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Sun drying is the most common technique used to dry various food products due to its economic convenience. However, it is not effective owing to its unreliable nature leading to microbial deterioration and aflatoxin contamination of food. In Tanzania, about 1.3 million tonnes of maize bran are at risk of deterioration annually due to improper drying. The aim of this study was to design, fabricate and test an efficient small-scale flash dryer for maize bran. Using principles of material and energy balance, a small-scale flash dryer with a throughput of 500 kg of dry product per hour was designed resulting in a nominal diameter of 387 mm and a drying length of 20 m. Design calculations and drawings were done using MS Excel 2021 and SolidWorks 2018 respectively. Empirical procedures were used to fabricate and test the dryer. The material of construction used in the flash duct was food grade (stainless steel, SS 201). A fuel blend of Waste Engine Oil (WEO) and diesel (85%-15%) was used with a novel heavy oil burner. It was observed that at an inlet air temperature of 150 °C and air velocity of 12 m/s, moist maize bran was dried from 37% to 10% w.b. The fabricated flash dryer's energy efficiency, specific energy consumption, and specific energy utilization are 74%, 3.4 MJ/kg water evaporated, and 1.71 MJ/kg dry maize bran respectively. It was concluded that the fabricated small-scale flash dryer displayed improved energy performance compared to others presented in literature. Better instrumentation was recommended for feedback control on burner operation and process monitoring which further enhances the performance of the fabricated small-scale flash dryer. [ABSTRACT FROM AUTHOR]

Drying food is an effective method to preserve fruits and vegetables, increasing their shelf life and preventing germination. Bottle gourds, known for their high nutritional value, can rot quickly due to their high moisture content, causing biochemical and microbial changes. To improve shelf life, moisture can be removed to prevent microbial activity. Different drying methods are used to preserve gourd family vegetables for long periods and off-season. Indirect solar drying shields foods from UV rays, dust, insects, and other contamination by avoiding direct exposure. This study aimed to utilize an indirect solar dryer to research the potential for drying bottle gourds and conduct physicochemical analyses for the dried products to compare the drying techniques. In this experiment, different samples of bottle gourd slices were dried using an indirect solar dryer and compared with sun and shade drying. Under physicochemical properties, moisture content (MC), retention of color, thickness, and shrinkage of dried samples were analyzed and compared. The result showed that the time taken to reach 10% moisture was 13 h for samples dried with sun drying. While shade and indirect solar drying took 17 h. The Midilli-Kucuk model outperforms other approaches for drying bottle gourd, with the greatest R2 values (0.9967, 0.9950, 0.9936) and the lowest RMSE values (0.0182, 0.0220, 0.0277) for direct sun, shade, and indirect solar drying, respectively. The indirect sun dryer showed good color retention compared to the fresh bottle gourd samples with L* value of 44.08, b* value of 15.40 and a* value of 7.01. The volumetric shrinkage was 97.64% in the direct sun drying method after 15 h, which is higher compared to sun and shade dryers due to the effect of time and temperature. In addition, there was a significant difference (p-value <0.05) between the thickness of the three drying methods. The use of indirect solar drying methods can be highly recommended to get high-quality dried food with zero energy cost. For future studies it is recommended to enhance the function and design of the indirect solar dryer to speed up drying times and improve the quality of dried samples. [ABSTRACT FROM AUTHOR]

Food waste is one of the biggest challenges we are facing nowadays. According to the Food and Agriculture Organization (FAO) of the United Nations, approximately one-third of all food produced in the world is lost at some stage between production and consumption, totaling 930 million tons of food per year. Meanwhile, 10.5% of humanity suffers from malnutrition, 26% are overweight and greenhouse gases derived from the food industry account for between 25 and 30% of total emissions (8 to 10% referring to food waste), exacerbating the current climate crisis. To address these concerns, there has been a growing inclination to seek alternatives to fossil fuels, including the adoption of solar energy across diverse sectors, including the food industry. Actions are needed in order to change these patterns. This review article aims to provide an overview of recent developments in the field of solar food dehydration and the types of dehydrators that have emerged. Extensive research and bibliographic analysis, including other review articles, have revealed a growing focus on investment in this area to develop solar dehydrators that are increasingly effective but as sustainable as possible. [ABSTRACT FROM AUTHOR]

Salam leaves, a traditional food flavoring spice, are a widely recognized herb in Indonesia and are used in many regions. This study aimed to investigate the drying kinetics of salam leaves, comprising mathematical modeling, moisture diffusivity, and other nutritional values as qualitative parameters. The drying process was examined using a forced convective system (CSD) and open sun drying (OSD). The drying behavior was examined by observing the drying kinetics characteristics using 12 thin-layer semi-theoretical mathematical for drying of agricultural products, determining the moisture diffusivity, as well as measuring the content of chlorophyll a, b, and total dissolved solids as nutritional quality indicators of the drying products. According to the obtained results from the non-linear regression analysis, the Midilli model demonstrates the highest degree of appropriateness for drying salam leaves. The moisture diffusivity of CSD is greater than that of open-air solar drying. Regarding nutritional composition, the study revealed that chlorophyll a, b, and carotenoid levels in the dried leaves obtained through CSD were more significant than those obtained by OSD. As an environmentally friendly dryer, CSD can potentially be applied in herb-drying industries, especially salam leaves. [ABSTRACT FROM AUTHOR]

