Analysis of the effect of intrinsic sludge properties on sludge drying characteristics from both sludge composition and type scales.

Convective drying is an effective method for reducing the moisture content of the sludge. Fewer studies have discussed the effect of sludge physicochemical properties on drying compared to air parameters. Eleven types of sludge were collected, and ultimate analysis, proximate analysis, and heat value analysis were performed. Meanwhile, the maximum drying rate (umax) of sludge convection drying at 70 °C was determined. The results showed that the cumulative variance contribution of the two extracted principal components (PCs) was 92.5 %. Then, a regression model of umax was developed based on the extracted PCs. The coefficient of determination of this model was 0.788, and the difference was statistically significant, with a negative correlation between umax and PC2. Further, the principal component score plot enabled the traceability of the integrated sludge, and based on this classification results, the drying characteristics of various types of sludge were discussed, and a high correlation (R2 = 0.9590) between the initial moisture content of sludge and umax was found. Mathematical models between sludge physicochemical properties and drying characteristics can be effectively developed from both sludge composition and type scales. This exploration deepened the knowledge of sludge drying and facilitates the prediction of drying rate.

Effect of drying system, layer thickness and drying temperature on the drying parameters, product quality, energy consumption and cost of the marjoram leaves.

The main aim of this work is to study the main factors affecting the quality of the dried product and the energy requirements through optimizing these factors. To achieve that different drying systems (solar, hybrid solar and oven dryings), layers thickness (1, 2 and 3 cm) and drying temperatures (50, 60 and 70 °C) were used. The obtained results indicated that, the accumulated weight loss of marjoram leaves ranged from 73.22 to 76.9%, for all treatments under study. The moisture content of marjoram leaves ranged from 273.39 to 333.17, 258.02 to 333.04 and 269.38 to 324.90% d.b. for hybrid solar, oven and solar drying systems, respectively. The highest value of the drying rate of marjoram leaves (223.73 gwater kg-1 h-1) was obtained when the marjoram dried by oven drying system at 70 °C at 1 cm layer thickness. The highest values of the basil and marjoram oil content (2.91%) was obtained when the marjoram dried under sun drying system. The energy consumption for drying marjoram decreases with increasing drying temperature and layer thickness for hybrid solar and oven drying systems. The cost of dried marjoram dried under hybrid solar drying system was lower than those of oven drying system, the highest cost (13.48 LE kg-1) was obtained at a temperature of 50 °C and a layer thickness of 1 cm.

Effects of thermal and salt water soaking pre-treatment on the physicochemical and nutritional properties of sundried tilapia fish (Oreocromis niloticus) products.

The effects of saltwater soaking (10-30 %, w/v) and thermal (60°C-90 °C) pre-treatment on the physicochemical and nutritional quality of sundried tilapia fish (Oreocromis niloticus) products were assessed. The wet reduction was 14.47 % in the sample treated with a 30 % salt solution at 90 °C, whereas the wet reduction of 21.23 % was observed in the sample without treatment (control). Protein, lipid, and ash content were increased significantly (P < 0.05) with higher pre-treatment salt concentration and temperature, while the moisture content showed the opposite trend. The content of essential and non-essential amino acids in the treated samples ranged from 7149.97 mg/100 g to 8063.42 mg/100 g and 10530.66 mg/100 g to 11365.59 mg/100 g, respectively, whereas the values were 7018.55 mg/100 g and 10400.84 mg/100 g, respectively in the control. The fatty acids composition, particularly ω-3 polyunsaturated fatty acids, was higher in pretreated samples (6.14-7.08 %) compared to the control. Mineral content was found to improve with saltwater and thermal pre-treatment, and the levels of heavy metals, including Ni and Cu, were significantly lower in the sundried tilapia fish. The sample pretreated with 10 % salt solution and 75 °C showed the highest rehydration capacity of 66.63 %. These findings suggest that saltwater and thermal pre-treatment can effectively enhance the physicochemical and nutritional properties of sundried tilapia fish products.

