Refractance Window Research Articles

Comparison of the energy and pollution parameters in solar refractance window (photovoltaic-thermal), conventional refractance window, and hot air dryer

The selection of a proper drying method can play a vital role in reducing the energy consumption and the quality of the final product. In this study, three dryers, including conventional refractance window (CRW), solar refractance window (SRW) based on the photovoltaic-thermal system, and hot air (HA) dryers, were used to dry the Aloe vera gel. Experiments were carried out at four levels of temperature (60, 70, 80, and 90 °C) and three levels of thickness (1, 2, and 3 mm) for the puree product. An increase in temperature and a decrease in thickness reduced specific energy consumption, specific heat consumption, specific heat utilization, pollutant emission, and social costs derived from the pollutant. The results showed that the SRW dryer significantly improved the energy and drying parameters compared to the HA method. The pollutant emission and social costs in the SRW dryer were zero, while these values were significant using the CRW and HA dryers. The highest amounts of antioxidant potential, phenol, flavonoids, and glucose were 98.61%, 0.0435%, 0.0103%, and 19.28% (mg/g dry matter), which were obtained at 60 °C and 3 mm thickness using the SRW/CRW dryers. However, these values were 76.69%, 0.0246%, 0.0039%, and 16.31% (mg/g dry matter) using the HA dryer. In general, according to energy consumption and drying parameters, the best experimental results were obtained at temperatures between 70 and 80 °C and a thickness of 2 mm.

Effects of different drying methods and ascorbic acid pretreatment on carotenoids and polyphenols of papaya fruit in Ethiopia.

Frequent consumption of fruits can prevent nutrient deficiencies and promote health. However, the perishability and unaffordability of fruits had led to very low levels of fruit consumption in low‐ and middle‐income countries (LMICs). The objective of this study was to evaluate the retention of nutrients and bioactive compounds of papaya fruit (Carica papaya L) with/without ascorbic acid pretreatment and drying under different techniques, to then estimate the vitamin A intakes for vulnerable population. Yellow pulp ripped papaya fruits (i.e., >75% level of skin color/stage level 4) (n = 14), with and without ascorbic acid pretreatment were dried using (a) solar drying: open‐air, tray driers, and glasshouse; (b) refractance window drying; (c) oven drying; and (d) freeze‐drying (control). The fresh fruit had high moisture content (87%) and an acidic pH. The dried papaya had a water activity of 0.5–0.6. The highest TPC, TFC, total carotenoids, and ß‐carotene were found in freeze‐dried papaya samples, followed by refractance window, and solar glass house (p < .05). The highest retention in total carotenoids (81.5%) and ß‐carotene (61.9%) relative to freeze‐drying was for the refractance‐window; 25 g of dried papaya could contribute to 38% of the retinol equivalents’ requirement for young children. Ascorbic acid pretreatment increased the retention of total carotenoids, ß‐carotene, TPC, and TFC (p < .05) by (6–11)%, (8–34)%, (7–58)%, and (6–30)%, respectively, for all the drying methods. Refractance window and solar glass house drying can improve diets and constitute a promising food systems’ intervention that can increase year‐round availability, accessibility, and affordability of vitamin A‐rich fruits like papaya.

The effect of process variables on the physical properties and microstructure of HOPO nanoemulsion flakes obtained by refractance window

Refractance window (RW) drying is considered an emerging technique in the food field due to its scalability, energy efficiency, cost and end-product quality. It can be used for obtaining flakes from high-oleic palm oil (HOPO) nanoemulsions containing a high concentration of temperature-sensitive active compounds. This work was thus aimed at studying the effect of temperature, thickness of the film drying, nanoemulsion process conditions, and emulsion formulation on the flakes’ physical properties and microstructure. The results showed that HOPO flakes had good physical characteristics: 1.4% to 5.6% moisture content and 0.26 to 0.58 aw. Regarding microstructure, lower fractal dimension (FDt) was obtained when RW drying temperature increased, which is related to more regular surfaces. The results indicated that flakes with optimal physical properties can be obtained by RW drying of HOPO nanoemulsions.

