This research aims to identify the phytochemical constituents of 79 different samples of black tea, including varieties from India, Iran (IrT), Turkey (TT), and Sri Lanka. In addition, this study investigates the effect of varying brewing times on the quality characteristics of tea. Therefore, we analyzed the phytochemical content of tea using a novel LC–MS/MS method that we developed, which identifies 53 different phenolic compounds. Furthermore, objective evaluations were conducted on the total phenolic compound, total flavonoid compound, antioxidant activity, and color values at 15, 30, and 60‐min brewing intervals. The prevailing phenolic compounds discovered in the corresponding tea classifications were quantitatively analyzed to be quinic acid, epicatechin gallate, epigallocatechin gallate, epicatechin, epigallocatechin, gallic acid, nicotiflorine, and isoquercitrin. The study found that the TT and IrT groups had the richest phytochemical content and the highest antioxidant activity. The Turkish tea group had the highest measurement for the desired red color, which is considered a sensory property. Infusion color, antioxidant activity, and total phenolic and flavonoid contents showed significant increases with prolonged brewing time. It was important to note that the chemical composition of tea varies according to its origin and brewing conditions. Extending the brewing time improved the quality of the tea. It should be noted, however, that longer brewing times result in a more intense release of flavonoids, and this increase may have a pro‐oxidant effect.

The purpose of this study is to investigate pesticide residues in the imported and domestic tea sold in Turkey and to detect their compliance with maximum residue limits (MRL) and Acceptable Daily Intake (ADI). A total of 79 samples were analyzed by using LC-MS/MS and GC-MS devices with AOAC 2007.01 method to investigate 603 pesticide residues. According to the results, pesticide residues were found in a total of 28 tea samples. Pesticide residues were found in the countries of origin at the rates as follows: Iran (100%), India (33.3%) and Sri Lanka (17.3%). No pesticide residue was detected in the tea produced in Turkey. The compounds such as Diuron, Ethion, Cypermethrin, Thiacloprid, Thiamethoxam, Fenpyroximate, Acetamiprid, Imidacloprid, Flubendiamide, Deltamethrin and Hexythiazox were detected in positive samples. Seven types of pesticide residues exceeded the MRL determined by the Turkish Food Codex for 15 types (53.57%) for 28 samples with pesticide residue detected. Additionally, 4 types of pesticide residues were determined to exceed the ADI determined by the Codex Alimentarius for 13 (46.42%) of 28 samples with pesticide residue detected. These results have showed that the imported tea entering Turkey was not adequately analyzed in the customs control laboratories or the maximum residual limits were not clearly determined.

Being widely used since its discovery, tobacco contains many chemical substances including nitric oxide, hydrocarbons, aldehydes, phenols, quinone and semiquinone radicals, and causes the formation of oxygen-induced free radicals directly or indirectly. Therefore, it is important to know the oxidant/antioxidant properties, phenolic content of Nicotiana rustica Linn., and the effect studies on Paraoxonase (PON 1) and Acetylcholinesterase (AChE) which are important metabolic enzymes. In the study, the effect of extracts (water and methanol) of Nicotiana rustica Linn on PON 1 and AChE enzyme activity was examined. Water extract of Nicotiana rustica Linn Maras Powder with walnut, (MPWW) and methanol extract Maras Powder with Nicotiana rustica, (MPNR), Maras Powder with walnut, (MPWW) and Maras Powder with copper cauldron, (MPCC) had an inhibitory effect on AChE (IC50 values in the range of 0.104-0.203 mg ml-1). Also water extract MPCC and methanol extract MPNR, MPWW and MPCC showed an inhibition effect on PON 1 (IC50 values 0.013-0.225 mg ml -1). MPNR water extract showed the highest activity with 26% DPPH radical scavenging activity. MPCC water extract showed a 13% ABTS radical scavenging activity.