Conventional Drying Research Articles

Kızılötesi kurutmada hurma (Phoenix dactylifera L.) pestilinin efektif difüzyon katsayısının belirlenmesi: Pişme süresinin etkisi

Longer process times in conventional drying methods can be improved by using rapid technologies. Infrared drying is one of these faster methods. Consumer awareness on health and wellness products has increased and boosted with Covid-19 pandemic. Therefore, consumption trend of snack products formulated with natural ingredients has increased. It is estimated that this trend will continue to rise. In accordance with this, fruit leather production from dates was done by infrared drying and effect of cooking time on drying behavior was investigated. Firstly, dates were washed and seeds were removed, then water was added at a ratio of 1:2.5 (dates:water), and cooked for 30, 45 and 60 min. Samples were pressed and dried at 10 mm thickness. Drying curves showed first order drying kinetics and effective moisture diffusivity (Deff) of fruit leathers were found as 1.5283×10-9, 1.6971×10-9 and 1.7351×10-9 m2/s for 30, 45 and 60 min of cooking time, respectively.

Sugarcane molasses spray drying by dehumidified air as the method to enhance powder recovery and physical properties of powders

AbstractThe aim of the study was to compare sugarcane molasses powders obtained by conventional high temperature spray drying (inlet/outlet air temperature: 180°C/80°C) and low temperature dehumidified air‐assisted spray drying (80°C/50°C) in terms of drying yield and physical properties. The addition of NUTRIOSE as a carrier was from 0% to 40% (w/w, solids). It was possible to obtain 100% high quality powders without the use of a drying carrier with high process efficiency (up to 93%—with using dehumidified air) by using both methods. Low temperature spray drying positively translated into increased drying yield, lower hygroscopicity and improved flowability of powders. Moreover, the powders obtained by low temperature method were brighter with small, less diversified particle sizes of spherical shapes.Practical ApplicationsMolasses is a by‐product of sugar production. Molasses have diverse applications as cheap food‐grade sweeteners as well as an economically feasible intermediate materials for production of some innovative food additives. Transforming sugarcane molasses from viscous, inconvenient liquid into free‐flowing powder, seems to be important by taking in consideration handling, transportation and the final application. Free‐carrier molasses powders fit well with the sustainability and clean label trends. Low‐temperature spray drying with dehumidified air is an innovation which allows to obtain higher quality powders.

Effect of the drying condition on the strength properties of Japanese larch board after vacuum heat treatment

This study aimed to investigate the effect of drying conditions on the strength properties of larch boards after vacuum heat treatment, using leftover boards from a previous study that were dried by four methods: conventional kiln drying, high-temperature drying, radio-frequency/vacuum-press (RF/VP) drying, and hot-air/vacuum drying. The boards were then heat-treated and tested for moisture content, density, bending strength, compressive strength, and tensile strength. The results showed that the drying method significantly affected the strength properties of the larch boards after vacuum heat treatment. After vacuum heat treatment, density increased in hot-air/vacuum drying and RF/VP drying, while bending strength was higher in high-temperature drying and hot-air/vacuum drying, and tensile strength was higher in hot-air/vacuum drying. Conditioning treatment after vacuum heat treatment had an impact on the decrease in density in RF/VP drying, the decrease in bending strength in hot-air/vacuum drying, and the increase in tensile strength in high-temperature drying. The drying method is a crucial factor in determining the chemical changes that occur during heat treatment, as it establishes the physical and chemical properties of the wood prior to treatment. Variations in these properties can result in different chemical transformations during the heat treatment process. Therefore, to minimize any adverse impact on the strength properties of the wood, it is necessary to carefully select an appropriate drying method before heat treatment.

Electrospray drying-mediated coating of cellulose nanocrystal

Cellulose nanocrystals (CNCs) have garnered significant attention in recent years due to their potential applications in coating, reinforcement, and packaging technologies. The present study focuses on the development of an efficient, low-cost, and scalable drying process for CNCs, adapted from the electrospray technique. CNCs were dispersed in various concentrations of tert‑butanol (t-BuOH) prior to electrospray drying. The resulting morphologies and micro-rheological behaviors were compared to those obtained through conventional air drying, oven drying, freeze-drying, and air-spray drying methods. The electrospray-dried CNCs derived from an 85% t-BuOH suspension exhibited superior physico-chemical properties and thermal stability, characterized by highly ordered crystals that self-assembled into thin lamellar structures. Furthermore, the relatively low re-suspension ability of these dried CNCs is advantageous for coating and thin film fabrication, providing high controllability over the morphology. Notably, this rapid drying process (≤ 35 min) can be extended to other nanomaterials, provided that their suspensions can be electrically charged to spread and dry uniformly on substrates.

