Variação de metionina em feijões (Phaseolus vulgaris, L) armazenados

AUTOR(ES)
DATA DE PUBLICAÇÃO

1979

RESUMO

The purpose of the present study was to test the sodium ferricyanide reagent in its ability to measure chemically available methionine in twelve experimental and commercial lines of common beans (Phaseolus vulgaris, L.) as a function of storage. Our interest in accurately determining methionine in beans comes from the fact that this amino acid occurs in limiting amounts in all legumes and often only a fraction of it is biologically available. Such low availability of the essential amino acid is most likely a result of excessive oxidation and substitution of the sulfur atom; a process that has been suggested to take place during the storage of seeds. Due to the lack of success in the application of the several procedures available, it was necessary to adapt the ferricyanide methodology. In order to circumvent the instability of the partly oxidized forms, for example, enzymatic hydrolysis with Streptomyces griseus protease was used. The special resistance that bean proteins pose to protease however, made it necessary to alter of hydrolytic conditions such as pH of solution and time. Furthermore there was a need to use 8 N hydrochloric acid instead of concentrated acid in the colorimetric reaction to improve the color yield. Once the analytical conditions were optimized, the ferricyanide-complexing methionine was determined in the twelve types of unstored beans. No significant difference was observed between the results thus found and those obtained the performic acid-oxidation ("total methionine") method when all the varieties were considered together. It was evident, however, that in the varieties Goiano Précoce, SP 7052 and SC 7010 only 44.4, 39.8 and 38.8% of their total methionine was complexable, respectively at the beginning of the storage. Te seeds were stored at 8 0% relative humidity and temperature that varied between 20 and 28°C for a total period of eight months. During this time the modified methodology demonstrated that complexing methionine decreased in all varieties. This finding was in agreement with results from other author who showed methionine losses by biological assays in beans stored under similar conditions. The lines that exhibited greater stability and/or "endurance" to storage were Piratã II, Piratã I and Cara Suja, respectively.

ASSUNTO(S)

metionina nutrição

ACESSO AO ARTIGO

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