Application of pulsed electric field in the production of juice and extraction of bioactive compounds from blueberry fruits and their by-products

Abstract

The influence of Pulsed Electric Field (PEF) pre-treatment of blueberry fruits (Vaccinium myrtillus L.), both on the extraction yield and antioxidant properties of juice obtained by pressing and on the on the recovery of bioactive compounds from berry by-products (press cake) by extraction with solvent, was investigated. PEF treatments carried out at field strengths of 1, 3, and 5 kV/cm and an energy input of 10 kJ/kg achieved a cell disintegration index (Z p ) of 0.70, 0.80, and 0.87, respectively. Mechanical pressing (1.32 bar for 8 min) of PEF-treated berries (1, 3, and 5 kV/cm at 10 kJ/kg) significantly increased the juice yield (+28 %) compared with the untreated sample. The juice obtained from PEF pre-treated berries also had a significantly higher total phenolic content (+43 %), total anthocyanin content (+60 %) and antioxidant activity (+31 %). However, PEF treatment intensity higher than 1 kV/cm did not significantly improve the quantitative or qualitative characteristics of the juice. Compared to the untreated sample, higher amounts of total phenolics (+63 %), total athocyanins (+78 %) and antioxidant activity (+65 %) were detected in the press cake extracts. PEF treatment of higher intensity resulted in better extractability of bioactive compounds from blueberry press cake. The results obtained from this study demonstrate the potential of PEF as a mild pre-treatment method to improve the efficiency of the industrial processing of berry fruits.

Keywords: Bioactive compounds; Blueberry; By-products; Extraction; PEF; Pressing.

Fig. 1

Cell disintegration index (Z _p) of blueberries as a function of electric field strength and total specific energy input. Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)

Fig. 2

Juice yield obtained after pressing untreated (0 kV/cm) and PEF-treated blueberries as a function of the electric field strength (W_T = 10 kJ/kg). Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)

Fig. 3

Total phenolic content (a) and total anthocyanin content (b) of blueberry juice obtained after pressing untreated (0 kV/cm) and PEF-treated berries as a function of the electric field strength (W_T = 10 kJ/kg). Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)

Fig. 4

Ferric reducing antioxidant power (FRAP) of blueberry juice obtained after pressing untreated (0 kV/cm) and PEF-treated berries as a function of the electric field strength (W_T = 10 kJ/kg). Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)

Fig. 5

Total phenolic content (a) and total anthocyanin content (b) of extracts from blueberry press cake obtained after pressing untreated (0 kV/cm) and PEF-treated berries as a function of the electric field strength (W_T = 10 kJ/kg). Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)

Fig. 6

Ferric reducing antioxidant power (FRAP) of extracts from press cake obtained after pressing untreated (0 kV/cm) and PEF-treated berries as a function of the electric field strength (W_T = 10 kJ/kg). Different letters above the bars indicate significant differences between the mean values (p ≤ 0.05)