Drying kinetics in cantaloupe melons dehydrated by osmosis, accompanied by conventional drying

Melon is considered a product of high commercial value, but its post-harvest shelf life is short at room temperature. As an alternative to reducing postharvest losses, osmotic dehydration arouses interest as a pre-treatment for fruit drying. The present work aimed to obtain the drying curves in osmotically dehydrated melons, followed by conventional drying. A syrup was prepared using crushed crystal sugar up to a concentration of 30 ºBrix, in the proportion 2:1 syrup/fruit, drying was at 50ºC and drying curves were determined as a function of weight losses per gram of the samples during the process until constant weight. The results showed that for both treatments, it is possible to observe a characteristic curve that decreases over time, with treatment 2, with the use of osmotic solution a lower loss of mass (g) during drying. The R² regression coefficients presented values of 0.7878 for treatment 1, and values of 0.848 for treatment 2. The melons treated with osmotic solution showed higher solids gain at the end of the drying process and better fit to the experimental drying data.

COMPARISON OF A NOVEL VACUUM-COMBINED INFRARED AND HOT-AIR CONVECTION METHODS FOR DRYING OF DEVECI (PYRUS COMMUNIS L.) PEAR SLICES

In this study, the quality characteristics of pear slices dried in vacuum-combined infrared dryer equipped with a two-way infrared heating (100-300 W infrared power) and convectional dryer (40-70 °C) were comparatively investigated. Increasing infrared power in vacuum-combined infrared dryer decreased the drying time. However, the differences between vacuum pressures (100 mmHg and 250 mmHg) were generally negligible. Drying process at 200 and 300 W IP under vacuum was approximately 2- and 2.5-times shorter than conventionally drying at 55 and 70 °C, respectively. Although a very low amount of HMF in dried pear slices by the conventional dryer was detected only at 70 °C after 300 min, high amounts of HMF was detected at 300 W after 120 minutes. The rehydration rate of pear slice dried with vacuum-combined infrared dryer was higher than those of pear slice dried with conventional dryer. Syringic, chlorogenic and ellagic acids were identified in dried pear samples. Chlorogenic acid was found to be the most among phenolic compounds in dried pears. While the ellagic acid was not detected in fresh pear, dried pears had ellagic acid content (8.14-16.93 mg/kg d.m.). It was found that total phenolic content, ABTS and DPPH values of dried pears by vacuum-combined infrared dryer was lower than those of dried sample by conventional dryer. The pear slices dried at 300W and 250 mmHg had the highest sensory scores. The results show that the vacuum-combined infrared drying provided a shorter drying time and better sensory quality for dried pear compared to conventional drying.

Pengeringan Kakao Menggunakan Rumah Pengering Hybrid

Cocoa (Theobroma cacao) is one of the plantation commodities in Indonesia that has an important role for the national economy to increase the country's foreign exchange. The process of cocoa drying will result in a dried product changes color, texture, and scent. The purpose of this study was to analyze the efficiency of drying cocoa using a hybrid dryer house with three treatments namely, drying using solar energy drying, drying using solar energy drying and gas energy (hybrid) and conventional drying. The results showed that drying cocoa in a drying house using solar energy takes 270 hours or 12 days, drying using a drying house using solar energy and gas (hybrid) takes 222 hours (9 days) and drying using a winch (conventional) takes 240 hours (11 days). Keywords: Cocoa, Drying, Hybrid Dryer House.

Development of drying system by using internet of things for food quality monitoring and controlling