This study presents a design for an absorber used in a solar air collector for an indirect solar dryer. The absorber comprises two aluminium plates corrugated and joined together to form parallel cylinders, enabling airflow within the collector. This research aims to experimentally examine the drying process of two types of bananas, one from Morocco and the other from abroad, using the designed solar air collector. Additionally, the study aims to investigate the peculiarities of the drying process and the performance of the solar dryer employed. The experiments were conducted by subjecting the bananas to the designed solar air collector, and the evolution of drying was monitored. The initial mass of the bananas used was 631.6 g for the Moroccan banana and 713.6 g for the Export banana. After the drying process, the mass of the Moroccan banana reduced to 77.5 g, while the Export banana reduced to 137.3 g, indicating significant moisture removal. The percentage of the amount of water extracted (Q) from the bananas was found to be 87.7% for the Moroccan banana and 80.8% for the Export banana. These results demonstrate the effectiveness of the corrugated aluminium plate absorber in facilitating the drying process in the solar air collector. The significant reduction in the mass of the bananas and the high percentage of water extraction highlight the efficiency of the solar dryer in removing moisture from the agricultural produce. The findings of this study contribute to the understanding of the drying process of bananas and offer valuable insights for the design and optimization of solar drying systems for agricultural applications. [ABSTRACT FROM AUTHOR]

Solar drying is a renewable, efficient, cheap, and sustainable method of preserving agricultural produce. Recent trends in hybrid and greenhouse–type solar dryers were studied. The study revealed that hybrid and greenhouse–type dryers are robust and efficient because they are mostly embedded with heat generating and circulation systems. They are designed to accommodate large-scale drying of fruits and vegetables with higher rates of drying, reduced drying time and some other specific advantages. Findings also revealed that hybrid and greenhouse type solar dryers are mostly designed for optimum retention of heat to compensate for periods with low illumination. The study also gave insight into design challenges peculiar to these types of dryers, and further revealed that most of the fabrications were based on assumptions, with limited data as references. This review also highlights the cost of procurement, uniformity of airflow, sizing of blower and material selection as some of the factors limiting the utilization of hybrid and greenhouse type solar dryers for drying of fruits, vegetables, and other staple crops. [ABSTRACT FROM AUTHOR]

Achieving food security in Mozambique is critical, since 80% of the population cannot afford an adequate diet. While increasing agricultural production is a necessary effort to address this challenge, inadequate post-harvest treatment leads to storage losses and quality degradation, with repercussions for food security. The use of solar drying is promoted as a solution to provide efficient and reliable access to food preservation that improves the food security situation in rural communities. However, there is a lack of clear evidence on how the use or access to solar drying affects food security. This study identifies the determinants of farmers' choice to use solar drying and evaluates the effect of a passive solar dryer on food security using survey data from 634 households. We allocated solar dryers to selected communities and all interested individuals belonging to these communities were eligible to use it. Propensity score matching and endogenous switching poisson regression are used to estimate the average effect. The use of solar drying with associated training significantly increases the food security status of participants by increasing household food availability, women's dietary diversity, and months of adequate household food provision and by decreasing the household food insecurity access scale. [ABSTRACT FROM AUTHOR]

Preservation of food and vegetable products is an age-old practice for the retention of flavor, appearance, and quality. From ancient times, driers for drying food grains work on direct sun rays, firewood, fossil fuels, and coals causing carbon release. These available methods are expensive, unreliable, and unhygienic; thereby the use of a solar dryer working on free and clean energy is better for higher value addition to food preservation. The objective of this exploration is to study the recent developments in the use of different types of solar dryers for drying foods, vegetables, seafood, etc. There exist many studies on the effects of the parameters such as temperature, relative humidity, and speed of air, turbulence effect, sun irradiation, and the latitude of the location in the solar drying process. The findings show that the climate conditions such as solar radiation and atmospheric air play an important role in the drying efficiency of the solar dryer. A phase change material stores thermal energy during the daytime and releases heat during the nighttime. This process improves thermal efficiency and reduces heat loss during the drying period. On the one hand, a hybrid dryer integrated with a solar panel produces electricity for the operation of a DC blower circulating hot air inside the drying chamber for better drying. In addition, a critical review has been performed on the usage of different absorbing plates increasing heat transfer rate, use of various phase change materials for heat storage, and analysis of CFD simulation. [ABSTRACT FROM AUTHOR]

Low/zero-head cross-flow turbines (LZH-CFT) possess vast potential in the field of renewable energy technology. This research presents a modified design of a cross-flow turbine specifically engineered to harness the untapped hydro-kinetic energy from low/zero-head water resources. Unlike traditional hydro turbines, the LZH-CFT leverages a cross-flow configuration to utilize the water flows of natural streams, making it an ideal solution for flow channels with low/zero head. The design is modified through ANSYS simulations by varying the rotor's blade angles (from 0 to 90°) and 60° angle is found optimum. The prototype model of modified design is prepared and tested, which represents 62.5% RPM efficiency and provides double power as compared to the typical cross-flow turbine. [ABSTRACT FROM AUTHOR]

An active solar dehydrator is designed for dehydrating fruits and vegetables. The solar collector transfers thermal energy to the drying air. The temperature inside the drying chamber is maintained between 45 °C and 50 °C by a feedback control system. The design is based on the December solar irradiance of Islamabad, which is found to be 572 watts per square meter. The energy required to dry one kilogram of apple and banana is 245 watts and 220 watts, respectively. The dried product from the solar dehydrator is better in terms of quality and taste compared to the product produced by ordinary open sun drying. [ABSTRACT FROM AUTHOR]

Solar energy provides desired thermal energy for diverse applications, including industrial heating, domestic cooking, power generation, desalination, and agri-food preservation. Despite extensive research on solar drying from the scientific community, there are limited practical applications for small-scale use. This review attempts to analyze the design features of three specific types of dryers for food drying applications: solar evacuated tube dryers, biomass dryers, and hybrid solar dryers. The thermal performance of the three dryers is evaluated in terms of drying time, moisture removal, and temperature attained during drying. The review also assesses the prospects of solar dryers, highlighting the need for further research into innovative designs and advanced drying capabilities. The study provides valuable information for enhancing dryer performance with various integrated solutions. [ABSTRACT FROM AUTHOR]

