Abstract:This study aimed to investigate the impact of conventional (citric acid) and novel pretreatments (ethanol solution and ultrasound) and hybrid microwave-assisted drying on the drying characteristics and bioactive compounds of the apples. Drying rate of apple slices considerably increased due to the pretreatments and hybrid microwaveassisted drying. The highest drying rate was observed in the samples dried at HMAD200. Among the pretreatments, immersing 100% ethanol solution showed the greatest effect on drying t… Show more
“…The DT reduced by increasing the microwave power due to faster mass transfer in the apple slices at a higher microwave power as a result of more heat generation and a large vapor pressure difference between the center and the surface of the product 56 . The DT also decreases by reducing the sample thicknesses as the exit of moisture will become easier, accelerating the moisture movement from the texture of the material to the sample surface 57 .…”
In the present research, response parameters such as specific energy consumption (SEC), thermal efficiency (TE), energy efficiency (EF), drying time (DT), greenhouse gas (GHG) emission (such as CO2 and NOx), and quality features (color variation and shrinkage) were modeled by response surface methodology (RSM) for apple slices dried in a microwave dryer under ultrasonication (30 ℃—10 min) and blanching (80 °C—2 min) pretreatments. Also, RSM was applied to optimize two independent parameters including microwave power and sample thickness in the levels 100, 200, and 300 W and 2, 4, and 6 mm, respectively. The results indicated the significant influence (P < 0.01) of the independent parameters on the response parameters. The vales of SEC, DT, GHG emission, shrinkage, and color difference were linearly decreased with the declining sample thickness and increasing microwave power, while the energy and thermal efficiencies were increased by a quadratic equation. The use of ultrasonication and blanching pretreatments decreased the SEC, GHG emissions, and DT; while improving the quality of the samples as compared to the non-treated slices. The optimization results showed the optimal drying times (31.55, 82.19, and 50.55 min), SEC (3.42, 10.07, and 4.37 MJ/kg), CO2 with natural gas (1539.75, 1518.75, and 4585 g), CO2 with gas oil (3662.53, 2099.25, 2721.25 g), NOx with natural gas (10.094, 9.956, and 12.906 g), and NOx with gas oil (12.934, 12.758, and 16.538 g) at a microwave power of 300 W and sample thickness of 2 mm with desirability of 0.921, 0.935, and 0.916 for control samples, ultrasonicated, and blanched, respectively.
“…The DT reduced by increasing the microwave power due to faster mass transfer in the apple slices at a higher microwave power as a result of more heat generation and a large vapor pressure difference between the center and the surface of the product 56 . The DT also decreases by reducing the sample thicknesses as the exit of moisture will become easier, accelerating the moisture movement from the texture of the material to the sample surface 57 .…”
In the present research, response parameters such as specific energy consumption (SEC), thermal efficiency (TE), energy efficiency (EF), drying time (DT), greenhouse gas (GHG) emission (such as CO2 and NOx), and quality features (color variation and shrinkage) were modeled by response surface methodology (RSM) for apple slices dried in a microwave dryer under ultrasonication (30 ℃—10 min) and blanching (80 °C—2 min) pretreatments. Also, RSM was applied to optimize two independent parameters including microwave power and sample thickness in the levels 100, 200, and 300 W and 2, 4, and 6 mm, respectively. The results indicated the significant influence (P < 0.01) of the independent parameters on the response parameters. The vales of SEC, DT, GHG emission, shrinkage, and color difference were linearly decreased with the declining sample thickness and increasing microwave power, while the energy and thermal efficiencies were increased by a quadratic equation. The use of ultrasonication and blanching pretreatments decreased the SEC, GHG emissions, and DT; while improving the quality of the samples as compared to the non-treated slices. The optimization results showed the optimal drying times (31.55, 82.19, and 50.55 min), SEC (3.42, 10.07, and 4.37 MJ/kg), CO2 with natural gas (1539.75, 1518.75, and 4585 g), CO2 with gas oil (3662.53, 2099.25, 2721.25 g), NOx with natural gas (10.094, 9.956, and 12.906 g), and NOx with gas oil (12.934, 12.758, and 16.538 g) at a microwave power of 300 W and sample thickness of 2 mm with desirability of 0.921, 0.935, and 0.916 for control samples, ultrasonicated, and blanched, respectively.
“…In the face of the advantages and disadvantages of each main ultrasound technology, most applications rely on ultrasound pre-treatments in ultrasonic baths followed by traditional drying techniques, such as oven [20] , [107] , forced convective [27] , [28] , [37] , [143] , [144] , fluidized bed [145] , [146] , microwave [147] , [148] , [149] , infrared [92] , [93] , [102] , [118] , vacuum-assisted [150] , [151] , and freeze-drying [152] , [153] , [154] .…”
Section: Goal #9 – “Industry Innovation and Infrastructure”mentioning
confidence: 99%
“… Fig. 18 Highest changes of color in fruits by applying ultrasound technologies [24] , [25] , [38] , [92] , [95] , [97] , [99] , [102] , [103] , [119] , [147] , [148] , [158] , [159] , [168] . Single-colored bars indicate unique values in the literature.…”
Section: Goal #12 – “Responsible Consumption and Production”mentioning
The drying process has been widely used for the preservation of foodstuffs. Among the drying methods, convective drying is frequently preferred. Although frequently used, various techniques need to be developed to overcome the existing disadvantages. The study aimed to enhance the drying and quality parameters of the pear slices by microwave-assisted convective drying and pretreatments (citric acid, ethanol, and ultrasound) and compare thin-layer and artificial neural network modeling (ANN). Microwave-assisted convective drying and pretreatments reduced drying time compared to convective-dried samples. The lowest drying time was obtained from the samples pretreated with 100% ethanol. On the other hand, ANN modeling gave the best prediction results for drying curves. Additionally, L* values decreased, whereas a* and b* values increased after the drying process. The citric acid pretreatment provided the lowest color change. Moreover, chroma values increased; however, hue angle values of the samples decreased compared to the 90.08 value of the fresh samples. An increase in the color intensity and a decrease in the yellowness were observed after drying. Total phenolic content (TPC) and antioxidant activity (AA) were highly affected by drying processes and pretreatments compared to fresh samples. The highest losses of TPC and AA were determined after ethanol and ultrasound after pretreatments. According to PCA results in terms of total phenolic content, antioxidant activity, and color values, ethanol and ultrasound-pretreated samples share a similar plane, while control and citric acid-pretreated samples exhibit a similar arrangement. Additionally, fresh and microwave-assisted convective-dried samples stand apart from each other and the rest of the examples, showcasing a unique positioning. In conclusion, microwave-assisted convective drying and pretreatments had a positive effect on drying time. However, these methods need to be enhanced in terms of quality parameters. Besides, ANN may be suggested for the prediction of the drying process.
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