Table 2.

Recent studies on the influence of ultrasound pretreatment on the drying performance of food materials

Food commodities	Ultrasound (power/intensities/frequency)/treatment time/temperature	Drying methods	Drying conditions (Temperature/time/air velocity)	Major findings	References
White mushrooms	100 and 200 W	Hot air drying	50 and 70 °C	The drying rate was increased by 41.73% and 76.77% for 100W and 200W, respectively, at 50 °C and 30.43% and 55.73% for 100 W and 200W, respectively at 70 °C Significant reduction of total drying time and intensification in the specific energy consumption rate were observed during drying More favorable retention of color and polyphenol content	Szadzińska et al. (2022)
Golden berries	Ultrasound: 100 W and 20 kHz with a pulse frequency of 50 Hz for 0.25 to 1 min	Convective hot air and ultrasound-assisted hot air drying	50 °C and 1 m/s	The drying time was reduced by 10.80% for ultrasound and 3.60–19.33% for the cold plasma treated sample as compared to the untreated sample The effective moisture diffusivity varied between 6.54 × 10−10 and 11.62 × 10−10 m2/s and increased by 11.30% treated with ultrasound The specific energy consumption was higher in ultrasound treated as compared to cold plasma Faster drying rate exhibited the retention of quality attributes	Ashtiani et al. (2022)
Apple slices	20 kHz, 5.5 cm probe diameter, 5 mm gap, time: 40 to 80 min	Airborne ultrasound-assisted drying system	60 °C, 1.7 m/s and 10% humidity	Pretreatments with sonication were capable to reduce drying time by 1.5–68.9% The drying performance was enhanced by increasing moisture diffusivity and lowering the activation energy The PPO activity showed less affected by sonication, whereas the ultrasound-assisted drying reduced the vitamin B2 content	Zhu et al. (2022)
Pineapple slices	250 W and 33 kHz for 20 to 40 min at 10 to 30 °C	Convective drying	60 °C with 1.5 m/s	The optimum conditions were observed to be at 50°Bx, 26.6 min, and 30 °C for solution concentration, sonication time, and temperature, respectively The solid gain of pretreated samples ranged from 0.02 to 0.119 g solid/g with an increase in mass transfer rate	Meena et al. (2022)
Kiwi slices	25 kHz and 100 W for 20 min	Convective drying	104 °C	The effective moisture diffusivity and solute diffusivity ranged between 5.46 × 10−10 to7.30 × 10−10 m2/s and 2.925 × 10−10 to 3.51 × 10−10 m2/s, respectively The lower value of the shape parameter ranged from 0.570 to 0.616, indicating a faster drying rate	Prithani and Dash (2020)
Persimmon	35 kHz for 10, 20, and 30 min at 30 °C	Tray dryer	60 °C and 1.8 m/s	Drying rates and effective diffusivities increased with the increase in US treatment time by 33% and 46%, respectively Mass transfer and weight loss increased with US treatment time and improved the rehydration capacity	Bozkir and Ergün (2020)
Strawberries	180, 240, and 300 W for 15 min at 25 ± 5 °C	Pulsed fluidized bed microwave freeze-drying	60 °C	The drying time was reduced by 45% as associated with the untreated control sample A better-quality retention rate was observed in the ultrasonication treated sample	Jiang et al. (2021)
Carrot slices	US: 0 and 80 W, 20 kHz IR: 900, 1200, and 1500 W, gap between tray and IR emitter 25 cm	Infrared drying	60 °C and 1 m/s	The drying time was shortened by 21%, 17%, and 11% for drying at 900, 1200, and 1500 W, respectively The moisture diffusivity was obtained in the range of 8.09 × 10−10 to 26.98 × 10−10 m2/s treated with ultrasound and 6.34 × 10−10 to 22.92 × 10−10 m2/s in the sample of solely IR drying Ultrasound showed a positive effect on the rehydration ratio, whereas vitamin, color, and shrinkage were not significantly affected	Guo et al. (2020)
Okra slices	80 to 320 W and 5 to 15 min	Convective drying	70 °C and 2 m/s	The optimum pretreatment conditions were found to be ultrasound power level of 250W, sample thickness of 0.5 cm, and ultrasonic duration of 15 min The drying time and effective moisture diffusivity were found to be 7.2 h and 5.78 × 10−8 m2/s, respectively, for the untreated sample and 6.3 h and 7.20 × 10−8 m2/s, respectively for the ultrasound treated sample The moisture diffusivity increased with the increase of ultrasound power and subsequently reduced energy consumption by 12.5%	Wang et al. (2019)