Conventional hot air and solar energy processes have been used for apricot. These processes had adverse effects on the quality due to the longer process times, and this indicates the need for an innovative approach. Radio frequency (RF) processing has innovation potential for drying with its volumetric heating feature, but an optimal process should be designed for process efficiency in industrial‐scale applications. Therefore, the objective of this study was to confirm the RF process for industrial‐scale apricot drying. For this purpose, a mathematical model was developed to predict temperature and moisture content change of apricots during drying, and experimental validation study was carried out. For the RF drying process, pre‐dried apricots (0.58–0.75 kg water/kg dry matter, db) by solar energy were used. The purpose was to start the RF process at a suitable moisture content level as this process was not feasible to apply directly due to the high initial moisture content of apricots (up to 4 kg water/kg dry matter, db). RF drying experiments were carried out in a 10 kW hot air‐assisted (50–60°C) staggered through electrode system. Optimum electrode gap was 81 mm with 2500 V potential of the charged electrode. Final moisture content of the dried apricots was 0.25–0.33 kg water/kg dry matter (db). Following the model validation for temperature and moisture content change, industrial‐scale apricot drying scenarios were demonstrated to confirm the RF process for feasibility and process design. Practical Application: A comprehensive mathematical model was developed for radio frequency (RF) drying of apricots. This model was experimentally validated with respect to the temperature and moisture content change. Various process design studies were carried out for an industrial‐scale apricot drying process to confirm the process feasibility. With this background, the results of this study can be directly used in an industrial drying for an optimal process design and energy efficiency. [ABSTRACT FROM AUTHOR]

• Shrinkage, effective diffusion coefficient (D e), surface transfer coefficients on solar drying are reviewed. • Their influencing factors were thoroughly discussed. • The main factors volume of water, moisture content, air temperature, air velocity are discussed. • Different mathematical models involved in the above parameters are reviewed. • Important results are listed and recommendations are given. Drying of food materials leads to an increase in shelf-life and gives quality end products. Drying with solar energy is an economical and environmentally friendly method than other drying methods. The food products are dried using solar energy in different methods such as open sun drying, direct, indirect, mixed-mode and hybrid solar drying. There are some parameters such as shrinkage, effective diffusion coefficient (D e), surface transfer coefficients, etc. majorly influence the solar drying of food products and these elements are extensively reviewed in this work. The shrinkage of food products affects the drying rate and quality of the food products as it involves surface cracking, volume, porosity and hardness changes. The D e gives the moisture transfer rate in the food products during solar drying. The values of surface transfer coefficients including mass transfer coefficient (h m) and heat transfer coefficient (h) give the mass and heat transfer rate from the surface of the food product as these parameters are surface parameters. The parameters such as shrinkage, D e , h m, and h of food products and their influencing factors need to be analyzed to understand more about the physics of the solar drying process. An extensive review is made on the factors of shrinkage, D e , h m and h such as volume of water, moisture content, air temperature, air velocity, the thickness of product and geometry of food. The values of shrinkage, D e , h m and h of different solar drying processes are tabulated and discussed. A brief review was performed on different mathematical models used to determine the values of shrinkage, D e , h m, and h during solar drying of food products. The influencing factors such as moisture content, air temperature, velocity, thickness and geometry of the product on these three factors shrinkage, D e , h m, and h were discussed. Important results and recommendations of this topic are mentioned at the final because it is an innovative review trial in the solar drying area. [ABSTRACT FROM AUTHOR]

Investigations were conducted to study the drying characteristics of potato slices prepared from three varieties of potato viz Kufri Chipsona-2, Kufri Chipsona-1 and Kufri Bahar. Potato slices samples of 500 g each were dried at 50, 60, 70 and 80oC in tray dryer. The initial moisture content of potato slices was determined as 309.83 per cent (Kufri Chipsona-2), 346.42 per cent (Kufri Chipsona-1) and 468.18 per cent (Kufri Bahar) on dry weight basis. The slices took 160 to 350 min drying time depending upon drying temperature, pre-treatments and potato varieties. The samples dried at lower temperature (50°C) took higher drying time to achieve the final moisture content as compared to those dried at higher temperature (80#176;C) irrespective of potato varieties and pre-treatments. The total drying time required to achieve the final moisture content was dependent upon potato varieties, pre-treatments and the drying temperature. The potato varieties having higher initial moisture content took higher drying time as compared to those with lower initial moisture content. The potato slices having lowest dry matter content exhibited little higher final moisture content at a particular temperature. The final moisture content of hot water-blanched potato slices was found to be little higher as compared to KMS-treated potato slices and control samples at the same drying temperature and drying time irrespective of potato cultivars. Total moisture loss increased with increase in drying temperature. The total moisture loss was highest in case of potato slices of Kufri Bahar, while the lowest in case of Kufri Chipsona-2, irrespective of the drying temperature and pre-treatments. The maximum moisture loss of 99.91 per cent was recorded in case of KMS-treated slices (KufriBahar) dried at 80#176;CC. [ABSTRACT FROM AUTHOR]

In this study, the impact of convective solar drying on the physiochemical characteristics of hot peppers harvested in Algeria was investigated. The freshly harvested peppers underwent convective drying until they reached a desired stable weight. Various parameters including moisture content, water activity (Aw), pH, crude protein, crude fat, total sugars, and polyphenol content were measured. The drying process, using an optimal method, took approximately 2 to 3 days and resulted in moisture content levels of (32.41 %), Aw of (0.26%), pH of (4.1), acidity of (2.8), ash content of (73.38%), dry matter of (67,59 %), total protein content of (0.83%), sugar content of (2.9%), polyphenol content of (89%), and crude fat content of (0.23%). In comparison, the values for the freshly harvested hot peppers were (89%), (0.92%), (5.34%), (3.6%), (8%), (11%), (1.64%), (1.64%), (125%), and (0.36%) respectively. These findings confirm that solar drying effectively preserved the nutritional quality of the hot peppers, with minimal losses in some properties compared to the values of the freshly harvested peppers. [ABSTRACT FROM AUTHOR]

