Kinetics, modeling and colorimetry of celery leaves dehydration by direct and mixed solar drying

In celery, leaves, roots, and fruit contain a high value in medicinal properties and are used to prepare syrups, tinctures, infusions, or oils; however, its leaves are commonly discarded, wasting their nutritional and medicinal content. The dehydration of these leaves is a conservation option, increasing their shelf life. This study analyzes direct and mixed solar drying (SD and SM) kinetics and their effect on celery leaves. The moisture contents, drying rate, water activity, and colorimetry were obtained. Moreover, the fitting of experimental data to the mathematical models proposed in the literature. The moisture content stabilized at 150 min in the SM at the shortest time with a maximum drying rate of 0.1179 g∙water/g∙ dm∙min. The initial and final water activity was 0.98 and 0.412 in the SM and 0.403 in the SD. The SD better conserved the leaf color, with a total color change (ΔE) of 2.56, while the value obtained with the SM was 5.42. The experimental results of both technologies were better adjusted to the model Two exponential terms with an R² of 0.999. The results show that the solar drying of the celery leaves is feasible, and a quality product is obtained sustainably.

Thermal Analysis of Tilapia Fish Drying by Hybrid Solar Thermal Drying System

The present work presents a hybrid solar thermal drying of Tilapia fish to improve the product quality and satisfy the importers. The developed hybrid dryer utilized direct solar drying, a solar air heater and a thermal backup unit which sustains the drying process during the night, cloudy and rainy weather conditions. Besides, a new feature of the developed dryer utilizes the flue gas exhausted from the thermal unit to enhance the updraft in the drying chamber by re-injection of the flue gases in the chimney. The initial moisture content of the Tilapia fish used in the investigation was 246.6% on a dry basis, equivalent to 74% on a wet basis. The investigations were repeated three times on different days. Experimental results showed that the moisture content was reduced to an average final of 17.0% db (5.0% wb) within 17.5 hours, while in the open sun drying, it required around 48-72 hours. Hybrid solar drying required around 72% shorter time than open sun drying. The average overall drying efficiency of the developed system for drying Tilapia fish was 13.0%. The Re-injection technique used in the present hybrid solar-thermal system has excluded the need for an electric source for air extraction from the drying chamber, which is highly desired in the rural and fishery regions.

The Effect of Drying Processes on the Nutritional and Phytochemical Levels of Chia Leaves (Salvia hispanica L.) at Different Stages of Growth

Chia leaf (Salvia hispanica L.) is an underutilized low-cost source of nutrients. The leaf is currently not widely utilized as compared to the chia seeds which have wide use in the food industry. The present study investigated the effect of solar-drying and oven-drying chia leaves harvested at different stages of growth on their nutritional and phytochemical composition. The chia leaves were harvested at four stages of early vegetative stage, late vegetative stage, budding stage and flowering stage. Oven drying was done at45 ºC for 24hours, and solar dried in a solar drier until a constant weight was achieved. The results indicated significant differences (p<0.05) between treatments and stages of maturity. Results also showed that solar dried had better nutritional and phytochemical retention over oven dried chia leaves. Crude protein was highest in solar dried leaves at early vegetative stage (FS1) 4.48%, compared to 4.44% for oven dried chia leaves. The fiber content increased from the fresh leaf at 12.4% to high content in solar dried leaf at the early vegetative stage at 23.33%, while oven dried leaves had high content at the flowering stage at 22.09%. There were minimal changes in fat content of the dried chia leaves compared to fresh sample at 5.908%, with high fat levels noted for oven dried leaf at the early vegetative stage (FS3) at 5.68% and solar dried leaves at 4.71% at the budding stage. The difference in fat content could be attributed to degradation during the drying processes. Ash content on the other hand showed difference at different stages of growth from raw samples for both solar- and oven dried leaves. Highest retention of phenolic content was recorded at 147.62 mg/GAE for solar dried leaves at the budding stage (FS3). However, oven dried leaf samples recorded high phenolic content at 124.06 mg/GAE at the late vegetative stage. The flavonoid levels were recorded highest for solar dried leaves at the budding stage at 299.8 mg/CE, compared to high content for oven dried leaves at the budding stage recorded at 270.4 mg/CE. Scavenging activity was highest recorded for solar dried samples at the budding and flowering stages at 100 µg/100g compared to oven dried leaves at 80.85 µg/100g at the late vegetative stage. Solar drying is the simplest and convenient low-cost technology for preserving the nutritional quality and retention of phytochemical ranges of chia leaves which will enhance their utilization when abundantly available.

Experimental and Simulation of Solar Drying Cabinet with PCM and SiO2 Materials

Solar energy is a potential renewable source in Indonesia, especially for the drying process. The process needs a drying cabinet as a support component to store the drying product. A high-quality drying cabinet to store heat for a long time is needed. This research aims to compare the thermal performance of the drying cabinet without PCM (phase change material) and SiO2 materials or DC I (drying cabinet I) with the drying cabinet that uses PCM and SiO2 materials or DC II (drying cabinet II). The research was carried out by experimental and simulation to investigate thermal performance and fluid flow characteristics. The experiment was carried out inside the laboratory to set uniform initial parameters and the simulation using computational fluid dynamics software. The drying cabinet was modeled in 3D. The experiment result showed DC II had a higher air temperature and lowered relative air humidity for two hours than DC I. The simulation result showed air temperature differences and backflow in the air streamline in the DC II.