The far-infrared drying technique was used to dry Stevia rebaudiana leaves, and the drying rate, drying kinetics, the glycoside content of dried Stevia rebaudiana leaves and surface structure of the ...dried material were explored at different drying temperatures (45 °C、50 °C、55 °C、60 °C、65 °C), irradiation height (60 mm、120 mm、180 mm、240 mm、300 mm). Under different conditions, the moisture rate decreased and the drying rate increased significantly with the increase in drying temperature and the decrease in irradiation height, Weibull model fits the drying curves well (R2 > 0.99). The range of the estimated water diffusion coefficient Dcal was 0.841 8 × 10−4–2.945 3 × 10−4 m2 s−1, and the range of the effective water diffusion coefficient Deff was 0.835 9 × 10−6–3.629 1 × 10−6 m2 s−1. The activation energy was 28.79 kJ mol−1 determined by Arrhenius equation. By comparing the glycoside content of dried products under different drying conditions, it was found that far-infrared drying could better retain the glycoside content. The drying temperature have the batter effect on active ingredients of samples when it increased from 45 °C to 55 °C, the stevioside and rebaudioside A increased from 7.01 to 7.88 mg to 7.44 and 8.58 mg, respectively. Far-infrared drying technology could increase the number of micropores on the surface and inside the materials and improve the quality of dried products. This study explored the law of water transfer during the drying process of Stevia rebaudiana leaves and provided a theoretical reference for the research and application of Stevia rebaudiana leaf drying technology.
•Far-infrared technology is applied to the drying of Stevia rebaudiana leaves.•Far-infrared drying technology improves the retention rate of glycosides in Stevia rebaudiana leaves.•The effect of far infrared drying technique on the surface microstructure of Stevia leaves was explored.
•Prevalent quality assessment of drying materials with solar energy was reviewed.•The potential application of solar drying for high-quality dried products was introduced.•The physical and chemical ...mechanisms of quality transformation during drying process were clarified.
Solar energy is a green and renewable clean energy. Using this as main or auxiliary energy to dry agricultural materials could reduce energy consumption and improve product quality. In the drying process of agricultural materials, not only drying technologies but also drying parameters would affect the quality of materials.
This paper provides a guided technological tour on solar drying through a literature research. An overview about the drying technologies to evaluate the drying quality, such as traditional sun drying, solar tunnel drying, solar greenhouse drying, solar-assisted drying system, is presented to demonstrate advances and application potential of solar drying. Finally, variable temperature drying is preliminarily proposed and tested to verify its superiority of energy saving and drying quality improvement. The literature research in this paper gives a reference on the effective application of solar drying through specifying the mechanisms of quality transformation.
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•Ultrasonic pretreatment induced mulberry softening and pectin depolymerization.•Ultrasonic pretreatment induced the side chains breakage of pectin.•Ultrasonic pretreatment reduced ...the internal water resistance of mulberry.•Ultrasonic pretreatment enhanced moisture migration rate of mulberry.•Ultrasonic pretreatment improved the quality of dried mulberry.
The effects of ultrasound pretreatment (20 kHz, 30 W/L) on mulberries' texture, microstructure, characteristics of cell-wall polysaccharides, moisture migration, and drying quality were investigated over exposure times ranging from 15 to 45 min. Ultrasound induced softening of mulberry tissue, accompanied by an increase in water-soluble pectin and a decrease in chelate-soluble pectin and Na2CO3-soluble pectin concentrations. Noticeable depolymerization of the pectin nanostructure was observed in the pretreated mulberries, along with a decrease in molecular weight, attributed to side-chain structure cleavage. Ultrasound loosened the cell wall structure, increased free water content and freedom, thereby reducing water diffusion resistance. Ultrasound pretreatment reduced drying time by 11.2 % to 23.3 % at various processing times compared to controls. Due to significantly enhanced drying efficiency, the optimal pretreatment time (30 min) yielded dried mulberries with higher levels of total phenolics and total anthocyanins, along with an increased antioxidant capacity. The results of this study provide insights into the mechanisms by which ultrasound pretreatment can effectively enhance the mulberry drying process.
The influence factors such as microwave power, vacuum degree and temperature were investigated using the color L*, thiosulfinate content, rehydration ratio and comprehensive score of garlic slices as ...responses. The microwave vacuum drying (MVD) parameters of garlic slices were optimized by response surface methodology. The electronic nose was used to compare the flavor differences between fresh garlic and dried garlic slices. The results showed that the drying curve and rate curve of MVD garlics accorded with the drying characteristics of foods, the optimum MVD conditions of garlic slices were microwave power 260 W, vacuum degree 81 kPa, and temperature 49.5 °C. Under these conditions, the color L*, the thiosulfinate content, the rehydration ratio and the comprehensive score of garlic slices were 82.26, 3.0378 mg/100 g, 2.796 and 0.9265, respectively. The principal component analysis results of electronic nose demonstrated that there was no difference in the composition between the dried garlic slices and fresh garlic, while the linear discriminant analysis of electronic nose could distinguish them. There was no significant difference in the volatile components of dried garlic slices under different drying conditions. Therefore, MVD process could be an effective drying method and quite suitable for garlic.
•MVD process is an effective method and quite suitable for garlic drying.•MVD curve and drying rate curve were consistent with the drying characteristics.•The optimal MVD conditions were 260 W, 81 kPa, and 49.5 °C.•LDA analysis could distinguish the composition of dried and fresh garlics.•There was no significant difference in volatile components of MVD dried garlics.