Physicochemical Properties, Sensory Acceptance and Storage Stability of Yogurt Flavored with Refractance Window Dried Passion Fruit Powder

Aims: The study evaluated the use of refractance window dried passion fruit powder as a flavoring for yogurt.&#x0D; Place and Duration of Study: Department of Food Technology and Nutrition, Makerere University, Kampala-Uganda between October 2020 and January 2021.&#x0D; Methodology: Passion fruit pulp was mixed in carboxymethyl cellulose and dried using a laboratory refractance window drier.&#x0D; Plain yogurt was flavored with 2% passion fruit powder. Passion fruit flavored, plain and commercial yogurt were analyzed for physico-chemical and sensory properties. Statistical analyses were performed using XLSTAT and all results were considered to be significant at P&lt;0.05.&#x0D; Results: pH values and titratable acidity for all yogurts ranged from 4.67 to 3.77 and 1.21% to 2.89%, respectively throughout the 14 day storage period. The apparent viscosity of all yogurts increased significantly during storage and ranged from 413.76 cP to 525.20 cP, the syneresis of yogurts ranged from 25.6% to 32.2%, vitamin C content of the yogurts ranged from 0.69 mg/100 g to 1.91 mg/100 g, the carotenoid content of yogurts ranged from 0.55 µgRAE to 1.07 µgRAE, phenolic content of the yogurts ranged from 0.50 mg/100 g GAE to 8.01 mg/100 g GAE, whereas total antioxidant activity of the yogurts ranged from 0.21mg/100g VCE to 9.96mg/100g VCE. For all yogurt types, there was no significant change (p&lt;0.05) in any of the sensory parameters (flavor, color, mouth feel, consistency, taste and overall acceptability) over the storage period of 14 days.&#x0D; Conclusion: Addition of passion fruit powder to yogurt resulted in increased levels of vitamin C, beta carotenoid, total phenolic content and total antioxidant activity, in comparison to plain yoghurt and commercial vanilla flavored yogurt. This will provide consumers with more nutritious options thereby improving nutrition of consumers.

3D printing of encapsulated probiotics: Effect of different post-processing methods on the stability of Lactiplantibacillus plantarum (NCIM 2083) under static in vitro digestion conditions and during storage

The increasing demand for functional foods is associated with the need to deliver probiotics through novel food matrices. In this study, a high-fiber high-protein composite flour matrix was selected as the food vehicle. To improve their stability, four encapsulation techniques (spray drying, freeze drying, spray-freeze drying, and refractance window drying) were used for the production of probiotic encapsulates in fructooligosaccharide: whey protein: maltodextrin matrix. Considering the need to develop customized/personalized products, the material supply was 3D printed using an in-house developed extrusion-based food 3D printer CARK (controlled additive-manufacturing robotic kit). The effect of four post-processing methods (freeze drying, refractance window drying, hot air drying, and microwave drying) was explored and the overall effect on probiotic stability during storage under two different conditions (4 °C and room temperature) was evaluated. No significant loss of probiotic viability was observed during the 3D printing process. Freeze drying method of post-processing achieved >90% survival rate for freeze dried and spray-freeze dried synbiotics incorporated products. Among the various treatments, spray-freeze-dried synbiotics incorporation followed by freeze drying post-processed 3D printed construct showed the best survival rate (79%) and viability (6.43 ± 0.17 log10 CFU/ml) under static in vitro digestion conditions. With around 96–98% survival rate with retained viability of 7.98 ± 0.48 log10 CFU/ml during the storage period of 35 days, the approach shows promising prospects for the delivery of probiotics in prebiotic matrices of customized shapes.

Impact of process parameters on drying behaviour, mass transfer and quality profile of refractance window dried banana puree

Refractance Window (RW) is a relatively new drying technique for producing dried powders, slices or leathers from fruits and vegetables. In the present study, the effect of temperature (70, 80 and 90 °C) and thickness of puree (2 and 3 mm) on drying characteristics, mass transfer and quality attributes of RW dried banana puree were investigated. Results showed that drying at 90 °C reduced drying time (~61–64%) and energy consumption (~30–44%), as compared to drying at a lower temperature (70 °C) for both the thickness. The effective diffusion coefficient (Deff) values obtained (2.89 × 10−9 to 8.84 × 10−9 m2/s) using Dincer and Dost analytical approach had higher R2 (0.980–0.991) and lower RMSE (0.029–0.053) values. RW drying at 90 °C resulted in higher ascorbic acid retention (~76–78%) with the least total colour change (3.4–6.9) compared to other studied conditions. Besides, retention of total phenolic (10.3 mg GAE/g dm) and flavonoid contents (3.4 mg QE/g dm), as well as antioxidant capacity (58.8 mM TE/g dm), were also better in samples dried at 90 °C. The study suggested that drying at a higher temperature during RW not only reduces drying time but also improves retention of quality attributes.

