Refractance Window Drying: A Novel Food Processing Technology Report

This report provides a comprehensive overview of refractance window drying, a modern food processing technique. It delves into the principles of this technology, including convection, conduction, and radiation, and examines the factors influencing its efficacy, such as food composition and consistency. The report highlights the nutritional benefits of refractance window drying, emphasizing its ability to retain essential vitamins and antioxidants compared to traditional methods. It also offers a comparative analysis with other drying techniques, focusing on texture, food safety, and energy efficiency. Furthermore, the report explores the current applications of refractance window drying in various food products and other industries, while also discussing potential future developments and innovations in this field. Case studies are included to support the claims and findings presented in the report.

Running head: REFRACTANCE WINDOW DRYING
REFRACTANCE WINDOW DRYING
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Executive Summary
A number of drying technique are present for the purpose of processing food for consumer
consumption and retail. Recently, refractance window drying has emerged to be as a novel
drying technique resulting in dried food products with advantageous qualities as compared to
those produced from established drying techniques. Refractance window drying relies on the
principles of convention, conduction and radiation. The food is placed on top of a plastic sheet,
and heated gradually underneath using circulating hot water. Such processes result in nutritional
and desirable textural property retention in foods. A number of fruits, vegetables, meat and dairy
products have found application for being dried using refractance window drying techniques.
However, future innovations are required consideration limitations associated with capacities and
consistency of the pre-prepared food before drying.

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Table of Contents
Introduction..........................................................................................................................3
Discussion............................................................................................................................4
Principle of Technology..................................................................................................4
Factors influencing Treatment Efficacy..........................................................................5
Nutritional Quality...........................................................................................................6
Comparison with Other Drying Techniques: Texture, Food Safety, Efficiency.............7
Applications and Current Status......................................................................................9
Future.............................................................................................................................10
Conclusion.........................................................................................................................10
References..........................................................................................................................11

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Introduction
Advancements in food science and technology have bolstered the emergence of a number
of novel food processing techniques, of which the unique drying procedure of ‘Refractance
Window Drying’ has gained considerable importance (Azizi et al. 2017). Food processing
technologies are undergoing frequent innovations at present due to the simultaneous need of
ensuring the nutritional qualities of a food item, along with adherence to altering the organoleptic
qualities of food into desirable quality parameters (Raghavi, Moses and Anandharamakrishnan,
2018). As observed by Nindo and Tang (2007), Refractance Window Drying is a unique food
processing technology of drying which aids in the conversion of raw food materials into dried
sheets, powders and flakes along with retaining their nutritional value. This drying procedure
involves the fruit and vegetable products such as juices and purees are dried within a short time
span of 3 to 5 minutes which leads to high retention of the characteristic properties of food such
as micronutrients, colors and antioxidants. As researched by Ochoa-Martínez et al. (2012), such
a technology was formulated first by MCD Technologies in Tacoma, Washington, United States.
The following paragraphs of this paper will aim to shed light on the salient features of
refractance window drying technology, along with its functioning principle, factors influencing
the efficiency of its treatment, nutritional qualities and food safety parameters of products
produced, comparative observations with alternative drying techniques, its present status,
application and future developments in the food processing industry.

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Discussion
Principle of Technology
As researched by Ortiz-Jerez et al. (2015), the food undergoing drying using the
refractance window procedure is to be kept over a thin layer of plastic under which, heat is
provided using circulation of hot water. Such a presence of a thin plastic material which appears
transparent to radiation of the infrared type, forms a window to allow thermal radiation to travel
from the heat producing source to the raw food material which is wet. Gradual heating compels
to window to ‘close’ along with drying of the food material resulting in disruption of further
circulation of infrared radiation and a prevention of the food to achieve extremely high
temperatures which may damage its desirable properties. As postulated by Nindo and Tang
(2007), refractance window drying technology relies on the heating principles of convection,
conduction and radiation. The circulating hot water is heated to achieve a temperature of 95 to
97C, using principle of convection where steam from insulated tanks are used followed by its
circulation using shallow trough to the plastic film. The thinness of the plastic permits its
immediate heating through processes of conduction and radiation resulting in the concerned food
to achieve a temperature not beyond 70C.
Hence, taking insight from Hernández-Santoset et al. (2016), refractance window
technologies relies on principles of self-limiting dehydration processes relying on the usage of
infrared light in replacement of harsh extremes of heat temperatures as compared to other
establishes drying techniques. The interplay of processes such as water conductivity, light
refractance and infrared is the characteristic functioning principle of refractance window drying.
Such a working principle is advantageous since it results in the retention of nutritional value of

