Spray drying is a well-established manufacturing technique which can be used to formulate amorphous solid dispersions (ASDs) which is an effective strategy to deliver poorly water soluble drugs ...(PWSDs). However, the inherently complex nature of the spray drying process coupled with specific characteristics of ASDs makes it an interesting area to explore. Numerous diverse factors interact in an inter-dependent manner to determine the final product properties. This review discusses the basic background of ASDs, various formulation and process variables influencing the critical quality attributes (CQAs) of the ASDs and aspects of downstream processing. Also various aspects of spray drying such as instrumentation, thermodynamics, drying kinetics, particle formation process and scale-up challenges are included. Recent advances in the spray-based drying techniques are mentioned along with some future avenues where major research thrust is needed.
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•Solar dryer with wind powered fan and glycerine as thermal storage was investigated with saline and blanched treated potato slice.•Shrinkage phenomenon was introduced in determining the ...thermos-physical properties of pre-treated potato.•The volume of samples treated by saline immersion was higher by 6% than non-treated samples.•Thermal effusivity and other thermos-physical parameters were presented as a function of moisture content or volume change.
The purpose of this study was to investigate the effect of adding pre-treatment to solar dried sweet potato chips. The tested pre-treatments were blanching using hot water and saline immersion. Indeed, the potato chips were dried using a convective indirect solar dryer, equipped with a wind generator and glycerine as thermal storage. The system was built locally at the University of Agriculture in Umuahia, Abia State, Nigeria. The obtained experimental drying curves and kinetics were directly affected by the weather conditions, as the drying rate increased with the increase of the radiation and the ambient temperature and decreased with their decrease. Drying of the various pre-treated potato slices took 8–14 h to attain equilibrium moisture level under the variable external drying conditions. The drying curves were fitted to semi-empirical models. The results showed that the two-term exponential model was the best model that fitted the experimental data. Shrinkage was a vital phenomenon observed during the drying process, as the volume of the chips was reduced by 50%. The volume of samples treated by saline immersion was higher by 6% than non-treated samples. Shrinkage phenomenon was then introduced to determine the thermos-physical properties of sweet potato chips, with particular attention to the particle density, the bulk density, shape analysis, specific heat capacity, thermal diffusivity, and thermal effusivity. The particle and bulk density peaked at 1.41–1.44 g/cm3, and 1.52–1.53 g/cm3 respectively for all treatments. The thermal effusivity ranged from 17.6 to 7.93 W.S1/2.m−2.K−1 while the specific heat capacity ranged from 1028 to 2288 J/kg °C. All the thermo-physical properties were presented as a function of the volume or moisture content variation with a high degree of association. The results demonstrated the importance of shrinkage and its direct effect on the determination of the thermos-physical properties of the studied product for both pre-treated and untreated samples.
Influences of drying air temperature, radiation distance, slice thickness and wavelength on drying time, energy consumption, and product quality (color, shrinkage, rehydration and total saponin) were ...investigated in combined infrared and hot air impingement drying (IR-HAD). Results illustrated that temperature and slice thickness were the most distinct factors affecting the drying time. Moisture effective diffusivity decreased with decrease in moisture content, and was influenced by drying conditions. Radiation distance significantly affected rehydration capability, while temperature and thickness affected almost all quality attributes. Drying caused an insignificant reduction in total saponin, and similar volume shrinkage results were found due to constant amount of water removed. Thickness of 6 mm maintained better quality than thicker bodies, coincidence with the calculated infrared penetration depth (5.30–7.25 mm). IR-HAD at wavelength of 2–4 μm increased drying rate slightly than that at 0.25–2 μm, while insignificant difference in product quality. Particularly, IR-HAD samples showed smaller thickness shrinkage and larger area shrinkage, as opposed to hot air drying. IR-HAD offered many advantages in minimizing the drying time and better preserving the quality over hot air drying under the same conditions, but markedly enhanced the specific energy consumption. This study proves that IR-HAD is a suitable technique that retains quality characteristics of vegetables.
•Moisture effective diffusivity was studied considering shrinkage effect.•Wavelength demonstrated an insignificant effect on drying time and quality.•IR-HAD shortened drying time and better preserved sponge gourd quality.•IR-HAD samples showed smaller thickness shrinkage, while larger area shrinkage.•Slice thickness near to IR penetration depth helped maintain better quality.
To obtain the predominant drying speed period of sliced persimmon during hot air drying, the aim of this study was to evaluate drying kinetics, effective diffusivity and its activation energy under ...different drying temperatures (50, 60 and 70 °C). Besides, the bioactive compounds, antioxidant activity and microstructure after drying were also compared with those of freeze-dried persimmon. Results showed that water loss of persimmon slices during hot air drying followed the second-order kinetic model. The effective diffusivities of sliced persimmon at 50, 60 and 70 °C were 6.45 × 10−7, 7.48 × 10−7, and 9.08 × 10−7 m2 s−1, respectively. No significant (p > 0.05) differences in the drying rate at different drying temperatures (50, 60 and 70 °C) after 180 min of drying were observed. Contrarily, increase of hot air drying temperature resulted in a significant decreases in majority of bioactive compounds. While, considering the high price and time consumption of freeze-drying technique, as well as the fact that higher drying temperatures did not further affect the drying rate after a certain drying time, controlling the temperature gradient during hot air drying processing might be useful in minimizing energy input and improving the retention of bioactive compounds during the processing of dried persimmon in food industry.
