Effects of in vitro gastrointestinal digestion on strawberry polyphenols stability

Strawberry fruits are highly appreciated for their taste, nutritional value and antioxidant compounds, mainly phenolics. However, little is known about the stability and bio-accessibility of phenolic compounds and their antioxidant activity after fruit processing and digestion. In this work, the content of total phenolic compounds, flavonoids and anthocyanins as well as the antioxidant capacity were determined in lyophilized and frozen fruits. Three methods were used to determine antioxidant capacity (TEAC, FRAP and DPPH). Lyophilized fruits were also subjected to an in vitro gastrointestinal digestion. There were no significant differences found in the total phenolic compounds and flavonoids content in frozen fruit compared to lyophilized fruit. However, freeze drying resulted in a reduction of anthocyanins concentrations. Antioxidant activity of frozen fruits was higher than that of lyophilized fruits by TEAC and DPPH assays (~1.5 fold in both assays) and lower by FRAP assay (~0.8 fold). When fruits were subjected to gastrointestinal digestion, phenolic compounds, flavonoids, anthocyanins and antioxidant capacity showed a larger release. In these sense, a higher amount of polyphenolic compounds from strawberry matrix was observed in the gastric fraction (81.99 mg GAE g^-1 DW_p) than in the intestinal compartment (14.75 mg GAE g^-1 DW_p). Similarly, flavonoids and anthocyanins submitted to the in gastric conditions decreased 5.9- and 18-fold in intestinal conditions, respectively. Likewise, antioxidant capacity decreased 15-, 20- and 8-fold by the TEAC, FRAP and DPPH assays, respectively. These results demonstrate that fruit processing methods and digestion processes affect the stability of antioxidant compounds. Moreover, the bio-accessibility of these compounds varies depending on the conditions during digestion.