RESUMO
In the present study, foam-forming and -stabilizing properties of potato proteins were studied using whipping and sparging tests. The soluble potato proteins are mainly composed of patatin and protease inhibitors. The whipping tests showed that less foam was formed from untreated patatin than from the protease inhibitors, but patatin foam was much more stable. The foam-forming properties of patatin could be strongly improved by partial unfolding of the protein. Whipping tests, at both low (0.5 mg/mL) and high (10 mg/mL) protein concentration, also indicated that foams made with an ethanol-precipitated protein isolate were more stable than those made with beta-casein and beta-lactoglobulin. More generally, it can be concluded that when proteins are used as a foaming agent, a high concentration is required, because the protein available is inefficiently used. Also, there are several variables that may all, in different ways, affect both foam formation (amount of foam, bubbles size distribution) and foam stability. These variables include the type and concentration of protein, solvent conditions (pH, I), and the method used to make the foam.
Assuntos
Proteínas de Plantas/química , Solanum tuberosum/química , Hidrolases de Éster Carboxílico/química , Caseínas/química , Fenômenos Químicos , Precipitação Química , Físico-Química , Etanol , Tecnologia de Alimentos , Lactoglobulinas/química , Inibidores de Proteases/química , Dobramento de ProteínaRESUMO
In this study, a protein isolate with a high solubility at neutral pH was prepared from industrial potato juice by precipitation at pH 5 in the presence of ethanol. The effects of ethanol itself and the effects of its presence during precipitation on the properties of various potato protein fractions were examined. The presence of ethanol significantly reduced the denaturation temperature of potato proteins, indicating that the preparation of this potato protein isolate should be performed at low temperature in order to retain a high solubility. In the presence of ethanol, the thermal unfolding of the tertiary and the secondary structure of patatin was shown to be almost completely independent. Even at 4 degrees C, precipitation of potato proteins in the presence of ethanol induced significant conformational changes. These changes did, however, only result in minor changes in the solubility of the potato protein fractions as a function of pH and heat treatment temperature.
