Convectively Dried Research Articles

Effect of Pulsed Electric Field Technology on the Composition and Bioactive Compounds of Black Soldier Fly Larvae Dried with Convective and Infrared-Convective Methods.

In recent years, an increasing interest has been shown in alternative food sources. Many studies are focused on the use of insects. The aim of this study was to investigate the changes in the chemical and thermal properties of black soldier fly larvae influenced by the pulsed electric field (PEF) and convective (CD) or infrared-convective (IR-CD) drying techniques. Examinations of the basic chemical composition, properties of extracted fat (fatty acid composition, acid and peroxide values, and oxidative stability), total polyphenol content, antioxidant activity, allergen content, and thermogravimetric analysis (TGA) were performed. Generally, the results showed that dried black soldier fly larvae are a good source of protein and fat, up to 33% and 44%, respectively. The fat extracted from the dried insects consisted mainly of saturated fatty acids (above 75%), in particular lauric acid (C12:0). A good oxidative stability of the fat was also observed, especially from samples dried with the IR-CD method. The convective drying technique allowed for better preservation of protein content compared to samples dried with the IR-CD method. Nevertheless, samples treated with PEF were characterized by significantly lower protein content. The samples after PEF pretreatment, with an intensity of 20 and 40 kJ/kg and dried with the IR-CD method, were represented by a significantly higher total polyphenol content and antioxidant activity. Furthermore, in most cases, the convectively dried samples were characterized by a higher allergen content, both crustaceans and mollusks. Taking into account all of the investigated properties, it can be stated that the samples without treatment and those that were PEF-treated with an intensity of 40 kJ/kg and dried with the infrared-convective method (IR-CD) were the most rewarding from the nutritional point of view.

Ultrasound-assisted ethanolic extraction of punicalagin from pomegranate by-products influenced by cultivar, pre-drying treatment, particle size, and temperature

The novelty of this research is to describe the effect of different ultrasound-assisted extraction operating conditions on the punicalagin (∑Pn) and total phenolic content (TPC) yield of pomegranate peel of two cultivars: Wonderful (W) and Mollar de Elche (ME). Besides cultivar, drying method (convective and freeze drying), particle size (<56 and 56–101 μm), extraction temperature (25 and 45 °C) and time (0–60 min) were categorical variables included in the experimental design to optimize the process using a polynomial regression model. Both ∑Pn and TPC extraction was higher in freeze-dried than in convectively dried samples. Although the interaction of the above-mentioned variables must be considered, the type of drying influenced the extraction of ∑Pn between cultivars, being higher in ME than W when the material was freeze-dried. For the smallest particle size and higher temperature (45 °C), the extracted ∑Pn and TPC was higher than samples with higher particle size and lower extraction temperature (25 °C).

Functional, conformational, topographical, and antioxidative properties of convectively- and freeze-dried sunflower protein and hydrolysate: a comparative investigation

This study focused on the influence of convection (at 40 °C and 50 °C) and freeze drying on functionality, structural properties and antioxidant potential of sunflower meal protein (SPm) and hydrolysate (SPHm). Likened to the respective convectively-dried isolates, lyophilized SPm and SPHm showed higher dispersibility and water binding efficacy, but lower oil binding efficacy (buttressed by surface hydrophobicity results) (p < 0.05). The alterations in sulfhydryl clusters and disulfide bridges due to convection drying (under varied temperatures) implied limited unfolding of SPm and SPHm structure and reduction in intermolecular interactions. Moreover, fluorescent intensity and deconvoluted Fourier transform infrared (FTIR) spectroscopy illustrated that convectively-dried (CD) preparations, considerably CDSPHm, possessed more flexible/movable secondary structures over freeze-dried isolates. Topographical study indicated that dehydrated SPHm-s had irregular small particles with partly destroyed/splitted micropores, suggesting disruption in the noncovalent bonds between SPHm-s molecules. Furthermore, isolates from the freeze drying process, notably lyophilized hydrolysate, showed higher antioxidative (DPPH scavenging, ABTS and reducing power) potential over the convectively-dried samples, supported by the analysis of amino acids composition. The current investigation could help the pharmacological and/or food industry to develop new therapeutic product and/or functional food from lyophilized isolates.

