The lipolytic activity in supernatant fractions of cultures of Saccharomycopsis lipolytica, Micrococcus caseolyticus, Bacillus licheniformis and a Staphylococcus sp. was studied. Nutrient broth with and without emulsified olive oil was used as substrate. Optimal pH values and temperatures for the lipase produced by the 4 different microorganisms were determined. The lipolytic activity generally reached a maximum after incubation for 2 to 6 days. The subsequent decrease in the lipolytic activity was associated with a high proteolytic activity only for Micrococcus caseolyticus. The lipolytic activity was decreased by the presence of olive oil in the medium. Determination of the lipolytic activity after a certain time of incubation, the maximal lipolytic activity and a time integrated lipolytic activity are compared as estimators for the potential hydrolytic capacity of micro organisms.
The amount of free fatty acids and their composition were studied during an add-back process of potato granules. Samples were taken at several different stages in the production, from raw tubers to final potato granules. Lipids were extracted and lipid classes separated by liquid chromatography. Free fatty acids were separated from the neutral lipid fraction by high performance liquid chromatography (HPLC). The fatty acid composition was analysed by gas chromatography (GC). The amount of free fatty acid increased in the first stages of the process and rose to its highest level in the samples from the steam-cooking step. During further processing the amounts of free fatty acids slowly decreased. Since enzymatic hydrolysis is one explanation for liberation of fatty acids, lipase activity was measured by a spectrofluorimetric method in the raw tubers, blanched slices and steam-cooked slices. After the blanching step, some enzyme activity was found but after steam-cooking there was none. © 1989.
Potato granules were produced by an add-back-process. The lipid composition of the potato tubers and the final potato granules were assessed in order to study the influence of the process. The extracted lipids were fractionated into three major classes, neutral lipids, galacto-lipids and phospholipids, on a silicic acid column. The free fatty acids were separated from the neutral lipids by high performance liquid chromatography (HPLC). The fatty acid composition of the three lipid classes as well as the free fatty acid fraction was analysed by gas chromatography. No changes could be observed in the galactolipids and the phospholipids but the free fatty acid content was found to be about ten times higher in potato granules than in the potato tubers. © 1989.
Active oxygen species are possible initiators of oxidative reactions in foods, and their elimination could provide one mechanism of antioxidative effect. In this work we studied the antioxidative properties of superoxide dismutase (SOD) from yeast (Saccharomyces cerevisiae) in various model systems. The crude yeast extract was partially purified by ammonium sulfate precipitation. The purified fraction was found to inhibit the oxidation of emulsified linoleic acid, emulsified cholesterol, and ascorbic acid. Catalase had a prooxidative effect in the linoleic acid system, while at high concentrations it protected ascorbic acid against oxidation. No synergistic effect was observed between catalase and SOD. In order to evaluate possible applications of yeast SOD as an antioxidant in food, the influence of pH and heat treatment on the antioxidative effect was studied. Within the range pH 4.5-9.0 the antioxidative effect of the SOD increased with increasing pH. In heat treatment experiments the SOD showed unusually high thermal stability and an interesting inactivation-reactivation behavior. The enzyme activity was for instance retained at about 60% of its original value after heating at 70°C for 15 min. A few percent of the original enzyme activity remained even after 30 min at 100°C. The possible technological implications of these results are discussed. © 1989 American Chemical Society.