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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 16, No. 9
The Rennin Coagulation of Milk
of sodium caseinate towards rennin a case of autoprotection, but I confess I do not quite understand the mechanism by which a Editor of Industrial and Engineering Ckemistry: colloidal dispersion protects itself. O n page 633 of the June, 1924, issue of THISJOURNAL, Leroy S. It is the behavior of dispersions of calcium caseinate, not Palmer, in speaking of the views of Alexander, and of Schryver, sodium caseinate, towards rennin which renders Dr. Alexander’s on the rennin coagulation of milk, says : theory untenable. The fact that such dispersions will clot with Both these purely colloidal theories of the rennin coagulation rennin a t the proper pH and in the presence of salts of the divalent are shown to be impossible by the observation of the writer that cations seems t o me t o be an experimental demonstration of perfectly stable suspensions of calcium caseinate can be prepared rennin coagulation which throws out of court the circumstantial without the presence of other protective colloids. Moreover, these calcium caseinate milks, in the proper concentration and evidence which Dr. Alexander has cited in support of his lactalwhen brought to the proper Sorenson value of 6 to 6.5 in the pres- bumin-protection theory. ence of a trace of calcium ions, show a normal rennin clot which As to whether there is a nucleus of verity in Dr. Alexander’s exhibits all the properties of syneresis, etc. These gels, however, theory, I am of the opinion that there is none a t all and that it lack the firmness of normal rennin gels, showing that this property constitutes one of the exceptions in Herbert Spencer’s philosophy is contributed in part by the other constituents of the milk. The chemical properties of calcium paracaseinate, as the prod- which caused him to insert the words “generally” and ‘‘usually’’ uct resulting from the action of rennin on calcium caseinate is in the quotation which Dr. Alexander gives. It was obviously called, indicate that the rennin coagulation is both chemical and impossible in my paper to review in detail the evidence which colloidal. Dr. Alexander brought forth in his paper.l He cites four points The view advanced by Alexander as to the rennin coagulation of in support of his theory, all of which fall to the ground on close milk1 is that the enzyme splits the lactalbumin, converting it examination : probably into products that exert a coagulative rather than a (1) The failure of mother’s milk to clot like cow’s milk is not protective action, the coagulation being aided by calcium ions due to a high protective ratio between casein and albumin, as Dr. Alexander believes, but to the very low concentration of released from adsorption. This view is supported by the fact casein in mother’s milk and to its higher pH. If cow’s milk is that the highly protected mother’s milk is coagulated slowly, if diluted with water so that it contains only 0.2 to 0.3 per cent a t all, by rennin, whereas the cow’s milk, having a low protective casein2 and the pH value raised to that of mother’s milka i t will ratio, is readily coagulated. Furthermore, lactalbumin, a proclot like mother’s milk without having its casein-albumin ratio changed. tector to silver chloride, becomes a coagulator when acted on by ( 2 ) It is undoubtedly trtie that lactalbumin will protect pepsin. colloidal dispersions of silver chloride, whereas the peptic digesWhile casein is generally considered a definite chemical sub- tion products will not do so, but this does not prove that it is stance, 8ny substance supposed to be such a chemical individual the lactalbumin in milk which stabilizes the calcium caseinates. Calcium caseinates are stable without the presence of lactalbumin. as “sodium caseinate” should have the closest scrutiny. Even (3) Dr. Alexander states that the products of peptic digestion granting that perfectly stable suspensions of “sodium caseinate” of lactalbumin “coagulate” the silver chloride in the reaction of unquestioned purity can be prepared, how does that prove the lactalbumin) NaCl AgNOa. This is obviously (pepsin impossibility of the view that protective action is a factor in the as much an error as to assume that the coagulation of calcium paracaseinate is caused by albumoses and peptones formed by behavior of milk (which it is)? If impurities in the “sodium rennin from lactalbumin. This assumption involves the further caseinate” will not account for its behavior, there is the question one that rennin digests lactalbumin a t a sufficiently rapid rate of autoprotection, a phenomenon of wider occurrence than is to account for the instantaneous coagulation which it is possible t o generally recognized. Dr. Palmer’s argument recalls that of the secure with rennin. Dr. Alexander must admit that he has not Irishman who, to rebut the testimony of witnesses who swore demonstrated the correctness of either of these assumptions, but has merely drawn his conclusions from the lactalbumin-silver they saw him steal the pig, offered to bring in ten times as many chloride experiments. Analogies sometimes lead to false conwitnesses who would swear that they never saw him steal it. clusions. It is not out of place to quote a few of the opening sentences (4) Dr. Alexander is correct in stating that “casein” prepared by the method described in his paper requires a smaller quantity from Herbert Spencer’s “First Principles:” of acid for coagulation than a like quantity of milk. This is not We too often forget that not only is there a soul of goodness due, however, to the absence of lactalbumin, but rather t o the in things evil, but very generally, also, a soul of truth in things absence of buffer salts in which milk abounds. According to erroneous. While many admit the abstract probability that a Dr. Alexander’s reasoning his casein preparation should also be falsity has usually a nucleus of verity, few bear this abstract more sensitive to rennin. He apparently failed to try this exprobability in mind, when passing judgment on the opinions of periment. Had he done so he would have found that his casein others. preparation was less sensitive to rennin and very probably would have failed to coagulate. As a matter of fact, there is no analogy Even granting that the AlexandePSchryver view does not take between the acid and rennin coagulation. The former is a into consideration all the factors involved, the nucleus of verity decalcification resulting in a curd of more or less isoelectric casein should be supplemented, not discarded. (depending on the experimental conditions), while the latter JEROMEALEXANDER is a gelation of calcium containing protein (paracasein) due 50 EAST4 1 s ~ST., NEWYORK, N . Y. apparently to chemical and physico-chemical changes not yet June 12, 1924 clearly understood. One thing is clear, however-namely, that neither lactalbumin nor its digestion products have ever been .......... demonstrated to play any part, either directly or indirectly, in the actual coagulation process. Editor of Industrial and Engineering Chemistry: L. S. PALMER Dr. Alexander apparently takes exception to my criticism of his UNIVERSITY O F MINNESOTA rennin coagulation theory because I did not permit a “nucleus UNIVERSITY FARM, ST. PAUL, MI“. of verity” in his opinion regarding the explanation of this pheJune 24, 1924 ___nomenon. He also inquires how the behavior of “sodium case18th Inlern. Cong. Apbl. Chem., 6, 12 (1912). inate” solutions disproves the possibility “that protective action 2 Bosworth,N e w York Agr. Expt. Sta., Tech. Bull. 43 (1915). 8 Clark, J . M e d . Res., 81, 431 (1914-15). is a factor in the behavior of milk.” Replying first to his question, I may say that the behavior of sodium caseinates throws no light on the rennin coagulation of E. F. Armstrong, the immediate past president of the Society milk, because (1) rennin will not clot such a caseinate, ( 2 ) casein of Chemical Industry, expects to sail for the United States on exists in cow’s milk, not as a sodium compound, but as a calcium September 13 and to address the New York Section of the Society of Chemical Industry on October 17. His address while compound. No doubt Dr. Alexander would call the behavior in the United States will be in care of Leber Brothers Co., Cambridge, Mass. 18th Intern. Cong. A p p l . Chem., 6, 12 (1912).
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