Refractance Window Research Articles

Effect of cold plasma pretreatment on drying kinetics and quality attributes of apple slices in Refractance window drying

Cold plasma (CP) is a state-of-the-art non-thermal technology with the potential to accelerate drying, preserve nutritional value, and inactivate enzymes in foods. The purpose of this study was to evaluate the impact of multipin atmospheric pressure CP pretreatment (5, 10, and 20 min) on Refractance window drying (RWD) of apple slices (2 mm thick). The results showed that CP pretreatment could accelerate the drying process and shorten drying time by up to, with the best results obtained after a 10-min CP exposure. Scanning electron microscopy revealed that the CP pretreatment significantly altered the surface morphology of apple slices by etching microchannels due to the bombardment of reactive plasma species, contributing to enhanced drying kinetics. The CP pretreatment also enhanced the rehydration ratio (up to 21.63%) and decreased the dried apple slices' hardness (up to 29.79%). CP pretreatment of 5, 10, and 20 min resulted in 18.33%, 39.4%, and 30.06% reductions in polyphenol oxidase enzyme activity, respectively. As a result, CP-pretreated samples showed better color values compared to other samples. Furthermore, compared to RWD samples alone, CP-pretreated apple slices retained significantly higher (P < 0.05) antioxidant activity, phenolics, flavonoids, and ascorbic acid content. Industrial relevanceChemical dipping and thermal blanching are commonly used as pretreatments for inactivating enzymes and improving the drying process of fruits. However, chemical pretreatments can leave residues, while thermal blanching results in the loss of bioactive compounds. The findings of this study demonstrated that CP as a pretreatment can effectively inactivate enzymes and enhance drying kinetics while preserving nutritional quality. Moreover, the results also showed that RWD can preserve better physicochemical properties than conventional hot air drying. Therefore, CP pretreatment coupled with RWD can be a promising alternative to conventional methods for drying fruits in industrial settings.

Refractance Window Drying as an Alternative Method for Brewer’s Spent Grain Preservation

Brewer’s spent grain (BSG) is a residue that holds significant potential for various applications. Given its inherently high moisture levels, it becomes imperative to explore methods for preserving it. This study investigates the use of refractance window (RW) for drying BSG. The final moisture content, water activity, and drying kinetics were assessed. Various kinetic models were analyzed, including Lewis, Page, Overhults, Brooker, and Midilli. Employing a central composite design, this study also investigated the effects of the variables temperature (55.9 to 84.1 °C) and drying time (1.6 to 4.4 h) on the quality of the dried product. The quality was assessed based on the content of bioactive compounds: phenolics, flavonoids, citric acid, and ascorbic acid. The results suggest that refractance window (RW) drying can yield a product with reduced moisture content and water activity levels (lower than 10.0% and 0.600, respectively). The phenolic, flavonoid, and citric acid higher contents were found at 70 °C and 3 to 4 h of drying. The best ascorbic acid results were found at 55 to 65 °C after 3 h of drying. The use of RW emerges as an interesting alternative for processing BSG, offering a sustainable approach to better utilize this residue.

Drying strategies of spent coffee grounds using refractance window method

The objective of this study was to evaluate, during the drying of spent coffee grounds, the application of pretreatments with ethanol and the application of ultrasound assisting the refractive window (RW) drying, and to compare with convective drying by hot air (AC). The effect on the kinetics parameters of the Fick and Page models were evaluated, as well as on the content of total phenolics and antioxidant capacity. For AC drying, samples of spent ground coffee were prepared in the form of fixed rectangular beds 0.7 cm high, which were placed on polyester sheets and pretreated up to 10 times sprayed with ethanol, then dried by AC at 80 °C and 0.8 m/s. For RW drying, the samples prepared in the same way as for AC were used. For this case, the application of ethanol as pretreatment and the use of ultrasound during process were tested. As results, regardless of the conditions applied, drying by RW was up to 50 % faster, evidenced in the highest values of effective diffusivity (from the Fick model) and the kinetic parameter (from the Page model). Regarding the treatments applied and their effect on the drying kinetics, any treatment had a significant effect on AC drying. On the contrary, the strategies applied in RW drying had significant effects, both the application of pretreatment with ethanol as well as the application of ultrasound assisting the process accelerated the drying kinetics. However, the treatment with ethanol and RW drying was the one that best preserved the phenolic compounds and the antioxidant capacity in the samples. Therefore, these strategies could be a good option to improve RW drying by accelerating the process and preserving the bioactive compounds in the spent coffee grounds for subsequent utilization.

