Influence of in vitro human digestion simulation on the chemical compositions and biological activities of cistus species growing in Turkey

Oxidative stress is one of the significant precursors of various metabolic disorders such as diabetes, Alzheimer's disease, cancer etc. Various scientific reports indicated that secondary plant metabolites play an important role in the prevention of oxidative stress and its harmful effects. In this respect, this study was planned to investigate the phenolic profile, antioxidant and antidiabetic potentials of methanolic and aqueous extracts from Turkish Cistus species (C. creticus L., C. laurifolius L., C. monspeliensis L., C. parviflorus Lam. and C. salvifiiolius L.) with employing in vitro methods. Even though bioavailability is an important parameter affecting the bioactivity of phenolic compounds, it has not been taken into account in most studies. Therefore, in vitro digestion simulation procedure was applied to all extracts for estimating the bioavailability of phenolic contents. Total phenolic, flavonoid, phenolic acid, saponin and proanthocyanidin contents were determined for all phases of digestion. In addition, quantification of the marker flavonoids (tiliroside, hyperoside and quercitrin) was also carried out by High-Performance Thin Layer Chromatography (HPTLC) analysis. Moreover, antioxidant activities of the extracts were studied with mechanistically different methods to reveal their activity profiles in depth. Free radical scavenging (DPPH and DMPD) and metal-reducing potential (FRAP and CUPRAC) assays, and a total antioxidant capacity assay were conducted on all phases of digestion. On the other hand, in vitro α-amylase and α-glucosidase enzymes and advanced-glycation end products (AGEs) inhibitory activities of the extracts were determined to evaluate the antidiabetic potentials of Cistus species. The results showed that aerial parts from Turkish Cistus species have rich phenolic contents and outstanding antioxidant and anti-diabetic potentials. Human digestion might have significant effect on phenolic profile and biological activities of plant extracts. Key words: Turkish Cistus species, Antioxidant ac