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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The wetting power of aqueous solutions of mixtures of an ethoxylated fatty alcohol (AE) and an alkylpolyglucoside (AG) and (concentration ratios expressed in dry weight AE:AG = 1:0, 4:1, 3:1, 2:1, 1:2, 0:1) has been evaluated. At low concentrations, the mixtures show better wettability than the pure surfactants. The wettability of mixtures of these surfactants is not significantly influenced by the water hardness or citric acid concentration. Together with the chemical nature of these surfactants, these properties make them especially interesting for the formulation of biodegradable detergents or wetting agents.

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Wettability of aqueous solutions of ethoxylated alcohols (EA), polyoxyethylene glycerin esters (PGE) and mixtures of them have been studied. For the EA assayed, the best wettability is reached when the EA have the lowest alkyl chain length and the lowest number of ethylene oxide units in the molecule. The best wettability for the PGE assayed is reached when the number of ethylene oxide units in the molecule is lowest. Aqueous solutions of these mixtures show a wetting power between those of the pure surfactants. The wettability of PGE can be improved by adding EA with a low alkyl chain length and a low number of ethylene oxide units. An exception and synergistic effect has been detected for aqueous solutions of EA (with alkyl chain length 12–14, number of ethylene oxide units 11) and PGE (with a number of ethylene oxide units equal to 2). These mixtures have better wettability than the surfactants separately, so that it might be advantageous to use both surfactants together.