One of the essential aspects in managing food safety is the drying, which helps to preserve food quality and extend the shelf life of food products. The temperature, relative humidity (RH), and air velocity in dryers should be carefully monitored and maintained to ensure food quality and safety during the drying process. Also, the components of heat pump dryers are at risk due to the electric current, the high temperature surrounding the condensing unit's compressor, and the high air velocity of the drying environment. These elements affect the quality of the foods being dried, and being able to communicate alerts in real-time is essential for taking precautions against hazards that can damage the dryer's internal components. Food technology's IoT-based control (IoT-BC) system with multipurpose sensors offers options for managing the post-harvest quality of leaves as they are being dried. This study set out to design and evaluates an IoT-BC system in order to remotely control, alert of imminent hazards, and monitor the microclimate parameters, including RH, temperature, and air velocity. The impacts of the created IoT-based drying system on the quality of dried leafy vegetables were also investigated utilizing a unique dryer as a case study. The results showed that the created IoT-BC system accurately maintained the drying environment, provided reliable data about the internal microclimate atmosphere of the dryer, and provided the appropriate alarm in case of an emergency and this was based on real-time data analyses. The most important quality characteristics for dried leaves were not significantly different between the IoT-based dryer and the conventional dryer dependant on drying time. Rehydration capacity decreased with the increase in the drying air temperature from 40 to 70 °C and was maximum (6.48) at 40 °C for coriander leaves and maximum (5.59) at 40 °C for Mint leaves dried in IoT based dryer. Maximum crude fibre and protein contents for mint leaves dried in an IoT-based drier were at 40 °C and were 4.97 mg/100 g and 10.62 mg/100 g, respectively. Maximum crude fibre and protein contents for coriander leaves dried in this method were 3.76 mg/100 g and 12.23 mg/100 g, respectively. The IoT based dryer kept the leaves' superior qualities throughout the drying process as a result.

Effect of Samples Length on the Characteristics of Moisture Transfer and Shrinkage of Eucalyptus urophylla Wood during Conventional Drying

Moisture transfer influences wood deformation and moisture content (MC) distribution during conventional drying of Eucalyptus urophylla wood. This study aims to investigate the effect of sample length (30, 100, and 200 mm) on moisture distribution and transfer in different directions and locations and on deformation of wood. The results showed that when the MC was above the fiber saturated point (FSP), the drying rate decreases exponentially with an increase of sample length; however, below the FSP, there was no obvious relationship between the drying rate and sample length and above the FSP, the moisture distribution was non-uniform along tangential, radial, and longitudinal directions and became even below the FSP, which was more significant in the middle location of wood. The greatest MC differences occurred between the surface and sub-central layers along the tangential and radial direction, which were between the end and sub-middle locations along the longitudinal direction. The effect of sample length on the MC distribution and MC differences along wood in the three directions depended on locations and the MC stage of wood; most of the free water and bound water transferred from the wood central to the ends along the longitudinal direction for three sets of samples. Bound water diffusion significantly slowed as the sample length exceeded 200 mm; sample length affects wood collapse and its recovery, but the drying rate has a lesser effect on collapse for samples with a length below 200 mm.

Coupling Interval Hyper-Active Drying (IHAD) with Instant Controlled Pressure Drop (D.I.C.) to define new swell-drying processes

To respond to the various issues of conventional drying (textural defects of collapse-shrinkage and case hardening, microbiological contamination, poor rehydrability, degradation of active molecules caused by high wet-bulb temperature, weak drying kinetics, and marketing difficulty), swell-drying has proven high relevance in combining conventional drying processes with the Instant Controlled Pressure Drop (D.I.C.). The international team of "Research & Engineering Platform for intensifying Drying Processes (REPID)" has studied phenomenological models and experimental trials combining D.I.C. with new Interval Hyper-Active Drying (IHAD) processes. Currently, IHAD includes interval starting accessibility drying (ISAD), interval infrared airflow drying (IIRAD), and interval microwave airflow drying (IMAD). All these "interval operations" are sandwiched into cycles, each comprising double separate independent mechanisms; a short, hyper-focused active period (that generates and sweeps out vapor to the surrounding environment) alternated by a passive period of internal water diffusion/moisture homogenization. Since surface evaporation is highly intensive, the wet-bulb temperature stays low, although highly effective drying kinetics. Thus, the operation results in avoiding biochemical damage risks. Coupled with the D.I.C. texturing-decontamination, these drying operations are very effective in terms of drying kinetics, energy consumption, and product quality of heat-sensitive solids. It has led to the manufacturing of effective drying equipment.

A review of solar drying technology for agricultural produce

Agriculture contributes to large export earnings for many countries and provides food all over the world. However, most agricultural products need some post-harvest processing, such as drying, to extend their shelf life while still maintaining their respective nutrient quality. One popular post-harvest processing method is drying using solar energy. It is a type of renewable energy that is abundant and free. Conventional dryers use grid electricity and can be expensive to operate. Consequently, there is a growing need for cost-effective solar-powered agricultural dryers that is reasonable for smaller-scale farmers. Although current solar dryers are still not on par with modern electricity-powered dryers, solar dryers have lower running costs and are sustainable and able to generate electricity. They can also be used practically anywhere with abundant solar energy. As numerous solar drying technologies have been proposed over the past decade, it is necessary to assess the current state of solar drying technology in the agricultural sector to identify current advancements and potential research gaps. In this paper, a review of existing solar dryers mechanism and the state of the art of solar drying technology research for agricultural products is presented.

