Effect of the pulsed electric field on olive enzyme activity –a model system experiment

Aim: Pulsed electric field (PEF) is an emerging new technology that is finding more and more applications in the food sector. Virgin olive oil is no exception, as its application can significantly increase oil yield. However, changes in the chemical composition of virgin olive oil vary from study to study. This could be due to the fact that the chemical composition of the oil is directly influenced by the endogenous enzymes of the olive fruit responsible for the distribution of polyphenols in virgin olive oil and its sensory properties. Therefore, the aim of this study was to determine the effect of PEF on endogenous olive enzymes in model systems. Methods: Model systems of commercial enzymes (β-glucosidase and lipoxygenase) and their substrates (p- nitropheniygluco-pyranoside and linoleic fatty acid, respectively) were treated with HVG60/1 PEF (Impel, Zagreb, Croatia) for 1, 2, and 5 min with voltages of 0.1 and 0.5 kV/cm2 and a frequency of 25 and 125 Hz. Then, the treated enzyme/substrate solution was incubated at 25°C for 30 minutes to simulate a malaxation process. The activities of the enzymes were determined spectrophotometrically. Results: The activity of PEF-treated enzymes increased 4.5- fold for β-glucosidase and 2-fold for lipoxygenase compared to the untreated enzymes. The β- glucosidase activity measured immediately after PEF treatment was significantly affected by all factors and also by the interaction of voltage and time and frequency and time. Higher voltage resulted in an increase in β-glucosidase activity with longer treatment duration. After an additional 30-min incubation at 25 °C, β- glucosidase activity was affected only by PEF voltage, whereas it increased with higher voltage. Immediately after PEF treatment, lipoxygenase activity for linoleic fatty acid was significantly affected by treatment duration, with longer PEF treatments increasing activity. However, after incubation, longer treatment time resulted in lower amounts of hydroperoxides produced, which might be related to their spontaneous degradation. Conclusion: The introduction of PEF in virgin olive production as a pretreatment of malaxation could lead to a higher concentration of phenols and an improvement of the sensory characteristics of the oil due to an increased enzymatic activity.