Solar drying is a sustainable process that may impact the quality of dried food. This is because, pigments contained in food are sensitive to sunlight, and exposure to ultraviolet radiation can affect them. We applied biopolymer-based coatings on strawberry, from hydro-colloidal solutions of Opuntia ficus indica-mucilage, fenugreek, xanthan gum, gum Arabic, and guar gum to evaluate their potential use as UV filters for solar drying of food. Thermal properties and the optical transmittance, absorbance and reflectance of the coatings were measured to assess their influence on food-sunlight interaction. During the drying experiments, the moisture content, total anthocyanins (TA), and total phenolic compounds (TPC) were measured. Optical and thermal properties are influenced by the biopolymer-based coatings. Also, the optical properties are influenced by the coating thickness. The differences in optical and thermal properties influence the drying process. Differences exist in the drying rate for strawberry slices with coating, compared with those without the coatings. In general, the TA and TPC content in the product are better preserved under solar drying than in control experiments done in a drying oven. A partial transmittance of solar UV radiation is recommended to obtain increased TA and TPC contents in the dried product. [ABSTRACT FROM AUTHOR]

• Solar drying of foods holds huge potential in on-farm food processing. • Dryer designs and selection of components significantly affect drying characteristics. • The use of energy storage materials in solar dryers can be of great benefit to food samples. • Computer applications and modeling can be integrated for improved process control. • Hybrid drying techniques to assist solar drying provide better quality end-products. Considering the growing energy crisis, the need for green-energy alternatives is inevitable. Food processing must consider the application of renewable energy for replacing conventional and energy-intensive unit operations; drying in particular. The utilization of solar energy for drying of foods remains to be attractive in terms of energy efficiency, cost-effectiveness, and rural applicability. However, a huge technological gap exists; developing low-cost and energy-efficient dryers for the production of high-quality foods is a challenge. Proper design and selection of components for a solar dryer are mandatory for the effective utilization of thermal energy. Considering these aspects, this review focuses on providing an exhaustive report on the available dryer designs and other critical considerations, along with a summary of diverse applications for different foods. Besides, various recent advancements, challenges, and limitations for implementing large-scale solar drying of foods are presented in terms of technology, energy considerations, and other socio-economic aspects. Thus, this review provides valuable insights into the state of the art of solar dryers, to assist the progress of this green and sustainable technology for food applications. [ABSTRACT FROM AUTHOR]

Solar energy represents an alternative source of energy supply, which has also found its application in wood processing technology. In particular, solar energy finds great application in the field of wood drying. Solar energy is defined as the emitted light and heat produced by the sun, which is harnessed with the help of developing technologies such as solar collectors, photovoltaic cells, solar and thermal collectors, various types of solar architecture, plantations and reactors that use molten salts, and technologies of artificial photosynthesis. The purpose of this paper is to give a brief overview of solar drying technology. A special review is given to solar drying methods. The method of work does not cause experimental research in practice but represents a collection of used literature and individual research. [ABSTRACT FROM AUTHOR]

Nigeria, as one of the countries in the African continent has its challenges regarding to agricultural crops cultivation and its preservation methods. Traditional methods of preserving crops are commonly adopted by the local populace over solar dryer appliances. The reason for these includes being cheaper method, does not require much technical know-how, is easily learnable, the area for drying the agricultural crop produce being unlimited etc as when compared to solar dryers that needs materials to be fabricated, required little or medium knowledge of technical know-how, financial requirement for its fabrication which could range from few dollars to thousands of dollars. Solar dryer working principles, components, various classifications, and its mode of air movement and mode of heat transfer were discussed on this article. The article also reviewed some of the experimental researches on solar drying in Nigeria carried out by various scholars. The review of the published works on solar drying of various crops under different drying techniques were carefully studied. The results showed that, significant works on solar drying in Nigeria have been carried out even though its potential is greatly under-utilized due to various factors militating against it. [ABSTRACT FROM AUTHOR]

Food waste valorization via its transformation into animal feed is a viable alternative for improving food security and the diversion of organic waste from landfills. The manuscript presents the environmental impact assessment of the construction and operation of a novel solar food waste drying unit on the island of Crete in Greece, which is treating food waste from hotels. Life cycle assessment is utilized for the impact assessment. The results indicate a total carbon footprint of approximately 217.5 kg CO2 eq. per ton of treated food waste. In conclusion, the operation phase is the major contributor to the environmental impacts, due to the utilization of electricity. [ABSTRACT FROM AUTHOR]

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Recently, the quality of food solar dried has been associated to solar irradiance, irradiation and UV-light. Different materials used as covering materials in direct solar dryers had different optical properties, thus, different quality should be expected in solar food drying. The objective of this study was to compare two direct solar dryers builder with different covering materials: Direct Solar Drying with Poly (methyl methacrylate) (DSD), and Greenhouse Solar Drying with polyethylene (SGD), based on their three aspects: chemical composition, heat-mass transference, economic-environmental effect. Chemical composition was evaluated as the total phenolic compounds (TPC), flavonoids (TF) anthocyanins (TA) and antioxidant activity (AA) of blackberry pulp (Rubus spp). Dehydrated blackberry pulp contains lower TA than raw samples because TA is sensitive to solar irradiation and UV solar irradiation. TPC, TF and AA averages do not show significant differences among all the drying processes. Evaluation of energy and heat transfer in the evaporative and diffusive periods of the drying technologies led to an assessment of the return of investment period for DSD and SGD technologies for different power sources. The results suggest payback periods between 39 and 121 months, considering only the 6 months of harvest duration without using the solar dryers the rest of the year. [ABSTRACT FROM AUTHOR]

In the present work, the use of automatic temperature controllers based on embedded systems for solar dryers is proposed, in order to improve the product quality in small scale drying operations. With this aim, from a scientific literature review, it was determined the temperature influence over the quality of the dried product, like spices, in solar drying operations for food conservation. Then, it was established the use of temperature controllers as a way to decrease the quality loses in the drying operation in solar installations. Finally, it was proposed the use of embedded systems, like microcontroller based systems, for the development of economical temperature control systems fitted to small scale solar drying productions. [ABSTRACT FROM AUTHOR]

