Is grape invertase a major component of the adsorption layer formed at theair/champagne wine interface?

The effects of ethanol concentration on the adsorption of beta -casein, gra pe invertase, and wine molecules have been studied at the air-solution inte rface by neutron reflectivity, by ellipsometry, and by static and dynamic s urface tension measurements (bubble tensiometer). At 12.5% ethanol content, the surface pressure increase caused by either protein is of the order of 3 mN/m, a value which suggests a low amount of adsorbed protein as compared to the buffer devoid of ethanol where the surface pressure reaches 23-25 m N/m. The amount of protein adsorbed at 12.5 or 20% ethanol was measured by neutron reflectivity and by ellipsometry and found to be at least equal to the amount adsorbed when no ethanol occurs in the buffer. It can be conclud ed from these data that the adsorption of protein is not impeded by ethanol . A simple model considering that the adsorbed protein forms a network and that ethanol adsorbs in the vacant space of that mesh allows the understand ing of the low surface pressure of the protein on a hydroalcoholic solution . The dilational modulus calculated from dynamic surface tension measuremen ts is a linear function of the surface pressure over a limited range of sur face pressure. The slope of this relation can be related to the fractal dim ension of the macromolecules covering the interface. The slope is smaller w ith beta -casein than with invertase and decreases when ethanol concentrati on increases in the former case, whereas it is the contrary in the latter. In the case of wine, the slope is intermediate between those measured with invertase and with p-casein and does not change much with ethanol concentra tion. These data indicate that adsorption layers of grape invertase are not good models for the adsorption layer formed at the interface between air a nd champagne still wine.