Process and product characteristics of refractance window dried Curcuma longa.

This work addresses the optimality of hot water bath based refractance window drying (RWD) characteristics of 1mm Curcuma longa (turmeric) slices. Mylar film thickness (125 to 350µm) and water bath temperature (65 to 95°C) havebeen considered as independent variables to evaluate drying kinetics and nutritional characteristics of the process product combination. Equilibrium drying time, moisture diffusivity, fitness of thin layer models, moisture content, total phenolic content, total flavonoids content, curcumin content, and antioxidant activity have been considered to evaluate the optimality of the RWD process parameters. It has been analyzed that while both parameters critically influence equilibrium drying time, only temperature had profound influence on nutritional characteristics. PRACTICAL APPLICATION: There is a need for a fast-drying method without significant loss in bioactive compounds. Refractance window drying (RWD) method is such a process. The study of RWD of turmeric slices will help in understanding the relations between different drying temperatures and mylar film thickness and its relation to nutritional characteristics of the product.

Techno Economic Analysis of Refractance Window Drying of Fruits: A Case of Small-Medium Scale Agro Processors in Uganda

Uganda produces a variety of fruits, vegetables and herbs with much of it going to waste because of limited post-harvest processing methods. Refractance window drying technology (RWDT) has a potential of producing high quality dried food products from fruits, vegetables and herbs. A techno economic analysis (TEA) was conducted to compare the processing potential of a new hybrid RWD model to existing fruit drying technologies in selected districts of Uganda. Technical and economic data was collected using in-depth interviews with small and medium scale dried fruit processors, farmers and exporters. Comparisons of the technical and economic parameters of the currently used dryers and the hybrid RWD were done to ascertain the competitiveness of hybrid RWD in the local market. Economic analysis was conducted using the cost benefit analysis and payback period tools. Findings indicated the solar box dryer was the commonest and cheapest dryer at USD. 163, while the UNIDO solar hybrid dryer model was the most expensive at USD. 58,378. The UNIDO solar hybrid dryer (USHD) had the highest loading capacity of 1,250 Kg compared to the hybrid RWD and solar box dryer that both had a loading of 30 Kg of whole pineapple per batch. The throughput for the different dryers was found to be 60 Kg, 7.5 Kg and 0.5 Kg for the USHD, RWD and solar box dryers respectively for a 10-hour production cycle. The drying time for the solar box dryer was 48 hours compared to 2 hours for the hybrid RWD and 10 hours for the USHD for pineapple flakes per batch. Additionally, the hybrid RWD presented more opportunities for producing a variety of high-quality dried products, including fruit dices, powders, leather and flakes. A recommendation is made for design modification for the hybrid RWD to increase effective drying surface area and throughput.

Performance Analysis of An Arduino Based Calibration and Temperature Control System for A Refractance Window Dryer

Automated control of temperature in fruit dryers is important for product quality and retention of nutrient content. In this study, the continuous refractance window dryer (RWD) was calibrated for drying temperature to enable the dryer to be set to dry a wide range of products. The drying operation in a RWD is carried out over a bed of hot water. The calibration system comprised of a computer program, calibrated knob, arrangement of sensors and output components. A computer program was successfully written in Arduino environment and a circuit board connected. A DS18B20 sensor was used to read the hot water temperature and a 5V potentiometer employed to vary the voltage as it corresponds to the desired water temperature. The system calibration focused on drying temperatures for mango, tomato and pineapple, but it can be applied to any other food products since the optimum drying temperature for most food products falls within the considered range. A calibration equation relating potentiometer voltage and temperature was formulated with the potentiometer maximum angular sweep found to be 295°. This angular sweep corresponded with 94.9996°C as the maximum calibration temperature. The system was found to be 97.6% accurate at attaining the desired temperature. A calibrated label was developed and marked accordingly. The developed system was simple to operate and robust throughout the testing hence it can be recommended for similar machines.

