Development of polyphenol-enriched vacuum and atmospheric fried matrices: Evaluation of quality parameters and in vitro bioavailability of polyphenols.

Polyphenols are very unstable and may be degraded when exposed to harsh conditions, such as those found in frying. The inclusion of vacuum seems to be a reasonable solution to avoid these adverse effects. Accordingly, the purpose of this study was to analyze the effect of olive-leaf polyphenol extract on quality parameters of vacuum and atmospheric fried gluten-starch matrices. Matrices were prepared using 12% (d.b.) gluten and 88% (d.b.) starch, using either native or a mixture of native (90%) and pre-gelatinized starch (10%). Polyphenols were added as a freeze-dried powder. Atmospheric and vacuum (91.4kPa, Twater boiling point=46°C) frying were compared using an equivalent thermal driving force, which is defined as the difference between oil temperature and water boiling point at the working pressure. Bioavailability of polyphenols was evaluated using simulated digestion and caco-2 cells absorption. The addition of pre-gelatinized starch significantly decreased oil absorption in vacuum fried matrices, however, no significant differences were noted when added into atmospheric fried ones. Polyphenols retention was higher than 70% in vacuum fried matrices. Their bioavailability was ~15%, much higher than in atmospheric fried ones (~8%), and that the one reported in other studies. Interestingly, polyphenol addition reduced the oil content of vacuum fried snacks by 20%. This could be attributed to the hydrating effect of polyphenols, which may facilitate starch gelatinization, improving structure formation during vacuum frying, which will be the focus of future research.