The impact of apple destructuring and thermal treatment on bioactive compounds: the fate of dietary fibre and polyphenols in puree and homogenate

The present study aimed at understanding the response of dietary fibres and phenolic compounds to apple matrix disintegration and thermal treatment. Apple was processed by mimicking industrial operations of blanching, destructuring by high-speed homogenisation (HSH) or high-pressure homogenisation (HPH), and pasteurisation. A viscous puree (0.73 Pa × s), made of juice embedding intact cells and large cell clusters, was obtained by HSH. Conversely, HPH completely disrupted apple tissue leading to a fluid homogenate (0.27 Pa × s) in which the fibrous matrix was suspended. Despite these differences, apple puree and homogenate presented similar content of total and soluble dietary fibre, with no significant differences in the chemical structure of apple pectin, as demonstrated by FT-IR and NMR analyses. Apple puree and homogenate retained more than 80% of the phenolic content originally present in apple pulp (about 2125 mg/gdw) without detriment to radical scavenging activity. This minor phenolic depletion, regardless of the different extent of mechanical disintegration, was mainly due to the decrease of thermolabile flavanols upon application of analogous heat treatments.