Role of expert reviews for assessment of current developments in global drying R&D

Keywords:

• Critical reviews
• R&D
• innovation
• superheated steam drying
• encapsulation
• solar drying
• ultrasonics

Most research is built on earlier research that is available in the public domain. Much innovation is incremental and also depends on prior knowledge. It is therefore very important for researchers and innovators in industry as well as academia to become familiar with relevant published works. With explosive growth and interdisciplinary nature of most research of technological interest, it is almost impossible to continuously access, assess and digest research that is being published. In the field of drying science and technology, however, the growth of literature is not as rapid as it is in pure sciences. For example, as many as 25,000 papers are being published monthly related to various aspects of Covid-19 in this pandemic period. This means much of the research is being carried out concurrently viz. in parallel. It also implies that there is a strong likelihood of duplication of effort. Fortunately, we do not face this problem in areas of our interest. Yet, the sheer volume of knowledge being generated is such that critical reviews prepared by domain experts are valuable for both novices and experts in the field.

In order to enable access to expert reviews that have appeared in this journal in recent years, we have devoted four Guest Editorials in the past, which covers critical review articles published during 2016 through 2020.^[1–4] In the present Guest Editorial, we aim to summarize the assessment of recent developments in global drying R&D by domain experts during 2021, with brief outlines of their content. A quick glance at the topics covered in the critical review articles published in 2021 other than published in special issue on reviews on drying science and technologies^[5] shows that they cover a broad range of topics of industrial interest and applicability in the food, pharmaceutical and chemical process industries as well those related to dyestuff and pigment recovery, effluent drying and wood drying.

Superheated steam drying

The recent developments in superheated steam drying (SSD) and its applicability in various types of dryers are reported by Patel and Bade.^[6] The past, present and prospects of superheated steam drying are critically analyzed and systematically presented; these include classification, working principles and recent developments. Further, the article mentions possibilities to improve energy efficiency by energy-saving due to the reuse of the energy from exhausted steam, mainly by recirculation, and the use of partial exhaust of excess steam for other operations. Various areas of R&D, e.g., experimental studies, analytical modeling and pilot scale tests of SSD, including energy recovery and energy efficiency are emphasized.

Ultrasound-assisted spray drying of food and bioactive compounds

Khaire and Gogate^[7] reviewed the extensive applications of ultrasound-based spray drying of food and bioactive compounds in the food-pharmaceutical industry for enhancing the stability of bioactive compounds, especially sensitive compounds required for different applications in the pharmaceutical industry. Use of ultrasonic spray drying resulted in promising outcomes in the pharmaceutical sector. The application in the food industry is nevertheless still in the developmental stage, possibly due to the absence of suitable designs, lower throughput values and scale of operations. The various applications of ultrasound in spray drying for encapsulation, microsphere generation, among others, in the food industry and the enhancement into such applications using ultrasonic nozzle are presented. The article concludes that ultrasound offers much promise for improving the operations, mainly with reduced processing time, enhanced production capacity and product quality.

Spray drying of sugar-rich products

Recent advances in spray drying of sugar-rich products such as fruit juices, pulp and honey, with and without the application of carriers, are reported by Sobulska and Zbicinski.^[8] Use of carbohydrates (e.g., maltodextrin, gum Arabic), prebiotic dietary fibers, proteins and natural carriers as carriers for spray drying of sugar-rich products is reviewed. The article discusses the effects of carrier type, carrier concentration and spray drying process parameters on the product yield and selected final product properties. Recent studies have proved that prebiotic dietary fibers or proteins may substitute conventional carriers, i.e., refined carbohydrates, providing higher product yield and additional nutritional value at a lower carrier concentration in a final product.

Microencapsulation of food bioactive components

Recent developments in microencapsulation of food bioactive components by spray drying method are discussed by Furuta and Neoh.^[9] Microencapsulation using spray drying is effective and provides several beneficial functionalities such as enhancing solubility, improving stability, easing the handling of liquid labile active compounds, providing protection against degradation, masking unpalatable tastes or smells and controlling or delaying release. The vast variety of food active compounds along with the various types of food core materials, e.g., oils, flavors, nutrients, pigments, antioxidants and polyphenols, vitamins and enzymes are critically discussed.

NCDT solar dryers

A comprehensive review of various designs of natural convective and direct type (NCDT) of solar dryers is reported by Chavan et al.^[10] Comparison on the performance of existing dryers based on such parameters as design simplicity, portability, thermal performance, capital cost, compactness and quality characteristics of dried products is made. Solar dryer based on the conduction mechanism appears to be cost-effective and more efficient.

Drying of edible insects

Hernández-Álvarez et al.^[11] reviewed recent developments in the drying of edible insects and their ingredients as these are considered novel, sustainable and high-quality nutritional sources of food and feed. Different drying technologies (sun drying, smoke drying, roasting, oven drying, and freeze-drying) along with different pretreatments (thermal blanching, pulsed electric field, and microwave-assisted drying) are explored to improve the final quality of insect products, extending their shelf life and reducing total energy consumption. The article highlights the recent advances in drying technologies, addressing their effectiveness and influence on different quality parameters such as protein/lipid extraction efficiency, microbiological safety, shelf-life, sensory characteristics of the final products and impact of such technologies on bioactive compounds.

Drying of cannabis

The state of the practices and challenges in cannabis drying as well as relevant recent developments are discussed by Challa et al.^[12] Although cannabis is an important source of biomolecules possessing medical applications, at present the cannabis industry relies on inefficient and slow drying practices that result in poor-quality products. Some potential low-temperature drying technologies of significance to cannabis industry are discussed. Non-isothermal, microwave-vacuum, electrohydrodynamic, radio-frequency and freeze drying are identified as potential candidates for industrial drying of cannabis.

We hope the critical reviews published in this journal continue to provide relatively easy access to the latest advancements in areas of contemporary interest to industry and to researchers in academia. We believe the reviews will stimulate innovation and promote further research and development in drying science and technology.

Shivanand S. Shirkole Department of Food Engineering and Technology, Institute of Chemical Technology Mumbai, Bhubaneswar, India [email protected] Aparupa Pani Department of Civil Engineering, Kalinga Institute of Industrial Technology, Bhubaneswar, India [email protected] Arun S. Mujumdar Department of Bioresource Engineering, McGill University, Montreal, Canada [email protected]