•Temperatures showed less significant effect on drying rate after certain drying time.•Increase in drying temperature resulted in decreases of most of bioactive compounds.•Freeze-drying exerted positive effect on bioactive compounds and microstructure.•Controlling drying temperature gradient was very effective for dried persimmon. Original research article.
In this work, a passive, mixed-type solar dryer was designed, constructed and evaluated. The solar dryer evaluated has the option of working as an indirect-direct dryer (mixed solar dryer, MSD) or in ...indirect solar dryer mode (ISD), since the drying chamber has a mobile opaque cover. The energy efficiency, drying efficiency, and the drying kinetics were the evaluation criteria for thermal performance of the dryer during the drying of tomato. During the experiments, the temperature inside the drying chamber at solar noon was in a range of 65˚C-70 °C operating in MSD and 55˚C-60 °C in ISD. The results showed that drying the tomato in ISD (26 h) took longer than the MSD (17 h). The efficiency of the solar collector was between 52.30% and 55.45%. The overall dryer efficiency in MSD and ISD mode were between 10.66% and 8.80% respectively, while the drying efficiency was in a range of 5.47% and 4.48%, respectively. The experimental data of the tomato drying kinetics were adjusted to five different mathematical models; the Modified Henderson & Pabis model showed the better fit with an r2 of 0.9888 and 0.9996 and an RMSE of 0.0027 and 0.008 for the MSD and ISD respectively.
•The passive, mixed-type solar dryer was designed, constructed and evaluated.•The solar collector and drying efficiencies were experimentally obtained.•The drying kinetics of tomato were experimentally determined.•The best fit to kinetic was done by the Modified Henderson and Pabis model.
Moringa leaves (Moringa oleifera) are a "Superfood" food ingredient rich in protein, phenolics, amino acids, and unsaturated fatty acids that benefit human health. Consumption in fresh form is ...prevalent, but the last decade has been plentiful in dry preparations. Pulse Electric Field (PEF) is one of the important preliminary treatments in drying vegetables and fruits. Electroporation on Moringa leaves is applied to determine the effectiveness and efficiency of drying on the leaves. The study aimed to determine the effect of PEF treatment before drying on the kinetics of drying and the microstructure of Moringa leaves. PEF treatment is carried out at voltages of 1000V, 1500V, 2000V and without PEF as a control. The treatment during drying was observed at the level of moisture content and effective diffusivity on each of the PEF and control treatments. Experimental data were entered into seven mathematical models and evaluated through Lewis, Page, Modified Page, Logarithmic, Two-term, Wang and Singh, and Simple exponential models. The results of the evaluation of the drying model were selected as the best drying mathematical model on the Logarithmic model. The highest diffusivity effective value at PEF with a voltage of 2000V of 3.25 × 10−9 m2/s. In the microstructure changes of Moringa leaves, the preliminary PEF treatment was conducted using the scanning electron microscope (SEM) test. Moringa leaves with pretreatment PEF 2000V color analysis was lightness (L*), redness (a*), yellowness (b*), and ∆E values of 41.74±0.34a, -8.64±0.28c, 20.16±0.94a, 7.08±0.53c. The results of moringa leaves extract with pretreatment PEF 2000V were total phenols and IC50 values of 55.60±1.24d mg GAE/gram and 76.79±0.77a ppm. Implementing PEF preliminary treatment on drying is expected to accelerate the drying process and maintain a decrease in the quality of the final product of Moringa leaves.
•CU-IRD displayed marked enhancements in heat and moisture transport efficiency.•CU and IR increased myosin denaturation and water fluidity.•CU destroyed the fiber integrity and improved the ...texture.•CU-IRD showed the shortest drying time and higher drying uniformity.
Drying, as a critical step in the production of air-dried beef, has a direct impact on the quality of the final product. Innovatively, a composite system incorporating contact ultrasound (CU) and infrared radiation (IR) as auxiliary measures within a hot air drying (HAD) framework was built in this research, and the effects of these techniques on the drying kinetics, protein denaturation, and moisture transformation of air-dried beef were investigated. In comparison to HAD treatment, the integrated CU and IR (CU-IRD) system displayed marked enhancements in heat and moisture transport efficiency, thereby saving 36.84% of time expenditure and contributing favorably to the improved moisture distribution of the end-product. This was mainly ascribed to the denaturation of myosin induced by IR thermal effect and the micro-channel produced by CU sponge effect, thus increasing T2 relaxation time and the proportion of free water. In conclusion, the composite system solved the problem of surface hardening and reduces hardness and chewiness of air-dried beef by 40.42% and 45.25% respectively, but inevitably increased the energy burden by 41.60%.
