Total phenolics, flavonoids, anthocyanins and antioxidant activity following simulated gastro-intestinal digestion and dialysis of apple varieties: Bioaccessibility and potential uptakeJaouad Bouayed, Lucien Hoffmann, Torsten BohnCentre de Recherche Public Gabriel Lippmann, Environment and Agro-Biotechnologies Department, 41, rue du Brill, L-4422 Belvaux, Luxembourga r t i c l ei n f oArticle history: Received 15 December 2010 Received in revised form 10 February 2011 Accepted 13 February 2011 Available online 17 February 2011Keywords: Apples Gastro-intestinal digestion Polyphenols Flavonoids Anthocyanins Antioxidants Antioxidant activity Bioaccessibility Dialysabilitya b s t r a c tIn the present study, an in vitro model simulating gastrointestinal (GI) digestion, including dialysability, was adapted to assess free soluble polyphenols from apples (four varieties). Results indicated that poly-phenol release was mainly achieved during the gastric phase (ca. 65% of phenolics and flavonoids), with a slight further release ( Jonagold Golden Jonaprinz.3.2. Total flavonoidsThe pattern of release was similar to total phenolics, with step- wise release from the gastric phase to the intestinal phase, whilenot all flavonoids were dialysable. Amounts of flavonoids detected after the gastric and the intestinal phase as well as free soluble(dialysable phenolics) were significantly lower than those deter- mined by chemical extraction for all apple varieties (Fig. 2). Forall varieties, the content of free soluble dialysable flavonoids wasalso significantly lower than the content of flavonoids found in the gastric as well as the intestinal digesta (p 0.001), except for Golden.3.3. Total anthocyaninsTwo of the four apple varieties (Golden and Mutzu) contained non-detectable amounts of anthocyanins. Unpaired Students t-testrevealed that there were no significant differences between the amount of anthocyanins detected by chemical extraction and fol- lowing gastric digestion for both Jonaprinz and Jonagold varieties (Table 1). However, after GI digestion, anthocyanins were no longer detectable in the intestinal digesta.3.4. Total reducing antioxidant capacity comparisonsThe overall trend of reducing antioxidant capacity followed theconcentrations of total phenolics and flavonoids. Reducing antiox- idant capacity natively present in apple varieties, as determined inmethanolic extracts by the FRAP test, was significantly higher com- pared to those found in gastric digesta for all apple varieties with exception for Jonagold (Fig. 3), to those recorded in intestinal digesta (p 0.001 for all varieties), and compared to free soluble antioxidants crossing the cellulose membrane (p 0.001 for allvarieties), with the latter being significantly lower compared to the gastric phase for all varieties, and partly when compared to the intestinal phase (Jonagold: p 0.05, Mutzu: p 0.001; Fig. 3).3.5. Total radical-scavenging activity comparisonsTotal radical-scavenging activity by ABTS followed, in general,concentrations of phenolics and flavonoids. Radical-scavenging activities natively present in apple varieties, as determined frommethanolic extracts by the ABTS test, were found to be signifi- cantly higher, compared to those displayed by gastric digesta for some applevarieties (Jonaprinz: p 0.001,Golden: p 0.05; Fig. 4), but not compared to the intestinal digesta, with the excep- tion of Jonaprinz. However, free soluble antioxidants displayed anantioxidant activity significantly reduced compared to their corre- sponding native antioxidant activity in apples, except for Jonagold, and compared to both gastric digesta (Jonaprinz and Mutzu) and intestinal digesta (all apple varieties).3.6. Overall comparison with combined resultsAs seen from pooled data obtained from the four studied varie- ties (Fig. 5), amounts of released phytochemicals (both phenolicsand flavonoids) after both the gastric phase and the intestinalphase were significantly lower than initial concentrations deter- mined by chemical extraction using methanol (p 0.001), indicat- ing incomplete release or degradation. Pooled results from dialysisFig. 1. Amount of total phenolics, expressed as gallic acid equivalents (GAE), as determined from fresh apple matrix (100 g) using methanolic extraction (MeOH) and after simulated gastro-intestinal digestion, i.e., phenolics remaining after the gastric phase, intestinal phase, and free soluble (dialysable through cellulose membrane) phenolics. Data shown represent means SD (n = 3 independent experiments).ap 0.05,bp 0.01,cp 0.001 significantly different from apple methanolic extracts, t indicating tendency, i.e., 0.05 p 0.1.p 0.05,#p 0.01,?p 0.001 significantly different from dialysable phenolics, + indicating tendency, i.e., 0.05 p 0.1. All p-values are 2-tailed following ANOVA and Bonferroni post hoc test.Fig. 2. Amount of flavonoids, expressed as catechin equivalents (CE), as determi