The combined effect of ultrasound and enzymatic treatment on the nanostructure, carotenoid retention and sensory properties of ready-to-eat carrot chips

- Both ultrasound and pectin lyase influenced the nanostructure of carrot tissue.
- Ultrasound altered the uronic acid content in a different way to enzyme.
- Ultrasound impacted the shape of carotenoid agglomeration in tissue substructure.
- Both ultrasound and enzyme can improve the colour of dried carrot.
- Applying both ultrasound and pectin lyase gave the most preferred vivid colour.

Fat-free crispy carrot snacks, could be an interesting proposal for consumers eager to increase their vegetable consumption, if the carotenoids naturally occurring in carrots could be retained during the drying processes used in their production. In an attempt to enhance carotenoid retention during the snacks production, ultrasound (US) and enzymatic treatment (EN) were applied as pre-treatment operations. Carrot slices were first sonicated for 20 min (25 kHz, 0.4 W/cm2), and then soaked in a light sucrose solution (110 g/L) with or without pectin lyase enzyme (2 g/L), and finally were conventionally dried to a crispy state. Final product quality was assessed, paying attention to the carotenoid content, and changes in molecular pectin structure. Both the applied pre-treatments caused transformations of diluted alkali soluble pectin fraction in the form of shortening the skeleton length. Moreover, a decrease in the diameter of pectin polymers was noticed for samples treated with ultrasound, whereas enzyme action resulted opposite alteration. The US turned out to be a less effective factor in enhancing carotenoid retention of dried carrot chips than the EN; however, their simultaneous application not only had a positive effect on carotenoid retention, but also led to a higher sensory appreciation of the product colour.