Stability of Fructooligosaccharides in Convectively Dried Fruits After Initial Osmoconcentration

The aim of this study was to determine the effect of temperature and time of convective drying on the content of fructooligosaccharides (FOS) in apples, plums and strawberries to which FOS had been introduced by osmoconcentration. The share of oligosaccharides in total sugars was analyzed. In apple tissue, fructooligosaccharides were stable in the temperature range 40–80 °C during drying for up to 8 h. Convective drying of osmotically dehydrated strawberries caused FOS losses; the FOS retention after 8 h at 80 °C was 40%. In the case of plums, 40% retention was recorded after just two hours at 80 °C. Therefore, in the case of some fruits, obtaining a satisfactory level of fructooligosaccharides in the dried material with the assumed level of dry substance requires the determination of appropriate process parameters.

Convective drying of unripe plantain: a comparative response surface methodology and genetic algorithm optimization study, certainty and sensitivity analysis

The requirement for reduction of post-harvest losses increased production, and cost-effectiveness of foods are driving continuous food process investigations. In this study, Response Surface Methodology (RSM) was utilized to understand, model, and optimize the effect of selected process factors on the moisture content (MC) of convectively dried unripe plantain fruit. For technical accuracies, Multi Gene Genetic Programming (MGGP) was also used to model the process and both MGGP and RSM models were statistically compared. Furthermore, Monte Carlo Simulation (MCS) was used to conduct sensitivity analysis of unripe plantain’s MC to each selected process factor. Results showed that increased sample thickness increased the MC while increased drying temperature and drying time decreased the MC of unripe plantain. RSM model had Chi-square, MBE, t-value, RMSE and R2 values of 15.2131, 0.7531, 7.6170, 0.9193 and 0.9674, respectively; while MGGP model had 3.0415, 0.2563, 2.6871, 0.4111 and 0.9956, respectively. Sensitivity analysis showed that sample thickness, drying temperature and drying time had +89.5 %, -10.2 % and -0.3 % contribution to the variances of MC, respectively. These results are useful in unripe plantain drying process prediction, optimization, and product standardization.

(Near‐) Infrared Drying of Lithium‐Ion Battery Electrodes: Influence of Energy Input on Process Speed and Electrode Adhesion

The drying of electrodes represents a critical process step in the production of lithium‐ion batteries. In this process step, unfavorably adjusted drying conditions can result in deteriorated electrode properties. Furthermore, the process speed is restricted by limited heat and mass transfer in purely convective drying. To counteract those effects, energy input by near‐infrared (NIR) radiation is a promising approach. Herein, analytical considerations are carried out to demonstrate the suitability of infrared radiation with regard to achievable electrode temperatures and drying rates. In an experimental approach, aqueous processed graphite anodes are dried with an NIR module, varying the power and the amount of convection for different experiments. The temperature profiles of the electrodes and the drying rates are measured and analyzed, and the electrodes are subsequently characterized using adhesion measurements. The results obtained show that energy input by NIR radiation during the drying of electrodes can lead to an increased drying speed, electrode temperature during drying, and adhesion force of the dry electrode. These findings indicate that the binder distribution during NIR drying is advantageous in terms of electrode adhesion, compared with convectively dried electrodes produced at comparable drying rates, positioning the process promisingly with regard to high throughput rates.

Semi-Empirical Mathematical Modeling, Energy and Exergy Analysis, and Textural Characteristics of Convectively Dried Plantain Banana Slices.

Thin-layer convective drying of plantain banana was performed at four different temperatures from 50 to 80 °C, with slice thicknesses from 2 to 8 mm. The drying curves, fitted to seven different semi-empirical mathematical models, were successfully used to fit experimental data ( 0.72–0.99). The diffusion approach had better applicability in envisaging the moisture ratio at any time during the drying process, with the maximum correlation value ( 0.99) and minimum value of (2 and RMSE (5.0 . The , , and values were calculated on the basis of the experimental data, and overall ranged from to m2 s−1, to 2.20 m s−1 and 13.70 to 18.23 kJ mol−1, respectively. The process energy consumption varied from 23.3 to 121.4 kWh kg−1. The correlation study showed that the drying temperature had a close correlation with value and sample hardness. A significant (p < 0.05) increase in hardness of dried plantain banana was observed at 80 °C compared to the other temperatures. Additionally, the sample hardness and process energy consumption were more positively correlated with the thickness of the samples.

