Analysis of juice colour and dry matter content during pulsed electric field enhanced expression of soft plant tissues

Abstract

The pulsed electric fields (PEF) enhanced expression of juice from slices of two different sizes was analysed for apple and carrot tissues. The experiments were carried out using a laboratory filter-press cell, equipped with PEF-treatment system operating at moderate electric field strength (250–400 V/cm) and at constant pressure ( P = 5 bar). In different experiments the PEF-treatment was applied at 30 and 1000 s after the start of pressing. The expressed juice was collected in different containers and its mass, absorbance and soluble dry mater content (°Brix) were measured. It was shown that PEF-application for juice expression from soft plant tissues allows to enhance the juice yields and to regulate qualitative characteristics of the juice. Enhancing of the juice expression ( Y) after PEF-application was accompanied with a noticeable decrease of absorbance ( C) and increase of °Brix value of the juice for both apples and carrots. The average characteristics of the juice divided in two (initial and final) portions were analysed. The PEF-application allows to separate the second portion of juice with the lowest absorbance and highest °Brix values at yields ≈20–30% for apple and ≈20% for carrot. The time of PEF-application and the size of slices affected noticeably characteristics of both initial and final portions of the juice.