Drying Kinetics of Microwave-Assisted Drying of Leaching Residues from Hydrometallurgy of Zinc.

In the hydrometallurgical process of zinc production, the residue from the leaching stage is an important intermediate product and is treated in a Waelz kiln to recover valuable metals. To ensure optimal results during the Waelz kiln process, it is necessary to pre-treat the residues by drying them first due to their higher water content. This work studies the residue's drying process using microwave technology. The study results indicate that microwave technology better removes the residue's oxygen functional groups and moisture. The dehydration process's effective diffusion coefficient increases as the microwave's heating power, the initial moisture content, and the initial mass increase. The Page model is appropriate for imitating the drying process, and the activation energy of the drying process for the residues is -13.11217 g/W. These results indicate that microwave technology efficiently dries the residues from the leaching stage. Furthermore, this study provides a theoretical basis and experimental data for the industrial application of microwave drying.

Effects of drying methods on bioactive components of Ganoderma lucidum fermented whole wheat in products & in vitro digestive model.

The content of bioactive components is the key to determining the quality of Ganoderma lucidum fermented whole wheat (GW) products, and drying is a necessary link in the initial processing of GW, which will affect the bioactivity and quality of GW. This paper was to assess the effect of hot air drying (AD), freeze drying (FD), vacuum drying (VD) and microwave drying (MVD) on the content of bioactive substances and the characteristics of digestion and absorption of GW. The results showed that FD, VD and AD were beneficial to the retention of unstable substances such as adenosine, polysaccharide and triterpenoid active components in GW, and their contents were 3.84-4.66 times, 2.36-2.83 times and 1.15-1.22 times of MVD, respectively. The bioactive substances in GW were released during digestion. The bioavailability of polysaccharides in the MVD group (419.91 %) was significantly higher than that in the FD, VD and AD groups (68.74 %-78.92 %), but their bioaccessibility (5.66 %) was lower than that in the FD, VD and AD groups (33.41 %-49.69 %). Principal component analysis (PCA) showed that VD is more suitable for GW drying due to the comprehensive performance of 3 aspects in terms of active substance retention, bioavailability and sensory quality.

Convective drying of mango stone for use as biomass.

Mango stone is an interesting biomass by-product with a considerable net calorific value. Mango production has significantly risen in the last few years, meaning that mango waste has increased as well. However, mango stone has a moisture content of about 60% (wet basis) and it is very important to dry the samples for using them in electrical and thermal energy production. In this paper, the main parameters involved in the mass transfer during drying are determined. Drying was carried out in a convective dryer through a set of experiments based on five drying air temperatures (100 °C, 125 °C, 150 °C, 175 °C and 200 °C) and three air velocities (1 m/s, 2 m/s and 3 m/s). Drying times ranged between 2 and 23 h. The drying rate was calculated from the Gaussian model whose values ranged from 1.5·10-6 to 6.3·10-4 s-1. Effective diffusivity was obtained as an overall parameter in the mass diffusion for each test. These values were found between 0.71·10-9 and 13.6·10-9 m2/s. The activation energy was calculated from the Arrhenius law for each test, made at different air velocities. These values were 36.7, 32.2 and 32.1 kJ/mol for 1, 2 and 3 m/s, respectively. This study provides information for future works on design, optimization and numerical simulation models in convective dryers for standard mango stone pieces according to industrial drying conditions.

Cider apple pomace as a source of nutrients: Evaluation of the polyphenolic profile, antioxidant and fiber properties after drying process at different temperatures.

Apple pomace, the by-product of the cider industry, contains a high content of antioxidant compounds and dietary fiber. Drying would allow its preservation for a later use. The aim of this study was to evaluate the effect of the drying temperature on the drying kinetics, antioxidant properties and the fiber characteristics. For this, drying experiments were performed at different temperatures (40-120 °C). The increase in temperature enhanced the drying rate, as was shown by the effective diffusivity and mass transfer coefficient identified by modelling. The influence of temperature was quantified through the activation energy (38.21 kJ/mol). Regarding the retention of antioxidant properties, the best results were found at 80-100 °C while 40-60 °C was the best temperature range for the fiber characteristics. Therefore, 80 °C could be an adequate temperature for drying of cider apple pomace, as it represents a good balance between kinetics, and antioxidant and fiber properties.

