Adsorption onto alumina and stabilization of cysteine proteinases from crude extract of Solanum granuloso-leprosum fruits

Proteolytic biocatalysts extracted from the ripe fruits of Solanum granuloso-leprosum, a native Uruguayan tree of the Solanaceae family, were stabilized by adsorption onto gamma-alumina supports. Conditions for preparing the biocatalyst-adsorbant system were evaluated for different crude extract (CE) protein concentrations and at different pHs and temperatures. All systems assayed reached equilibrium within 2-4 h. The best proteolytic activity (measured as direct enzymatic activity) was found to be at pH 6.0 and 5 °C. The biocatalyst-adsorbant system was more stable upon storage than the free enzyme in solution, which loses activity over time due to autolytic processes. Stability (resistance to desorption) was studied after ten cycles of incubation at different pHs and temperatures. There was a general tendency to retain higher activity (more than 60%) when the incubation conditions were the same as those used for preparing the biocatalyst-adsorbant system. The best conditions for using this system to treat industrial effluents were evaluated using milk whey from cheese-making and hemoglobin (the main constituent of wastewater from cattle slaughter-houses) as trial substrates.