Analytical solutions for the modeling, optimization, and control of microwave-assisted freeze drying

Freeze drying, aka lyophilization, is a process by which a pharmaceutical product is dried via sublimation under vacuum. An alternative to the conventional process is microwave-assisted freeze drying, which relies on microwave irradiation for drying the product, offering a reduction in the drying time by 70%–80%. This article derives exact and approximate analytical solutions to a mechanistic model for conventional, microwave-assisted, and hybrid freeze drying. The exact solution serves as a reference solution for validating numerical or approximate results due to its highest accuracy up to machine precision. The approximate solution can be computed about 4-fold faster than the numerical solutions and 200-fold faster than the exact solution with the maximum error of less than 1%, which is highly computationally efficient and accurate. Applications of the analytical solutions are demonstrated in the context of parameter estimation, optimal control, and parameter space analysis.

Changes in, and correlation analysis of, volatile compounds, key enzymes, and fatty acids in lemon juice vesicles during freeze drying and hot-air drying.

Lemon juice vesicles are distinguished by their unique and abundant volatile flavor compounds, which can undergo complex changes during drying. In this study, integrated freeze drying (IFD), conventional freeze drying (CFD), and hot-air drying (AD) were used to dry lemon juice vesicles to investigate the changes in, and correlations among volatile compounds, fatty acids, and key enzyme activity during the drying process. Twenty-two volatile compounds were detected during the drying processes. Compared with fresh samples, seven compounds were lost in the dried samples after IFD, seven after CFS, and six after AD, and the loss rates of the total content of volatile compounds in the dried samples were 82.73% in CFD, more than 71.22% in IFD, and more than 28.78% in AD. In total, 1.015 mg/g of seven fatty acids were detected in the fresh samples; the content loss rates of total fatty acids after drying were 67.68% in AD, more than 53.00% in CFD, and more than 36.95% in IFD, respectively. During the three drying processes, IFD retained relatively higher enzyme activity in the samples. Many positive and negative correlations (P < 0.05) were observed among the key enzyme effects, fatty acids, and volatile compounds, showing close associations. The current work provides information that is important for the selection of suitable drying techniques for lemon juice vesicles and suggests how to control their flavor during the drying process. © 2023 Society of Chemical Industry.

Use of Fe-H3BTC and GO Compounds To Prepare N/Fe-Doped Carbon for a High-Performance Oxygen Reduction Reaction Catalyst.

Zinc-air batteries (ZABs), as a new type of energy storage and conversion device, have received lots of attention due to their high energy density and low cost. The electrode material is a key factor for improving the performance of ZABs. Here, a facile strategy for the fabrication of N-rich porous carbon is reported. H3BTC and GO are selected as carbon precursors, histidine and Fe(NO3)3 are used as ligands, and urea is used as a N source and template. After the conventional drying of the complex and following carbonization process, serial N-doped carbon materials are prepared. The composition and structure of the material are characterized, and the effect of the ligand is studied. The hierarchical porous structure facilitates the full exposition of N and trace of Fe active sites and benefits the transportation of electrolytes, thus improving the oxygen reduction reaction (ORR). The ORR performances show that the porous carbon has a positive initial and half-wave potential, good limiting current density, a near four-electron transfer process, and better methanol resistance and durability. The assembled ZAB exhibits high specific capacity (880.4 mAh gZn-1), excellent open-circuit voltage (1.54 V), and superior cycling stability, which further provides the significant potential for its application.

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.

Experimental investigation on volumetric heat transfer coefficient during intermittent spray drying of mannitol solution

The paper presents a detailed experimental investigation on volumetric heat transfer during intermittent spray drying of a 20% w/w of mannitol solution in a custom-made spray dryer. Unlike the conventional intermittent drying process, which achieves intermittency by pulsating the properties of the carrier gas medium, the present works achieve intermittency by pulsating the nozzle spray. The estimated volumetric heat transfer coefficient varies between 0.8 and 2 kW/m3K, and the volumetric mass transfer coefficient is between 0.6 and 2.5 s−1. The correlation for heat and mass transfer coefficients is evolved that relates the heat and mass transfer coefficient with the flow properties and thermophysical properties of both the carrier gas and the precursor fluid in terms of Ohnesorge number and Nusselt number. The investigation uses response surface analysis to analyze the effect of Reynolds number of air and Ohnesorge number of precursors on the volumetric heat transfer coefficient. The results show that a decrease in Reynolds number for a wide range and Ohnesorge number causes the volumetric heat transfer coefficient to increase.