Refractance window drying of food and biological materials: Status on mechanisms, diffusion modelling and hybrid drying approach.

Refractance window (RW) dryer has an immense advantage in terms of final product quality (textural and color attributes, nutrient retention), energy consumption, and drying time over other conventional dryers. RW is a thin film drying system and a technologically evolving drying process. RW drying is an energy-efficient (re-circulation of water) short drying process as the drying of food materials occurs due to a combined mode of heat transfer conduction, radiation, and convection (hot air circulates over film). The high-quality dried product is obtained because the product temperature remains below 80 °C. RW dryer application is not only limited to drying food products, but it can also be further used for improving the gelling and emulsion properties, formation of leather and edible film, and can be used for handling high protein products, drying leafy vegetables or marine foods as this process does not change any functional properties. Due to these advantages over other drying techniques, RW drying has gained academic and industrial interest in recent years. The industrial application of this technology at large scale is becoming difficult due because of large surface area requirement for mass production. Researchers are trying to scale-up by combing this technology with others technology (Infrared, ultrasound, solar energy, and osmotic dehydration). RW dryer is now extending from the food sector to other sectors like pharmaceutical, cosmetic, pigment, edible film formation, and encapsulation. Majority of the reviews on RW drying focuses on the product quality aspects. This review paper aims to comprehend the RW drying system more mechanistically to understand better the principles, diffusion models explaining the transfer processes, and emerging novel hybrid drying approaches.

Effect of Electrohydrodynamic (EHD) on Drying Kinetics and Quality Characteristics of Shiitake Mushroom.

The effect of an electrohydrodynamic (EHD) drying system on the drying kinetics, microstructure and nutritional composition of shiitake mushrooms was studied. Shiitake mushroom slices were dried at 0, 18, 22, 26, 30 and 34 kV. The results showed that the drying rate, effective moisture diffusion coefficient and shrinkage of the EHD treatment group were significantly higher than those of the control group. The 34 kV treatment group had the highest drying rate (0.24 g W/g DM × h) and the highest effective moisture diffusion coefficient (1.01 × 10-10 m2/s), which were 6.75 and 7.41 times higher than those of the control group, respectively. The control group had the highest rehydration ratio (7.72) and showed unsatisfactory color performance. The scanning electron microscopy (SEM) results showed that compared with the control group, the surface of samples dried by EHD exhibited different degrees of encrustation, and the area of encrustation increased with increasing voltage. After analysis by Fourier transform infrared (FTIR) spectroscopy, it was found that the samples of both the EHD-treated and control groups had similar absorption peak positions, but the intensity of the absorption peak of the EHD-dried samples was greater. Compared with the control group, the shiitake mushroom slices dried by EHD had a higher protein content and polysaccharide content. The polysaccharide content in 22 kV treatment group was the highest (4.67 g/100 g), and the protein content in 26 kV and 34 kV treatment groups was the highest (17.0 g/100 g). This study provides an experimental and theoretical basis for an in-depth study of the drying kinetics of shiitake mushrooms and provides theoretical guidance and clues for the wider application of EHD drying technology.

Effect of polymer addition on the physical properties of freeze-dried soup solid.

The effect of polymers (gelatin, starch, and maltodextrin) on the physical properties of freeze-dried model soup (sodium chloride, sucrose, and monosodium glutamate) was investigated. The polymers were added to the soup solution at 1 or 3% (w/v), which was then freeze-dried at 25 or 50 °C. Gelatin and maltodextrin prevented crystallization of sodium chloride to a greater extent than starch under freezing. Freeze-drying was conducted above the freeze-concentrated glass transition temperature. Polymer addition prolonged drying time, but prevented structural deformation. Gelatin enhanced the physical strength of the freeze-dried solid more than starch and maltodextrin because of its gel-network. In a dissolution test, 1% gelatin, and 1 and 3% maltodextrin exhibited greater dissolution than the other samples. The drying rate was lower at 50 °C, with minor modifications to the other properties. From these results, it was concluded that 1% gelatin was useful as a physical stabilizer for freeze-dried soup. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13197-021-05161-x.