Quantitative review and machine learning application of refractance window drying of tuber slices

Abstract Refractance window drying (RWD) is a preferred drying technique due to its suitability for heat-sensitive products. Although this drying technique appears promising, it is yet largely unexplored. In this study, the authors provide a review of the existing milestones on RWD using a sample of 40 articles from 2000 to date to quantify the state of investigations across multiple studies and establish specific areas needing further attention. Results show that experimental analyses constitute about 53–59 % of the reported cases, followed by a literature review 24–28 %. Furthermore, 17 % of the total study cases was observed across all modelling categories, with machine learning (ML) techniques constituting only about 8 %. Driven by the outcome, this study thus utilized three ML techniques to model the moisture ratio (MR) of 1.5–4.5 mm thick yam slices, operated over the range of 65–95 °C temperature in an RWD chamber. Unlike the routine procedures, the yam thickness versus air temperature effects on moisture ratio were investigated to determine the more significant factor as well as the air velocity effect or its lack thereof on MR. To investigate the validity window for the entire dataset, all data points were considered, with a training-testing ratio of 7:3 used in each case. For scenario one, prediction based on the yam thickness effect showed a greater influence on the MR. The air velocities at 0.5–1.5 m/s had little effect on MR as compared to the case where air velocity was ignored (i.e., the control case in this study). Also, model accuracy for all tested samples has been determined to be better than 93 %. Insight from this study is to guide in the future design of RW dryers for direct measurement of the moisture ratio of harvested root tubers at various conditions.

Drying of Tarhana dough by Refractance Window™ technology under vacuum/atmospheric conditions: Characterization of physical and quality parameters.

This study aimed to produce dried tarhana using a refractance window drying (RWD) system. The drying process was also carried out under vacuum; the current study is the first in the literature. Using different heating mediums, the maximum temperature can be adjusted to a level above that used in RWD studies. Considering results, process time savings in RWD were over 85% and 75% compared to control groups (oven and hot air dryer), respectively. Tarhana samples dried in RWD were also faster (50%) under vacuum conditions than atmospheric ones. The highest preservation of total phenolic content (TPC) and total antioxidant activity (TAA) was for samples dried by RWD at 110°C under atmospheric conditions. Techno-physical properties were better than the control group. The rheological behavior of tarhana soups was similar to pseudoplastic flow behavior and well defined by the Power law and Herschel-Bulkey models. In conclusion, RWD can be a promising technique for tarhana production.

Effect of wall material on lipophilic functional compounds of high oleic palm oil emulsions encapsulated by Refractance Window drying

High-oleic palm oil is a food-grade oil with desirable properties, as it is characterised by having an oleic acid concentration above 50 % and a high vitamin E and provitamin A content. This study investigated the effect of different combinations of two wall materials (whey protein (WP) and Capsul®, a commercial octenyl succinic anhydride modified starch (OSA-MS)) on the concentration of provitamin A, vitamin E and oleic acid, and the physical properties of high oleic palm oil emulsions encapsulated by Refractance Window drying technology. Wall material composition significantly affected (p < 0.05) all response variables, and R2 values were above 0.75 for all responses. Phytonutrient preservation showed its highest at an OSA-MS: WP concentration ratio of 1: 3. Optimal results were achieved (minimum moisture content, water activity and hygroscopicity, and maximum encapsulation efficiency and phytonutrient preservation) at an OSA-MS concentration of 8.13 % and WP concentration of 91.87 %. Flakes were obtained as a solid structure that protects oil's phytonutrients with 94 %, 75 % and 87 % of preservation of oleic acid, vitamin E and carotenoids, respectively. It shows that the wall material combination and encapsulation technique are suitable for obtaining lipophilic functional compounds.

