Abstract
The influence of Moderate Electric Field (MEF) pre-treatment of blueberry fruits on the yield and quality of the expressed juice as well as the subsequent extraction yield of bioactive compounds from berry by-products (press cake left after MEF-assisted pressing), was investigated. Thermal MEF pre-treatments were performed under different combinations of electric field strengths (E=18-55 V.cm-1) and final heating temperature (Tf=25-80 °C) before applying a pressure of 1.32 bar for 5 min. For the sake of comparison, the effect of conventional heating (CH) (Tf=25-80 °C), was also investigated. Results showed that the Zp values increased with increasing the field strength and heating temperature. However, at the same final heating temperature, MEF treatment achieved higher Zp values (up to 0.66) than CH (up to 0.45). Coherently, thermal MEF pre-treatment (36.4 V.cm-1, 60 °C) significantly increased the juice yield, which also showed higher TPC, TAC, and AA, as compared with either untreated or CH-treated samples. Moreover, compared to the untreated and CH-treated samples, higher amounts of total phenolics, total anthocyanins and antioxidant activity were detected in the press cake extracts. These results were explained by the combined non-thermal and thermal effect of MEF on the cell disintegration and extraction efficiency.
