Isolamento, purificação e caracterização bioquimica da peroxidase de carambola (Averrhoa carambola, L.)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

Peroxidases (POD, EC 1.11.7.1 donor: hydrogen peroxide oxydoreductase) are a group of isoenzymes whose action results in discoloration and off-flavours in foods, but are also used in food and clinical analyses, as well as in food conservation, combined with the action of other enzymes. A lot of tropical fruits and vegetables have yet to be biochemically characterised with respect to their peroxidases. This study aimed at to isolating, purifying and characterising the peroxidase from carambola (Averrhoa carambola, L.) fruit. The histochemical localisation of peroxidase from carambola was carried out by immersing slices of green, green-mature and overripe carambolas in a reaction mixture of 1% guaiacol in 0.1 M potassium phosphate buffer, pH 6.0 and 0.1 M hydrogen peroxide. The development of browning was observed and photographed. In green and green-mature slices the POD was localised near the fibrous parts such as vascular bundles, internal stem, gynoecium and peel. In overripe slices the colouring of the pulp and the reaction medium could be seen, indicating the presence of greater amounts of soluble POD at this stage of maturation. Separate analysis of POD activity in the parts: internal stem with gynoecium, pulp and peel of carambola, confirmed the findings of the histochemical localisation. The internal stem with gynoecium had the highest activity per gram of fruit part, followed by the peel. The pulp showed appreciable activity only in overripe fruits. Green carambolas showed the highest POD activity in relation to the other maturation stages tested. The best extraction buffer was found to be 0.2 M potassium phosphate buffer, pH 8.0. The extraction of POD activity with the addition of other chemical substances, showed that the addition of 0.2 M CaCI2,2% PEG and 0.01 M EDTA in 0.2 M potassium phosphate buffer, pH 8.0, was the best medium for total extraction. The total extract yielded 1.29 times the amount of POD activity as the sum of sequential extractions: Soluble enzyme (three times), lonically bound enzyme (three times) and Triton X-100 soluble enzyme (an other three times). Precipitation studies using 65% solutions of ethanol or acetone and 90% saturation of ammonium sulphate showed that ammonium sulphate resulted in only 3% more activity per gram of fruit than acetone ...Note: The complete abstract is available with the full electronic digital thesis or dissertations

ASSUNTO(S)

peroxidase

ACESSO AO ARTIGO

Documentos Relacionados