Abstract: L-glutamine is purified by concentrating a fermentation liquor containing at least 40 g/l or more of L-glutamine, or a solution obtained therefrom by filtering off microbial cells, at pH 5.6.+-.0.5, or by cooling the fermentation liquor or the solution after concentration or without concentration at a temperature in the range of 2.degree. to 30.degree. C., thereby giving a slurry of L-glutamine crystals of 70 g/l or higher concentration; (2) separating the crystals from the mother liquor and then dissolving the separated crystals in a water; and (3) bringing the solution thus obtained into contact with an OH-type anion-exchange resin, thereby removing impurities through adsorption.

Abstract: A method for purifying aspartic acid comprising suspending aspartic acid crystals containing chloride ion impurities in an aqueous solution at a temperature of 50.degree. C. or higher, followed by separating the purified aspartic acid crystals, is disclosed.

Abstract: Hemi-alkali metal salts of 2-pyrrolidone-5-carboxylic acid, believed to have the formula: ##SPC1##Wherein Me is an alkali metal, is formed by reaction of 0.75 to 0.99 moles of an alkali metal hydroxide per mole of 2-pyrrolidone-5-carboxylic acid.