The Modelling of Convective Drying Variables' Effects on the Functional Properties of Sliced Sweet Potatoes.

Drying is a commonly used technology that provides a long post-harvest storage time for produce such as sweet potatoes. Convective drying (CD) is a method that, when conditions are optimized, provides produce with a better appearance and improved textural properties. In this study, changes in water activity (aw), moisture content (MC), rehydration capacity (Rc), shrinkage (Sb) and color attributes were modelled for the optimization of drying factors (temperature, thickness and time) using response surface methodology (RSM). The total phenol content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC) and antioxidant activity of CD samples (63.79 °C, 4.78 h, 3 mm) were investigated as functional aspects and compared with results for FD samples (−45 °C, one term). Optimum convective drying conditions caused an increase in general antioxidant properties, such as total phenol (TPC), total anthocyanin (TAC), DPPH and CUPRAC. The TPC was 190.94 mgGAE/100 g, the DPPH scavenging activity was 12.05%, the TAC was 11.37 mg/100 g, and the CUPRAC was 0.469 mmolTR/g in convectively dried samples under optimum conditions. Although improved appearance and textural properties are obtained by freeze drying, it is possible to produce sweet potatoes with good appearance and functional properties by optimizing the variables of the convective drying process.

In‐depth investigation of incremental layer build‐up from dried deposited droplets

AbstractThis study presents an approach to closely investigate the process of incremental layer build‐up from convectively dried sessile droplets. In a droplet‐by‐droplet manner, three layers of sodium benzoate solution droplets are consecutively applied on a glass substrate and successively dried in a laboratory‐scale drying chamber. The morphology of the simplified layer structure that incrementally forms from the individual deposits is analyzed via white‐light interferometry, after every addition of a new droplet. Furthermore, complementary X‐ray micro‐tomography measurements of the deposits were carried out to monitor inner structure development. Recurring steps and phenomena throughout the experimental build‐up process were identified and could be characterized through these methods. Moreover, these phenomena could be linked to specific combinations of droplet positioning and drying conditions. Finally, the overall influence of convective drying parameters as well as droplet properties on the layer formation process was investigated with regard to morphology and porosity.

Convective drying of cambuci, a native fruit from the Brazilian Atlantic Forest: Effect of pretreatments with ethanol and freezing

AbstractCambuci is a native fruit from the Brazilian Atlantic Forest, with high sensorial and nutritional potential. However, this fruit is very perishable, which impairs its exploration and study. This work reported the convective drying of cambuci for the first time, as an approach to achieve stability. Moreover, it also evaluated for the first time the combination of ethanol and freezing pretreatments to convective drying. Pretreatments were performed by immersion of fresh and previously frozen and thawed cambuci slices in ethanol (5 min at 25°C). Pretreated samples were then convectively dried (50°C, 1 m/s). Drying time was reduced up to ~36% by combining the pretreatments, which was associated with the reduction in the external resistance to mass transfer, once the convective mass transfer coefficient increased up to 94%. In contrast, pretreatments that include freezing had a greater influence on reducing the internal resistance to mass transfer, increasing the effective diffusive coefficient. In addition, the thermal surface profile evidenced the temperature increased faster and reached high levels in pretreatments that include freezing, which could be correlated to their higher drying rates and structure modifications. The obtained results corroborate the modifications produced by freezing and the effects of ethanol on the surface of samples significantly accelerate the convective drying of cambuci.Practical ApplicationsThe present investigation shows that convective drying is a feasible alternative for cambuci processing. Further, being this fruit very perishable, with short harvest and production far from the markets, freezing is a common practice to preserve them in the farms. Consequently, the impact of this unit operation was also evaluated. In addition, the proposed pretreatments (freezing and ethanol) have great application potential to improve the conventional convective drying of fruits. It has been shown that the combination of pretreatments accelerated drying, reducing the processing time by 36%.