In this article, an experimental estimation of thermal efficiency of horizontal and vertical-finned double-pass solar air collectors integrated with drying chamber has been carried out. The rig consists of two main parts as solar collector and dryer. The system was installed in the laboratory of Szent István University, Gödöllő, Hungary. The absorbers were made from a copper integrated fins in horizontal and vertical directions. The test results showed that the daily efficiency increased by10% when the direction of fins have been changed from vertical to horizontal. After 5 h drying of 2 kg apple slices, the final weights were 1.16 and 1.37 kg by using horizontal and vertical-finned collectors, respectively. [ABSTRACT FROM AUTHOR]

Abstract Algeria industry fruit processing generates a huge amount of waste which causes a serious environmental problem. Thereby, the use of solar drying as a clean energy process seems to be a promising solution. This will enhance the value of fruit waste by reusing it in a dry form, and will also contribute to the protection of the environment. For this purpose, an innovative greenhouse solar dryer has been designed at the Solar Equipment Development Unit in Bou Ismail. An experimental study of solar drying kinetics of industrial tomato pomace was conducted to test the performance of the new solar dryer as a waste processing dryer. The drying temperature of the tomato waste, using this type of dryer, varies between 40 and 58 °C. The duration of the drying operation for a final product is only 5 h. Five new universal and dimensionless models and five different drying models chosen from the literature were evaluated in order to select the model that better fits the experimental data generated during the drying process. Among the different models tested, it emerged that the new model2 was the most suitable to describe the drying process of tomato waste. Also, the diffusion coefficient and the activate energy were studied and determined. The effective diffusivity varies between 3.2E-9 and 4.7E-10 m2/s with activation energy is 75.6 kJ/mol. Highlights • A new greenhouse solar dryer was used to dry tomato waste from fruit and vegetable processing plants. • The tomato waste lost 86% of its original weight and the time of the drying process is 5 h. • Five new universal and dimensionless models were used. • The new model2 characterizes well the drying curves of tomato waste and different agricultural products. • There is a direct liaison between temperature and the effective diffusion coefficient. [ABSTRACT FROM AUTHOR]

Abstract The quality of Theobroma cacao L. is influenced by different variables both in the crop and in the processes of postharvest, the latter it includes the fermentation and the drying, fundamental for the formation of aroma and flavor precursors, determinants in the characteristics of quality and differentiation of cocoa in the chocolate industry. The objective of the present research was to evaluate the effect of the solar drying process using a plastic roof solar dryer on the sensory and chemical quality of a mixture of cocoa cultivated in a region of Antioquia, Colombia. The content of total polyphenols, anthocyanins, sugars, mannitol, pH, total acidity, humidity, ethereal extract, ash, crude fiber and odor and flavor descriptors were analyzed. For analyzing the data, we used the methodology of longitudinal data analysis and repeated measurements, a Principal Component Analysis (PCA), and a principal factor analysis. The analyzed sensory characteristics are statistically different over time (p < 0.05). There was a decrease in the content of anthocyanins, total polyphenols and sucrose, and an increase in glucose and fructose during fermentation and drying. The analysis of factors allowed to define a series of groupings as indexes of quality according to the chemical and sensory properties analyzed in the drying process. Overall, the mixture of cocoa clones evaluated in the solar drying process presented indicators of sensory and chemical quality associated with descriptions of odor (spicy, dairy, nut, fruity, sweet cane), flavor (floral and spicy), ethereal extract, and pH that indicate a good benefit of cocoa and show the potential that Colombia has as a producer of fine aroma cocoa in high demand in premium markets. Graphical abstract Unlabelled Image Highlights • Anthocyanins were a key indicator to determine the quality of the fermentation process. • Fermentation and drying process showed that 132 hours were enough to produce desirable descriptors in cocoa. • Principal component analysis can distinguish the chemical and sensory characteristics that influence the quality of cocoa. [ABSTRACT FROM AUTHOR]

Kiln-dried fruit drying time is readily predicted from initial moisture content since the environment is tightly controlled. For uncontrolled environments, such as a greenhouse solar dryer, a product's drying time varies depending on ambient conditions and is thus more difficult to predict. Prediction of the drying time is needed to better schedule dryer use. Data was obtained from a set of wireless scales that weigh the waste during solar drying after initial moisture content measurement of a sample. A set of linear and quadratic models for drying rate are tested with the best yielding a 39% reduction in RMSE over traditional models. The results indicate that the modelling approach is likely to be useful for open solar dryers where the temperature, and thus the drying rate, is not controlled. [ABSTRACT FROM AUTHOR]

Highlights • Study the drying kinetics of two cherry cultivar in a convective solar dryer. • Determine the effect of drying air temperature and the drying air flow rate on the drying kinetics of the cherry. • Determine the characteristic drying curve of sweet cherry (CDC). Abstract This study presents the convectional drying process of two types of Moroccan sweet cherry, namely, Burlat and Van. 40 g of cherries were taken, pitted, cut in two halves, and were dried using a partially indirect solar convective dryer, which has an area of 2.5 m2. The thin-layer drying of sweet cherry were carried out in July 2017 at three air temperatures of 60, 70 and 80 °C and for two drying air flow rate 150 and 300 m3/h. Moreover, the cherry fruits are sufficiently dried in the ranges between 34 and 40 °C of ambient air temperature, 17–27% of relative humidity, and 200–900 W/m2 of solar radiation. The evolution of the moisture dry content and the drying rate as a function of drying time for different temperatures are shown graphically. Experience shows that as the air drying temperature increases the drying time decreases. During the experiments, pitted cherries were dried and the moisture content was decreased from 82.12 for Burlat and 85.45 for Van to 23 ± 3% (w.b). The drying temperature of 80 °C and air velocity of 300 m3/h were the optimum values for cherry fruit drying in a minimum time of 240 min. The characteristic drying curve (CDC) applicable to both types of cherry has been established as a polynomial of order 3 in reduced moisture content. [ABSTRACT FROM AUTHOR]

