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Surfactants --- Surfactants --- chemicophysical properties --- chemicophysical properties --- Rheological properties --- Rheological properties

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Casein --- Casein --- Cheese --- Cheese --- C heesemaking --- C heesemaking --- Rheological properties --- Rheological properties --- technical properties --- technical properties

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Surface-active properties of two classes of Bacillus subtilis S499 lipopeptides, surfactins and iturins A, were studied. These lipopeptides were purified until molecules with unique lipidic structure were obtained. Then, adsorption kinetics and monolayer properties at the air-water interface, micelle forming capacity in aqueous solution, and foaming properties for both homologous lipopeptides and mixtures of main components, were characterised. Lipopeptide interfacial behaviour depends on lipophilic moiety structure, concentration, and presence of NaCl in solution. Diffusion coefficients of lipopeptides having lipidic chain with 13 to 15 carbon atoms were equivalent to those of classical surfactants. Increasing the lipidic chain length over 15 carbon atoms decreased the diffusion coefficient. The addition of NaCl 0.1M in solution induced similar effect. When the concentration exceeded a critical value, the surfactin adsorption rate decreased with increasing the lipidic chain hydrophobicity. Monolayer study in compression showed the importance of lipidic part on molecule orientation and film stability, especially for iturin A. Micelle forming capacity also increased with the lipidic chain length. Lipopeptides with lipidic chain of 14 and 15 carbon atoms efficiently formed and stabilised foam with moderate density but constituted with fine bubbles. Therefore, they appeared as excellent foaming agents. Surfactin produced foam with higher density but less stable than iturin A. The optimal structure for these properties was formed by a lipophile part with 14 carbon atoms. Mixtures of surfactin and iturin A having lipidic chain of 15 carbon atoms showed synergistic effects on adsorption properties, film stability, foam density and foam stability. These effects specifically appeared with a surfactin-iturin A mixture in a proportion 40 : 60.

Bacillus subtilis --- Bacillus subtilis --- Surfactants --- Surfactants --- peptides --- peptides --- Lipids --- Lipids --- Foams --- Foams --- Rheological properties --- Rheological properties --- Surfactine --- Iturine --- Surfactine --- Iturine

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Agricultural wastes --- Agricultural wastes --- Waste management --- Waste management --- Starch --- Starch --- Starch industry --- Starch industry --- industry --- industry --- Oxidation --- Oxidation --- Rheological properties --- Rheological properties --- technical properties --- technical properties