Qualitative characteristics of sugar beet juices obtained in pilot extractor with pulsed electric field (PEF) pre-treatment

摘要

The conventional method of sugar extraction from sugar beets requires high temperatures (70–72 °C) and rather long duration (70 min). It results in high content of impurities (like pectins and melanoidins) in obtained juices and high water and energy consumption. This work studies the sugar extraction from sugar beets preliminary pre-treated by pulsed electric field (PEF). The extraction was carried out in a countercurrent pilot extractor with 14 extraction sections. The cossettes were obtained by semi-industrial slicing machine. The extraction temperature varied from 70 to 30 °C, and draft (juice to cossettes ratio) changed from 120 to 90%. The PEF treatment was done with electric field intensity between 100 and 600 V/cm. The quality of extracted juices was characterized by measuring the content of soluble solids (in °Brix), sucrose content (by polarimetry), juice purity (P = (sucrose concentration)/(total soluble solids)), concentration of colloidal substances (or alcohol insoluble solids), concentration of pectin (enzymatic determination) and proteins (Bradford method). UV-Vis absorption spectra of juices were also compared. The sucrose content was measured in cossettes and in pulp for control of sugar losses and kinetics of cossette exhaustion during processing. It was shown that juice obtained by mild thermal (50 °C) and cold (30 °C) extraction has higher purity, lower concentration of colloidal impurities (especially, pectins) and lower coloration. Diminishing of draft permitted better concentration of the extracted juice, but the cossettes were worse exhausted. The value of draft should be considered as a function of different factors like permissible sucrose loss in the pulp. The pulp obtained by cold extraction of PEF-treated cossettes had dryness noticeably higher than the dryness of the pulp obtained by conventional hot water extraction. The obtained data confirm that “cold” sugar extraction assisted by PEF treatment may be a promising energysaving method, permitting obtaining of high quality juices.