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BACKGROUND: The economic value of many fruit and vegetables is often linked to the ability to preserve such natural products. In the case of tomatoes, the manufacture of 1 kg of powder or concentrate requires the evaporation of about 16 kg water kg−1 dry matter. In the present work, the effectiveness and economic analysis of solar drying systems for drying of tomato paste with and without geothermal water heat exchanger (GWHE) were studied. RESULTS: The GWHE integration significantly increased the recorded drying temperature up to 53.41 °C, with an improvement of 11.5 °C compared to the conventional dryer. Moreover, the drying temperature inside the drying chamber exceeded ambient temperature after sunset and at night by 30.8 °C. GWHE ensured a continuous drying process, while drying time was 22 consecutive hours, compared to the basic dryer with 18 h in 3 days. Effective moisture diffusivity was found to be 1.617 × 10−9 and 1.202 × 10−9 m2 s−1 for hybrid and basic drying systems, respectively, using the slope. Three methods were used to perform economic analysis. The cumulative present worth of savings, at 23 382.6 USD, is much higher than the capital cost of the hybrid dryer, at 467 USD. The payback period is quite acceptable, at 2.21 years as compared to dryer lifetime of 15 years. Therefore, the hybrid dryer will dry tomato paste without additional charges for 12.79 years and is recommended for a large‐scale tomato paste dryer. CONCLUSION: The hybrid system with GWHE ensures a continuous drying process during night‐time, in addition to reduced drying time. The economic study revealed a high feasibility for the hybrid dryer, with a short payback period. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

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 H2O/kg db, respectively. In the current study, mechanical dewatering and geothermal‐assisted solar drying (SD) of tomato paste at 5.8 kg H2O/kg db allowed reaching the required final moisture level of 0.053 ± 0.002 kg H2O/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−1. 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 × 10−9 to 3.67 × 10−9 m2 s−1 for T = 70°C. The lowest activation energy was recorded for DIC samples with 25.69 kJ mol−1 compared with 41.87 kJ mol−1 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 Applications: High 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. [ABSTRACT FROM AUTHOR]

The present work aims to improve the quality of Algerian Deglet-Nour dates using an indirect solar drying technique preceded by hot water pretreatment. The final product quality was evaluated by three simultaneous testing parameters: microbiological degradation, sugar composition and color change. Convective solar drying experiments were firstly performed with a variable mode at an average temperature ranging between 39-55°C. Four other experiments were conducted in constant mode under regulated temperatures (50°C, 55°C, 60°C and 65°C). The results of drying tests, led towards the choice of the treatment under controlled air temperature of 50°C with air flow of 1.2m/s. Resulting drying time of 8 hours presents the advantage of to discard the night conservation problems by ensuring a continuous drying process. Owing to its low cost and green energy use, this study could offer a practical alternative to the conventional means currently used in industrial applications of postharvest heat treatments of dates. Practical applications Drying of naturally high humid dates and the rehydrated dry dates by direct exposure to the sun, is an old method for valorization the 'Deglet-Nour' dates. Considerable losses occur during this drying process so the food quality can be seriously degraded. For an industrial application with improvement the quality of dried product, the natural sun drying should be replaced by the indirect solar drying means. This article aims to improve the quality of Deglet-Nour dates using an indirect solar drying technique preceded by adequate water steeping pretreatment. The results of the study will be useful in the sense of ensuring an added value by enhancing the product quality and avoid eventual problems induced by night storing of treated products. The obtained results also could offer a practical alternative to the conventional means currently used in industrial applications for post-harvest heat treatment of Deglet-Nour dates. [ABSTRACT FROM AUTHOR]

This paper aims to promote the artificial ripening of Algeria's dry Deglet-Nour dates commonly named Frezza, by successive treatments using hot water soaking and hot vapor steaming. The main objective of the study was to optimize the gain in mass during the proposed hydrothermal process using an experimental design method. Water uptake during rehydration has been optimized according to two complete factorial designs; the first 23 based on eight experiments and the second 22 of four experiments. The conducted experimental investigations showed a maximum of water gain by water soaking and a little part by steaming operation. Obtained and analyzed results led to optimal conditions defined by soaking in water at 30 °C during 8 h followed by hot vapor treatment in a confined chamber at 60 °C under 90% RH. Practical Applications Artificial ripening of Deglet-Nour dates, with different hydration techniques, is an industry practice known in Algeria since the 1950s, but under nonoptimized operating conditions. This paper presents a contribution to the optimization of the rehydration process of dates by water soaking and hot vapor steaming. The results of the study will be useful in the sense of ensuring an added value by enhancing the product quality. The obtained results also permit to minimize the necessary energetic consumption for steam production. [ABSTRACT FROM AUTHOR]