Impact of acceleration of agricultural and industrial waste conditioning on thermal drying of sewage sludge.

Improving the dewatering performance of sludge is a necessary advancement for collaborative sludge disposal and energy-efficient utilization in power plants. Herein, the effects of temperature changes and the addition of drying accelerators derived from agricultural and industrial waste on the drying characteristics of sewage sludge (SS) were investigated from the perspectives of drying kinetics and micromorphology. According to the results, the drying time for sludge significantly showed a clear downward trend via medium-low temperature (160 °C) thermal drying, which subsequently reduced the energy input substantially. When the drying temperature was 160 °C, the ideal addition proportions of rice husk (RH), sludge ash (SA), and coal ash (CA) comprised 15%. The addition of SA prominently boosted the drying rate constant of the original sludge by 48%. Additionally, SEM images along with the spectral dimension obtained via fractal theory explicitly clearly demonstrated that SS + SA had more loose pore channels than other mixed samples. This provided a convenient approach to ensure the evaporation and migration of moisture and thereby shorten the drying time effectively. Consequently, the addition of sludge ash as a drying accelerator can promote the deep dewatering of sludge.

The kinetics of thin-layer drying and modelling for mango slices and the influence of differing hot-air drying methods on quality.

This study compared the thin-layer drying kinetics of hot-air methods, namely, convective oven drying (OVD), uncontrolled solar drying (UAD) and modified ventilation greenhouse solar drying (MVD). Additionally, the effects of these drying techniques on colour, rehydration characteristics and microstructure of Tommy Atkin mango slices were investigated. The experiments were conducted on mango slices of three different thicknesses: 3 mm, 6 mm and 9 mm. The drying curves generated from the experimental data revealed that the rate of drying increased with thickness and that a thickness of 3 mm is optimal. It was discovered that increased drying rates resulted in a decrease in the drying time. When 3 mm slices were dried using OVD and MVD, the duration of the drying process was reduced by 85% and 80%, respectively, in comparison to the samples dried under UAD conditions. Lemon juice pre-drying treatment had no significant (p < 0.05) effect on the drying rate or duration of the drying process. Non-linear regression analysis was used to optimise the drying coefficients by fitting the moisture ratio data to eleven suitable thin-layer models. The model parameters developed by Midilli et al. performed the best in terms of predicting the experimental moisture ratio (R2 = 0.9810-0.9981, χ 2 = 1.465 × 10-6-3.081 × 10-5 and RMSE = 0.0003-0.0004). Additionally, increasing the slice thickness to 6 mm and 9 mm prolonged the drying times, resulting in significant changes in sample quality, including the total colour (ΔE), rehydration and microstructure. In comparison to OVD- and MVD-dried samples, UAD-dried samples exhibited the greatest colour change and had the highest rehydration ratio values. Also, the surface of the UAD-dried samples developed a more porous structure with distinct cracks. Based on the results, MVD was determined to be a viable alternative method for drying 3 mm mango slices on a large scale.

Kinetics of dehydration and appreciation of the physicochemical properties of osmo-dehydrated plum.

The experiment was conducted to evaluate the dehydration kinetics and quantify its effect on the various physicochemical properties of the osmo-dehydrated plum during storage at an ambient condition. The six treatments with a combination of three different sucrose-sodium chloride concentrations and two peeling conditions were selected in the experiment. Among the treatments, peeled plum dipped into 5% NaCl solution exhibited a faster drying rate. Concerning the rehydration properties of the osmo-dehydrated plum, the whole plum immersed into 500B sucrose solution showed the highest reconstitution behavior and the lowest moisture content (wb). The highest values of water activity of 0.514 and the lowest values of texture 1.79 N-mm2 were investigated in 500B sucrose treated whole plum. The peeled plum obtained the highest lightness (L), redness (a*), and yellowness (b*) compared to the unpeeled plum. Osmo-dehydrated plum with high sugar solution contained more sugar and less total phenolic content nevertheless using only 5% NaCl resulted in less sugar and more total phenolic content after the treatment. The osmo-dehydrated whole plums prepared in 500B sucrose scored the highest overall acceptability (8.0, e.g., like very much) followed by the 500B sucrose with peeled plum envisaged the sensory evaluation analysis. In conclusion, the osmo-dehydrated plum treated in 500B sucrose and unpeeled condition performed better with a view to the overall plum quality, color, and acceptability judged by the expert panelists even after 12 months of storage at room temperature.

