Patent GB-682762-A (GB)
Title: Fractionation of amino acid mixtures
IPC: A23J3/30
Filed: 1948-03-02
Abstract: The separation of an aqueous solution mixture of amino carboxylic acids, such as a protein hydrolysate, into groups of acidic-, neutral- and basic-amino acids respectively by treatment with cation and anion exchange materials, is characterized in that the mixture is passed through a bed of acid-regenerated cation-exchange material thereby absorbing thereon the amino acids of all of said groups while any impurity anions present pass in the effluent from the bed, and then selectively unloading the acidic and neutral amino acids by displacing them from their combination with the exchange material by passing through the bed an unloading solution comprising ammonium hydroxide as a base which converts the acidic and neutral amino acids, but substantially not the more strongly held basic amino acids, into noncationic form in which they are eluted from the exchange material whereby the material is left containing basic amino acids along with NH4+ cations, meanwhile collecting the resulting effluent solution in a first fraction up to a point defined substantially by a point of abrupt increase in the pH change of the effluent, the said fraction containing acidic and neutral amino acids uncontaminated with NH4+ cations and basic amino acids, and in a second fraction containing substantially the remainder of the acidic and neutral amino acids contaminated by NH4+ cations from the unloading solution and by a minor quantity of basic amino acids displaced by the unloading solution, the major quantity of the basics remaining on the exchanger bed, and employing the second fraction in addition to the unloading solution in a subsequent unloading operation whereby acidic and neutral amino acids in the said fraction are recovered in the unloaded effluent while NH4+ cations and basic amino acids in the fraction act as unloading agents so that the exchange material is left containing the basic amino acids substantially free from the acidic and neutral amino acids.  The unloading solution may also contain non-contaminating anions which in the course of the unloading process form water or carbonate ions forming volatile compounds with NH4+ ions easily eliminated by evaporation of the solution, or which are minor amounts of basic, neutral or acidic amino acids.  The exchange material containing basic amino acids substantially freed from acidic and neutral amino acids by the unloading process is treated to remove the basic acids by passing there-through a stripping solution comprising as stripping agent a salt of the group consisting of ammonium carbonate and bicarbonate, which provides a high concentration of ammonium cations as compared with the less ionized ammonium hydroxide, for effecting ionic exchange between the ammonium cations and the cationic basic amino acids on the exchanger whereby there result in the effluent the basic amino acids as salts together with unretained stripping agent; the preferred stripping solution contains excess of ammonium bicarbonate and carbon dioxide; the effluent fraction containing stripped basic amino acids is normally concentrated down, thereby volatilizing off any NH4HCO3 present, and then passed through a bed of regenerated cation exchange material until the effluent has a pH of 7.0-8.0, whereby any acidic and neutral amino acids present in the feed are flushed out of the bed, leaving the basics and any fixed cations such as K+ on the bed which is then treated with NH4HCO3 as above, yielding a pure basic amino acid containing effluent from which, if desired, the individual amino acids may be isolated.  The first effluent fraction obtained in the main unloading operation above and containing substantially pure acidic and neutral amino acids is treated to separate the two groups of amino acids by passing the effluent fraction through an alkali regenerated anion exchange material whereby the acidic amino acids are absorbed while the neutral amino acids pass through in the issuing effluent; if the feed contains insufficient acidics to cause a break-through, then the whole of the issuing effluent may be subjected to evaporation to recover the neutrals in the concentrate, otherwise the feed is introduced to saturate the bed with glutamic and aspartic acids and all the issuing solution having a pH below 6.0 is recycled through the freshly regenerated anion-exchanger in its subsequent operating cycle to obtain a pure neutral amino acid effluent with more effective use of the anion exchanger.  The retained acidic amino acids are recovered by alkali-regenerating the anion-exchanger, whereby the issuing effluent contains the acidics in the form of their alkali salts; the regeneration may be effected by means of ammonium or sodium hydroxide solution.  