Due to the adverse side effects of synthetic antioxidants, the search for natural and safe antioxidants has become crucial. In this study, the total PHENOLIC COMPOUND contents and antioxidants activity of persimmon skin was investigated. The extraction was carried out by means of maceration method using ethanol and methanol solvents with ratio of 1 part persimmon skin to 5 parts of solvents. Afterwards, the total PHENOLIC COMPOUNDs and antioxidants activity was measured. According to the results, ethanolic and methanolic extracts contained 255.6 and 214.15 mg gallic acid per 100 g of persimmon skin, respectively. Moreover, ethanolic extracts showed a higher activity for scavenging free radicals compared to methanolic extracts.

The aim of this study was to determine Total PHENOLIC COMPOUND (TPC) and antioxidant activity changes depending on the ripening in Rosa canina, R. dumalis, R. dumalis ssp. boissieri and R. villosa rosehip species. Rosehip fruits were harvested in 6 different times from July to September. TPC content and antioxidant activities were determined by spectrophotometric methods. TPC and antioxidant activities of the studied species increased during ripening. TPC (1510.57 mg GAE 100 g-1/H-6) and antioxidant activities (TEAC: 364.12 mmol trolox equivalent g-1/H-6 and FRAP: 286.79 mmol trolox equivalent g-1/H-6) were higher in R. dumalis (MR-15) than the other studied species. There was a high correlation between the TPC and the antioxidant activity. Also, there was a positive correlation between maturation, PHENOLICs and antioxidant activities. This correlation was high in R. dumalis and low in R. canina. However, it was not possible to express the existence of a relationship between temperature, TPC, and antioxidant activity. It was possible to express the existence of correlations between the color of fruits and some studied characteristics. The correlations between the colors of the fruits and TPC and antioxidant activity of R. dumalis were found higher than the other species.

Hydroquinone (HQ) sensitive electrochemical biosensing was performed using new nanocomposites of carboxylated graphene (GrCOOH) embedded in metal-organic coordination polymers (MOCPs) as efficient matrices for laccase (Lac) immobilization. GrCOOH nanosheets were used to pre-adsorbotion of HAuCl4 and acted as anchor sites. They help to form MOCPs and more coordinates between gold ions and 4-aminothiophenol (4-ATP) ligand. According to the Tafel plot, the mechanism was diffusion for HQ redox reactions on the proposed modified electrode surface and an electron process was in the rate-determining stage. It was concluded that this redox reaction was involved the same number of protons and electrons. The construction of GrCOOH-MOCPs one-pot entrapped Lac exhibited enhanced redox currents over MOCPs for HQ electrochemical oxidation and reduction and enhanced sensitivity and low detection limit (1. 70 µ, M), being superior to other Lac biosensors. Furthermore, this biosensor was tested in real samples and demonstrated acceptable recoveries in real water samples, and showed a good stability for one week.