Arduino based control of the Food and Water Conveyance Systems of a Refractance Window Dryer

A refractance window dryer with a 14.5kg/hr throughput capacity was developed to effectively dry food product of 3mm on the conveyor belt. For efficient dryer performance an automated system for the conveyor belt movement and water conveyance system was designed. The automated system comprised of an ARDUINO centered control system, an arrangement of sensors, water pump and the conveyor motor. A computer program was written in Arduino environment, successfully compiled and uploaded on to the controller board to process all commands. The system was first simulated successfully in ISIS Proteus environment and connected onto a bread board for testing before attaching the motor onto the main circuit board. Performance tests done at 85°C revealed that there was no movement of the belt as temperature built steadily from 31.19°C until it reached a temperature of 92.0°C in the boiler. The maximum recorded water temperature was 98.06°C and the system had an operating range of 95±3°C. Achieving this led to an automated food conveyance system that was reliable and ensured high product quality. The Arduino based system worked well and is recommended for the refractance window dryer and can be up scaled to a bigger similar machine.

Effect of conductive hydro-drying on physiochemical and functional properties of two pulse protein extracts: Green gram (Vigna radiata) and black gram (Vigna mungo)

In this study, the effect of two drying methods (conductive hydro-drying – CHD and freeze-drying – FD) on the physical and functional properties of green gram (GG) and black gram (BG) protein powders was investigated. CHD dried protein powder showed excellent powder characteristics with moisture contents ranging from 3 to 6%, water activity of ~0.4 and Carr index ≤10. The CHD samples were dried in 210 min; with higher drying rates, CHD samples showed no significant changes in powder characteristics, color value, and water and oil absorption indices. The solubility of both proteins were found to be lower at pH 4 to 7 and higher at pH 1, 2, 8, 9 and 10; at certain pH, the solubility of CHD protein was higher than that of the FD counterparts. No significant differences were observed in the oil absorption capacity, surface hydrophobicity, protein gel formation, pasting and thermal properties. XRD and FTIR analyses were used to explain changes in protein structure and the presence of both α-helix and β-sheet was observed, with higher β-sheet levels in both pulses dried using CHD. Results confirmed that CHD, a variant of the refractance window drying (RWD) offered protein quality in par with FD.

A comprehensive review of recent advances in renewable-based drying technologies for a sustainable future

Conventional drying technologies generally rely on drying processes driven by using hot air, where these processes have significantly high energy consumption and greenhouse gas emissions. With our knowledge based on the limited nature of fossil fuels and the impact of climate change, it is clear that every technology has to be cleaner, cheaper, and more efficient to limit our carbon footprint while maintaining sustainable development. In this regard, the present study comprehensively reviews the recent advances in drying technologies and energy consumption and the efficiency and economic performances of several alternative drying technologies. The reviewed drying technologies include adsorption mediated, agitated thin film, electrotechnologies, hybrid systems, impingement, heat pumps, microwave, ohmic-heating, refractance window, rotating drum, superheated steam, and vacuum. The selected performance criteria are final heat use, final electricity use, primary energy use, thermal and energy efficiencies, and operating cost. With these criteria taken into account, the results show that the refractance window has the highest sustainability ranking (8.28/10), and superheated steam has the lowest sustainability ranking (2.90/10). Besides, the sustainability of the different drying fuels and technologies is conducted, and the results show that renewables have the highest sustainability ranking. Besides, it is seen that some novel approaches in drying, such as solar-based hybrid drying systems and refractance window drying, are amongst the most promising sustainable technologies. They could be the key to clean, affordable, reliable, and efficient drying of different kinds of products in industrial processes.

