DISCOLORATION OF VEGETABLE JUICES. 403 



L. LINDET (I.) in 1893 explained this discoloration as resulting from 

 the action of an enzyme, to which he subsequently gave the name 

 of laccase without, however, implying the identity of this with 

 the oxydase of the lac-tree. The name of malase would probably 

 be more suitable for this apple enzyme. In the case of apple- 

 juice also, oxygen is carried by the enzyme to the tannin, and 

 thus dark coloured oxy-compounds are produced, which are pre- 

 cipitated on the cell walls as a fast, permanent dye. The spotting 

 of sound apples under the rind, the so-called brown spotting, is 

 explainable in the same manner. So long as the structure of the 

 cell remains perfectly intact, the atmospheric oxygen cannot obtain 

 access to the enzyme (in the plasma) or to the tannin. As soon, 

 however, as by mechanical action (e.g. the dropping of the apple 

 from the tree, pressure in packing or transit, &c.) any of the cells 

 become ruptured, then an opportunity is afforded the oxygen to 

 act on the now exposed constituents of the plasma. If the rind 

 of the fruit remains uninjured, the air gains admission to the 

 interior merely through the intercellular spaces alone, and, in such 

 event, will produce only a faint reaction and slight discoloration. 

 Whether, as assumed by Lindet, the enzyme and tannin are con- 

 tained in separate cells (i.e. distinct from each other), is a question 

 still requiring more accurate research on the part of the botanist 

 to decide. 



The darkening of beet-juice, or the rapid discoloration of the 

 fresh slices of beet in the sugar-works, evidenced even when 

 cutting tools devoid of iron are employed, is equally attributable 

 to the action of an oxydase present in the sugar-beet. This was 

 discovered by G. BERTRAND (IV.), and received the name of 

 Tyrosinase, because it carries atmospheric oxygen to the tyrosine 

 well known to be abundantly present in the cells of the sugar- 

 beet and thus produces the discoloration in question. On the 

 other hand, laccase has no effect on the said amido-compound. 

 Apart from this property, tyrosinase is also characterised by its 

 greater susceptibility both to heat and chemical influences. It 

 occurs in other plants, e.g. the bulbs of the dahlia (Dahlia vari- 

 abilis). According to the researches of G. BERTRAND (V.), oxidising 

 enzymes are also found in other plants, e.g. in the carrot; the 

 tubers of the potato (which, as is well known, rapidly become 

 discoloured when cut in an uncooked state) ; in the pear, quince, 

 and chestnut; in the sprouts of asparagus, clover, lucerne, and 

 rye-grass ; in the leaves of the potato, sugar-beet, &c. For detect- 

 ing this class of enzymes Bertrand recommends the employment 

 of guaiacum tincture, which produces therewith a blue coloration 

 when dabbed or poured on to the cut surface or juice under exa- 

 mination. To isolate these enzymes the plant juice is mixed with 

 alcohol, the resulting precipitate being dissolved in a little water 

 and filtered. On pouring the filtrate into five volumes of alcohol, 

 a precipitate consisting of the desired enzyme will be formed. 



