"Application of voltametric and HPLC techniques on the monitorins of organic acids production in fermented milk samples by Kefir and Tibet grains" / "Monitoramento da produção de ácidos orgânicos em amostras de leite fermentado pelos grãos de Kefir e do Tibet utilizando técnicas voltamétricas e HPLC"

AUTOR(ES)

Lidia Santos Pereira Martins

DATA DE PUBLICAÇÃO

2006

RESUMO

The products formed during the milk fermentation using the kefir and tibet grains (popularly known species) were studied in this work. The kefir grain is a symbiotic association of microorganisms that includes several species of lactic acid bacteria (Lactobacillus, Lactococcus, Leuconostoc), yeasts (Saccharomyces cereviseae) and acetic acid bacteria (Acetobacter). The tibet grain is also composed by a symbiotic association of yeasts and lactic acid bacteria. In spite of, the kefir and tibet grains are very similar in microbiologic components, cultivation procedure, structure and fermentation products, they differ in visual aspect. For the determination of the organic acids contained in fermented milk by the kefir or tibet grains and in a sample of commercial yogurt, the cyclic voltammetry and high performance liquid chromatography (HPLC) in reverse phase techniques were applied, the later was operated in isocratic elution mode with detection in the UV (210nm) region. In both techniques used, the obtained results showed the presence of organic acids in milk and in the fermented milk by the grains kefir and tibet and in the sample of commercial yogurt. Those matrixes showed electroactivity on a gold ultramicroelectrode and their analyses using HPLC was also possible. Thus, the presence of organic acids in great amounts for five acids of the eight presents in the samples was confirmed. In this work, the detection of 8 organic acids was carried out. In the mentioned samples were identified the lactic, oxalic, pyruvic, acetic, uric, citric, succinic and formic acids. This identification was performed by comparison among the retention times of the compounds in the samples of fermented milk with the retention times of the patterns of the acids, injected individually for the HPLC technique. Nevertheless, in the voltammetry application for the analysis of the fermented milk, the tibet grain demonstrated larger analytical signals (current – concentration relationship), compared to the kefir grain and the commercial sample of yogurt. Making a comparative analysis of the two techniques, HPLC became more appropriate due its larger selectivity.

ASSUNTO(S)

ácidos orgânicos voltammetry organics acids leite fermentado hplc hplc voltametria fermented milk

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