Research on Determination of Water Diffusion Coefficient in Single Particles of Wood Biomass Dried Using Convective Drying Method

Determination of the mass diffusion coefficient for dried, inhomogeneous material is difficult as it depends on the drying agent temperature and the moisture content and physical structure of the material. The paper presents a method for efficient determination of the water diffusion coefficient for wood solid cuboids dried using convective drying methods. In this work, the authors define a theoretical dependence of the Fourier number on reduced water content in a convectively dried cuboidal solid, based on a simplified theoretical solution of the diffusion equation for such a body. The material for drying included shoots of common osier, robinia (false acacia), multiflora rose, and energy poplar, dried at temperatures of 40, 50, 60, 70, and 80 °C, in free convection. The obtained results differ from the theoretically anticipated changes of the coefficient.

Effect of different blanching Pre-tretment and drying methods on quality of Pea pods powder

The aim of this study is to utilize the vegetable by-product for value addition in food. In this study, pea pod powder is developed using different pre-treatments of blanching and drying methods. Pea pods were subjected to different pre-treatments such as citric acid blanching (CB), potassium metabisulphite dipping (KMS) and hot water blanching (HB). A control or untreated sample (UT) was kept for comparing with treated sample. Pre-treated samples were dried using different drying techniques i.e. convective tray drying (55°C, 65°C and 75 °C), sun drying and solar drying. The dried samples were evaluated for its moisture content, drying time, crude fibre content, lignin content and colour attributes. The result of the study showed significant effect (p< 0.005) of blanching and dying on the quality of pea pods. The lignin content was minimum for control (UT) sample and crude fibre content was higher for UT samples convectively dried at 75 °C whereas maximum rehydration ratio was observed in convectively dried KMS pre-treated samples at 75 °C. Overall, the UT samples followed by 75 °C convective drying was found to be the best combination for retaining quality attributes of pea pods.

Ethanol pre-treatment to ultrasound-assisted convective drying of apple

For the first time, the ethanol as pre-treatment to the ultrasound-assisted convective drying of food was evaluated. Pre-treatments were performed by immersion of apple slices in ethanol (0–30 min). Pre-treated samples were convectively dried (50 °C, 1 m s−1), without/with ultrasound (21.77 kHz, 20.5 kW/m3). As results, if both technologies were considered, conventional drying time reduction reached 70 ± 2%. From drying kinetics modelling, it was identified that ethanol pre-treatments mainly reduced the external resistance to mass transfer, while ultrasound had a greater influence on the internal one. In dried samples, as the ethanol pre-treatment time increased, the shrinkage decreased, and their rehydration capacity was greater. After rehydration, samples showed a decrease of >85% in viscoelastic characteristics. The antioxidant capacity and total phenolic content were better retained with ultrasound application. The obtained results corroborate that the proposed technologies are complementary significantly accelerating the drying without negative effects on physical properties.

Influence of coating pretreatment with carboxymethyl cellulose in an electrohydrodynamic system on convective drying of banana slices

AbstractFor the first time, a carboxymethyl cellulose (CMC) coating pretreatment was used in an electrohydrodynamic (EHD) system to produce convectively dried banana slices with improved quality and nutritional attributes. To this end, the impacts of the sample to CMC solution ratio (S:CSR) parameter at two levels of 1:1 and 1:2 and the EHD voltage parameter at four levels of 0, 16, 18, and 20 kV were investigated. The results showed that an increase in the EHD voltage from 0 to 20 kV significantly increased the water absorption capacity (WAC) (117.86%) and the total phenolic content (TPC) (20.83%) of the dried banana slices and significantly reduced their total energy consumption (SETotal) (30.03%), the drying time (27.9%), the shrinkage (74.52%), the shear stress (SS) (76.48%), and the total color difference (ΔE) (78.74%). Moreover, an increase in the S:CSR from 1:1 to 1:2 significantly reduced the shrinkage (20.62%), the SS (21.93%), and ΔE (33.02%) of the dried banana slices and significantly increased their WAC (24.40%) and TPC (16.88%).Practical applicationsAccording to the results obtained in this study, carboxymethyl cellulose coating pretreatment in an EHD system can be introduced as an innovative and practical pretreatment technique for production of convectively dried products. This approach improves both the quality indexes and nutritional attributes while increasing the performance of the convective drying process.

