In the present study, the thermal properties (drying time, effective moisture diffusion (Deff), specific energy consumption (SEC)), and quality (color and shrinkage) of kiwi slices were optimized using the response surface methodology (RSM). The optimization process was done using central composite design (CCD) in Design Expert software with three independent variables including microwave power (100, 200, and 300 W), sample thickness (4, 6, and 8 mm), and ultrasound pretreatment time (10, 20, and 30 min). The results showed that by increasing the microwave power and ultrasound pretreatment time and decreasing the thickness, the SEC, and drying time decreased in quadratic form, while the Deff linearly increased. Moreover, decreasing microwave power and sample thickness as well as increasing the treatment time diminished the shrinkage and color. The obtained optimal results (4 mm thickness, ultrasound for 30 min, 257.2 W of microwave power) were: drying time for 13.779 min, Deff equal 6.67 × 10−9 m2/s, SEC equal 6.343 MJ/kg, the total color difference of 17.94, and shrinkage of 46%. Novelty impact statement Numerous studies have addressed the drying of food products using ultrasound pre‐treatment. However, the optimization process is required for different methods of drying, parameters of treatment as well as type of the material. Thus, the response surface methodology (RSM) was applied for optimization and modeling the drying process and chosen physical properties of ultrasound‐treated kiwifruits slices prior to microwave drying.

Potatoes are one of the most demanded products due to their richness in nutrients. However, the lack of attention to external and, especially, internal defects greatly reduces its marketability and makes it prone to a variety of diseases. The present study aims to identify healthy-looking potatoes but with internal defects. A visible (Vis), near-infrared (NIR), and short-wavelength infrared (SWIR) spectrometer was used to capture spectral data from the samples. Using a hybrid of artificial neural networks (ANN) and the cultural algorithm (CA), the wavelengths of 861, 883, and 998 nm in Vis/NIR region, and 1539, 1858, and 1896 nm in the SWIR region were selected as optimal. Then, the samples were classified into either healthy or defective class using an ensemble method consisting of four classifiers, namely hybrid ANN and imperialist competitive algorithm (ANN-ICA), hybrid ANN and harmony search algorithm (ANN-HS), linear discriminant analysis (LDA), and k-nearest neighbors (KNN), combined with the majority voting (MV) rule. The performance of the classifier was assessed using only the selected wavelengths and using all the spectral data. The total correct classification rates using all the spectral data were 96.3% and 86.1% in SWIR and Vis/NIR ranges, respectively, and using the optimal wavelengths 94.1% and 83.4% in SWIR and Vis/NIR, respectively. The statistical tests revealed that there are no significant differences between these datasets. Interestingly, the best results were obtained using only LDA, achieving 97.7% accuracy for the selected wavelengths in the SWIR spectral range.

Drying is one of the methods used for preserving fruits and vegetables. However, due to the lengthy process and elevated temperature of convective drying, other pretreatment and drying methods are studied to shorten the drying time and obtain high-quality products. This study aimed to examine the effect of ultrasonic (US) pretreatment and microwave–hot air drying (MW–HA) on the drying time, specific energy (SEC), qualitative properties (e.g., color, shrinkage, and rehydration ratio), and bioactive compound properties (e.g., antioxidant activity, phenolic, and flavonoid contents) of hawthorn fruit. Experiments were performed using ultrasound pretreatment and a microwave dryer (microwave power: 180, 360, and 540 W) at air temperatures of 40, 55, and 70 °C. Drying of hawthorn lasts from 35 min for the ultrasound-treated sample (dried at 540 W and 70 °C) to 180 min (dried at 180 W and 40 °C without US treatment). The lowest amount of SEC (24.11 MJ/kg) was obtained using the US–MW–HA air drying method (dried at 540 W and 70 °C). The lowest values in total color change (13.37) and shrinkage (22.47%) were recorded for the sample dried with a MW power of 360 W and air temperature at 55 °C with US pretreatment prior to drying. Generally, the use of US and MW–HA air drying reduces the antioxidant activity (AC), total phenolic content (TPC), and total flavonoid content (TFC) during processing compared to fresh samples. The highest values for AA (28.01%), TPC (69.44 mg GAE/g d.m.), and TFC (64.38 mg QE/g) obtained at 360 W and 55 °C with US pretreatment for hawthorn fruit dried.