Full resolution (JPEG) - On this page / på denna sida - XIII. The Milk - Cow’s Milk
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
CASEIN. 651
amounts of lime-salts the paraeasein-lime precipitates out while the
proteose-like substance (whey protein) remains in solution. In the
coagulation in an acid medium the conditions are entirely different and
proteoses and peptones are hereby formed to a considerable extent.
The paracasein is very similar to casein, but cannot be recoagulated
by rennin. A solution of alkali-paracaseinate is much more readily
precipitated by CaCb than an alkali-caseinate solution of the same con-
centration, and the precipitation limits for saturated ammonium-sul-
phate solution, the upper as well as the lower limit, lie, according to
Laqueur, lower with paracasein than with casein. The internal friction
of paracasein solutions is also, in his opinion, less than that of casein
solutions and indeed even to 20 per cent.
By continued action of rennin upon paracasein a further transformation
has been found in many cases (Petky, Slowtzoff, v. Hekwerden l
). This
is explained by the presence of another proteolytic enzyme in the (impure) rennin
preparation. This assumption seems to be plausible, and we are here probably
dealing only with a secondary process which has nothing whatever to do with the
true formation of paracasein. Whey protein is also formed after the very short
action of rennin, and the continued cleavage occurs with varying .speed. Thus
Schmidt-Nielsen found that the quantity of whey protein was even 3 per cent
of the casein nitrogen after the action of rennet for 15 minutes, and only 4.25
per cent after 6 hours’ action. These and other recent investigations favor
the assumption that the casein coagulation by rennet is a hydrolytic cleavage,
but the conditions are not so clear that this can be considered as proved.2
Frtsh, unchanged milk does not, as is known, coagulate on boiling; but in
not too rapid action of rennin a state may be observed in which the milk coagu-
lates on heating (metacasein reaction). A solution of paracasein lactate, accord-
ing to Laxa, 3
coagulates with rennin the same as a solution of casein lactate,
which indicates, he believes, that the paracasein is transformed into casein again
by the lactic acid. But as a precipitation of the paracasein from the acid solu-
tion is perhaps a pepsin action, the transformation of the paracasein into casein
by the lactic acid must not be considered as proved.
In the digestion of casein with pepsin-hydrochloric acid primarily a
phosphorized proteose is formed, from which then the pseudonuclein is
split off (Salkowski). The quantity thus split off is variable, as shown
by the researches of Salkowski, Hahn, Moraczewski, Sebelien,
and Zaitschek.4
The amount of phosphorus in the pseudonucleins
obtained also varies considerably. Salkowski considers that the quan-
tity of pseudonuclein split off is dependent upon the relation between
the casein and the digestion fluid, e.g., the quantity of the pseudonu-
^etry, Hofmeister’s Beitriige, 8; Slowtzoff, ibid., 9; v. Herwerden, Zeitschr. f.
physiol. Chem., 52; \V. van Dam, ibid., 61.
2
See also Werncken, Zeitschr., f. Biol., 52.
3
Laxa, 1. c.
4
Salkowski, Zeitschr. f. physiol. Chem., 27; Salkowski and Hahn, Pflii^er’s Arch.,
59; Salkowski, ibid., 63; v. Moraczewski, Zeitschr. f. physiol. Chem., 20; Sebelien
ibid., 20; Zaitschek, Pfluger’s Arch., 104.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