Mathematical and artificial neural network modelling for refractance window drying kinetics of coriander (Coriandrum sativum L.) followed by the determination of energy consumption, mass transfer parameters and quality

Mathematical and artificial neural network modelling for refractance window drying kinetics of coriander (Coriandrum sativum L.) followed by the determination of energy consumption, mass transfer parameters and quality

Effect of Different Drying Systems on Drying Performance of Maraş Green Pepper (C.annum)

Drying is the simultaneous transfer of heat and mass, which is defined as the reduction of moisture in food. The aim of the study the drying performances of refractance window drying (95°C), fluidized bed drying (95°C, 2m3/m air velocity), and convective drying (95°C) were examined in the drying of Maraş green pepper (C.annuum). Drying performance was evaluated for effective diffusion coefficient (Deff), activation energy (Ea), Chroma (C) and total color change (ΔE). Drying curves were obtained by recording sample weights in 10-min periods. For the refractance window drying, fluidized bed drying and convective drying the time for the samples to reach 6-7% humidity level according to the wet base was found to be 70, 80 and 110min, and the effective diffusion coefficient was 6.49x10-10, 5.68x10-10 and 4.87x10-10 m2/s the activation energy was 53.54, 54.65 and 55.93kJ/mol, respectively. When the color properties are examined the Chroma value was determined as 18.23, 8.85 and 4.80 and the total color as 15.42, 26.29 and 30.33, respectively. It was seen that the closest value to the fresh product was in the samples dried with a refractance window drying. In the study, it was concluded that the use of a refractance window drying shortened the drying time by 14-36%, increased the effective diffusion coefficient, provided drying with lower activation energy, and better preserved the color quality in the production of dried Maraş green pepper.

THE USE OF REFRACTANCE WINDOW-DRIED EGG POWDER IN CAKE PRODUCTION

The study aimed to evaluate the use of refractance window-dried egg powders in cake production. It was found that liquid egg white (WL) resulted in the lowest batter density of 1.05 g/mL, followed by egg white powder (WP) at 1.16 g/mL. The highest specific volume was determined in WL samples at 2.71 ml/g, followed by WP samples at 2.46 mL/g. In addition, the use of powdered eggs reduced baking loss but also caused a decrease in the crumb lightness value. Furthermore, the usage of WP had a positive effect on the hardness value of cake samples, which decreased from 884.01 g to 720.53 g. Finally, the alternative use of egg powder had a positive effect on crumb appearance, increasing both cell count and total cell area. Therefore, the incorporation of powdered eggs by refractance window drying instead of liquid eggs in cake production can be considered an applicable approach due to the various benefits it offers.

Mass transfer parameters and quality characteristics of aonla slices under refractance window drying

This study investigates the effects of refractance window (RW) drying process parameters on mass transfer and quality characteristics of dried aonla slices. RW drying of aonla slices was carried out at three levels of water temperature (75, 82 and 90 °C) and slice thickness (2, 4 and 6 mm). In terms of quality characterization, the total phenolic content, ascorbic acid content, and browning index were determined. Higher retention of ascorbic acid (64.49 ± 0.34%) and phenolic content (37.84 ± 0.08 mg GAE/g dry matter) was found at 90 and 82 °C water temperature, respectively with inconsequential variation in browning index. Mass transfer parameters such as Biot number, effective moisture diffusivity and mass transfer coefficient were estimated using Dincer and Dost model. Effective moisture diffusivity during drying varied from 4.27 × 10−10 to 1.09 × 10−09 m2s−1 and Biot number was observed to be in the range of 0.268 to 8.666 for different drying conditions. XRD pattern suggested that RW dried aonla slices had semi-crystalline structure. The changes in crystalline structure to amorphous was pronounced more at high water temperature. It was also revealed by the disintegration of cell wall/membrane and connecting surfaces, which resulted into smooth and flaky microstructures with sharp edges. The gamut of crystallite size was obtained as 49.12 ± 0.26 to 99.12 ± 1.19 nm. The presence of bound water after completion of drying was represented by FTIR peaks centered around 3577 cm−1. The infrared spectroscopy of RW dried aonla postulated that peak intensity of absorption bands negligibly changed with varying processing conditions, but minor peak shift was observed. This study elucidates the suitability of RW drying for retention of heat-sensitive compounds in food produce such as aonla with better quality retention and morphological characteristics.

