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We study the enzymatic hydrolysis of lactose by a commercial enzyme from a selected strain of Kluyveromyces fragilis. The variables analyzed were: temperature (25-40 • C), enzyme concentration (0.1-3.0 g l −1 ), lactose concentration (0.0278-0.208 M), and initial galactose concentration (0.0347 M). On the basis of the data analyzed, both published and in the present work, we propose a Michaelis-Menten kinetic model with inhibition by the product (galactose), which reveals that the substrate (lactose) and the product (galactose) present similar affinity for the active site of the enzyme.

A commercial lipase (E.C. 3.1.1.3) from Thermomyces lanuginosus was studied in order to assess its interaction with commercial nonionic (Findet Ò 1214N/16, Findet 1214N/23 and Glucopon Ò 650) and anionic (linear alkylbenzene sulphonate; LAS) surfactants, as well as the cleaning action exerted by the enzyme on hard surfaces. Nonionic surfactants seem to prevent or delay enzyme penetration at the interface, thereby decreasing lipase activity. Notably, no inhibitory effect of the anionic surfactant LAS on lipase action was found, higher conversions being achieved after 20 min of enzymatic hydrolysis in the presence of this surfactant than in its absence. A device for testing detersive performance, the so-called bath-substrateflow, was used in washing experiments with the lipase at different temperatures with or without surfactant. Employing two different oily stains (tributyrin and triolein), it was found that the lipase by itself increases detergency significantly, preventing the subsequent redeposition of the removed dirt. Expressions relating detersive efficiency to lipase concentration and temperature were obtained using ''Statistical Design of Experiments'' methodology.

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