Drying is an important and influential process to prolong the shelf‐life of food in the food industry. Recent studies have shown that cold plasma (CP) as an emerging drying pretreatment technology ...can improve drying performance, reduce drying energy consumption, and improve dried food quality. This paper comprehensively reviewed the mechanism of CP improving drying performance, related equipment, energy consumption, influencing factors, and impact on drying quality. This review also discusses the advantages and disadvantages and proposes possible challenges and suggestions for future research. Most studies indicated that CP pretreatment could improve the drying rate and quality and reduce the drying energy consumption. CP can promote moisture diffusion and improve drying efficiency by etching the surface and affecting the internal microstructure. In addition, CP can enhance the quality of dried products by reducing drying time and enzyme activity. Further research is needed to explore the drying mechanisms and equipment innovations to promote the application of CP in the food drying industry.
The reasons of white spots appearance in the middle of oak timber are determined. These white spots reduce the cost of the lamina made of oak timbers - the front covering of floorboards. It is ...proposed to intensify the drying process by using oscillating drying schedules to avoid this defect. A method for calculating the duration of such drying is proposed. This method includes the peculiarities of heating and cooling periods kinetics of oak timbers with 25 mm and 30 mm thickness. The inexpediency of using the oscillation of the drying agent parameters in the range of wood moisture content below 20% has been established. An adequate model for calculating wood temperature and air humidity during wood heating and cooling periods has been developed using heat and mass transfer criteria and experimentally determined oak wood moisture conductivity coefficient. Based on the results of theoretical and experimental studies oscillating drying schedules of different thickness oak timbers are offered. Tests of the proposed schedules in industrial conditions showed no discoloration of the central layers of European oak (Quercus robur) timbers. The drying process duration was reduced by 1.5–2.4 times and energy consumption were reduced by 1.53 times.
Effects of five different drying methods on the antioxidant properties (AOP) of leaves of
Alpinia zerumbet,
Etlingera elatior,
Curcuma longa, and
Kaempferia galanga were assessed. All methods of ...thermal drying (microwave-, oven-, and sun-drying) resulted in drastic declines in total phenolic content (TPC), ascorbic acid equivalent antioxidant capacity (AEAC), and ferric-reducing power (FRP), with minimal effects on ferrous ion-chelating ability and lipid peroxidation inhibition activity. Of the non-thermal drying methods, significant losses were observed in air-dried leaves. Freeze-drying resulted in significant gains in TPC, AEAC, and FRP for
A. zerumbet and
E. elatior leaves. After one week storage, AOP of freeze-dried
E. elatior leaves remained significantly higher than those of fresh control leaves. Freeze-dried tea of
A. zerumbet was superior to the commercial tea for all AOP studied.
Infrared Heating in Food Drying: An Overview Riadh, Muhmmed Hussain; Ahmad, Siti Anom Binti; Marhaban, Mohd Hamiruce ...
Drying technology,
01/2015, Volume:
33, Issue:
3
Journal Article
Peer reviewed
This article aims to review and analyze the aspects and characteristics related to infrared food drying. Indeed, with a review of 100 relevant publications all dealing with infrared food drying, this ...article notes that infrared drying has several advantages over other common food drying methods. Shorter drying time, a better final dried product quality, and more energy savings in the process are revealed as the most important advantages of infrared drying over convective heat drying. Infrared dryers can also be easily combined with other drying methods such as hot air, microwave, vibration, and vacuum. This article clearly shows that using infrared heating for food drying purposes has become more popular in the last decade and its application in the industrial drying of different foodstuffs has been employed widely.
The objective of this work was to study the influence of spray drying conditions on the physicochemical properties of açai powder. The process was carried out on a mini spray dryer and maltodextrin ...10DE was used as carrier agent. Seventeen tests were made, according to a central composite design. Independent variables were: inlet air temperature (138–202
°C), feed flow rate (5–25
g/min) and maltodextrin concentration (10–30%). Moisture content, hygroscopicity, process yield and anthocyanin retention were analysed as responses. Powder moisture content and process yield were positively affected by inlet air temperature and negatively affected by feed flow rate, which are directly related to heat and mass transfer. Process yield was also negatively influenced by maltodextrin concentration, due to the increase on mixture viscosity. Powders hygroscopicity decreased with increasing maltodextrin concentration, decreasing temperature and increasing feed flow rate. Powders with lower moisture content were more hygroscopic, which is related to the greater water concentration gradient between the product and the surrounding air. Anthocyanin retention was only affected by temperature, due to its high sensitivity. In respect to morphology, the particles produced at higher temperature were larger and a great number of them showed smooth surface.
The present study investigated the changes in total phenols (TP), rosmarinic acid content and antioxidant capacity of six Lamiaceae herbs (rosemary, oregano, marjoram, sage, basil and thyme) after ...three drying treatments (air-, freeze- and vacuum oven-drying) stored for 60
days at −20
°C and compared to fresh samples. Ferric reducing antioxidant property (FRAP) and oxygen radical absorbance capacity (ORAC) were used as markers for antioxidant capacity. Air-dried samples had significantly (
p
<
0.05) higher TP, rosmarinic acid content and antioxidant capacity than had freeze-dried and vacuum oven-dried samples throughout the storage period. Fresh samples had the lowest values for the parameters tested. Vacuum oven-drying resulted in higher TP and FRAP values in rosemary and thyme during 60
days of storage than did freeze-drying. In ORAC assay, the difference was significantly higher only in thyme. Storage did not show any effect on the dried samples for the parameters tested.