Far infrared assisted refractance window drying: Influence on drying characteristics and quality of banana leather

The market demand for fruit-based healthy snacks in dried form is increasing rapidly. Novel and efficient drying techniques are being explored to meet market demand of fruit-based snacks with better nutritive value and sensorial attributes. In this study, suitability of far infrared assisted refractance window (FIR + RW) drying to obtain banana leather was ascertained and drying behavior, bioactives, flavor, microstructure, and sensory attributes were compared with RW and hot air (HA) drying. FIR + RW and RW reduced the drying time by 60–75% and energy consumption by 38–45% as compared to HA. RW drying preserved color and retained higher phenolics (19%), ascorbic acid (22%) and antioxidant capacity (16–47%) compared to HA. Among the studied methods, HA resulted in higher browning index and hydroxymethylfurfural content. FIR + RW and RW dried banana samples had maximum flavor compounds, better overall consumer acceptance and improved cellular structure with widened pores. The study indicated that RW and FIR + RW have good potential to be considered as alternative drying techniques to HA for producing high-quality fruit leather.

Effect of Maltodextrin on Drying Rate of Avocado (&lt;i&gt;Persea Americana&lt;/i&gt; Mill.) Pulp by Refractance Window Technique, and on Color and Functional Properties of Powder

1. Abul-Fadl, M., Ghanem, T. (2011). Effect of refractance-window (RW) drying method on quality criteria of produced tomato powder as compared to the convection drying method. World Applied Sciences Journal, 15(7), 953–965. Google Scholar

Effect of CO2 Laser Microperforation Pretreatment on the Dehydration of Apple Slices during Refractive Window Drying.

This research studied the use of CO2 LASER microperforation as a pretreatment for the refractive window (RW) drying of apple slices with respect to total polyphenol content (TPC), antioxidant capacity, color ΔE, and product stability under accelerated storage. For this purpose, the processing variables assessed were pore size (200-600 µm), pore density (9-25 pores/cm2), and drying temperature (70-90 °C). As baseline criteria, a comparison with respect to the control without microperforations and samples subjected to conventional tunnel and lyophilization were also considered. The increase in the pore size from 200 to 600 µm resulted in shorter drying times (≤40 min), minimal change in color (ΔE) and loss of TPC, while DPPH was negatively affected by the combined effect of the pore density and the drying temperature. In general, the use of RW with CO2 resulted in apples of higher quality than those obtained in conventional drying and comparable to those obtained through the use of freeze-drying. Finally, during accelerated storage, quality attributes decreased significantly for samples dried at 90 °C regardless of whether microperforations were used, suggesting that a compromise between drying temperature and pore size must be weighed to reduce processing time and to avoid further quality losses during storage.

Improvement of phytochemical and quality characteristics of Dracocephalum kotschyi by drying methods.

This experiment was conducted to evaluate the effects of different drying methods on drying parameters and qualitative characteristics of Dracocephalum kotschyi in a completely randomized design with three replications. Treatments included shade drying as control, sun drying, cabinet drying (CD at 50 and 60°C), refractance window drying (RWD), infrared drying (IRD) at 200 and 300 W, and combination of RWD+ IRD at 200 and 300 W. According to the results, IRD, RWD, and RWD+ IRD effectively maintained valuable secondary metabolites compared to the conventional drying methods. The maximum total phenol content (2.7 and 2.66 mg GAE/g dry weight), total flavonoid content (2.26 and 2.33 mg QE/g dry weight), antioxidant activity (79% and 78.33%), and essential oil content (0.65% and 0.76%) were obtained from plants dried by RWD and IRD. Samples dried by RWD, IRD, and RWD+ IRD had high color quality, acceptable green color, and less browning. Also, RWD and IRD methods effectively reduced microbial contamination of dried plants compared to the control and other methods. The minimum aerobic mesophiles, mold, yeast, and coliforms were observed at 3.11, 0, and 1.47 log CFU/g in IRD 300 W and 3.17, 1, and 1.30 log CFU/g in RWD. D. kotschyi dried at CD 50°C had the maximum microbial contamination. Generally, according to the obtained results, RWD and IRD methods are suggested for drying of D. kotschyi and similar herbs due to shortening the drying time, preserving and improving the quality properties of dried plants.

