MICROBIAL METABOLISM AND ITS INDUSTRIAL IMPLICATIONS 



food for future human consumption is an unlawful, although mainly 

 temporary, interference with their rights. 



Anyhow, we all know that this situation has led to the develop- 

 ment of a prosperous food preservation industry in which nowadays 

 the battle against the microbe world is directed along scientific lines. 

 However, as is demonstrated by the 'flat sours', the 'hard swells' and 

 the cases of 'sulphide spoilage' which from time to time occur in the 

 canning industry, this battle does not always end victoriously. A thor- 

 ough study of the micro-organisms responsible for these various types 

 of spoilage is, therefore, a point of primary importance. It is interesting 

 to note that even after several decades of intensive research sometimes 

 new types of spoilage and new microbial culprits may still be discov- 

 ered. I can refer here to a recent investigation made by my collaborator 

 Verhoeven who found that in nitrate-cured canned ham the swelling 

 of the cans is not due as usual to an evolution of hydrogen and carbon 

 dioxide in the can, but mainly to the evolution of a mixture of nitrogen 

 and nitrous oxide by some denitrifying bacterium. 



The circumstance that we meet 'laughing gas' here is particularly 

 noteworthy when we think of the remarkable physiological effects of this 

 gas on man. In this historic place, a short digression may perhaps be 

 permissible. Through a historical study made by my late colleague Cohen 

 of Utrecht I am acquainted with the fact that thanks to Davy's en- 

 thusiasm nitrous oxide has played a prominent role in the early his- 

 tory of the Royal Institution and that exactly one and a half centuries 

 ago these revered surroundings were the scene of remarkable demon- 

 strations of its physiological action. The fact that nitrous oxide can be 

 a product of microbial metabolism or, in other words, can originate 

 in a living cell, therefore appears in a special light. 



A characteristic example of an industry in which an invasion of 

 microbes can easily be expected is offered by the sugar industry. In 

 this connexion the interesting observations made in this country by 

 De Whalley and Scarr on the microflora which sometimes interferes 

 with sugar refining should be mentioned, but it seems to me that a 

 more systematic, investigation of the role which micro-organisms play 

 in the sugar industry as a whole still remains to be done. 



It had already been recognized some 60 years ago that the clogging 

 of pipelines in this industry which often led to serious difficulties in 

 manufacturing was due to the proliferation of a capsule-forming strep- 



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