Volume 1

Chemical technology and analysis of oils, fats, and waxes / by J. Lewkowitsch.

  • Julius Lewkowitsch
Date:
1904
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Chemical technology and analysis of oils, fats, and waxes / by J. Lewkowitsch. Source: Wellcome Collection.

    44/454 (page 24)
    24: CHAP. CLASSIFICATION OF OILS, FATS, AND WAXES instances rancidity sets in and continues for some time, without the liberation of any free acid. Lewkowitsch1 has also shown in the case of a specimen of cacao butter that although the fat contained free fatty acids, it could not be declared rancid. Hence, rancidity is not due, as is still widely held, to the presence of free fatty acids alone; in other words, rancidity must not be considered as coterminous with acidity. The frequent confounding of these two terms is caused by the fact, that acid oils and fats are frequently rancid as well. It is only when oxygen and light gain access to the acid fats, that the conditions favouring the setting in of rancidity are given. Rancidity is rather due to the direct oxidation of the air, assisted and intensified by the exposure to light. Oxygen and light must act simultaneously, either of these agents alone being unable to produce rancidity (fiitsert). Hence, the greater the surface offered to the atmosphere, the greater will be their influence. I therefore define as rancid those oils and fats, the free fatty acids of which have been acted on by the oxygen of the air, in the presence of light. Similar explanations have been given before, and the only new element I can claim here would consist in more emphatically ascribing the initial phase of rancidity, namely, the hydrolysis, to the action of enzymes than has been done hitherto.2 Thus, to leave out older statements, Duclaux3 has drawn from an experimental research the conclusion that rancidity is due to slight hydrolysis and subsequent action of the oxygen in the air assisted by light. Geitel4 has further elaborated this ex- planation by laying stress on the influence of moisture in the initial hydrolysis. Some authors have maintained that rancidity is due to the action of micro-organisms, a view which seems to have been supported by the discovery of living micro-organisms in poppy seed oil (Kirchner)/' and further by a number of observations made on butter. Butter, however, containing as it does a considerable amount of organic, non-fatty substances, cannot be put on the same basis with oils and fats which we are considering, for it is butter fat and not butter with which we are concerned here. It is quite true that bacteria decom- pose fats to a large extent, but they accomplish this only when suitable nutriment is offered to them with the fat. In that case the micro-organisms will grow, and as all the necessary conditions are provided, free play is given to those agencies which produce rancidity. It may, however, be left an open question whether these changes are due to the direct action of the living organisms, or rather to the action of an enzyme produced by them, much as the alcoholic fermentation of sugar can no longer be ascribed to the living sacharomyces cells, but rather to the zymase produced by them. 1 Journ. Soc. Chem. Jnd. 1899, 557. - Lewkowitsch. Journ. Soc. Chem. Jnd. 1903, 68; Jahrbueh f. Chemie, 7 (1897), 368 ; 8 (1898), 392 ; 9 (1899), 351 ; 10 (1900), 382 ; 11 (1901):_360 ; 12 (1902), 363. 3 Anncdes de VInstitut 1‘asleur, 1887 ; Compt. rend. 102, 1077. 4 Journ. f. prakt. Chain'c, 1897 [55], 448.