# Integrated multi-dimensional micro-structure reveals the changes in moisture migration and quality attributes during drying of apple slices with ultrasonic pretreatment

## TL;DR

Ultrasonic pretreatment improves apple slice drying by altering microstructure, speeding up moisture removal, and preserving quality.

## Contribution

This study demonstrates how ultrasonic pretreatment alters apple cell wall structure to enhance drying efficiency and product quality.

## Key findings

- Ultrasonic pretreatment reduces drying time by 13.31–38.82% for hot-air drying and 32.60–36.88% for infrared drying.
- Ultrasonic treatment increases water-soluble and chelate-soluble pectin, aiding moisture migration.
- Optimal ultrasonic pretreatment preserves key metabolites like chlorogenic acid and malic acid.

## Abstract

Optimizing drying efficiency and enhancing product quality are crucial for industrial apple dehydration processing. This study focused on multi-dimensional micro-structure changes of apple slices with ultrasonic pretreatment (US). The results indicated that US pretreatment significantly enhanced mass transfer by depolymerizing cell wall pectin to increase water-soluble pectin (72.15 to 90.35 mg/g AIR) and chelate-soluble pectin (35.31 to 54.69 mg/g AIR), converting bound water to free water, disrupting the structural integrity of the cells, thereby reducing drying time by 13.31–38.82 % for hot-air drying and 32.60–36.88 % for infrared drying. Concurrently, the microscopic structural changes induced by US treatment enhanced rehydration capacity and minimized bio-active compound's loss, particularly chlorogenic acid and malic acid. Although the reduction in total phenols and flavonoids resulted in decreased antioxidant activity, appropriate US treatment enhanced color by activating polyphenol oxidase (PPO). Consequently, optimal US pretreatment is essential for enhancing both the drying efficiency and quality of apple slices.

•Ultrasonic pretreatments accelerate moisture migration of apple slices.•Ultrasonic induced depolymerization of polysaccharide from apple cell wall.•Ultrasound enhances key metabolites retention in dried apples.•Optimal ultrasonic pretreatment boosts apple slice drying efficiency and quality.

Ultrasonic pretreatments accelerate moisture migration of apple slices.

Ultrasonic induced depolymerization of polysaccharide from apple cell wall.

Ultrasound enhances key metabolites retention in dried apples.

Optimal ultrasonic pretreatment boosts apple slice drying efficiency and quality.