Quality characteristics of pomegranate juice concentrates produced by ohmic heating assisted vacuum evaporation.

BACKGROUND: Vacuum evaporation process, is widely utilized in fruit juice evaporation to preserve quality attributes of final product. However, it has some disadvantages such as possible degradation of aroma components or volatile fatty acids due to long process time, and low energy efficiency of process. Pomegranate juice (PJ) having 17.5% total soluble solids (TSS) content was evaporated to 40% TSS by ohmic heating assisted vacuum evaporation (OVE; 7.5 V/cm, 10 V/cm and 12.5 V/cm) and vacuum evaporation (VE) in present study. Effects of evaporation methods on pH, titratable acidity and colour values, antioxidant activity (AA), total monomeric anthocyanin (TMA), total phenolic content (TPC), hydroxymethylfurfural (HMF) and invert sugar content of pomegranate juice concentrates were compared.

RESULTS: The colour properties, TMA, TPC and AA values of PJ concentrates evaporated by OVE were more influenced than those evaporated by VE. The degradation of sugars was minimized for OVE processes at high voltage gradients (10 V/cm and 12.5 V/cm), and HMF content of PJ concentrated by OVE was lower than VE.

CONCLUSION: It is thought that electro-chemical reactions occurred because of using the titanium electrodes during OVE process caused these quality changes in PJ concentrates having high acidity. Hence, it was concluded that utilization of relatively more electrochemically inert electrodes should be investigated in further studies to better evaluation of influence of ohmic heating assisted vacuum evaporation method on quality attributes of different fruit juices. This article is protected by copyright. All rights reserved.