Intelligent modeling and detailed analysis of drying, hydration, thermal, and spectral characteristics for convective drying of chicken breast slices

AbstractChicken breast slices were convectively dried at three different temperatures (60, 70, and 80°C). Drying characteristics were analyzed and the predictive capabilities of artificial neural network (ANN) and semiempirical models were exploited. Low complexity ANN model with 10 hidden layer neurons was developed which provided improved results over eight tested semiempirical models. Influence of drying temperature on water activity, rehydration, shrinkage, color, thermal, and spectroscopic properties of the dried product was investigated. Samples dried at 70°C displayed lower moisture content (7.13% w.b.), water activity (aw = 0.45) and color change; while, exhibiting better rehydration potential. Effect of pH on hydration showed that alkaline pH (12.0) facilitated the hydration rate in the samples. Shrinkage in dried samples varied within 20–40% and increased with increase in drying temperature. Thermograms of the dried samples revealed a shift in glass transition temperature from 93° to 140° with an increase in drying temperature, indicating a change in protein structure, which was later confirmed by Fourier transform infrared spectroscopy.Practical ApplicationData on drying, thermal, and hydration characteristics for chicken slices generated in this study could aid the meat industry in developing faster and more convenient processes. Moreover, the low complexity model engineered in this study will facilitate the development of robust control systems for industrial applications. Salient findings of the study such as: (a) optimum time and temperature combination (i.e., 70°C/5 hr) for drying of chicken breast slices; (b) increased rehydration rate with increase in pH from 3.0 to 12.0; and (c) thermal and spectral characteristics have been reported for dried chicken slices which provides vital information on drying process for improvement in the end product obtained.

The effect method of preservation on selected bioactive compounds and antioxidant activity in blackthorn fruits (Prunus spinosa L.)

The effect of freezing (M), freeze drying (L) and convection drying (S) of blackthorn fruits on the content of selected bioactive compounds and antioxidant properties compared to the control sample – fresh fruit (PK), was tested. Changes in the content of flavonoids, anthocyanins, pectins, general acidity and the ability to reduce the DPPPH radical, were determined. The obtained results showed that the freeze-dried fruits had the highest content of anthocyanins and flavonoids, respectively 0.07 and 0.17%. Pectin contents in freeze-dried and convectively dried fruits were similar at the level of 1.66 and 1.64% as well as for acidity respectively 0.076 and 0.071 g·100 g–1 infusion. Frozen fruits did not differ significantly compared to the control in terms of the content of anthocyanins, flavonoids, pectin and acidity. The highest scavenging capacity of free radical DPPH was characterized by the infusion obtained from fresh fruits.

Convective and microwave drying of onion slices regarding texture attributes

The textural characteristics of onion slices (Allium cepa L.) of 3- and 7-mm thicknesses undergoing convective drying (50, 60, and 70°C) and microwave drying (68, 204, and 340 W real effective power levels) techniques with or without pre-treatment were evaluated. Pre-treatment consisted of dipping into brine solution (8% NaCl). Texture profile analysis at 25% compression was applied and hardness, chewiness, springiness and gumminess values of onions were recorded. As the temperature (convective) or real effective power level (microwave) increased, the hardness and chewiness levels of dried onion slices were enhanced. The values of these parameters were higher in response to microwave application compared to convective drying. Pre-treatment had an additive effect on hardness and chewiness in convectively dried samples. Maximum springiness was observed in response to convective drying. Dipping in brine solution generally caused no significant changes among slices of the same thickness (P &amp;lt; 0.05). With respect to gumminess, the results were quite similar to those for hardness and chewiness, i.e., markedly higher in microwave-dried onions.

Improvement of Mass Transfer by Freezing Pre-treatment and Ultrasound Application on the Convective Drying of Beetroot (Beta vulgaris L.)

