Drying kinetics of onion (Allium cepa L.) slices with convective and microwave drying

The present study investigated the effects of microwave (90 and 160 W) and combined microwave‐convective (90 W–55 °C, 90 W–65 °C, 90 W–75 °C, 160 W–55 °C, 160 W–65 °C and 160 W–75 °C) drying techniques on the drying kinetics, color parameters (L∗, a∗, b∗, C, α° and Δe), total phenolic content (TPC), and antioxidant capacity (ATC) of pomelo samples. The drying data were fitted to 10 typically used thin‐layer drying models to select a suitable model for drying of pomelo. Comparing the statistical parameters of applied models, the Diffusion Approach, Midilli et al., and Page models were found to be the best‐fitting models in describing drying kinetics of the pomelo samples. It was observed that the drying temperature and/or microwave power changed significantly the all color parameters, TPC, and ATC. The combined microwave‐convective drying resulted in shorter drying times with higher drying rates and high‐quality dried pomelo samples. Practical applications A significant improvement in the quality retention of combined microwave‐convective drying of pomelo slices was achieved. This piece of work will provide a novel method to produce microwave‐convective‐dried pomelo fruits with a significantly improved product quality. A practical implication is that drying of pomelo slices with an optimum condition by combined microwave‐convective process can be used to get a high‐quality product with a higher ATC, TPC, and color.

Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Influence of microwave and microwave‐convective drying on the drying kinetics and quality characteristics of pomelo

Yıldız

İzli

2018

“…These increments in D eff value can be related with the increasing vapor pressure inside the sample that made the moisture diffusion against the surface faster (Sharma & Prasad, ). The values of D eff in the current study were therein the common series 10 −12 to 10 −8 for drying of food materials (Demiray, Seker, & Tulek, ). Doymaz () also reported an increase in D eff values of mint leaves from 3.06 × 10 −9 m 2 /s to 1.94 × 10 −8 m 2 /s with the rise in the drying temperature.…”

Section: Resultsmentioning

confidence: 99%

Investigation of drying kinetics and physicochemical properties of mulberry leather (pestil) dried with different methods

Suna

Karabacak

2019

The effects of microwave (90 and 180 W), hot air (60 and 70°C) and vacuum (60 and 70°C with 250 mbar) drying techniques on drying characteristics, total phenolic content (TPC), antioxidant capacity (AC), color and texture of mulberry pestils were investigated. L*, b*, C*, and h° decreased while a* value was generally increased in pestils. Hardness, springiness, chewiness, and gumminess of the samples were found to be significantly different (p < 0.05). Between the applied seven thin layer drying models, Page and Modified Page were best fitted with the highest R2 (0.9997) and the lowest values of RMSE (0.000927) and χ2 (0.000011). Effective moisture diffusivity (Deff) of pestils ranged from 4.42 × 10−8 to 8.47 × 10−7 m2/s. Drying treatments caused an increment in TPC (1.41%–57.13%) and AC (0.37%–72.79%). These highest results were both obtained from microwave 180 W (TPC: 209.14 mg GAE/100 g dw and AC: 181.37 μmol TE/100 g dw). Practical applications Mulberry is a perishable fruit with several health benefits. It can be consumed raw or in the form of fruit leather (pestil), jam, jelly, marmalade. By pestil production, in which fruit pulp is dehydrated into leathery sheets, mulberry can be processed into a nonseasonal shelf life prolonged product for markets without the additon of preservatives. In this study, drying kinetics of mulberry pestil by microwave, hot air, and vacuum methods were evaluated via mathematical modeling. Page and Modified Page were the best thin layer drying models for pestil production. Drying characteristics were assessed for the development of food specific system in industrial usage and the simulation and optimization of the drying process. Drying treatmens affected texture and color of pestils significantly while exerting higher total phenolic content and antioxidant capacity when compared to non‐dried formulation. Microwave was determined as a promising method to yield high‐quality pestils with greater nutritional properties and the advantage of reduced drying times.

“…In this method, the modified version of the Arrhenius' equation was used to show the relation between the kinetic rate constant ( k ) and the ratio of the MIC output power over the weight of the walnut samples (m/p) and was used instead of the temperature to calculate activation energy. After data analysis, the relationship between the kinetic rate constant and the MIC output power to weight ratio for walnut samples measured using Equation (11), was obtained (Demiray, Seker, & Tulek, ):

k = k_{0} \exp (- \frac{E_{a} . m}{P})

…”

Section: Methodsmentioning

confidence: 99%

The effect of microwave and convective dryer with ultrasound pre‐treatment on drying and quality properties of walnut kernel

Abbaspour‐Gilandeh

Kaveh

Jahanbakhshi

2019

In this study, the drying kinetics of walnuts was investigated including specific energy consumption (SEC), shrinkage, and walnut kernels' color in two dryers, namely ultrasonic‐convection (US‐CON) and ultrasonic‐microwave (US‐MIC). To carry out this study, walnut samples were dried at three MIC powers (270, 450, and 630 W), three input air temperatures (40, 55, and 70°C) and four duration of ultrasonic pre‐treatment (0 min (control sample), 10, 20, and 40 min). Fifteen mathematical models were used to describe the walnuts' moisture ratio. The results showed that the Midilli et al. model was the best model for describing the process of drying walnuts in US‐CON and US‐MIC dryers. Effective moisture diffusivity (Deff) values were calculated to be between 2.77 × 10–9 and 5.56 × 10–9 m2/s for the US‐CON dryer and 3.12 × 10–9 to 8.99 × 10–9 m2/s for the US‐MIC dryer. The lowest rates of color change were observed in the US‐MIC dryer at the lowest microwave power and the lowest duration of ultrasonic pre‐treatment. The lowest SEC for the US‐CON dryer was 19.52 kWh/kg, and it was 15.90 kWh/kg for the US‐MIC dryer. The highest rate of shrinkage was 14.21%, which was seen in the US‐CON dryer at the air temperature of 70°C and the duration of ultrasonic pre‐treatment of 40 min. According to the results, the best quality of walnut with the lowest changes of color and shrinkage in the microwave dryer was calculated at microwave power 270 W and control sample. Practical applications Drying foods and agricultural products using microwave dryers is a relatively cheap method and has attracted the attention of many researchers today. Also, numerous studies have been conducted on drying agricultural products through microwave and convection dryers with ultrasound pre‐treatment. The result of this study could be applied for gathering comprehensive information regarding the drying process (kinetic, Deff, Ea, and SEC) as well as the qualitative properties (color and shrinkage) of walnut kernels dried using the microwave and convective hot air dryers accompanied by ultrasound pre‐treatment.