Characterization and properties of purple yam (Dioscorea trifida) powder obtained by refractance window drying

Purple yam, Dioscorea trifida (DT), is characterized by its valuable nutritional properties and as powder it could be used as an ingredient in various foods. In this research, the DT paste was dried by refractance window (RW) at 70, 80, and 90 °C for 40 min, a technique for obtaining powders with microbiological stability (aw < 0.35), good fluidity and low cohesiveness. In the powders obtained from DT, carbohydrate was the major constituent (85.66 to 86.47%) with starch content higher than 69.0%. Among the technological properties, the oil absorption index of the powder was strongly dependent on the RW drying temperature. The highest retention rates of bioactive compounds (>50%) in powders occurred at temperatures of 70 and 80 °C. The drying by RW was promising and presented industrial potential to produce DT powder with technological and nutritional quality to be applied in food.

Far infrared assisted refractance window drying of apple slices: Comparative study on flavour, nutrient retention and drying characteristics

In the present investigation, far infrared (FIR) assisted refractance window (RW) drying (FIR+RW) of apple slices (2 and 5 mm) was evaluated in comparison with RW and hot air (HA). FIR+RW reduced drying time by 50 and 69% compared to RW and HA, respectively. Also, FIR+RW drying retained a significantly higher amount of phenolics, flavonoids, ascorbic acid, and antioxidant activity, as compared to HA. Increase in FIR temperature from 50 to 60 °C reduced drying time by 10–19% without having any deleterious effect on quality. Colour, flavour, and microstructure of FIR+RW dried slices were comparable to that of RW. Nearly 46% saving in energy consumption was observed for FIR+RW drying compared to HA. Results suggested that FIR+RW drying can be explored as a potential technique for drying of fruits in a shorter time, with better retention of flavour, nutrients and also enhance energy efficiency.Industrial relevanceDried apple slices have a good market potential as a raw material in many processed foods and can be an alternative to deep fat fried chips for health-conscious consumers. This work focuses on assessing the efficacy of developed FIR assisted RW drying system in terms of drying time, energy, and quality attributes (colour, nutritional, flavour, microstructure) in comparison with conventional drying methods. The results showed that FIR assisted RW drying technique has great industrial potential in saving processing time as well as energy with better retention of quality of dried products.

Conductive hydro drying of beetroot (Beta vulgaris L) pulp: Insights for natural food colorant applications

AbstractNatural food colorants are often unstable and undergo rapid degradation reactions. These are significant at higher temperatures, as in the case of drying of food powders. In this research, conductive hydro drying (CHD), a variant of the refractance window drying technology was used to prepare flakes from beetroot pulp. Three different temperatures (40, 50, and 60°C) were used and the results were compared against tray dried counterparts. Significant differences in moisture content, water activity, color, powder characteristics, reconstitution behavior, total phenolic content, antioxidant property, and betalain content (both betaxanthin and betacyanin) were observed between the drying methods. With significantly lower drying time, CHD can be conveniently used for commercial applications requiring the drying of natural pigment‐rich foods.Practical applications CHD is an effective alternative method for drying of natural colorant rich foods “Non‐thermal” drying approach showed significant retention of betalains, phenolics, and antioxidant activity as compared with tray drying CHD is commercially viable and can be conveniently scaled up This novel drying approach shows significant savings in cost, energy, and time

Optimization of process variables on physicochemical properties of milk during an innovative refractance window concentration

An innovative refractance window (RW) concentrator was developed and used to concentrate milk samples at temperatures of 50–70°C and pressures of 0.4–0.8 bar. Optimum process conditions were found through response surface methodology to compare RW at optimal conditions with the conventional concentration (CC). Also, the effects of process parameters and their interactions on the RW process and product specifications were analyzed. According to the results, optimal RW conditions were a pressure of 0.4 bar and a temperature of 69.1°C. Besides, the energy efficiency and overall heat transfer coefficient of RW at optimal conditions were higher than those of CC by 125.2% and 15.3%, respectively. Compared to CC, RW reduced the concentration-time by 60.8% and minimized the changes in the chemical composition and color of the milk. RW process was found to be a time- and energy-saving concentration technique that can produce concentrated milk with improved quality. Practical applications Alternative concentration techniques that can reduce energy consumption and processing time while guaranteeing the quality retention of the product might be considered by the food industry. The innovative RW milk concentration method that was developed in the present study showed to be a promising time- and energy- saving concentration technique. This method was able to retain the quality characteristics of milk during the concentration process. Also, the optimization information provided in the present study can be used for developing upscaled units that can be used for the commercial concentration process of milk.