The effects of freezing pre-treatment and ultrasound application during drying on microstructure, drying curves, and bioactive compounds of beetroot have been evaluated. Raw and previously frozen (at − 20 °C) beetroots were convectively dried (40 °C and 1 m/s) with and without ultrasound application using two acoustic densities (16.4 and 26.7 kW/m3), and a diffusional model was proposed to simulate the drying curves. Freezing pre-treatment and ultrasound application caused significant disruptions in the beetroot microstructure and reduced the drying time, enhancing the mass transfer. The external mass transfer coefficient significantly (p < 0.05) increased by 28–49% when ultrasound was applied; moreover, the effective diffusion coefficient significantly (p < 0.05) increased by 60–73% and 204–211%, respectively, due to the ultrasound application on the drying of raw and pre-frozen samples. Freezing caused significant (p < 0.05) increases in betalain and total polyphenol contents and antioxidant activity compared with the raw sample (16–57%), probably due to the release of free forms from the food matrix; meanwhile, drying had the opposite effect (8–54% decrease). Significantly (p < 0.05) higher decreases (32–81%) in bioactive compounds and antioxidant activity were observed when drying was assisted by ultrasound compared with dying without ultrasound. Therefore, freezing pre-treatment and ultrasound application enhanced mass transfer during drying. However, significant changes in quality parameters of the final product were observed.

A technique for lyopreservation of Clostridium ljungdahlii in a biocomposite matrix for CO absorption.

A system capable of biocatalytic conversion of distributed sources of single carbon gases such as carbon monoxide into hydrocarbons can be highly beneficial for developing commercially viable biotechnology applications in alternative energy. Several anaerobic bacterial strains can be used for such conversion. The anaerobic carbon monoxide-fixing bacteria Clostridium ljungdahlii OTA1 is a model CO assimilating microorganism that currently requires cryogenic temperature for storage of the viable strains. If these organisms can be stabilized and concentrated in thin films in advanced porous materials, it will enable development of high gas fraction, biocomposite absorbers with elevated carbon monoxide (CO) mass transfer rate, that require minimal power input and liquid, and demonstrate elevated substrate consumption rate compared to conventional suspended cell bioreactors. We report development of a technique for dry-stabilization of C. ljungdahlii OTA1 on a paper biocomposite. Bacterial samples coated onto paper were desiccated in the presence of trehalose using convective drying and stored at 4°C. Optimal dryness was ~1g H2O per gram of dry weight (gDW). CO uptake directly following biocomposite rehydration steadily increases over time indicating immediate cellular metabolic recovery. A high-resolution Raman microspectroscopic hyperspectral imaging technique was employed to spatially quantify the residual moisture content. We have demonstrated for the first time that convectively dried and stored C. ljungdahlii strains were stabilized in a desiccated state for over 38 days without a loss in CO absorbing reactivity. The Raman hyperspectral imaging technique described here is a non-invasive characterization tool to support development of dry-stabilization techniques for microorganisms on inexpensive porous support materials. The present study successfully extends and implements the principles of dry-stabilization for preservation of strictly anaerobic bacteria as an alternative to lyophilization or spray drying that could enable centralized biocomposite biocatalyst fabrication and decentralized bioprocessing of CO to liquid fuels or chemicals.

Effects of Ultrasound Assistance on Dehydration Processes and Bioactive Component Retention of Osmo‐Dried Sour Cherries

Despite having numerous health benefits, dried sour cherries have proven to be more acceptable to consumers when infused with sugar or other sweeteners to enhance their flavor, which, in turn, leads to serious anthocyanin losses. For this reason, a consideration was made for the application of ultrasound to accelerate solid gain and shorten drying time, thus favoring bioactive component retention. To determine the usefulness of ultrasound as a tool for sour cherry osmotic infusion enhancement, the effect of sonication time on dehydration effectiveness, as well as the stability of bioactive components during osmotic treatment and consecutive convective drying, was investigated. Fruits were osmo-dehydrated using a 60% sucrose solution for 120 min (40 °C), during which, ultrasound of 25 kHz (0.4 W/cm(2) ), was applied for 0, 30, 60, 90, and 120 min, after which, the fruits were convectively dried. In the range of the applied ultrasound energy no significant effect of sonication on mass transfer intensification was observed; moreover, longer acoustic treatment seemed to retard moisture removal during subsequent convective drying, which can be related to the breakdown of the parenchyma cell walls caused by the prolonged ultrasound (US) action. It was concluded that although US assistance could be considered neutral for bioactive component retention, excessive sonication time can lead to some anthocyanin deterioration. According to high-performance liquid chromatography analysis, the particular anthocyanin alterations, both during dehydration and final drying, occurred in a similar way. Sonication time prolongation caused approximately 10% more bioactive compound deterioration, than earlier, shorter trials.