402 THE OXYDASES. 



of wine during storage. According to G. TOLOMEI (V.), oxydases 

 are also produced by the wine-yeasts Sac char omyces apiculatus 

 and Sacch. ellipsoideus. 



215. The Rapid Discoloration of Fresh Vegetable 



Juices 



is in many cases attributable to the action of oxydases. Technical 

 interest in the discoveries made on this point is chiefly centred in 

 the researches of G. BERTRAND (II.) on Japanese lacquer, that 

 lustrous and extremely durable varnish employed in Eastern Asia 

 for coating wooden furniture and similar articles. By making 

 incisions in the bark of the indigenous Rims vernicifera a tree 

 of the family Anacardiacece and closely allied to the European 

 garden-tree Rhus cotinus (Venice sumach) a juice is obtained 

 which, on admixture with the oil from Biynonia tomentosa and 

 (for red lacquer) vermilion, yields the lacquer in question. This 

 juice resembles a thick pale cream and will keep unchanged for 

 a long time if stored in closed bottles, but quickly turns brown 

 when air is admitted, becoming covered in a few minutes with a 

 tough black skin, and finally hardening, this being, in fact, the 

 property for which it is so highly prized. That a process of 

 oxidation is here in question cannot be doubted. The constituent 

 thus converted has been isolated by Bertrand under the name of 

 laccol, and recognised as a compound allied to the polyatomic 

 phenols, and capable of producing extremely violent reddening and 

 inflammation of the skin if applied in even very minute quantities. 

 The juice also contains an oxydase, named by Bertrand laccase, 

 by the known oxygen-carrying powers of which the laccol is 

 rapidly converted into a hard, black, oxy-compound, insoluble in 

 water, alcohol, &c. This product is not obtained in the absence 

 of the enzyme, only a resinous soluble grease, that remains sticky 

 for a long time, being obtained under such circumstances. In 

 addition to laccol, other polyatomic phenols (pyrogallol, hydro - 

 quinone, &c.) and their acid derivatives (e.g. gallic acid and tannin) 

 are quickly oxidised by laccase in presence of air. According to 

 the further discoveries of BERTRAND (III.), the polyphenols con- 

 taining at least two groups of OH or NH 2 (either in the ortho- 

 or in the para-position) are also easily and readily oxidised by this 

 oxydase. 



This interesting discovery gave an impulse to the elucidation 

 of several other phenomena interesting both to the food-stuff 

 chemist and the agriculturist. It is well known that the freshly 

 broken or cut surfaces of raw apples rapidly become discoloured 

 on exposure to the air, at first turning reddish and then becoming 

 brown. This is the cause of the ugly colour of expressed apple- 

 must. Housewives skilled in cookery are aware that this altera- 

 tion of colour does not ensue if the cellular structure of this 

 fruit is preserved unbroken until after the apple has been boiled. 