In this paper, a review on solar drying is presented. The review comprises the main components, classifications and affecting parameters. Advantages, disadvantages and limitations of such technology are also investigated. That said, solar dryers are assessed according to three key-elements: way of air movement (passive and active), mode of transferring heat (direct and indirect, hybrid and mixed) and type of drying chamber (cabinet, greenhouse and tent). Moreover, economic and environmental studies are performed for the Lebanese case in order to assess the Payback Period (PP) and the amount of CO 2 reduction. The examined parameters are the percentage of time where solar dryer is utilized (Pr), the mass of dried food and food type. Results show that for Pr equals to 0.6, when drying 120 kg of carrots using solar dryer the amount of Saved Money (SM) is 780 $/month, PP is 10 months and the amount of CO2 emissions decreases by 6400 kg/month. [ABSTRACT FROM AUTHOR]

This work aimed at modeling thin-layer solar drying of cassava noodles (tapioca). The selection of good drying models for dryers helps to improve their efficiency. Drying data of tapioca was obtained using a forced convection solar dryer. The treatment combinations of the experiment comprise of air flow velocities (V) of 1.5, 2.5, and 3.5 m s-1; drying layer thicknesses (B) of 0.48 and 0.72 cm; and initial moisture contents (Mi) of 297%, 186%, and 122% (dry basis). Eleven thin-layer drying models from literature, in addition to a new model developed in this work were all fitted to the solar drying data of tapioca. Least square regression analysis was carried out and comparison between drying models was made using goodness of fit statistical parameters. Drying kinetics of the tapioca was determined. Effective moisture diffusivity and activation energy of the tapioca were also determined. The results obtained from the analysis show that the new model (Modified Aghbashlo model) was the best fitted to the drying data of tapioca. The determined effective moisture diffusivity of the tapioca samples varied from 4.93×10-11 to 8.82×10-11 m2 s-1. Also, the activation energy of the tapioca samples was determined as 28 kJ mol-1. [ABSTRACT FROM AUTHOR]

An integrated solar system was examined and worked for drying chamomile during the summer season 2013 in Germany. The system consisted of collector, heat exchanger, reflector, main drying chamber below collector, additional drying chamber and supplementary electric heaters immersed in water tank. It could also storage of solar energy into water during the time of sun-shine and reuse this energy at cloudy weather or off sunshine time to raise the temperature of drying air inside the system. The capacity of main drying chamber ranged 32–35 kg of fresh chamomile and 10–12 kg for the other separate drying chamber. Air temperature inside the dryer could be maintained as desired range for drying chamomile using a temperature controller. The integrated dryer was operated about 30–33 h to reduce the moisture contents of chamomile from 72-75%–6% (wb) compared to 60 h to reduce it to 9–10% (wb) using open sun drying method. Nine mathematical models for drying kinetics of chamomile were tested to determine the parameters of the best suitable models for those plants. It is found Midili model was the best model to define drying kinetics of chamomile for the main and additional drying chambers in solar system. [ABSTRACT FROM AUTHOR]

Abstract: The effect of two passive drying methods on the degradation of ascorbic acid (vitamin C),  α‐tocopherol (vitamin E), and β‐carotene (provitamin A) in ripe mango and tomato was determined. Samples of both commodities were dried outdoors in a solar drying cabinet or indoors in sealed plastic boxes containing ceramic zeolite drying beads in a bead‐to‐fruit ratio of 1:10. Nutrient content of the dried samples was compared to fresh samples (undried control) obtained from the same batch of fruit. Mango samples tended to reach an equilibrium weight of approximately 18% of their initial weight after 28 to 30 hr of drying in both drying methods, while tomatoes equilibrated at 5% to 6% of their initial weight after 8 to 10 hr of drying in the solar drying cabinet and after approximately 30 hr using drying beads. The content of all three nutrients in solar dried tomato, and of β‐carotene in mango were significantly (P < 0.05) lower than the control. α‐Tocopherol and β‐carotene content in tomato and β‐carotene content in mango were significantly lower than the control in samples dried using drying beads. Drying method had a significant (P < 0.05) effect on nutrient content; ascorbic acid and β‐carotene content were lower in solar dried tomato than in tomato dried with drying beads. For mango, β‐carotene content was lower after solar drying as compared to drying with drying beads. Drying fruit at lower temperatures using drying beads resulted in higher overall nutrient content of the dried fruit. Practical Application: Agriculturalists in developing countries still depend largely on solar drying methods as a means of extending the shelf life and increasing the value of fruit and vegetable products. Zeolite drying beads are reusable and are capable of drying fruit relatively quickly in a controlled environment, and may reduce the degradation of certain nutrients due to heat during solar drying. [ABSTRACT FROM AUTHOR]

The application of solar drying (SD) and heat pump-assisted solar drying (HPSD) on the retention of flavonoid components, total color changes, and water activity ofClinacanthus nutansLindau leaves were investigated. Analysis of data shows significantly higher extractable yield and flavonoid (orientin and vitexin) percentage during the drying with HPSD. The same drying technique also revealed optimum color values and low water activity. Thin-layer models fitted to the experimental data show that Hii and Law model is suitable for SD, while logarithmic model is able to give a good fit to HPSD. [ABSTRACT FROM AUTHOR]

Solar crops drying as a process has currently become a decisive factor to improve the efficiency in the industrial, residential and farm sectors. Given its considerable importance, different researchers have proposed and developed a great number of theoretical and experimental models to predict the drying kinetics of the process, including the machine and the product. In the use of solar thermic driers, there have been great advances on developing models; however, the major part of these works has concentrated in driers of industrial scale. The unified models that allow predicting temperature profiles and moisture content for many types of crops, using handmade driers to small scales have been less applied. It has been mainly due to the wide diversity of products and the big differences between the existing processes. The purpose of this research is offering a panoramic about the state of the art related to models and present the basic theoretical foundations to develop a model for solar seed drying. [ABSTRACT FROM AUTHOR]