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the food along with preservation of its organoleptic properties such as taste, aroma, flavor, color
and texture (Jafari et al. 2016).
Factors influencing Treatment Efficacy
The textural properties and composition of the food are some of the key factors which
influence the efficiency of refractance window drying. The food mixtures or purees of fruits and
vegetables which need to be dried are required to have be preprocessed into a slurry of the
adequate consistency which is easy to apply and spread on the conveyor belt (Zotarelli, Carciofi,
and Laurindo, 2015) Hence for the purpose of uniform drying, the product must be thinly with
equally distributed layers. The product must also be consistent in composition since varying
consistence and thickness can hinder the drying process (Castoldi et al. 2015). Further, fruit or
vegetable products which possess high content of sugar may not be appropriate for being
processed into powders by refractance window drying since such products tend to possess a
hygroscopic property due to the sugar resulting in stickiness in texture and difficulty to remove
from the conveyor belt (Sabarez, 2015). Another key factor which affects the efficiency of
refractance window drying technology is its capacity where the drying equipment may not be
Schematic Diagram of Refractance Window Drying (Source: Bolland,
2017)

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able to function effectively when treated with large volumes of food (Sogi, Siddiq and Dolan,
2015).
Nutritional Quality
Food products like fruits and vegetables are considered to possess a rich nutritional
composition filled with essential micronutrients like vitamins, minerals and bioactive compounds
such as antioxidants (Wang et al. 2016). Recent advocacy and global trends associated with an
increased awareness concerning maintenance of nutritional needs have necessitated the
production of nutritious food products by food manufacturing companies which must retain their
benefits to the health of individuals (Germer et al. 2016). It must be considered that essential
vitamins and antioxidants like B and C vitamins which are present in fruits and vegetables are
volatile compounds which easily encounter losses amidst and environment of high temperatures
(Rothwell et al. 2015). Traditional food drying technologies other than refractance window
drying usually utilize excessively high temperatures which, despite yielding favorable textural
qualities, result in key nutritional losses (Augustin et al. 2016).
Refractance window drying, due to its usage of relatively gentler window drying
techniques of thermal radiation and conduction utilize relatively lower drying temperatures as
compare to traditional drying processes hence resulting in improve nutritional qualities of the
dried product (Celli et al. 2016). In order to demonstrate the same, this paper will highlight a
case study by focusing on the experimental research conducted by Abonyi et al. (2002). In this
study, the nutritional qualities of pomegranates and strawberries which were dried using
refractance window drying techniques were compared with the nutritional properties of those
dried using traditional drying methods such as drum drying, spray drying and freeze drying
technologies. The authors reported a high retention of ascorbic acid in purees of strawberries at

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94% as compared to 93.% in those dried using freeze drying methods. However, carrots dried
using refractance window drying techniques demonstrated higher losses in beta-carotene (5.4%),
alpha-carotene (7.4%) and total carotene (8.7%) as compared to those dried using freeze dried
methods which reported results of 5.4% beta-carotene, 4.0% total carotene and 9.9% alpha-
carotene. The authors further reported that the strawberries dried using refractance window
drying techniques retained a higher overall perception of color, aroma and textural properties.
Hence, from the above case study, it can be observed that, while refractance window drying
reported improved rates of vitamin C retention, further innovations may be required to improve
technologies aimed at improving carotenoid retention in fruit and vegetable products.
Comparison with Other Drying Techniques: Texture, Food Safety, Efficiency
When compared to additional drying techniques, refractance window drying has been
found to demonstrate production of dried food products of superior textural and organoleptic
qualities, as compared to traditional drying technologies (Minjares-Fuentes et al. 2017). Freeze
drying implies a rapid drying technique which dehydrates a food product using sublimation and
vacuum-inducing low pressure. Despite the efficiency of this method, the food product often
suffers from extreme losses of nutrients and necessitates the presence of chemical treatments
which defeats the purpose of a ensuring the retention of the natural qualities of the food and
produces a highly porous product (deAncos et al. 2018). Drum drying methods are one of the
most prevalent drying techniques requiring addition of products to be dried to a set of drum
rotating with high internal heating of 180C. as observed from the high temperatures applied,
drum drying results in nutrient depletion at high rates and the production of products with
unfavorable textural qualities and uneven surfaces (Karthik, Chhanwal and
Anandharamakrishnan, 2017). Spray drying techniques of drying are often considered as highly

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efficient due to their production of finely powdered, free flowing dry products by projecting the
food slurry through high temperature and pressure atomizers. Despite the favorable textural
qualities, spray drying products continue to suffer from nutritional losses and increased
susceptibility to spoilage due to high porosity (Keshani et al. 2015).
Refractance window drying has been implicated to yield beneficial results and surpass all
the limitations mentioned above in comparison to various drying techniques. Due to the lack of
usage of chemical pre-treatments to the food, products dried using refractance window drying
retain their natural properties and remain free from artificial substances (Rostami et al. 2018).
The usage of low, gentle heating results in retention of essential micronutrients as well as
maintenance of a uniformly structured food product free from porosity. The homogenous textural
quality so produced, not only makes it desirable to the palate, but also enhances its shelf life and
reduces its susceptibility to oxidation and harmful free radical infiltration (Zotarelli, Carciofi and
Laurindo, 2015).
Further, refractance window drying has also been implicated to be more efficient in
energy utilization during drying when compared to additional drying technologies. To
demonstrate the same, this paper will take insights from the research case study highlighted in
the study by Ochoa-Martínez et al. (2012), which compared the features of drying encountering
when processing mango slices using refractance window technique at 90C as compared to
traditional tray drying processes at 62C. Within 1 hour of refractance window drying, the mango
slices were reported to yield moisture content of 0.013 (1mm thickness) and 0.048 (2mm
thickness) kg water/kg dry solid respectively. In comparison, mango slices dried in the tray dryer
took approximately 4 hours to achieve higher moisture content of 0.966 (1mm thickness) and

