Valorization of coffee silver skin as a functional ingredient in muffins: In vitro bioaccessibility of bioactive compounds

This study aimed to investigate the effects of coffee by-product silver skin (SS) addition as a flour substitute in muffins on the content and bioaccessibility of phenolic compounds. The total phenolic content (TPC), total antioxidant capacity (TAC), and individual phenolic contents in SS-enriched muffins were analyzed during in vitro gastrointestinal digestion. According to the results, 30 % SS-enriched muffins showed the highest TPC (101.1 ± 6.8 mg GAE/100g dw) value and the highest TAC, according to both CUPRAC (165.3 ± 11.6 mg TE/100g dw) and DPPH (192.9 ± 8.7 mg TE/100g dw) assays among the undigested samples. The highest TPC and TAC results were obtained for 30 % SS-enriched muffins at the end of the gastric and intestinal digestion phases. The TPC and TAC were typically reduced by gastric digestion for all concentrations compared to the undigested samples, whereas there was a 2 to 3-fold increase in TPC and TAC values of the samples after intestinal digestion. In addition, gallic acid, syringic acid, and epicatechin were predominantly identified in all SS-enriched samples. The results demonstrated that the use of silver skin at different concentrations as a functional compound enhanced the TPC and TAC values of muffins both before and after digestion, indicating that the coffee by-product SS holds potential for application in food products.