Evaluation of sensory and physico-chemical properties of Langra variety mango leather

The sensory and nutritive quality attributes of fruits have observed to be lost when dried to leathers using solar, hot air convection and several other traditional drying processes. Refractance Window (RW) technique is a novel thin-film drying process, generally used for drying of heat sensitive food products for retention of necessary quality attributes. Six samples of mango leathers have been prepared using RW and tray drying process and one sample was procured from the market. Fuzzy logic sensory analysis of seven samples of mango leather was done by a panel of 20 judges. Mango leather sample S4 dried using RW drying process was ranked first among all the mango leather samples with sensory scale as ‘Good’ and the highest similarity value as ‘0.9116’ followed by others. Market sample S5 was rated lesser than RW dried samples and higher than tray dried samples. The order of preferences for analyzed mango leather samples was S4 > S2 > S7 > S5 > S3 > S1 > S6. However, the ranking of sensory attributes of mango leather in-general was taste > mouthfeel > color > aroma.

Refractance Window drying of goldenberry (Physalis peruviana L.) pulp: A comparison of quality characteristics with respect to other drying techniques

Refractance window drying (RWD) is a novel drying technique, in which heat transfer is by conduction and radiation. In this study, RWD technique has been performed in a static mode at a temperature of 70 °C that is lower than that used in common practice, which led to a consequently prolonged drying time of 180 min to reach equilibrium. Goldenberry (Physalis peruviana L.) pulp was dried under these RWD conditions and several quality characteristics were assessed and compared to the products from freeze-drying, convective drying and infrared radiation drying. It was found that RWD even under a prolonged drying time produced a high-quality product, comparable in many aspects to freeze-dried products; total phenolics contents were not significantly different, while total flavonoid and total carotenoid contents were only slightly lower. RWD samples maintained a color closer to that of the fresh sample than did freeze-dried product. Antioxidant activity determined by DPPH and ORAC assays was maintained at a high level. Amino acid profiles of RWD and freeze-dried samples were similar. The capacity of RWD samples to inhibit α-glycosidase is of the same order as displayed by the dried products from the other drying techniques.

Development of a dehydrated product with edible film characteristics from mammee apple (Mammea americana L.) using Refractance Window drying

Abstract The Mammee apple (Mammea americana L.) is a widely grown fruit, popular in tropical areas, which is mainly consumed fresh. Refractance Window (RW) drying is used to produce food films, flakes, and powders, and may be an alternative to commercially used dry food production methods. The aim of this study was to obtain a dehydrated product from the pulp of mammee apple using RW. The dehydrated product presented a homogeneous microstructure and good mechanical (TS = 1.15 Mpa, %E = 13.93) and technological properties (hygroscopicity = 21.46 g.100 g-1, water solubility index = 32.73 ± 0.67 g.100 g-1). RW drying was found to be a viable and low-cost method for edible film production, generating products with adequate technological characteristics and high nutritional value. Its dehydrated products can be consumed directly or used as ingredients in the development of food products.

Physicochemical Properties of Guava Snacks as Affected by Drying Technology

Guava is widely consumed because of its agro-industrial use, and its antioxidant properties attributed to vitamin C and carotenoids content. However, it has a short shelf life. Guava has been dried by atomization, fluidized bed, lyophilization (FD) and convective drying (CD). CD requires long operation times and the product characteristics are not desirable. In contrast, FD produces high quality products, but requires long processing times, high energy consumption and high operation costs. As an alternative, the Refractance Window® (RW) drying is relatively simple and cheap technique. The objective of this study was to compare the effect of CD, FD and RW techniques, on the moisture content, water activity, color, porosity, volume change, vitamin C and carotenoids content in guava samples. The samples dried by RW required less time to reduce the moisture content and exhibited smaller changes in color than CD or FD. There were greater losses of carotenoids and vitamin C when drying by CD whereas RW had similar losses than FD. Lyophilized products exhibited minor change in volume and greater porosity. RW results in better retention of properties, compared with other drying techniques. Based on this, RW is a promising technique for the development of guava snacks.