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3.614 (2mm thickness) respectively. Hence, this case study demonstrated the energy and drying
efficiency of refractance window drying as compared to other technologies.
Applications and Current Status
At present, the drying technology of refractance window drying has found applications in
the production of a variety of fruit and vegetable products such as concentrated purees, single
strength mixtures, pulps, juices, semi solid purees with chunks and seeds as well as by-products
of vegetables and fruits (Rostami et al. 2018). Additional food production areas where the
refractance window drying find their application include drying of meat, poultry and fish broths
and purees, dairy and egg products, starches, cereals and grain products as well as variety of
concentrated beverages and beverage mixtures. Additionally, refractance window drying has also
found application in the production of food additives such as food colors and flavors as well as
fine chemicals (Tontul and Topuz, 2017). Other product manufacturing areas which are currently
witnessing the application of refractance window drying, include, drying of nutraceuticals,
pharmaceuticals, pigments, cosmetics. It is however, worthwhile to note that the above food
product drying applications have mostly been performed on test and trial procedures (Raghavi,
Moses and Anandharamakrishnan, 2018). The production of dried fruit and vegetable purees by
refractance drying methods was first applied by Clermont of Hillsboro, Oregon. Currently,
commercially used refractance window drying technologies are being explored and applied in
novel food production fields such as the drying of by-products obtained from dairy as well as
herbal products, micro-algae substances rich in essential antioxidants such as carotenoids, dried
mixtures of scrambled eggs, avocado powders and brine shrimp (Shende and Datta, 2018).

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Future
Refractance window drying technologies has currently witnessed a wide variety of
applications and drying experiments, primarily fruit and vegetable products. Considering the
current limitations of this technology associated with difficulty to manage large volumes of food
products, and drying of high sugar containing products, future innovations can concentrate on
mitigation of these constraings (Moses et al. 2014). Further, taking insights from the research
conducted by Baegbhali and Niakousari (2018), future technologies of refractance window
drying can focus on enhancing efficiency of energy consumption and process design of the
overall equipment. Additionally, future technologies of refractance window drying must consider
the expanding its application in the drying of products like leafy vegetables, granules of starch,
marine and seafood items, meat products and dehydration of microbial strains like probiotics and
yeast for easy incorporation into food products or additives.
Conclusion
Hence to conclude, the drying technique of refractance window drying is a relatively new
technology which has been implicated to be effective in the processing of a wide range of food
products. When compared to other drying techniques, the characteristic low temperature
radiation drying techniques by refractance window drying results in the production of foods with
desirable textural and nutritional properties. Further, the refractance window drying also yields
higher rates of drying as compared to other techniques. However, considering its limitations, it
can be concluded that the need of the hour is to conduct further research to explore innovative
modifications of this technology to suit a wide variety of foods and processing conditions.

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References
Abonyi, B. I., Feng, H., Tang, J., Edwards, C. G., Chew, B. P., Mattinson, D. S., & Fellman, J.
K. (2002). Quality retention in strawberry and carrot purees dried with Refractance WindowTM
system. Journal of Food Science, 67(3), 1051-1056.
Augustin, M. A., Riley, M., Stockmann, R., Bennett, L., Kahl, A., Lockett, T., ... & Cobiac, L.
(2016). Role of food processing in food and nutrition security. Trends in Food Science &
Technology, 56, 115-125.
Azizi, D., Jafari, S. M., Mirzaei, H., & Dehnad, D. (2017). The influence of Refractance Window
drying on qualitative properties of kiwifruit slices. International Journal of Food Engineering,
13(2).
Baeghbali, V., Niakousari, M., & Farahnaky, A. (2016). Refractance Window drying of
pomegranate juice: quality retention and energy efficiency. LWT-Food Science and Technology,
66, 34-40.
Bolland, K. M. (2017). Refractance Window Food Drying System Delivers Quality Product
Efficiently. Retrieved January.
Castoldi, M., Zotarelli, M. F., Durigon, A., Carciofi, B. A. M., & Laurindo, J. B. (2015).
Production of tomato powder by refractance window drying. Drying technology, 33(12), 1463-
1473.
Celli, G. B., Khattab, R., Ghanem, A., & Brooks, M. S. L. (2016). Refractance Window™ drying
of haskap berry–preliminary results on anthocyanin retention and physicochemical properties.
Food chemistry, 194, 218-221.