Production of grape pekmez by Ohmic heating-assisted vacuum evaporation

Abstract

Pekmez is a concentrated syrup-like food conventionally produced by vacuum evaporation process from sugar-rich fruits. In this study, the applicability of grape pekmez production by ohmic heating assisted vacuum evaporation (omega VE) method was investigated. Conventional vacuum evaporation (CVE) and omega VE methods were compared in terms of physicochemical properties, HMF (5-hydroxymethylfurfural) contents, rheological properties, and energy consumptions. omega VE was run at four different voltage gradients (17.5, 20, 22.5, and 25 V/cm). Total process times for grape pekmez production were determined as 57, 28.5, 32, 39, and 50 minutes for CVE, omega VE (25 V/cm), omega VE (22.5 V/cm), omega VE (20 V/cm) and omega VE (17.5 V/cm), respectively. Energy consumption of CVE method was higher than omega VE method for all voltage gradients. Energy efficiency increased as the voltage gradient increased. There was no significant difference between CVE and omega VE methods for HMF contents. The results show that the omega VE method could be an alternative to the CVE process for grape pekmez production.