The aim of this study was to determine the optimal parameters of pulsed electric field treatment to increase the activity of β-glucosidase and lipoxygenase, crucial enzymes that improve the nutritional quality and sensory properties of virgin olive oils. The activity of the enzymes was determined spectrophotometrically immediately after treatment of model systems (commercial enzymes and their substrates) with pulsed electric fields and after simulation of the malaxation process for 30 min at 25 °C. Pulsed electric field treatments were performed with electric field strengths of 2.67 and 13.33 kV/cm at frequencies of 25 and 125 Hz for 1, 2, and 5 min. The results showed a positive correlation of β-glucosidase activity with the electric field strength and time, with the first of the two factors having the greatest influence. Lipoxygenase activity was affected only by the duration of treatment: positively immediately after treatment and negatively after simulation of the malaxation process. Based on these results, pretreatment with a moderate pulsed electric field for 2 min before the malaxation process could be proposed to increase the activity of β-glucosidase and lipoxygenase, e.g., for the production of virgin olive oils with higher concentrations of polyphenols and desirable volatile compounds.

Flash thermal pretreatment (FTT) is a promising technique for enhancing virgin olive oil (VOO) quality. This study investigated the effects of FTT, both cooling (15–25 °C) and heating (30–40 °C), on phenolics, tocopherols, fatty acid composition, oxidative stability (OSI), antioxidant capacity (AC), and volatile composition in VOOs from three Croatian varieties: Istarska Bjelica, Levantinka, and Oblica. A full factorial experimental design was used with two independent variables: treatment temperature and olive variety. Olive pastes were treated after crushing and before malaxation. Data were evaluated using ANOVA, partial least squares (PLS) regression, and response surface methodology (RSM). Istarska Bjelica showed the highest OSI improvement (+16%) mostly linked to elevated phenolic compounds. Levantinka exhibited moderate responses, with slight OSI and AC declines. Oblica was most sensitive to heating, showing OSI and AC reductions (up to 28%), despite increased oleocanthal and olacein. RSM identified optimal FTT temperatures for each variety: 18.9 °C (Istarska Bjelica), 15.4 °C (Levantinka), and 15.5 °C (Oblica). These findings support variety-specific FTT as an effective strategy to improve VOO functional and sensory quality.

The aim of this study was to investigate the influence of thermal treatment and ultrasound on the activity of β-glucosidase and lipoxygenase, enzymes that determine the phenolic composition and sensory profile of virgin olive oil. Enzyme activity was determined spectrophotometrically in model systems consisting of commercial enzymes and their substrates. Thermal treatment was performed by tempering the enzymes and substrates at temperatures between 15 and 40 °C. Enzyme activity was measured 1 min after reaction and again after the additional incubation of the reaction mixture at 25 °C for 30 min to simulate the behavior of the enzymes during the malaxation process. Ultrasonic treatment of the model solutions was performed at 128, 320, and 640 W of the ultrasonic bath power for 1, 5, and 12 min. Enzyme activity was determined immediately after treatment and again after incubation at 25 °C for 30 min. The higher temperatures during thermal treatment increased the activity of both enzymes. During ultrasound treatment, the activity of both enzymes was positively affected by its duration. The higher power of ultrasound was a better choice for β-glucosidase and the lower one for lipoxygenase. The stimulation of enzyme activity by the studied techniques resulted in an acceleration of enzymatic reactions during the additional incubation, suggesting that the malaxation process could be shortened in virgin olive oil production.

Flash thermal pretreatment (FTT) is a promising technique for enhancing virgin olive oil (VOO) yield and quality. This study investigated the effects of FTT, both cooling (15 – 25 °C) and heating (30 – 40 °C), on oil yield, phenolics, tocopherols, fatty acid composition, oxidative stability (OSI), antioxidant capacity (AC), and volatile composition in VOOs from three Croatian varieties: Istarska Bjelica, Levantinka, and Oblica. A full factorial experimental design was used with two independent variables: treatment temperature and olive variety. Olive pastes were treated after crushing and before malaxation. Data were evaluated using two-way ANOVA, partial least squares (PLS) regression, and response surface methodology (RSM). Istarska Bjelica showed the highest OSI improvement (+16 %) linked to elevated phenolics and α-tocopherol, and the largest yield increase (+8.1 % at 25 °C). Levantinka exhibited moderate responses, with slight OSI and AC declines and enrichment in lipoxygenase (LOX)-derived volatiles. Oblica was most sensitive to heating, showing OSI and AC reductions (up to 28 %), despite increased oleocanthal, olacein and LOX volatiles. RSM identified optimal FTT temperatures for each variety: 18.9 °C (Istarska Bjelica), 15.4 °C (Levantinka), and 15.5 °C (Oblica). These findings support variety-specific FTT as an effective strategy to improve VOO functional and sensory quality.

This study investigated, for the first time, the effects of pulsed electric field (PEF) pretreatment—applied prior to malaxation at 2–7 kV/cm for 30–90—on oil yield, quality parameters, and volatile profiles of virgin olive oils (VOO) from four representative Croatian autochthonous varieties: Istarska Bjelica and Rosulja (Istria), and Levantinka and Oblica (Dalmatia). Mild PEF conditions significantly increased oil yield (2.5–36%), with the strongest effects observed in varieties with low baseline yields. Basic quality parameters were largely unaffected, but volatile organic compound (VOC) profiles were markedly altered. PEF increased VOCs from the lipoxygenase (LOX) pathway, particularly at lower field strengths, and altered their composition, suggesting changes in the activity of the enzymes involved in their biosynthesis. Among these enzymes, LOX was analyzed, and its activity responded to PEF treatment in a cultivar-dependent manner. Furthermore, PEF generally reduced minor VOCs associated with oxidation and microbial activity. These findings demonstrate the potential of PEF as a non-thermal, sustainable technology for improving oil extraction efficiency while simultaneously enhancing the aroma profile of VOOs.

This study investigated the effects of ultrasonic treatment of olive paste prior to malaxation on oil yield (Y), enzyme activity and virgin olive oil (VOO) quality in four Croatian olive varieties: Istarska Bjelica, Rosulja, Oblica and Levantinka. The oils were extracted using the Abencor system according to a central composite experiment design, with treatment durations of 3–17 min and power levels of 256–640 W. The parameters analyzed included Y, oxidative stability index (OSI), antioxidant capacity (AC), phenolic and α-tocopherol content, volatile compounds, fatty acid profile, and the activity of lipoxygenase, β-glucosidase, polyphenol oxidase, and peroxidase. Olive variety was the most influential factor in all variables. The response surface methodology showed that ultrasonic treatment at low-to-medium intensity improved several quality attributes. For example, Y increased by 4% in Oblica, phenolic content increased by up to 17% in Istarska Bjelica, and OSI and AC increased by 13–15% in Istarska Bjelica and Levantinka. In contrast, longer treatment and higher ultrasound power had a negative effect. No significant differences were found in other parameters examined. Overall, the application of ultrasound led to measurable, though moderate, improvements in Y and VOO quality, with results strongly dependent on olive variety and treatment conditions. These results underline the need for further optimization tailored to each variety.