Production and Evaluation of an Instant Maize-Soy Flour Enriched With Refractance Window Dried Jackfruit (Artocarpus heterophyllus L.) Powder

Porridge is a staple food in many developing countries and is usually used as a weaning or breakfast food. The increased preference for convenient and healthy meals has increased the desire for nutrientenriched instant flours. Jackfruit is an underutilised fruit that is rich in vitamin C and other bioactive components. This study aimed to evaluate dried jackfruit powder as an ingredient for porridge flour. Formulations were made by substituting varying levels (0, 10, 20 and 30, 40 and 50%) of an extruded maize-soy blend (MSB) constituting 70% maize and 30% soy with refractance window dried jackfruit powder. The composite flours were used to make porridges which were analysed for their sensory acceptability by a 60-member semi-trained panel. The viscosity, water holding capacity, oil holding capacity, solubility index and bulk density of the flours were also assessed. Porridge acceptability, flour proximate composition, ascorbic acid and carotenoid content for the most preferred experimental formulation were compared to commercial maize-based instant flour and plain maize-soy instant flour. The most acceptable porridge was made from the 50% MSB and 50% jackfruit flour blend. The 50% jackfruit - MSB blend and control commercial instant flours attained drinking viscosity (2,500–3,000cP) at 20% and 31% flour rates. The energy, protein, iron, calcium, β-carotene, and vitamin C densities of jackfruit - MSB porridge were 47.8 %, 48.9 %, 158.1 %, 226.5 %, 230.3 % and 125.9 % higher than those obtained from plain MSB porridge respectively. The results showed the potential of jackfruit as an ingredient for the nutritional enrichment of flours meant for making porridge.

Drying kinetics and quality assessment of refractance window dried beetroot

AbstractThin‐layer drying of red beetroot having slice thicknesses of 0.5, 1, and 1.5 mm was carried out using a solar‐assisted continuous refractance window dryer at 75, 80, and 85°C drying temperatures for 30, 45, and 60 min. The drying kinetics including moisture ratio, drying rate, and moisture diffusivity was observed to understand the drying behavior of beetroot. The moisture ratio was fitted to the drying models for thin‐layer modeling of the beetroot drying. The drying operation reduced the firmness and water activity of the fresh beetroot; however, the antioxidant properties of dried beetroot increased with drying treatment. The minimum alteration was observed with a color difference and hue angle of dried slices. Process optimization was carried out to obtain the ideal drying conditions, which indicated the use of a dryer at 85°C temperature, 0.5 mm slice thickness, and 60 min exposure time with a desirability value of 0.874.Practical applicationsFourth‐generation drying technology refractance window drying dried the beet root slices without case hardening and improve its antioxidant properties. Dried beetroot contains carotenoids, vitamins, nitrates, flavonoids, and various minerals that have antioxidant, anti‐inflammatory, anticarcinogenic, and hepato‐protective activities. Dried beetroot flakes or powder is useful for the development of different functional foods that have anti‐diabetic, cardiovascular disease lowering, hypertensive, and wound healing benefits.

Impact of Different Drying Methods on the Phenolic Composition, In Vitro Antioxidant Activity, and Quality Attributes of Dragon Fruit Slices and Pulp.

The aim of this study was to compare the refractance window drying method (RWD) with the hot air oven drying (HD), vacuum drying (VD), and freeze-drying (FD) methods in order to analyze the outcomes of the qualitative properties of dragon fruit slices and pulp. Moreover, the impact of temperature on the phenolic content, antioxidant activity, color, and texture of the dragon fruit slices and pulp were studied. The results showed that the RWD samples exhibited a high nutritional quality in contrast to the other drying methods. The RWD method had a short drying time of 960 min to reach the final moisture content of 6.50% (dry basis), while the FD, VD, and HD methods had significantly higher drying times of 1320, 1200, and 1080 min, respectively, to reach the final moisture content. Higher values of TPC (182 mg GAE/100 g) and crude fiber (0.98%) were obtained in the RWD dragon fruit samples, indicating the potential of RWD to preserve the quality of dried samples. In conclusion, this study revealed that RWD provides an appropriate drying temperature as an alternative to freeze-drying. RWD may improve dragon fruit drying, adding value to the food industry.

