Síntese de galacto-oligossacarídeos a partir de Soro de queijo por reação enzimática

Abstract

The aim of this work was the synthesis of galacto-oligosaccharides (GOS) fromlactose present in cheese whey by commercial enzyme β-galactosidase fromKluyveromyces lactis. The enzyme activity was first determined as a function of pH andtemperature, and then the conditions for maximum activity were obtained. Next, thethermal stability of the enzyme was studied and the best temperature for carrying out thereaction for long periods was determined. These experiments were performed in a batchreactor, and the activity determined by the method of initial rates. The synthesis of GOSwas performed, in an orbital shaker incubator in a non-aqueous medium and thecarbohydrates identified and quantified by High Performance Liquid Chromatography (HPLC). First, the enzyme capacity to perform the transgalactosylation reaction at highlactose (30%) concentration was studied and then the hydrolysis of lactose was followedthroughout the reaction, when the concentration of lactose was low (10%). The activity ofthe commercial enzyme β-galactosidase from Kluyveromyces lactis (Lactozym 2600L) was1663.75 U.mL-1 and the maximum specific activity 2.67 U.mg-1 determined at 45 °C andpH 6.5, and the lowest activity 0.85 U.mg-1 at 50 °C and pH 7.5. For long reactions it isrecommended use the enzyme at temperatures below 45 °C, with 40 °C being the mostappropriate value because it gives an activity only 12 % lower than the maximum. Themaximum concentration of GOS 71.45 U.mL-1 was achieved in 6 hours of reaction at 40°C, pH 6.5, 10 U.mL-1 of enzyme and 40 % lactose (w/v). Under these conditions themaximum yield of synthesis obtained was 23.82 % and the formed product containsgalactose 27.14 g.L-1, glucose 46.13 g.L-1 and lactose 155.28 g.L-1