Comparison of quality characteristics of tomato paste produced under ohmic-vacuum combination heating and conventional heating

Abstract

The proposed work compares a combination of ohmic and vacuum heating (OH-VC) with conventional heating. Tomato paste was freshly extracted from tomatoes and subjected to 0-220 V alternating current (AC) with 50 Hz frequency under a pressure of 0.3-0.7 bar until the temperature reached 87 °C and compared with tomato paste heated in a double jacket vat. Tomato paste was further analyzed using Fourier transform infrared spectroscopic analysis (FTIR), volatile analysis using gas chromatography-mass spectrometry (GC-MS), minerals analysis using scanning electron microscope – energy dispersive spectrometer (FEG-SEM), scanning electron microscopy, and colour measurements. Based on FTIR analysis, tomato paste processed with OH-VC heating was found to have higher deformations of sugars than conventionally heated paste. Similarly, OH-VC heated product contained caramel-like odours associated with furfural and 5-methyl furfural generation due to electric treatment of food. Electrodes used in ohmic heating did not cause any changes in the minerals content due to heavy metal ion migration. Structurally, OH-VC treated cells were found to have a more regular and preserved structure than conventional heating. No effect on the colour of the tomato paste was observed. These results demonstrate the advantageous effect of OH-VC heating compared to conventional heating, primarily attributed to the lower treatment time and higher heating homogeneity. Yet, the generation of caramel-like odours suggests the need to optimize OH-VC treatment for each particular product.

Keywords

• Ohmic heating
• Tomato
• Vacuum
• Conventional heating
• Pasteurization
• Volatile organic compounds