The effects of drying and fermentation on the bioaccessibility of phenolics and antioxidant capacity of Thymus vulgaris leaves

Abstract

Fresh thyme leaves (Thymus vulgaris L.) were dried at 45 ??C for 5 h and naturally fermented at 20 ??C in a brine solution containing salt and vinegar for 18 days. The ethanolic extracts of fresh (FT), dried (DT), and fermented-pickled (PT) thyme leaves were assessed in terms of total phenolic content (TPC), total flavonoid content (TFC), antioxidant capacity values and subjected to in vitro gastrointestinal digestion. TPC, TFC, and antioxidant capacity values of fermented thyme leaves were found significantly higher than of dried and fresh samples. The bioaccessibility index (BI) value for TPC and TFC was highest for PT and lowest for DT, indicating that both processes had different effects on the structure of phenolic compounds present in the thyme leaves. Similarly both Recovery and BI values of DPPH antioxidant capacity were highest for PT, but lowest for fresh samples. When CUPRAC assay was applied, the recovery % for FT and PT was similar, and the BI was higher for FT. Results showed that compared to the results of fresh thyme leaves, drying and pickling had a considerable effect on the initial phenolic compounds extracted and their fate during in vitro digestion.