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the rancidity of oils (the oxygen ot the air, light, moisture, enzy- 

 matic substances, chemicals), it was shown in a preliminary 

 examination that the action of water and air in the dark even 

 at a high temperature (40" C) was of no importance ; the 

 flavour odour and acid value were only slightly changed. As 

 soon as light co-operates however, a distinct change can be 

 observed ; the flavour and odour become acrid and disagreeable, 

 whilst the acid value increases very slightly. These changes are 

 still more noticeable when small quantities of acid (sulphuric 

 acid) or oxidising substances (iron chloride or hydrogen per- 

 oxide) are added to the cocoa nut oil. Through the action of 

 pancreas- or castor seed lipase cocoa nut oil soon undergoes an 

 important splitting operation, noticeable by the odour of lower 

 fatty acids. Under the simultaneous action of hydrogen per- 

 oxide and lipase, especially when free acid is added, a very 

 sharp and disagreeable odour in caused, which reminds one of 

 aldehydes or pyrouvic acid. 



During all these experiments however, the typical rancidity 

 of cocoa nut oil did not occur. Here we have to deal with 

 oxidation processes, which may be accelerated by emulsifying 

 cocoa nut oil with a solution of agar-agar to which the above 

 mentioned substances have been added. The large surface of 

 the fine fatty globules cause a quickened oxidation. Similar 

 changes may also be observed in all sorts of other fats and 

 oils and in this respect cocoa nut oil and palm kernel oil are no 

 less constant. 



Experiments showed that the well-known ester odour of rancid 

 cocoa nut oil appears only when it is subject to the influence 

 of microbes. It is easy to demonstrate this by exposing to 

 the air for some time a solid nutrient medium consisting of 

 agar-agar in which cocoa nut oil has been emulsified, or by 

 inoculating it with soil. After a few days several colonies of 

 microbes (yeasts, moulds, bacteria) develop on such plates and at 

 the same time the smell of rancid cocoa nut oil can be observed. 

 On closer examination they appear to be only moulds which 

 in pure culture are apt to render cocoa nut oil rancid. 



Therefore a clear distinction ought to be made between this 

 form of rancidity and the one caused by oxidation under the 

 influence of light. 



