Evolution of mechanical and optical properties of French fries obtained by hot air-frying

•Optical and mechanical changes are faster in deep-oil frying.•The lower increase of a* during air-frying suggests a lower acrylamide generation.•Texture of French fries exhibited a softening followed by the crust development.

The aim of this study was to analyse the influence of frying technique (air-frying and deep oil-frying) and type of pre-treatment (freezing and blanching) on the evolution of mechanical and optical properties of French fries. The results showed that the chromatic parameters, a* and b*, experimented an increase regardless of the frying method. The increase in a* was significantly higher in deep-oil frying as a result of Maillard's reactions. The texture analysis reported a first stage of initial softening related to starch gelatinization followed by a second stage where the maximum force increased due to the gradual formation of a crust, both stages being faster in deep-oil frying. Pre-frozen potatoes presented the highest value of maximum force parameter independent of the type of frying.