Sanhua plum	40 kHz for 15 min at 30 °C	Heat pump dryer	60 °C	Total drying time was decreased by 24% at 90% US power for 15 min ultrasound treated sample as compared to control The moisture diffusion coefficient was observed to be 1.45 × 10−10 to 1.59 × 10−10 m2/s which was increased by 11%, 14%, and 22% with the increase of ultrasound power Quality retention was found to be higher at lower ultrasound intensity	Li et al. (2021)
Kiwi fruit slices	Electrical (ET): 100 V for 0.67 min. Ultrasound: 35 kHz for 30 min	Convective dryer	50 °C and 1.5 m/s	Both the pretreatments increased the drying rate by 18.34% for ET and 21.65% for the US The drying process improved with the increase of treatment time in both the ET and US treatment and combined pretreatments (ET and US) and enhanced the drying rate by 35.7% US treated sample increased the rehydration and vitamin C content	Bozkır and Ergün (2021)
Apple slices	21 and 35 kHz for 30 min	Convective dryer	70 °C and 2 m/s	The total drying time was reduced by 13 to 17% for the ultrasound treated sample The moisture diffusivity was increased in the ultrasound treated sample from 1.037 × 109 to 1.059 × 109 m2/s The color changes were retained and showed an increase in the lightness and chroma values	Fijalkowska et al. (2016)
Garlic	480 W and 35 kHz for 10 to 30 min at 30 °C	Convective drying and microwave drying	60 °C and 1.0 m/s Microwave: 2450 MHz operated at 540 W	The drying rate improved in the HAD + US and the MWD + US treatment process by 19.30% and 13.82%, respectively as compared to control sample Effective moisture diffusivity was obtained as 1.42 × 10–10 m2/s, 1.83 × 10–10 m2/s, 1.17 × 10–8 m2/s, and 1.36 × 10–8 m2/s for HAD, US + HAD, MWD, and the US + MWD process, respectively The moisture diffusivity and drying rate were found to be higher in the US-assisted microwave drying as compared to the US-assisted hot air drying	Bozkir et al. (2018)
Shiitake mushrooms	600 W and 28 kHz for 15 min	Infrared drying (IR)	60 °C, 2.11 m/s and IR of 1350 W	Ultrasound pretreatment reduced the drying time by 21.43% as compared to the control samples The texture and color were retained, reduced hardness, and exhibited a higher lightness value of 78.46	Zhao et al. (2018)
Sweet potato	300 W and 28 kHz for 20 to 60 min	Vacuum oven method	70 °C	The moisture diffusivity of ultrasound assisted osmotic dehydration was higher by 30.82% and 41.62% with solely treated by osmotic dehydration and ultrasound treatment, respectively The maximum color value was retained in ultrasound-assisted osmotic dehydration with enhanced croma value	Oladejo et al. (2017)
Ginger	600 W and 33 kHz for 30 min at 30 °C	Convective dryer	30 to 75 °C, 2 m/s, and 1.2 kW	Ultrasound treatment enhanced the drying rate and reduced drying time by 140 min for Chinese ginger and 170 min for Ghanaian ginger The drying performance was enhanced with the retention of bioactive compounds in ultrasonication treated samples	Osae et al. (2019)
Carrot slices	Power of 30 to 90% and 20 kHz for 0.5 min	Infrared drying	60 °C and 1.5 m/s	The total drying time was decreased by 6.3%, 15.6%, and 25% and β-carotene content was improved by 5.46%, 13.07%, and 17.62% at power level 30%, 60%, and 90%, respectively The ultrasound treated samples were observed to enhance flavor, hardness, and color retention	Wang et al. (2018)
Banana, mango, guava	45 W and 20 kHz for 15 min	Convective drying	50 °C and 0.2 m/s	The US treated drying of fruit exhibited a reduction in drying time between 16.23 and 30.19%, 11.34 and 32.73%, and 19.25 and 47.51% for the banana, mango, and guava, respectively The US treatment increased the moisture diffusivity while retaining the polyphenol content and the antioxidant activity	Méndez et al. (2015)