Patent GB-654629-A (GB)
Title: Improvements in the manufacture of glutamic acid
Filed: 1946-06-12
Abstract: l(+) Glutamic acid is obtained by hydrolysing a protein with sulphuric acid, adding to the acidic protein hydrolysate an alkaline earth metal oxide or hydroxide in an excess amount sufficient to bring the pH to between 10.5 and 11.5, removing the resultant alkaline earth metal sulphate precipitate, treating the remaining solution to effect the removal of the residual alkaline earth metal ions and to reduce the pH to a value at which amino acids having an isoelectric point above that of l(+) glutamic acid will crystallize but throughout such treatment keeping the pH substantially above that which is optimum for the crystallization of l(+) glutamic acid, allowing the said amino acids other than l(+) glutamic acid to crystallize, removing such crystals, adding an acidifying agent to lower the pH of the solution to 3.2 to permit the l(+) glutamic acid to crystallize and finally recovering the crystallized l(+) glutamic acid from the solution. In a modification sodium hydroxide is used in addition to the p  excess of alkaline earth metal oxide or hydroxide to secure the desired pH of 10.5 to 11.5.  The specified proteins are gluten and the protein derived from soy beans.  The residual alkaline earth metal ions may be removed by treating the filtrate, after removal of the sulphate precipitate, with a substance which will react with the residual ions to form a precipitate, specified substances for this purpose being sulphur dioxide, acid sodium carbonate, carbon dioxide and sodium carbonate.  It is desirable to concentrate the solution which remains after removing the residual alkaline earth ions.  The concentration should be effected at a temperature not exceeding 65 DEG  C. and the concentrated solution should have a specific gravity of from 1.20 to 1.25 at 40 DEG  C. The concentrated filtrate contains amino acids having an isoelectric point above that of l(+) glutamic acid, e.g. tyrosine, leucine and iso-leucine.  To remove these amino acids the pH is reduced, e.g. to about 5.0, and this reduction may be effected by the use of carbon dioxide or sulphur dioxide in the treatment for the removal of the residual alkaline earth metal ions, or another acidifying agent such as hydrochloric acid may be used.  After removing the said other amino acids the glutamic acid is crystallized out by adding an acidifying agent such as hydrochloric acid to a pH of substantially 3.2.  The crystals may be converted to monosodium glutamate in known manner.  The end liquor may be recycled once or twice but it is eventually desirable to remove it from the system and convert it into a by-product which will contain amino acids having an isoelectric point lower than that of l(+) glutamic acid and some sodium chloride resulting from the use of any sodium reagent and hydrochloric acid in a prior step of the process.  In examples: (1) gluten is hydrolysed with sulphuric acid and the hydrolysate diluted with water, hydrated lime, e.g. in the form of a slurry of calcium hydroxide, is then added to raise the pH to between 10.5 and 11.5.  The calcium sulphate and humin material are removed by filtration and the filtrate treated with sulphur dioxide, the pH being maintained close to neutrality. This may be attained by adding sodium hydroxide or the latter may be added along with the neutralizing lime.  The calcium sulphite is filtered off and a mineral acid, preferably hydrochloric acid added to reduce the pH to between 5.5 and 6.0.  The filtrate is then concentrated and the unwanted amino acids allowed to crystallize, the glutamic acid being then recovered for the filtrate by crystallization as above described; (2) as in (1) except that acid sodium carbonate is used instead of sulphur dioxide and no sodium hydroxide is employed in the liming step.  The bicarbonate is added to a pH of about 8.5 and hydrochloric acid is added to reduce the pH to 5.5.ALSO:In the production of l(+) glutamic acid (see Group IVb), by hydrolyzing a protein with sulphuric acid, adding to the hydrolysate an excess of alkaline earth metal oxide or hydroxide to bring the pH to between 10.5 and 11.5, removing the resultant alkaline earth metal sulphate precipitate, treating the remaining solution to effect the removal of the residual alkaline earth metal ions and to reduce the pH to a value at which amino acids having an isoelectric point above that of l(+) glutamic acid will crystallize but throughout such treatment keeping the pH substantially above that which is optimum for the crystallization of l(+) glutamic acid, allowing the said amino acids to crystallize, removing the crystals, adding an acidifying agent to lower the pH to 3.2 to permit the l(+) glutamic acid to crystallize and recovering the latter, the end liquor may be recycled once or twice but is eventually removed and converted into a by-product which contains amino acids having an isoelectric point lower than that of l(+) glutamic acid and some sodium chloride resulting from the use of any sodium reagent and hydrochloric acid in any prior step of the process.  This end liquor in its original, concentrated or dry form is as stated to be a valuable flavouring material after its acidity has been neutralized by known methods.