Black Grape Juice Concentration via Ohmic-Vacuum Hybrid Heating: Quality Parameters, Energy Consumption and Exergy Efficiency

Zandi, Nazila; Khodaei, Jalal; Darvishi, Hosain; Behroozi-Khazaei, Nasser; Koushesh Saba, Mahmoud

doi:10.22104/ift.2025.7587.2212

Black Grape Juice Concentration via Ohmic-Vacuum Hybrid Heating: Quality Parameters, Energy Consumption and Exergy Efficiency

Document Type : Research Article

Authors

¹ Department of Biosystems Engineering; Faculty of Agriculture; University of Kurdistan, Sanandaj, Kurdistan, Iran

² Department of Horticultural Science, Faculty of Agriculture, University of Kurdistan, Sanandaj, Kurdistan, Iran

10.22104/ift.2025.7587.2212

Abstract

In this study, the concentration process of black grape juice using a combined vacuum ohmic heating system was investigated, focusing on the effects of pressure parameters (50, 70, and 100 kPa) and voltage gradient (10, 20, and 30 V/cm) on processing time, specific energy consumption, exergy efficiency, and quality parameters (pH, total phenolic content, and antioxidant activity). The results indicated that increasing the voltage gradient significantly enhanced the heating rate and reduced processing time, while the combination of ohmic heating with vacuum (at 75 and 50 kPa) increased processing time. Specific energy consumption at atmospheric pressure (100 kPa) varied between 1.92 to 2.27 MJ/kg water, while reducing the pressure to 50 kPa led to an increase in specific energy consumption by 4.42 to 5.54 times. The highest exergy efficiency (18.78%) was observed at 100 kPa and a voltage gradient of 30 V/cm. In terms of quality, the reduction in pH (up to 16%) and the retention of total phenolic content (857 mg GAE/100 ml) and antioxidant activity (IC50 = 19.36%) at 50 kPa and a voltage gradient of 10 V/cm yielded the best quality results. Based on the findings, it can be suggested that optimizing the concentration process by selecting appropriate levels of pressure and voltage gradient to achieve a balance between energy efficiency and product quality could be explored in future studies.

Graphical Abstract

Highlights

Higher voltages (20–30 V/cm) improved processing rate but reduced quality retention.
Lower pressures better preserved quality but increased energy demand.
The highest exergy efficiency (18.78%) was achieved at 30 V/cm and 100 kPa.
The best condition for quality retention was 10 V/cm and 50 kPa.

Keywords

Main Subjects

Novel technologies

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