Patent GB-676762-A (GB)
Title: Improvements in or relating to a method of preparing crystalline amino acids
Filed: 1947-09-03
Abstract: Crystalline amino acids or their salts are prepared from solution in a substantially saturated natural protein hydrolysate or mixtures thereof, by adding to the protein hydrolysate with the pH thereof within the range of 4 to 6.8 an organic liquid as hereinafter defined, distilling off the original aqueous solvent from the resulting solution and recovering the crystalline amino acids or salts from the organic liquid, the organic liquid being added initially to the hydrolysate in an amount such as substantially prevents a shift in the pH of the solution during the distillation step, the organic liquid being one which is miscible in substantially all proportions with the original aqueous solvent under the conditions present during the distillation step, has a higher boiling-point than the original aqueous solvent, is chemically inert with respect to the amino acids or salts thereof, and either has a dielectric constant lower than that of water or on addition of 1.5 volumes of the organic liquid to one volume of a substantially saturated natural protein hydrolysate having a pH value within the range of 4 to 6 will yield a solution having a pH value within the range of 4.5 to 5. Suitable organic liquids are acetal, acetonyl acetone, diacetone alcohol, acetyl piperidine, butylene glycol, carbitol or its acetate, diethylamine ethanol, ethyl lactate, glycol methyl ether and glycol ethyl ether.  In general, from 1 to 5 volumes of organic liquid are added to the saturated protein hydrolysate. The aqueous solvent may be distilled off under reduced pressure whereupon the amino compounds precipitate in crystalline form unless the organic liquid is a solvent for these compounds in which case further distillation is effected to remove this liquid. The protein hydrolysate may be prepared by acid, alkaline or enzymic hydrolysis of proteins such as yeast, casein, soya flour, wheat, corn and rice proteins.  When the hydrolysis destroys certain acids, e.g. trypophane and cystine, these acids may be added to the resulting hydrolysis product.  In an example, casein is hydrolysed under pressure with aid of sulphuric acid, the hydrolysate treated with excess calcium hydroxide to remove sulphuric acid, clear liquid decanted off and concentrated down to remove ammonia, last traces of calcium removed by treating with carbon dioxide and then with oxalic acid and finally treated with barium hydroxide to eliminate any sulphate and concentrated to a saturated sterile solution of amino acids; 3 litres of this solution is mixed with 4.5 litres of ethyl lactate resulting in a solution of pH 4.5-5, which is vacuum distilled to remove water and then ethyl lactate; the crystalline amino acids are washed and dried.  The Specification as open to inspection under Sect. 91 is not limited to the use of a substantially saturated natural protein hydrolysate as starting material and it is stated that the method may be applied to the production of individual crystalline amino acids or salts thereof or mixtures thereof.  This subject-matter does not appear in the Specification as accepted.ALSO:Crystalline amino acids or their salts are prepared from solution in a substantially saturated natural protein hydrolysate or mixtures thereof, by adding to the protein hydrolysate with the pH thereof within the range of 4 to 6.8 an organic liquid as hereinafter defined, distilling off the original aqueous solvent from the resulting solution and recovering the crystalline amino acids or salts from the organic liquid, the organic liquid being added initially to the hydrolysate in an amount such as substantially prevents a shift in the pH of the solution during the distillation step, the organic liquid being one which is miscible in substantially all proportions with the original aqueous solvent under the conditions present during the distillation step, has a higher boiling point than the original aqueous solvent, is chemically inert with respect to the amino acids or salts thereof, and either has a dielectric constant lower than that of water or on addition of 1.5 volumes of the organic liquid to one volume of a substantially saturated natural protein hydrolysate having a pH value within the range of 4 to 6 will yield a solution having a pH value within the range of 4.5 to 5. Suitable organic liquids are acetol, acetonyl acetone, diacetone alcohol, acetyl piperidine, butylene glycol, carbitol or its acetate, diethylamine ethanol, ethyl lactate, glycol methyl ether and glycol ethyl ether.  In general, from 1 to 5 volumes of organic liquid are added to the saturated protein hydrolysate. The aqueous solvent may be distilled off under reduced pressure whereupon the amino compounds precipitate in crystalline form unless the organic liquid is a solvent for these compounds in which case further distillation is effected to remove this liquid. An example is given. The protein hydrolysate may be prepared by acid, alkaline or enzymic hydrolysis of proteins such as yeast, casein, soya flour, wheat, corn and rice proteins.  Where the hydrolysis destroys certain acids e.g. trypophane and cystine, these acids may be added to the resulting hydrolysis product.  In an example, casein is hydrolyzed under pressure with aid of sulphuric acid, the hydrolysate treated with excess calcium hydroxide to remove sulphuric acid, clear liquid decanted off and concentrated down to remove ammonia, last traces of calcium removed by treating with carbon dioxide and then with oxalic acid and finally treated with barium hydroxide to eliminate any sulphate and concentrated to a saturated sterile solution of amino acids; 3 litres of this solution is mixed with 4.5 litres of ethyl lactate resulting in a solution of pH 4.5-5 which is vacuum distilled to remove water and then ethyl lactate; the crystalline amino acids are washed and dried.  The Specification as open to inspection under Sect. 91, includes the treatment by the above method of aqueous solutions of individual amino acids or salts thereof of or mixtures thereof. This subject-matter does not appear in the Specification as accepted.