258 CHAPTER XIII 



The Colouring Matter of Cane Juice. The principal colouring matters in 

 cane juices are chlorophyll, anthocyan, saccharetin, and bodies of a polyphe- 

 nol nature (tannins), all of which occur naturally. Formed in the process of 

 manufacture are caramel and lime-glucose decomposition products. Chloro- 

 phyll is the substance to which the green colour of plants is due ; whatever 

 quantity of this passes into the juice is removed in the press cake. Anthocyan 

 is the term applied to the red and purple colouring matter to which the 

 colour of some canes is due. Actually the term means nothing more than 

 colouring matter. It is dark green in alkaline solution, and is precipitated 

 by an excess of lime. Saccharetin is the term applied by Steuerwald 3 to an 

 " incrusting " material obtained by cold alkaline digestion of bagasse. This 

 body is probably a waste product of the plant metabolism and is found 

 deposited on the fibre. It is an aromatic carbon compound, giving pyro- 

 gallol on dry distillation and catechol on fusion with potash. On heating 

 with hydrochloric acid, vanillin is given off. This substance is colourless in 

 acid, and deep yellow in alkaline solution, and is connected by Steuerwald 

 with causing the dark colour of cane products in combination with iron salts. 



The incrusting material of lignified plant tissues have been identified 

 by Tiemann and Harman with coniferin, but Czapek 4 regards it as an alde- 

 hyde, closely related to coniferylic alcohol, to which he has given the name 

 hadromal. 



Tannins were first observed in the cane, by Szymanski 5 and were after- 

 wards studied by Went 6 , by Browne 7 , and mere recently by Schneller 8 and 

 by Zerban 9 . These bodies are located mainly in the actively vegetative 

 portions of the cane, especially the tops and the eyes. Schneller regards the 

 incrusting material or saccharetin of Steuerwald as derived from these tannins 

 or polyphenols, and deposited as waste matter on the parenchyma. These 

 bodies have the property of forming, with ferric salts, dark-coloured bodies, 

 which are nothing but inks, and to these inks the dark colour of cane juices, as 

 well as the greyish tint often seen in white sugars, may be attributed. 

 This coloration is, however, also connected with the action of oxidizing 

 enzymes occurring in the juice, the presence of which is first shown by 

 Raciborski 10 , and the action of which has been further studied by Zerban 9 . 

 He shows that cane juices expressed in the absence of contact with iron are 

 originally nearly colourless passing to brown, due mainly to the action of a 

 laccase on the polyphenols, and also, but to a much smaller degree, of a 

 tyrosinase on the tyrosin of the cane. In the presence of a ferrous salt, these 

 oxidizing ferments rapidly convert the ferrous salt to the ferric state with 

 the formation of a dark green colour. In juices where the enzyme has been 

 destroyed by boiling or by precipitation with alcohol, the addition of a 

 ferrous salt does not produce the dark green colour at once, but only after 

 exposure to the air. 



In addition to the naturally occurring colouring matters, others are 

 formed by the action of lime on the reducing sugars. Schneller thinks 

 these decomposition bodies are allied to the polyphenols, and they also form 

 dark- coloured ferric salts. A second artificially formed colour is caramel 

 formed at the expense of the cane sugar, and due to the action of heat. Of 

 its chemistry and composition little is known, and it is probably a mixture 

 of bodies. 



Acidity and Alkalinity. Under the generally accepted theory, acidity 

 and the presence of free hydrogen ions are synonymous terms, and an acid 