Fresh leaves used for culinary and medicinal purposes are highly perishable by nature. Quite often, post-harvest losses occur and there is noticeable deterioration in quality due to moisture enhanced ...enzymatic and microbial activity, climate changes, improper handling, delayed transportation, improper storage and delay in sales. To preserve leaves for a longer duration and to ensure their easy availability for off-seasonal use without considerable deterioration in nutrient levels, an appropriate drying method is essential for the removal of moisture to a safe activity value. Low moisture content of products made from dried leaves helps improve their shelf life, reduce shipping weight and minimize the transportation cost. A controlled heat treatment process is employed for the removal of the required water content from the leaves. An optimized drying process is necessary not only for the preservation of leaves to achieve concentrated nutrients, but also to minimize the energy consumption to make it eco-friendly. The optimized process of drying leaves is to ensure desired final moisture content retaining the original high level of nutrients as that of fresh leaves. The selection parameters for the drying technique of individual leaves is based on local climatic conditions, drying air temperature, relative humidity of air, drying time, size, shape and age of leaves, etc. The present review work explores the influencing parameters on water loss in leaves, drying kinetics, various available drying methods, range of operating conditions, and the effect of different drying methods on nutritional properties. This research paper highlights the best fit thin-layer models employed for drying of different leaves. The major challenges faced by the drying industry such as energy conservation while drying, emission reduction and hot spots for possible future research are also reviewed in this paper.
•Natural drying methods have lesser control over rate of drying and the quality of dried product. Mechanical dryers and active dryers have higher rate of drying which can also be controlled to meet quality requirements/standards.•In case of leaf drying, as the major drying time involves the removal of internal moisture, falling rate is the predominant drying mechanism involved.•The energy required for drying increases with humidity in the air. In natural drying, dry climate results in faster drying and less energy for drying process. In humid locations, increase in temperature of air is required to decrease the relative humidity.•Higher inlet dry bulb temperature, lesser relative humidity and optimum air flow rate results in higher drying rate. Operating conditions such as moderate air temperature (40-60 °C), lower relative humidity, and higher air velocity play vital role in ensuring an efficient drying process. At these optimum conditions, minimum loss of nutrients, desirable final moisture content, and maximum possible exergetic efficiency are observed.•Various mathematical models have been proposed by various researchers for drying of leaves. The Page, and Midilli and Kucuk models give the best fit in describing the drying behavior of many leaves.
An innovative and compact mixed-mode vertical solar dryer (MVSD) with a circular solar collector is developed and tested for ginger slices drying under partial and fully loaded conditions. Ginger ...slices samples of 4, 5 and 6 mm thick were used for natural convective drying in MVSD under partially loaded condition. The thickness of the ginger slices was observed to affect the performance of the MVSD. The drying rate and thermal efficiency were observed to be highest for 5 mm thick ginger slices sample under partially loaded condition. The MVSD was further tested with full loading capacity for 5 mm thick ginger slices drying under natural and forced convection modes (NC and FC modes). The drying behavior of ginger slices was well described by Midilli-Kucuk model. Heat transfer coefficients and efficiency (thermal and exergy) were observed to be higher under forced convection mode. Embodied energy and energy payback time were observed as 554.44 and 585.53 kWh; and 2.85 and 2.99 years under NC and FC modes, respectively. The values of annualized capital cost and payback period were observed as INR 389.41 and 408.17; and 1.85 and 6.86 years under NC and FC modes, respectively. The quality of the ginger dried under FC mode was found comparatively better than that of under NC mode.
•A mixed-mode vertical solar dryer was tested for ginger drying.•Drying rate was found better in forced convection mode.•Thermal and exergy efficiency were found better in forced convection mode.•Forced convection mode was found more suitable.
Performances of a mixed mode forced convection solar dryer integrated with paraffin wax based thermal energy storage have been studied for drying the sliced black turmeric (curcuma caesia). Thin ...layer drying kinetics of sliced black turmeric dried in a solar dryer has been compared with the open sun drying. Two 200 g samples of black turmeric were chosen and one was placed in the solar dryer and another was placed in the open sun. The samples were dried from initial moisture content of 73.4% (w.b) to 8.5% (w.b) in 18.5 hr in the solar dryer and the sample took 46.5 hr in open sun drying. Ten thin layer drying kinetic models were fitted with experimental data and Two term model and Page model were found to be best suited for predicting the drying kinetics of sliced black turmeric dried in the solar dryer and in open sun, respectively. The overall solar air heater efficiency and the overall solar dryer efficiency were found to be 25.6% and 12.0%, respectively. Quality analyses of fresh, solar dried and open sun-dried samples were also carried out in terms of colour, anti-oxidant activity, and flavonoids.
•A mixed mode forced convection solar dryer with thermal storage has been developed.•Drying kinetics of black turmeric has been investigated.•Over all drying efficiency of the system was 12%.•Developed solar dryer saves 60% of drying time compared to open sun drying.•Quality analyses of samples dried in solar dryer and open sun drying are presented.
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