Drying Kinetics, Physicochemical and Thermal Analysis of Onion Puree Dried Using a Refractance Window Dryer

Onions have a high moisture content, which makes them more susceptible to microbial growth. Drying is one of the postharvest preservation methods applied to decrease onion moisture content, thereby increasing its storage life. In this study, onions were peeled, washed, cut into quarters, hot water blanched, and pureed. The puree was further dried using two different drying methods: refractance window drying (RWD) (water temperature: 70 °C) and convective drying (CD) (50 °C). The puree was spread on prefabricated trays at varying thicknesses of 2 mm, 4 mm, and 6 mm. It was observed that, irrespective of the drying method, moisture ratio (MR) decreased and drying time and effective moisture diffusivity increased with respect to the thickness of the puree. In addition, the Lewis model and the Wang and Singh model showed the highest R2 and lowest SEE value for RWD and CD, respectively. Moreover, the MR of onion puree during RWD and CD was predicted using a multi-layer feed-forward (MLF) artificial neural network (ANN) with a back-propagation algorithm. The result showed that the ANN model with 12 and 18 neurons in the hidden layer could predict the MR, with a high R2 value for RWD and CD, respectively. The results also showed that the thickness of the puree and drying method significantly affected the physicochemical quality (color characteristics, pyruvic acid content, total phenolic content, total flavonoid content, antioxidant capacity, and hygroscopicity) of onion powder. It was concluded that RWD proved to be a better drying method than CD in terms of the quality of dried powder and reduced drying time. Irrespective of the drying method, 2 mm-thick puree dried yielded the best-dried onion powder in terms of physicochemical quality, as well yielding the lowest drying time. These samples were further analyzed for calculating the glass transition temperature.

The impact of refractance window drying on the physicochemical properties and bioactive compounds of malbhog banana slice and pulp

The present study aimed to design and evaluate the effect of different drying methods, viz. refractance window drying (RWD), hot air drying (HD), freeze-drying (FD) and vacuum drying (VD) on qualitative properties such as crude fiber, ash content, total phenolic content (TPC), total flavonoid content (TFC), Antioxidant activity (AA), FTIR spectra, color and texture of banana slice and pulp fractions. In this experimental investigation, malbhog variety banana was selected. The average drying time of the banana sample in RWD, HD, FD and VD was found as 760 min, 930 min, 1125 min and 975 min at drying temperatures of 60 °C, 60 °C, -40 °C and 60 °C respectively. A qualitative evaluation revealed that the anti-oxidant, phenolic and flavonoid content were rich in freeze-dried and RWD-dried samples compared to that of hot air-dried and vacuum-dried samples. The color retention was also significant in FD and RWD samples. Total phenolic content (TPC) of 441mg GAE/100 gm and crude fiber content of 1.92% was found to be higher in RWD banana samples in comparison to other drying methods. Antibrowning agents coated dried banana samples viz. slice and pulp has shown less color change and nutrient retention as compared to untreated dried banana samples. The highest nutrient retention in less drying time was found in RWD banana samples.

Optimization of Caper Drying Using Response Surface Methodology and Artificial Neural Networks for Energy Efficiency Characteristics

One of the essential factors for the selection of the drying process is energy consumption. This study intended to optimize the drying treatment of capers using convection (CD), refractive window (RWD), and vacuum drying (VD) combined with ultrasonic pretreatment by a comparative approach among artificial neural networks (ANN) and response surface methodology (RSM) focusing on the specific energy consumption (SEC). For this purpose, the effects of drying temperature (50, 60, 70 °C), ultrasonication time (0, 20, 40 min), and drying method (RWD, CD, VD) on the SEC value (MJ/g) were tested using a face-centered central composite design (FCCD). RSM (R2: 0.938) determined the optimum drying-temperature–ultrasonication-time values that minimize SEC as; 50 °C-35.5 min, 70 °C-40 min and 70 °C-24 min for RWD, CD and VD, respectively. The conduct of the ANN model is evidenced by the correlation coefficient for training (0.976), testing (0.971) and validation (0.972), which shows the high suitability of the model for optimising specific energy consumption (SEC).