To obtain the free acidic amino acids, the effluent solution of their alkali salts is contacted with acid regenerated cation exchange material, the feed being passed until first a barren effluent issues and next a fraction containing the liberated acidics, any residual acidics being then displaced by means of NH4OH; the effluent fraction of liberated acidics may next be passed to a crystallizer and the resulting crystals of acidic amino acids removed by centrifuging, the mother liquor being recycled to the cation-exchanger freshly regenerated for use in another cycle of liberating acidics from their salts.  Reference is made to the neutral amino acids glycine, alanine, valine, leucine, isoleucine, serine, threonine, proline, hydroxy proline, tyrosine, phenyl alanine, cystine and methionine, the acidic acids aspartic and glutamic acids and the basic acids histidine, lysine and arginine. The separation of the acidic, neutral and basic acids contained in a hydrolysate obtained by heating soya bean meal with 6N. sulphuric acid for three hours under 15 lbs./sq. inch pressure is described in detail with reference to flow diagrams (not shown). Suitable hydrolysates may also be obtained by hydrolysis with other acids, e.g. HCl, or by enzymical hydrolysis; gluten or casein may also be used in the hydrolysis.  The amino acid solution may be naturally occurring as with sugar juices from cane or beet.  The separated basic and neutral amino acid fractions may be combined for use in nutritional foods while the acidics may be used in flavouring.  The Specification as open to inspection under Sect. 91 relates to the purifying of amino acids solutions, comprising passing the solution through a hydrogen activated cation exchanger so loading the exchanger with the amino acids, passing through the loaded exchanger an unloading solution containing cations from the group NH4, alkali metals, alkaline earth metals including magnesium and basic amino acids, along with (nutritionally) non-contaminating anions such as OH -, HCO3 -, CO3 =, glutamate- and aspartate-, and separating a production fraction from the resulting effluent up to a point of abrupt increase in rate of pH change, this fraction being free from the above-mentioned cations.  Reference is also made to the stripping of basic amino acids from a bed of cation exchange material by means of a solution containing a volatile salt.  This subject-matter does not appear in the Specification as accepted.ALSO:The separation of an aqueous solution mixture of amino carboxylic acids, such as a protein hydrolysate, into groups of acidic-, neutral-and basic-amino acids respectively by treatment with cation and anion exchange materials, which neutral- and basic-amino acids may subsequently be combined to form a nutritional food and which acidic amino acids may be used in food flavouring, is characterised in that the mixture is passed through a bed of acid-regenerated cation exchange material thereby absorbing thereon the amino acids of all of said groups while any impurity anions present pass in the effluent from the bed, and then selectively unloading the acidic and neutral amino acids by displacing them from their combination with the exchange material by passing through the bed an unloading solution comprising ammonium hydroxide as a base which converts the acidic and neutral amino acids, but substantially not the more strongly held basic amino acids, into non-cationic form in which they are eluted from the exchange material whereby the material is left containing basic amino acids along with NH4+ cations, meanwhile collecting the resulting effluent solution in a first fraction up to a point defined substantially by a point of abrupt increase in the pH change of the effluent, the said fraction containing acidic and neutral amino acids uncontaminated with NH4+ cations and basic amino acids, and in a second fraction containing substantially the remainder of the acidic and neutral amino acids contaminated by NH4+ cations from the unloading solution and by a minor quantity of basic amino acids displaced by the unloading solution, the major quantity of the basics remaining on the exchanger bed, and employing the second fraction in addition to the unloading solution in a subsequent unloading operation whereby acidic and neutral amino acids in the said fraction are recovered in the unloaded effluent while NH4+ cations and basic amino acids in the fraction act as unloading agents so that the exchange material is left containing the basic amino acids substantially free from acidic and neutral amino acids.  The unloading solution may also contain non-contaminating anions which in the course of the unloading process form water or carbonate ions forming volatile compounds with NH4+ ions, easily eliminated by evaporation of the solution, or which are minor amounts of basic, neutral or acidic amino acids.  The exchange material containing basic amino acids substantially freed from acidic and neutral amino acids by the unloading process is treated to remove the basic acids by passing therethrough a stripping solution comprising as stripping agent a salt of the group consisting of ammoni