Pulsed electric field assisted drying of Actinidia kolomikta fruits
Actinidia kolomikta (Maxim. & Rupr.) fruits are valuable medicinal and edible fruits, containing high amounts of vitamins C, E and K, lutein, minerals and phenolics. The plants exhibit short growth and maturation time (2 – 3 month), however the widespread usage of Actinidia fruits is limited due to their short shelf life. Drying is one of the most common methods of food preservation. However, A. kolomikta fruits have quite firm skin, which results in long drying time. Pulsed electric field (PEF) is a new non thermal processing method, based on short duration (µs to ms range), but high voltage (1 – 10 kV/cm) treatment, allowing increased water and mass transfer from the cells.
The aim of this study was to evaluate the influence of PEF pre-treatment on drying of A. kolomikta fruits. Three different drying methods were used: freeze-drying (lyophylization), fluid bed hot air and infrared drying. The moisture loss, color coordinates and extures were analyzed. PEF pre-treated (5 kV/cm, 20 Hz, 20 ms, 2 min) A. kolomikta moisture loss was 14% higher after 20 hours of freeze-drying, 13% higher after 3 hours of hot air drying, and 6% higher after 30 min of infrared drying, when compared to the respective controls. In the CIELAB color scale, the only parameter which was influenced by PEF treatment was L* color coordinate, measuring lightness. For PEF pre-treated vs. control conditions L* was 42.0 vs. 34.3 for infrared heating, and 66.7 vs. 41.8 for freeze-drying, while after hot air drying L* did not change. Texture analyzer showed that freeze-dried PEF-pretreated fruits required smaller maximal penetration force, which was 163 ± 20.2 N/cm2, in comparison to control without PEF 120 ± 7.9 N/cm2. In conclusion, PEF pre-pretreatment accelerated drying process of A. kolomikta fruits when applying all three drying methods, thus saving time and energy. The effect of PEF-pretreatment on drying rate was mostly pronounced for the freeze-drying.
Acknowledgement: This work was supported by the grant SVE-08/2014 from the Research Council of Lithuania.
Keywords: Actinidia kolomikta, PEF, Hot air drying, Freeze-drying, Infrared drying.