Natural Drying of Astringent and Non-Astringent Persimmon "Rojo Brillante". Drying Kinetics and Physico-Chemical Properties.

Persimmon (Diospyros kaki L.f.) crop has markedly increased in Spain, and "Rojo Brillante" persimmon is the main cultivated variety. This astringent cultivar requires de-astringency treatment before commercialization, which may involve an extra cost. Its short commercial season implies handling large volumes of fruits with consequent postharvest losses. Therefore, the development of derived added-value products is of much interest. In this study, astringent and non-astringent "Rojo Brillante" persimmons were dehydrated by following a natural drying method used in Asia. The drying kinetics and physico-chemical properties were analyzed for 81 days. The results indicated subsequent reductions in weight, water content, and water activity throughout the drying process, and the equatorial diameter decreased. All the employed thin-layer mathematical models were suitable for representing the drying characteristics of both products with similar behavior. The effective water diffusivity values were 5.07 × 10-11 m2 s-1 and 6.07 × 10-11 m2 s-1 for astringent and non-astringent persimmon samples, respectively. The drying treatment significantly decreased the soluble tannins content, and the astringent samples obtained similar values to those obtained for the non-astringent samples in 20 days. The external and internal flesh of the astringent fruit remained orange through the drying period, while brown coloration in the non-astringent fruit was observed after 57 drying days. Therefore, prior de-astringency treatment would not be necessary.

[Effect of different drying methods on drying characteristics, appearance and active components of Belamcandae Rhizoma].

In order to explore the effect of different drying methods(drying-in-the-shade, sun-drying, and hot air drying) on appearance characteristics, internal structure and composition of Belamcandae Rhizoma, so as to provide a theoretical basis for screening out suitable drying methods for primary processing. In this study, the Belamcandae Rhizoma's dynamic changes of the moisture content ratio and drying rate with different drying time under different drying methods, as well as the effects of different drying methods on the appearance, drying rate, density, ash, extractives and the contents of six flavonoids(mangiferin, tectoridin, iridin, tectorigenin, irigenin, irisflorentin) were compared. The results showed that fresh Belamcandae Rhizoma consumed the longest time to reach the water balance point by traditional dry drying in the shade, whiche was about 311 h; that by sun drying was 19.3%, which was shorter than drying in the shade; both drying curves were smoother. The section color of the sun drying samples was the closest to that of fresh samples, but the interior is full of holes, with a low density and loose structure. Hot air drying(40, 60, 80 ℃) could save about 27% to 88% of the drying time, which was greatly shorter, with less pores, a larger density and compact structure. Compared with the traditional drying method, the drying rate of hot air drying was reduced by 13.7%. Ash was affected by temperature, the drying conditions under 40 ℃ and below were not significantly different from those of conventional drying. The ash content decreased by 7.73% to 18.5% compared with conventional drying at 60,80 ℃. After conventional drying and 40 ℃ hot air drying, the contents of tectoridin and iridin(glycosides) in the samples were significantly higher than those in 60,80 ℃ hot air drying, while the contents of tectorigenin, irigenin and irisflorentin(aglycones) dried at 60 ℃ were the best. Therefore, considering comprehensive appearance characteristics and content of medicinal ingredients, traditional Chinese medicinal materials after 60 ℃ hot air drying show a solid texture, tight internal structure, good appearance, appropriate reduction of toxic parasides and higher aglycone content.