Intermittent Drying of Soybeans in Conical Spouted Beds: Modeling Approach

Intermittent drying is a promising methodology to conventional drying which offers benefits related to energy and better-quality products. However, modeling of this technique remains a challenge. Thus, this study aims to propose a fully predictive model for intermittent drying in conical spouted bed dryers. A single-phase model is used to account for the heat and mass transfer on the soybean surface and their inside, and the predictions are compared with the experimental results. The proposed model provides physically consistent results and is coherent with the experimental data, mainly for drying under moderate air temperatures with moderate and long resting periods. As the average moisture content and the average particle temperature are estimated based on the spatial discretization used in the numerical solution, as well as on the boundary conditions adopted, the internal gradients of moisture and temperature are also estimated by the model, thus providing a physically consistent representation of the internal gradient behavior. Therefore, this study describes the successful application of an accurate model for continuous and intermittent drying. Accordingly, it contributes to obtain optimal drying parameters in order to minimize drying costs and improve product quality.

Influence of refrigerated adsorption dehumidified drying towards the retention of phenolic, flavonoid and antioxidant properties of small cardamom (Elettaria cardamomum): Performance comparison with convection, solar and fluidized bed dryer

Cardamom, known by the botanical name Elettaria cardamomum, is a well-known spice which is increasingly used in the field of cosmetics and industrial applications in the form of dried powders and oil. However, usage of cardamom is limited by its moisture content (around 80% in wet basis) and for effective oil extraction and usage, cardamom needs to be dried to a moisture content of less than 10% (in wet basis) prior to usage. Solar driers are traditionally used for cardamom drying and fluidized bed driers and tray driers are also used for industrial-level large-scale drying. During drying, loss of bioactive like phenolics, flavonoids and antioxidants become inevitable. Under such a scenario, this study explores the performance of low-temperature, low-humidity dryers namely refrigeration adsorption dehumidified dryers (RADD), designed and developed by CSIR-NIIST, for retention of bioactives during drying. To assess and compare the RADD with traditional dryers, experiments were performed in a tray dryer, solar dryer and fluidized bed dryer and the results are compared with RADD. It was found that cardamom dried in RADD retained around 70–75% of total phenolic, flavonoid and anti-oxidant compounds, whereas retention in other conventional drying methods was in the range 35–60% only. Advanced analysis such as SEM, FTIR and GC-MS was also done to evaluate the morphological changes, functional group changes and difference in essential oil composition due to different drying methods. Considering the overall result it has been proved that RADD has several advantages over the conventional dryers (due to low temperature and low humidity inside RADD) and thus can be used for drying cardamom which will promise good quality cardamom with maximum retention or preservation of all the bioactives. Thus, RADD is found to be a promising alternative for fluidized bed dryers and also it performs better than other conventional drying methods.

The physicochemical quality of yellow chrysanthemum flower (Chrysanthemum indicum) brewed drink

Chrysanthemum flowers (Chrysanthemums indicum) are processed into several products such as brewed drinks because they have good health benefits. The production process of commercial chrysanthemum flower brewed drinks still uses a conventional dryer with solar energy, this can reduce the quality of dried chrysanthemum flower both physical and chemical quality. Our objectives were to evaluate the chemical and physical quality of yellow chrysanthemum flower brewed drink by a cabinet dryer (CD). The materials used were fresh yellow chrysanthemum flowers with a moisture content of 83.00% (wb). The experimental design of this study used six treatments, including CD at 40°C, 50°C, 60°C, fresh flowers, and commercial chrysanthemum brewed drinks obtained from the market with storage of 1 day and 2 weeks. The parameters analyzed were moisture content, water activity, shrinkage, colour, antioxidant activity, total phenol, and sensory analysis. After evaluation demonstrated that the drying method using a CD at 60°C was the most optimal drying, with an average moisture content value of 15.18% (wb), the value of water activity is 0.25, shrinkage value for length and width, respectively 18.17% and 14.89%, the antioxidant activity of 87.67%, total phenol of 15.17%, and sensory evaluation results with the best formulation obtained in the sample with drying CD at 60°C.

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.