On expressed yeast-cell plasma (Buchner's 'zymase') / by Allan MacFadyen, G. Harris Morris and Sydney Rowland.

  • Macfayden, Allan, 1860-1907.
Date:
[1900]
Catalogue details

Licence: In copyright

Credit: On expressed yeast-cell plasma (Buchner's 'zymase') / by Allan MacFadyen, G. Harris Morris and Sydney Rowland. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    These further investigations, Buchner considers, are confirmatory of the conclasion dravui liy him from his original experiments, viz., that the activity of the yeast-cell as an alcoholic ferment depends upon the action of a soluble enzyme of an albuminoid character elaborated b}^ the living cell. To this soluble ferment Buchner applies the name “ Zymase.” The subject presented so many phases not only of special but also of general biological interest that we were led to pursue its investiga- tion. We considered this the more necessary since Buchner’s experi- ments were carried out entirely with bottom-fermentation yeasts, and it appeared of interest to ascertain whether top-fermentation yeasts (as used in English brewing) give parallel results. At the outset we carefull}’ adhered to Buchner’s method of expressing the cell plasma ; Init owing to the tediousness of the process we were led, after many attempts, to adopt the following arrangement for the extraction of the cell plasma or juice. Method of Preparation of the Cell Plasma.—The yeast as received from the brewery is a thick, pasty, frothy mass, consisting of yeast- cells intermixed with more or less fermented wort. For the purpose^ in view it is necessary to separate the yeast-cells from all adherent matter which would by its presence influence the composition of the expressed juices. The purification of the yeast is thus a necessary pi’eliminary operation, and is accomplished as follows:— To the pasty mass of crude yeast is added an equal part of water and the mixture stirred together. This suspension of yeast-cells is then centrifugalised, whereby the contained cells are separated as a thick creamy mass at the bottom of the containing vessel. The super- natant liquor is decanted and the mass of cells again stirred into a suspension in a fresh quantity of water. The mixture is again centri- fugalised, and the process repeated until the last added water comes away clear and colourless. The final product of this process is a firm mass of yeast-cells closely packed together, with a minimal quantity of adherent water. It is necessary to remove even this quantity of water if a natural juice is to be obtained. The pasty mass of yeast is wrapped in a double thickness of “ hydraulic chain cloth ” and intro- duced into one of a series of shallow iron trays, so constructed that the pile can be strongly compressed in a hydraulic press and the expressed liquor run off. In this process, which is a modified form of filter- pressing, the last adherent portions of water are removed from the yeast-cell, and the mass of yeast as removed from the cloths appears as a perfectly dry white powder, consisting of yeast-cells ■Hath approxi- mately dry exteriors. The pressure necessary to produce this result is from 70—100 atmospheres. The disintegration of the yeast-cell is the next process. This is accomplished by a mechanical contrivance which maintains the yeast.