The Potential Migrated Mechanism of Water-Soluble Components in Pellets Prepared by Wet Extrusion/Spheronization: Effect of Drying Rate.

INTRODUCTION: At present, there are numerous researches on the migration of components in tablets and granules, however, the investigation in the pharmaceutical literatures concerning the effect of drying rate on the migration of water-soluble components of pellets is limited. Temperature and Relative Humidity (RH) are crucial parameters during the drying process, which is an essential step in the preparation of pellets via wet extrusion/spheronization. To quantify these variables, the water loss percentage of pellets per minute is defined as the drying rate. AIM: The study aimed to investigate the influence of drying rate on the migration of water-soluble components in wet pellets and the potential migrated mechanism. METHODS: The pellets containing tartrazine as a water-soluble model drug and microcrystalline cellulose as a matrix former were prepared by extrusion/spheronization and dried at four different drying temperatures and relative humidity. Afterwards, the extent of migrated tartrazine was assessed regarding appearance, in-vitro dissolution test, Differential Scanning Calorimetry, X-Ray Powder Diffraction, Attenuated total reflectance Fourier transform infrared spectroscopy and Confocal Raman Mapping. RESULTS: Results demonstrated that red spots of tartrazine appeared on the surface of pellets and more than 40% tartrazine were burst released within 5 minutes when pellets were dried at 60°C/RH 10%. When pellets were dried at 40°C/RH 80%, none of these aforementioned phenomena were observed. CONCLUSION: In conclusion, the faster the drying rate was, the more tartrazine migrated to the exterior of pellets. Adjusting drying temperature and relative humidity appropriately could inhibit the migration of water-soluble components within wet extrusion/spheronization pellets.

Effect of different drying methods on drying characteristics, appearance and active components of Belamcandae Rhizoma / 中国中药杂志

In order to explore the effect of different drying methods(drying-in-the-shade, sun-drying, and hot air drying) on appearance characteristics, internal structure and composition of Belamcandae Rhizoma, so as to provide a theoretical basis for screening out suitable drying methods for primary processing. In this study, the Belamcandae Rhizoma's dynamic changes of the moisture content ratio and drying rate with different drying time under different drying methods, as well as the effects of different drying methods on the appearance, drying rate, density, ash, extractives and the contents of six flavonoids(mangiferin, tectoridin, iridin, tectorigenin, irigenin, irisflorentin) were compared. The results showed that fresh Belamcandae Rhizoma consumed the longest time to reach the water balance point by traditional dry drying in the shade, whiche was about 311 h; that by sun drying was 19.3%, which was shorter than drying in the shade; both drying curves were smoother. The section color of the sun drying samples was the closest to that of fresh samples, but the interior is full of holes, with a low density and loose structure. Hot air drying(40, 60, 80 ℃) could save about 27% to 88% of the drying time, which was greatly shorter, with less pores, a larger density and compact structure. Compared with the traditional drying method, the drying rate of hot air drying was reduced by 13.7%. Ash was affected by temperature, the drying conditions under 40 ℃ and below were not significantly different from those of conventional drying. The ash content decreased by 7.73% to 18.5% compared with conventional drying at 60,80 ℃. After conventional drying and 40 ℃ hot air drying, the contents of tectoridin and iridin(glycosides) in the samples were significantly higher than those in 60,80 ℃ hot air drying, while the contents of tectorigenin, irigenin and irisflorentin(aglycones) dried at 60 ℃ were the best. Therefore, considering comprehensive appearance characteristics and content of medicinal ingredients, traditional Chinese medicinal materials after 60 ℃ hot air drying show a solid texture, tight internal structure, good appearance, appropriate reduction of toxic parasides and higher aglycone content.

Comparative nutritional and microbiological quality of ready to cook mixed vegetable curry.