The main objective of this investigation was carried out to study the ability of utilizing greenhouse solar dryers for drying of corn in order to obtain the best quality of dried grains for using it as seeds with the least drying time, and comparing with the natural sun drying method. Thus, contributing to increase the productivity. Corn cv. (Giza 168) was used for the experimental work at initial moisture content of 31.73% on dry basis (d.b). Two different drying methods of corn were tested for drying of ear and shelled corn. The two methods were natural sun drying and solar drying using greenhouse type solar dryers at different air velocities (0.5, 1.0 and 1.5 m/s). The experiments were carried out in rice mechanization center at Meet El- Dyba, Kafr El-Sheikh Governorate, Egypt during September 2016. Experiment included the flowing variables 1. Two different drying methods (Solar drying method using greenhouse type solar dryer and natural sun drying method). 2. Two different conditions of corn (complete earshelled corn). 3. Three different air velocity (0.5, 1.0 and 1.5 m/s). High moisture ear and shelled corn was dried by using solar energy for heating air inside a greenhouse and compared with natural sun drying method. The results of quality tests that included standard germination test, vigor test and tetrazolium test for both drying methods for ear and shelled corn recorded high percentages for all treatments except solar drying of ear corn at air velocities 0.5 and 1.0 m/s. The average air temperature inside the solar dryer at air velocities 0.5 and 1.0 m/s reached to 43.9 and 42.4 ˚C respectively. High temperatures killed the germ of corn so the quality tests were reduced. Germination percentage of natural sun dried ear corn was 97 % and for solar dried samples at air velocities 0.5, 1.0 and 1.5 m/s was 79, 81, and 89%, respectively. The corresponding values for shelled corn were 93, 97 and 98 %.and 95 % for natural sun dried ones. The vigor test of dried ear corn recorded 90 for natural sun drying method and 34, 45, and 66% for solar drying at air velocities of 0.5, 1.0 and 1.5 m/s, respectively. The corresponding values for shelled corn were 86, 96 and 97% respectively, and 82 for natural sun dried samples. The recorded drying times were 26, 24 and 28 hours to reduce the moisture content from an initial level of 31.73 to final level of 14.07% (d.b.) for ear corn and for shelled corn were 20, 16 and 24 hours to reduce the moisture content from an initial level of an initial level of 31.73 to final level of 14.07% (d.b.) for ear corn and for shelled corn were 20, 16 and 24 hours to reduce the moisture content from an initial level of 27.23% to 14.12% compared with 46 and 38 hours for ear and shelled corn dried by natural sun drying method. Hourly costs of ear corn drying were 0.95, 0.88, 1.00 and 1.03 L.E/ kg for solar drying at air velocities 0.5, 1.0 , 1.5m/s and natural sun drying respectively. The corresponding values for shelled corn were 0.74, 0.58, 0.89 and 0.96 L.E/ kg. [ABSTRACT FROM AUTHOR]

The drying characteristics of edible seaweed Durvillaea antarctica subjected to hot-air drying at 40, 50, 60, 70, and 80°C were investigated. Desorption isotherm was performed to estimate the equilibrium moisture content. Ten mathematical models were applied on the drying kinetics. The effect of drying temperatures on the proximate composition in this seaweed was also evaluated. Drying process resulted in an apparent increase of the ash and crude protein contents as compared to fresh sample. Midilli-Kucuk model presented the best-fit quality on drying curves. An effective diffusional coefficient from 0.74 × 10−9 to 2.37 × 10−9 m2 s−1 was determined. At last, the energy consumption and efficiency value at 80°C were 13.54 kWh kg−1 and 34.57%, respectively. Furthermore, it is possible to estimate the hot-air drying conditions and obtain a dehydrated product as alternative to solar drying. Practical applications Durvillaea antarctica is a brown seaweed, which has proving to be very significant in terms of its nutritional value and bioactive compounds, which can benefit human health. For this reason, it is expected that its commercialization and consumption will increase strongly. Usually, D. antarctica requires of a drying process due to large amount of water that contain in its fresh state. Traditionally, it is dried under the sun but this operation can cause losses of material, degradation of nutritional values and poor quality on this seaweed. The use of a convective dryer with controlled conditions can be a good alternative to explore for this seaweed. Several mathematical modeling have been widely used for analysis of drying of various marine products such as seaweed to determine the best operation conditions and to understand the water transfer mechanisms from seaweed to surrounding air. [ABSTRACT FROM AUTHOR]

In this research, the effects of different drying methods on the two biomarker compounds concentrations, such as sinensetin (SEN) and rosmarinic acid (RA) of Orthosiphon staminues Benth leaves, flowers, stems and mix were investigated. SEN and RA retention among the dehydrated samples were maximum 83.07% in leaves and 92.54% in flowers, respectively by heat pump assisted solar drying method. For heat pump assisted solar dried samples, there are no significant differences ( p > .05) in the retention of SEN and RA as compared to fresh samples. However, there are significant differences ( p < 0.05) in SEN and RA retention in solar dried leaves, flowers, stems and mix as compared to fresh samples. Besides, an optimization study was performed to evaluate the optimal drying conditions for obtaining high SEN yields from Misai Kucing's leaves, flowers, stems and mixes with high RA contents within the drying parameters. Practical applications Sun drying is the standard practice adopted by most of the Malaysian Orthosiphon staminues (or also known as Misai Kucing) herbal producers due to its low capital and processing cost. However, long drying time was taken by sun drying due to unpredictable weather conditions and the active ingredients are degraded due to very high drying temperature in long processing time under sun exposure. Hence, a combining solar energy and other effective drying method such as heat pump technology are needed. Heat pump assisted solar dryer systems can overcome all the difficulties by solar drying solely and satisfy important demands in industrial drying with respect to product quality control, reduced energy consumption and reduced environmental impact. The objective of this research was to determine the relationship between the drying methods (sun drying and heat pump assisted solar drying) and bioactive metabolites compositions of different parts in Orthosiphon staminues plant. [ABSTRACT FROM AUTHOR]

