Solar–geothermal drying/instant controlled pressure drop‐swell drying of mechanically dewatered tomato paste

Abstract

The economic value of many fruits and vegetables is closely related to their suitability for processing and preservation. In the case of tomatoes (about 94% wet basis wb), the manufacture of 1 kg of dry basis (db) powder (5% wb) or concentrate (30% wb) requires the evaporation of 15.9 or 15.7 kg H 2 O/kg db, respectively. In the current study, mechanical dewatering and geothermal-assisted solar drying (SD) of tomato paste at 5.8 kg H 2 O/kg db allowed reaching the required final moisture level of 0.053 ± 0.002 kg H 2 O/kg wb with low-cost energy. The instant controlled pressure drop (DIC) was used for texturing the predried tomato paste using the operative parameters of absolute saturated steam-pressure P = 0.3 MPa and thermal holding-time t = 30 s. The final hot air-drying step of tomato paste was carried out at 39, 50, and 70 C with a constant velocity of 3 m s À1 . The phenomenological modeling of the drying kinetics allowed identifying the starting accessibility and the effective water diffusivity. DIC texturing reduced drying time from 7 to 1.5 hr and improved the effective water diffusivity from 1.43 Â 10 À9 to 3.67 Â 10 À9 m 2 s À1 for T = 70 C. The lowest activation energy was recorded for DIC samples with 25.69 kJ mol À1 compared with 41.87 kJ mol À1 for control samples. A comparison of visual quality revealed a huge enhancement for DIC-samples compared with the control samples (RM). Moreover, the high economic value of dewatered tomato water was noticeable. Practical ApplicationsHigh quality, low energy consumption, and processing time are decisive factors for the industrial drying operations of agro-products. Solar-geothermal drying combined with innovative treatment technology called instant controlled pressure drop (DIC)swell drying can be a good alternative to conventional drying methods such as hot air drying. Mechanical dewatering as a first step followed by solar-geothermal drying/ DIC-swell drying may greatly reduce drying time and improve the quality of the dried product on the one hand, and reduce energy consumption on the other hand. In addition to that, mechanical dewatering and separation allow us to benefit the peels and seeds, in addition to free product juice with less energy. | INTRODUCTIONToday, large quantities of tomatoes are produced in Algeria. According to FAO (2014), Algeria ranks 18th in the world tomato production with 1,065,609 tons per year. Due to their fragility and the distances between production and consumption areas, tons of harvested tomatoes are lost every year. There is therefore a considerable need for conservation and processing techniques. Drying is a remarkable way

Drying kinetics and shrinkage rate of thin‐sliced pears in different drying stages

“…In the following, in order to study the effect of drying temperature on the variation of the effective moisture diffusion coefficient, Arrhenius's equation (Equation (13)) is used (Hadibi et al, 2021). In Equation (13), is the constant coefficient of exponential function, is the activation energy, and R is the global constant of the gas constant.…”

“…In the following, in order to study the effect of drying temperature on the variation of the effective moisture diffusion coefficient, Arrhenius's equation (Equation ( 13)) is used (Hadibi et al, 2021).…”

Recent developments in tomato drying techniques: A comprehensive review

“…Work has also been reported to achieve targeted drying in tomatoes using solar dryers by integrating advanced methods to harness superior performance. Examples of these include the use of PV‐assisted solar dryer using a sun tracking system (Samimi‐Akhijahani & Arabhosseini, 2018), liquid desiccant‐assisted solar dryer coupled with a photovoltaic‐thermal regeneration system (Dorouzi et al, 2018), and geothermal‐assisted solar dryer (Hadibi, Boubekri, Mennouche, Benhamza, Besombes, & Allaf, 2021; Hadibi, Boubekri, Mennouche, Benhamza, & Kumar, 2021). Several attempts were also reported in the literature to tap the potential of solar drying in tomatoes, which has been summarized in Table 1.…”

“…As far as the economy and environmental impact are considered, using renewable energy sources has been encouraged. From this perspective, several attempts have been made to use solar energy systems in tomato drying (Djebli et al, 2019; Hadibi, Boubekri, Mennouche, Benhamza, Besombes, & Allaf, 2021; Hadibi, Boubekri, Mennouche, Benhamza, & Kumar, 2021; Samimi‐Akhijahani & Arabhosseini, 2018). Despite its advantages, solar drying has some limitations, like the possibility of drying in the daytime only, dependence of drying on weather conditions, and longer drying time (El Hage et al, 2018).…”

Heat Balance of Combined Heat Exchanger Aerodynamic Heating Dryers

“…The amount of heat supplied to the combined heat exchanger with the spent drying agent, 𝑑𝑄 о.а 𝑑𝑄 о.а = 𝐿 0 𝑖 2 (𝑡)𝑑𝑡, (4) where i2(t) -enthalpy of the spent drying agent depending on the time during the drying period, J/kg. Amount of heat removed by the drying agent after heat exchange with heat-receiving surfaces, 𝑑𝑄 с.𝑎 = 𝐿 0 𝑖 1 (𝑡)𝑑𝑡, (5) where i1(t) -enthalpy of the drying agent depending on the time during the drying period, J/kg.…”