Increasing urbanization, busy lifestyles has been providing a huge impetus to prefer ready to cook (RTC) food products. The research project was conducted to develop such a RTC product which fits the busy lifestyle of people as well as does not compromise on part of nutritional profile. The curry was prepared by washing, cutting, boiling (till vegetables gets soft) and blanching (5 min in 5% brine solution) followed by drying of five seasonal vegetables viz., carrot, peas, potato, cauliflower, beans in hot air dryer at 65 ± 5 °C for 10-12 h. A standardized gravy mix powder (onion, garlic, spices and herbs) was used to add flavor. Serving size for one person i.e. sachet contained 25 g dried vegetables, 10 g gravy mix powder and 200 ml water was prepared and packed. The recipe was finalized after sensory trials. The curry was ready in approximately 5 min in pressure cooker. The product remained well acceptable up to 4 months when packed in LDPE pouches under normal room temperature conditions. However, the shelf life of 4 months at 25 °C for a dried product is by all means considered good by the general expectations of dried foods and keeping the quality of dried foods reported in the literature.

Effect of different pretreatment methods on far-infrared drying characteristics and polysaccharides of Lycium barbarum / 中草药

Objective: To shorten the drying time of Lycium barbarum, increase its shelf life, improve the quality of dried L. barbarum products, and provide technical support for the development of wolfberry drying industry. Methods: Using L. barbarum as experiment material, after being permeated, ultrasonic treating, blanching, ultrasonic treating + permeation and ultrasonic treating + blanchting, far infrared drying test was carried out. The effects of different pretreatment methods on the far-infrared drying characteristics of L. barbarum were studied. Weibull distribution function was used to fit the drying process. The quality and microstructure of dried L. barbarum products were analyzed. Results: After being pretreated, the drying time of L. barbarum was significantly reduced, the drying rate was increased; Compared with L. barbarum without pretreatment before pre-dried, drying time after blanching pretreatment shortened 27.5%, the moisture ratio of the material decreased fastest, and drying rate was the highest. Weibull distribution function can simulate the far infrared drying process of L. barbarum under different pretreatment conditions. The range of r2 and χ2 was 0.991 73-0.999 15 and 8.13 41 × 10-5-8.846 79 × 10-4. The drying characteristics described by scale parameter (α) and shape parameter (β) were consistent with those in the drying characteristic curve. The dried product pretreated with ultrasound + permeation had the smallest color difference (6.756 4) compared with the fresh sample. The polysaccharide content inside the material (991.27 mg/g•DW) was the highest; The microstructure of the dry product obtained by the ultrasound + penetration group had the most voids, and the drying treatment had the least damage to its surface. Conclusion: Ultrasonic and osmotic pretreatment of L. barbarum before drying can not only shorten the drying time, but also improve the quality of its dried products.

Changes in unfrozen water content and dielectric properties during pulse vacuum osmotic dehydration to improve microwave freeze-drying characteristics of Chinese yam.

BACKGROUND: As a pretreatment before drying, the purpose of osmotic dehydration (OD) is to reduce the initial water content of samples and shorten the drying time. When OD is combined with pulse vacuum, the mass transfer is enhanced. Furthermore, the properties of materials, which affect the absorption and dissipation of microwaves, can be changed by OD. In this work, pulsed vacuum osmotic dehydration (PVOD) with sucrose solution was adopted before microwave freeze-drying (MFD). The effects of PVOD on the drying characteristics and quality of dried products were studied. RESULTS: Results showed that the unfrozen water content was increased by PVOD, which made the dielectric constant and loss factor of Chinese yam larger than that of untreated samples, and the difference amplified with the increasing temperature. Thus, the shortened drying time (up to 38.5%) and increased average drying rate (up to 16.8%) were achieved by MFD combined with PVOD. While in traditional freeze-drying, PVOD resulted in slightly shortened drying time but decreased drying rate. The mechanism of PVOD on improving drying rate of MFD was analyzed from the perspective of unfrozen water content and dielectric properties. Furthermore, the quality assessments indicated that PVOD treatment retained a better color and improved the total phenolic content of dried yams compared to untreated and dried samples. CONCLUSION: PVOD using sucrose solution was an effective method to change the characteristics of yam, enhancing the MFD rate and improving the product qualities. © 2019 Society of Chemical Industry.