Daylily flowers is an important vegetable in eastern Asia, widely used in many dishes. Daylily flowers are usually sold in dried forms in the supermarkets. There are a few method for processing fresh daylily flowers, however, no study has been conducted to analyze the effects of the processing methods in the composition of final products. In the present study, a flow-injection mass spectrometric fingerprinting (FIMS) method in combination with principal component analysis (PCA) was used to differentiate two species of daylily flowers (Mengzi and Chongli) with three different treatments (vacuum freeze drying, solar drying and hot-air drying treatments) for each. The results showed the fast and simple FIMS method could successfully differentiate between species (raw material) and treatments among each species. However, the two species could not be discriminated very well after being processed in hot-air drying treatment. The difference in chemical profiles of species and treatments were discussed. [ABSTRACT FROM AUTHOR]

Fruit and vegetable pomaces are co-products of the food processing industry; they are underutilized in part because their high water activity (aw) renders them unstable. Drum drying is one method that can dry/stabilize pomaces, but current drum drying methods utilize conventional, high-environmental-impact heating mechanisms. In this work, a small-scale double drum dryer (20 cm length x 15 cm diameter) was interfaced with a 98.3 m2 External Compound Parabolic Concentrator (XCPC) [solar thermal collector] array designed to produce up to approximately 40 kW of heating power. The conditions for drying prune and tomato pomaces were optimized on this system via a split-plot design. The design had 4 variables: added water, added maltodextrin carrier, dwell time and drum surface temperature. Moisture content, aw and color of the dried pomaces were assessed to determine the effectiveness of the drying. Both pomaces were rendered shelf-stable (aw < 0.6) for all tested conditions. However, prune pomace exhibited a narrower range of aw values than did tomato pomace. Conditions for adequate drying with minimal color change (and thus expected minimal nutrition loss) were established. This work demonstrates the potential for solar thermal energy to provide the heat for drum drying fruit and vegetable pomaces. [ABSTRACT FROM AUTHOR]

In this study, a temperature-controlled solar air collector was designed and tested for drying. Solar drying systems have two disadvantages. First one is the lack of ability to store energy and the second one is the lack of temperature control. This study presents the experimental analysis of an air collector that is able to keep the drying air temperature at 40°C even in cases where the level of solar radiation received by the collectors changes. Most of the tests were performed at a solar radiation level ranging from 500 to 900 W/m2and at an air flow of 3 to 5 m/s. The system tested for drying three different crops separately performed 21 h of a total of 27-h drying period at or above the temperature set of 40°C. The thermodynamic analysis of the relationship between solar radiation, air temperature, flow, and the produced energy was performed. The relationship between productivity, energy produced, and set temperature was analyzed using distribution charts. Moreover, an artificial neural network model was used to estimate outlet air temperature from the solar collectors based on air flow, solar radiation, and outside air temperature. [ABSTRACT FROM PUBLISHER]

The objective of the work being presented is to investigate the thermal performance of indirect, multi-tray solar drying system. Expressions for exergy in, exergy out and exergy loss for flat plate solar collector, drying chamber and trays kept in drying chamber were written under steady state conditions. Experiments were performed for 6 to 8 hours on two days namely 14/03/2014 and 24/03/2014 and the observations taken on 24/03/14 has been analyzed using Energetic and Exegetic approach. The value of first law efficiency for flat plate solar collector and solar dryer varied between 10% to 30.49% and 4.009% to 9.45% respectively. Second law efficiency of solar collector and solar dryer have been found varying from 0.7126% to 1.829%.and 49.85% to 67.75% respectively. The Exergetic efficiency for tray 1, tray 2 and tray 3 has been computed and these values varied from 90.43% to 93.412%, 72.684% to 92.352% and 78.179% to 94.61% for each trays respectively. Considering heavy energy and exergy losses from flat plate solar collector and drying chamber, the results of first Law and second Law efficiencies are in fair agreement with each other. [ABSTRACT FROM PUBLISHER]

In the present study, certain quality parameters of raw and traditionally sun-dried (TSD) Bombay duck samples are compared with dried fish samples obtained from hot air dryer (HAD), freeze dryer, and a newly developed and patented solar conduction dryer (SCD). The parameters analyzed are total viable count, total fungal count, total volatile nitrogen, and trimethylamine (TMA) content and color. It is found that the experimentally dried fish have better microbial and biochemical quality as compared to TSD fish. This study addresses the issue of unhygienic open sun drying and handling of dried products and the need to adopt use of dryers based on the recently developed appropriate drying technology such as SCD which is expected to be transformed into sustainable technology. [ABSTRACT FROM PUBLISHER]

In Developing Countries postharvest loss of fruits is very high due to the perishable nature of fruits, poor postharvest handling, and lack of cheap and appropriate postharvest technology. Adequate solar drying techniques may be a promising sustainable technology for transforming local products to obtain foods easily storable at room temperature. Five pilot innovative mild solar drying processes on fruit and vegetable products were carried out at the Research Centre for Engineering and Food Transformation (Milan, Italy) to verify the influence of the process on some physico-chemical properties of fruits and their shelf life, for a process scale transposition. Samples were analysed for water activity (aw), colorimetric parameters and VIS spectral profiles. Solar drying allowed the production of dehydrated products with attractive visual characteristics and microbiologically safe due to low aw values. Dried product can be used as both final products ready to direct consumption and food ingredients in their milled form in fortified foods. The possibility to store the products at room temperature can support the rural sector of the Developing Countries by reducing food loss, poverty, and improving nutritional status of the population. [ABSTRACT FROM AUTHOR]