Teor de isoflavonas e atividades de ß-glucosidase em grãos de soja germinada e de diferentes grupos de maturação. Purificação e caracterização bioquímica parcial da ß-glucosidase

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Soy Isoflavones are phenolic compounds comprised of aglucones, b-glucosides and b-glucosides conjugated with malonyl and acetyl groups. b-glucosidase (b-glucoside glucohydrolase, EC 3.2.1.21) hydrolyses b-glucosidic isoflavones releasing aglucones that possess human health benefitial role. Thus the objective of this work was to determine the isoflavone forms contents, b-glucosidase activity and their correlation in 18 soybean cultivars of different maturity groups under the same cultivation conditions. In addition an experiment was carried out in order to observe the behavior of these components throughout germination of a soy cultivar (BRS 213) that presented the highest enzyme activity for 72 h at 25°C. Furthermore soy cotyledons b-glucosidase was chromatographically purified and biochemically partially characterized. Regression analyses between number of days of maturity and all isoflavone forms were not significant. The relationship between maturity days and b-glucosides and malonyl-glucosides showed no correlation. However, a correlation was observed between maturity days and aglucones (P<0.08). Regression analysis and correlation between b-glucosidase activity and cultivars of different number of days of maturity were not significant, and b-glucosidase activity did not correlate with isoflavone forms contents (P<0.05). In the germinated soy cultivar BRS 213, the b-glucosidase activity increased 3.3-fold in the radicles and 2.3-fold in the cotyledons. In the radicles there was a significant decrease in the total isoflavone content (6.3-fold), while in the cotyledons there was an increase in total isoflavone content (2.4-fold). b-glucosidase was purified by ion exchange chromatography on CM-Sephadex C-50 and gel filtration on Sephadex G-100. A b-glucosidase fraction named F42 was partially biochemically characterized presenting reactions optimum conditions of pH at 5.0 under 30 min of incubation at 45°C. The enzyme was stable at 25°C while at 45°C the activity reduction was 60.0% after 1h of incubation. Finally, low stability was found at temperature above 60°C reducing its enzyme activity of 95% after 5 min of incubation. The enzyme Km and Vmax having p-nitrofenil-b-D-glucopiranoside as substrate was 0.16 mM and 4.3 mM p-nitrofenol/min, respectively. Lastly, the enzyme presented a specificity for p-nitrofenil-b-D-glycopiranosides derivatives and also for substrates possessing ligants in para position and linkages of a or b type and finally 1®4 or 1®6 type.

ASSUNTO(S)

isoflavonas germinação b-glucosidase - purificação e caracterização soy proteins soy - germination soja - maturação

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