GB651396A - Improvements in and relating to the purification of zein - Google Patents

Abstract

In a process for the decolorization of zein a solution of zein is treated with a solid decolorizing medium or media and a liquid bleaching agent or agents. The treatments are employed after the removal of the bulk of the impurities from the zein by normal processes. Stated to be catalysts which promote the action of the liquid bleaching agents are sodium silicate or pyrophosphate, ammonia, calcined ammonium perchlorate, ammonium hypochlorite, nitrate, carbonate, oxalate, formate or arsenate or mixtures thereof. The process may employ temperatures between 0 DEG C. and the boiling point of the solvent in which the zein is dispersed and any pH between 1-12. Examples of solid decolorizing media which may be used are activated wood, bone or animal charcoals, activated alumina, Fuller's earth, kieselguhr, bentonite, diatomaceous silica, precipitated chalk or mixtures thereof. Examples of liquid bleaching agents which may be used are solutions of hydrogen peroxide, sodium bisulphite, hydrosulphite, hyposulphite, hypochlorite, hypobromite, hypoiodite, oxalate, potassium permanganate and oxalic acid. In examples other than (5) and (11) commercial zein dissolved in 90 per cent aqueous alcohol is treated with decolorizing and bleaching agents and in all examples after filtering the zein is precipitated by forcing through an orifice into a stream of water, the precipitated zein being then collected and dried. The solution is boiled under reflux with, in examples (1) sodium bisulphite after which the zein is precipitated with ether, redissolved in alcohol, refluxed with sodium bisulphite and then activated animal charcoal; (2) hydrogen peroxide made alkaline with ammonia, sodium bisulphite, activated charcoal and sodium bisulphite again, successively; (3) hydrogen peroxide containing sodium phosphate and then activated bone charcoal; (6) Fuller's earth and activated bone charcoal together and after filtration with hydrogen peroxide rendered alkaline with ammonia; (7) hydrogen peroxide, sodium bisulphite and Fuller's earth together and after filtering and precipiting the zein with ether, decanting and redissolving in alcohol with activated bone charcoal; (8) with hydrogen peroxide made alkaline with ammonia followed by heating with activated alumina; (9) sodium hyposulphite solution followed by activated animal charcoal; (10) Fuller's earth and activated bone charcoal together and after filtration, with hydrogen peroxide made alkaline with barium hydroxide and then activated alumina. In examples (5) zein is dissolved in ethylene glycol monomethyl ether and heated with Fuller's earth and after filtration, hydrogen peroxide made alkaline with barium hydroxide and (11) zein is precipitated from an aqueous ethyl alcoholic extract from maize gluten by addition of dry ether, the precipitate redissolved in aqueous alcohol is warmed with hydrogen peroxide made alkaline with calcined magnesia and then with a mixture of Fuller's earth and activated bone charcoal. On pressing the product from each process, a pale coloured sheet is obtained. The activated charcoal or other solid medium may be employed in a column through which the zein solution is percolated. Any of the known methods of obtaining dry zein from a solution may be used in the process. The products may be formed into plastic masses with or without plasticizers and may be used for the production of coating and impregnating solutions, films and filaments, laminated filled and cellular products and like forms of high clarity and freedom from colour.