of the microbial enzyme, making it virtually indistinguishable from the action of calf rennet. Also some microbial rennets help impart a flavor that is popular with consumers. 

The action of the enzyme rennet on milk, known to destabllze a K-caseln and trigger agglomeration of a multl-caseln micellar suspension (ot,3,Y E <) to produce coagulated milk for cheese-making, has been shown to produce a reaction suspension with power law behavior also described by eqns (2.4-2.5)(Tucznlckl and Scott Blair). ... 

The action of reimet on milk is characterized by very striking external manifestations. With i g. of active product, 50 liters and more of milk can be coagulated in 30 to 40 minutes under favorable conditions. The velocity with which the coagulation takes place in a determined volume furnishes a relative measure of the power of the active substance, and most of the studies made on rennet from the point of view of its mode of action are based upon the coagulation produced in milk, although the phenomenon, as we shall see later, may be much less simple than one might at first believe. 

Influence of Various Substances. — Albumoses and peptones added to milk considerably retard the action of rennet. Thus it is that 0.5 per cent of peptone retards coagulation, and that in the presence of 5 per cent, rennet has almost no action on the milk. This paralyzing effect is partially explained by the possibility that peptones may enter into combination with add phosphates of the milk and render the action of the reimet more difficult by changing the reaction of the medium. 

Rennet is very sensitive to the action of antiseptics. Solutions of rennet, saturated with chloroform or thymol, are very rapidly rendered inactive. Yet milk, containing chloroform, affords a normal action with rennet not treated with chloroform, the coagulation being not at all retarded. With formaldehyde this difference is not observed. This last may be considered as... 

We have just seen that the rennet of brown algae acts even Gerber has shown that this manifestation of activity at a temperature so low does not constitute a very important distinctive characteristic, since all rennets are capable of coagulating milk at o if the precaution is taken of sensitizing the system by increasing the quantity of alkaline-earth salts which are already present. But while the salts of calcium are extremely active, the acids and the other alkali salts have only very slight activating actions, or even none at all. 

Parachymosin and reimet show perceptible differences to the action of KCl and of CaCU. KCl paralyzes coagulation and CaCb accelerates it to a greater extent with parachymosin than with ordinary rennet, very small quantities of CaCl rendering parachymosin much more active. 

To these differences already existing between parachymosin and ordinary chymosin, Briot adds another, drawn from the existence of an anti-rennet of parachymosin, different from that of calf reimet. While the coagulating action of anti-parachy-mosin is retarded by mixing with CO2, that of anti-rennet is not influenced. Further, the action of heat is different. While anti-rennet is sensitive to a temperature of 60 , anti-parachy-... 

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