The studies on the mechanism of greening resulted from the chemical reaction of chlorogenic acid or its related compounds with amino acids, peptides or proteins had been carried out by URITANI et. al in detail. But the chemical structure and properties have not been elucidated yet. So the authors tried to make clear these problems.
The green solution was prepared from the mixture of chlorogenic acid and L-phenylalanine by two methods of oxidation, polyphenoloxidase in the presence of air and only air. Each green solution prepared was treated by Sephadex G-25 and fractionated into three color bands (brown, green and blue-purple), respectively. Of these, the green and blue-purple fractions were purified and powdered by acetone treatment. In this paper, the method of fractionation and some chemical properties of the powdered pigments are described.

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After heating the aqueous model solution containing carbonyl compounds and amino acids, its reactivity was investigated by gas chromatography.
1) At pH6.5, n-propionaldehyde easily reacted with L-arginine HCl, L-lysine HCl, L-histidine HCl, L-tryptophan and especially with L-cysteine. After heating, browning was found in each solution and volatile flavor of n-propionaldehyde was reduced. These amio acids reacted with n-capronaldehyde as well as n-propionaldehyde. The volatiles formed by the reaction between the carbonyls and L-cysteine were sulfurous flavor.
2) On varying the contents of L-arginine HCl, L-lysine HCl and L-histidine HCl, about a half amount of carbonyl compound in the simple model system was made nonvolatile by addition of 5 fold amino acid in molarity to carbonyl compound. In case of the mixed model system of carbonyl compounds (1mM formaldehyde-1mM acetaldehyde-1mM n-propionaldehyde-1mM n-valeraldekyde-2.5mM n-carpronaldehype), L-lysine HCl or L-histidine HCl was most effective to make nonvolatile about a half amount of carbonyl compounds in model system. Its amino acid concentration was 20 fold in molarity to carbonyl compounds. L-cysteine made entirely nonvolatile carbonyl compounds in equal molarity to carbonyls.

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Rice stored for 2 years was cooked in aqueous solution containing amino acids, and the volatile carbonyl compounds produced from cooked rice and flavor were investigated by gas chromatography and sensory test respectively.
1) L-cysteine, L-lysine HCl and L-histidine HCl were effective to make nonvolatile n-valeraldehyde and n-carpornaldehyde, which were attributed to the stale flavor (komai-shu). Of these amino acids, L-cysteine was most reactive, accompanying sulfurous flavor in cooked rice. About a half amount of carbonyl compounds (n-valeraldehyde and n-capronaldehyde) in cooked rice was made nonvolatile by adding about 300mg of L-lysine HCl or L-histidine HCl to 100g of milled rice.
2) As the result of sensory test, it was necessary to add 80-160mg% of L-lysine HCl in stored rice for elimination of the stale flavor. Flavor was more improved by the addition of the mixture of 80mg of L-lysine HCl, 20mg% of L-histidine HCl and 5mg% of L-tryptophan in stored rice. The addition of amino acids as described above might be also useful for improvement of nutritive value of rice.

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