Effect of ultrasound‐ethanol pretreatment on drying kinetics, quality parameters, functional group, and amino acid profile of apple slices using pulsed vacuum drying

The influence of ultrasound‐ethanol (US‐E) pretreatment durations (10, 20, and 30 min) on apple slices dried with varied temperatures (60, 70, and 80°C) using pulsed vacuum dryer was investigated. The results showed that untreated sample (control) took 375, 325, and 225 min to achieve a constant weight of drying whereas drying time for 30 US‐E samples were 275, 225, and 175 min, indicating that 30 US‐E reduced the total drying time by 26.66, 30.77, and 22.22% at 60, 70, and 80°C, respectively. Moisture effective diffusivity and activation energy were in the range of 1.98–4.08 × 10⁻⁸ m²/s and 12.58–23.43 kJ/mol, respectively. Color (L*, a*, b*) and texture were affected significantly (p < .05) at high temperature and longer US‐E. Shorter US‐E duration and lower temperature could preserve most functional groups. Also, total free amino acid values were significantly higher at lower temperature and longer US‐E pretreatment. PRACTICAL APPLICATIONS: Drying time, nutrient retention, and energy efficiency are at the heart of the food industry. The remarkable reduction obtained in the drying time as well as retaining of some functional groups (nutrients composition) with the use of ultrasound‐ethanol as a pretreatment for pulsed vacuum dryer indicates that this technique will serve a great purpose in food processing industries. This in effect will reduce production cost thereby making the business operations of food processors competitive as it provides value proposition to their customers.