Ohmic pre-drying of tomato paste

Abstract

In this study, the effects of ohmic pre-drying technique on moisture ratio, drying rate, drying time, specific energy consumption, drying efficiency, and effective moisture diffusivity of tomato paste were investigated. Pre-drying experiments were carried out in an ohmic laboratory dryer at voltage gradient levels of 6, 8, 10, 12, 14, and 16 V/cm and oven at 105 and 1.0 m/s air velocity (control sample). Pre-drying was accomplished till the moisture content of the tomato paste reduced from initial moisture content of 90% (w.b.) to a safer level of 70% (w.b.). The ohmic pre-drying reduced the drying time of tomato paste by 80-97%, compared with the hot air drying. Pre-drying took place mainly in warming up, constant rate, and falling rate periods. Six available moisture-ratio models were fitted to the pre-drying data. The results showed that the Midilli et al. model is the most appropriate model for pre-drying behavior of tomato paste. The effective moisture diffusivity varied from 5.39 × 10(-8) to 3.91 × 10(-7)m(2)/s with an activation energy of 2.082 (V/g.cm). Both specific energy consumption and drying efficiency were considerably enhanced by increasing voltage gradient. It was found that the specific energy consumption and drying efficiency varied from 3.72 to 2.29 MJ/kg water and 67.8 to 83.8%, respectively.

Exergy and energy analyses of liquid food in an Ohmic heating process: A case study of tomato production

“…The results indicated, as the voltage gradient increased, the heating times to reach the prescribed temperature decreased. This finding is similar to results of several researches (Darvishi et al, 2013;Hosainpour et al, 2014;Icier & Ilicali, 2005a,2005b.…”

“…One reason may be that the heating time was longer under a lower voltage gradient and resulted in an increase in energy consumption. Similar results were reported by Hosainpour et al (2014); Darvishi et al (2013) and Bozkurt and Icier (2010). Specific energy consumption was correlated as follows:…”

“…After washing with tap water and removal of surface water using absorbent paper, crushed 0.03 g/g salt (3% NaCl salts) was added and then mixed at medium speed in a Sunny mixer (Model SEP-1010). Tomato samples had an initial moisture content of 9.3 ± 0.12% (kg water/kg dry matter), which was determined by a standard oven method at 103 ± 1°C for 24 h (Hosainpour et al, 2014).…”

“…Ohmic heating has tremendous potential in food processing with use in preheating (Hosainpour, Nargesi, Darvishi, & Fadavi, 2014), blanching (Allali, Marchal, & Vorobiev, 2010), cooking (Bozkurt & Icier, 2010;Liu, Jayasingh, Gao, & Farid, 2007;Ozkan, Ho, & Farid, 2004), sterilization and extraction (Darvishi, Khoshtaghaza, & Najafi, 2013;Sarang et al, 2008), evaporation and dehydration (Assiry, Galiy, Alsamee, & Sarifudin, 2010;Lebovka, Shynkaryk, & Vorobiev, 2006;Zhong & Lima, 2003).…”

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

“…The use of the ohmic heating technique for the purpose of heating, pasteurization, sterilization of liquid foods (fruit‐vegetable juice, milk, liquid egg) has been allowed by some organizations such as the Food and Drug Administration (FDA) and the US Department of Agriculture (USDA) . However, studies on the utilization of ohmic heating as a heat source are limited in open literature . Assiry and Elansari applied atmospheric ohmic evaporation to concentrate date syrup from 27 ± 0.03 total soluble solid (TSS) to 70% TSS content.…”