Abstract: Optically active tryptophan is crystallized by a modification of a method of crystrallization of optically active tryptophan through neutralization by mixing an acidic or alkaline aqueous solution of optically active tryptophan, which is obtained by the removal of impurities from an acidic or alkaline aqueous solution of optically active tryptophan containing impurities which inhibit flocculation and crystallization of optically active tryptophan, with an alkali or an acid, by combining portions of an alkali or acid with portions of an acidic or alkaline aqueous solution of optically active tryptophan, from which the impurities have been removed, thereby neutralizing the aqueous solution containing optically active tryptophan such that the pH of the solution to be crystallized is kept in a range of 3 to 8, and simultaneously crystallizing optically active tryptophan as flocculated crystals.

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 sugar hydrolyzate, containing both glucose and fructose, is mixed with calcium hydroxide, and a fructose addition precipitate is recovered. The residual liquor is neutralized, calcium ions are removed, and then the liquor is used as a carbon source for citric acid fermentation.The present method may supply very inexpensive fructose to the market.