Turkey is the leading producer and exporter of hazelnuts, producing approximately 64% of global hazelnut production. This research investigated the effects of cultivars and altitude on the phenolic, antioxidant, and fatty acid compositions of five hazelnut cultivars grown at three different altitudes, 100 m, 350 m, and 800 m, in Ordu province, one of the territories that produce the most hazelnuts. The results showed that the cultivar and location significantly affected phenolic compounds, antioxidant activity, and fatty acid (FA) content. The lowest (2.30 mg/kg-Yağlı) and highest (21.11 mg/kg-Kara) gallic acids were obtained at 100 m. The highest total phenolic content and antioxidant activity were found in the nuts grown at 350 m in the Kara and Palaz cultivars, at 100 m in the Yağlı and Sivri cultivars, and at 800 m in the Çakıldak cultivar. Oleic acid was the predominant FA in the cultivars and possessed a diverse trend according to the altitude and cultivar, ranging from 76.04% to 84.80%, increasing with altitude in all cultivars except Çakıldak. Palmitic acid was the predominant saturated FA followed by stearic acid, which significantly varied according to the elevations. This study suggests that the responses of hazelnuts to altitude depend on the cultivar; hence, a proper approach to producing nuts containing more phenolic, fatty acids, and antioxidant activity includes choosing a suitable cultivar for a specific elevation.

The present study aims to investigate the substrate (4-methyl catechol and catechol) specificity and inhibition mechanisms (l-ascorbic acid, citric acid, and l-cysteine) of the tyrosinase enzyme (TYR), which is held responsible for browning in foods and hyperpigmentation in the human skin, through kinetic and molecular docking studies. During the experimental studies, the diphenolase activities of TYR were determined, following which the inhibitory effects of the inhibitors upon the diphenolase activities of TYR. The inhibition types were determined as competitively for l-ascorbic acid and citric acid and noncompetitive for l-cysteine. The kinetic results showed that the substrate specificity was better for catechol while l-cysteine showed the best inhibition profile. As for the in silico studies, they also showed that catechol had a better affinity in line with the experimental results of this study, considering the interactions of the substrates with TYR's active site residues and their distance to CuB metal ion, which is an indicator of diphenolase activity. Besides, the inhibitory mechanisms of the inhibitor molecules were explained by the molecular modeling studies, considering the binding number of the inhibitors with the active site amino acid residues of TYR, the number and length of H bonds, negative binding energy values, and their distance to CuB metal ion. Based on our results, we suggest that the novel method used in this study to explain the inhibitory mechanism of l-cysteine may provide an affordable alternative to the expensive methods available for explaining the inhibitory mechanism of TYR and those of other enzymes. Communicated by Ramaswamy H. Sarma Graphical Abstract

Hydrogen peroxide (H ₂ O ₂ ) is a chemical that is widely used in many industrial processes, and, except at certain concentrations, it is toxic in biological systems such as water and air. Among enzymes, catalases are important industrial enzymes because of their role in the conversion of hydrogen peroxide to water and molecular oxygen. Herein, catalase (CAT) from Hydnum repandum was purified 3.02-fold with a yield of 68.10% by three-phase partitioning (TPP) for the first time. The purified catalase was immobilised on glutaraldehyde-activated chitosan (Glu-Cts), and its applicability for the removal of hydrogen peroxide released from industrial processes was investigated. The results of the present study showed that the optimum pH and temperature were found to be 7.0 and 30°C for both free and immobilised catalase (CAT-Glu-Cts). The catalytic efficiency ( V _max / K _m ) of the immobilised enzyme increased 8-fold compared to the free enzyme. CAT-Glu-Cts was shown to have better pH, thermal stability, and storage stability than free CAT. In this study, >96% of 6 mM, 15 ve 24 mM H ₂ O ₂ was removed from artificial wastewater after 2 h using immobilised catalase. We expect that CAT-Glu-Cts, obtained by purifying a plant-derived catalase and immobilising it into an environmentally friendly and biocompatible material, is a promising candidate that can be safely used for H ₂ O ₂ removal in various branches of industry.

The polyphenol oxidase (PPO) enzyme leads to undesirable consequences by causing enzymatic browning during the processing of vegetables and fruits. As these browning reactions occur, many phenolic compounds of PPO can lead to significant changes in active metabolites due to substrate utilization. This may cause a loss of appearance and nutritional and commercial value of food. The sickleweed (Falcaria vulgaris Bernh.) plant studied in the current research is considered an edible and medicinal food. In the present research, polyphenol oxidase was purified 15.65-fold with a yield of 23.61% by affinity chromatography. The optimum pH and temperature for catechol, 4-methylcatechol, and 3,4-dihydroxyphenylpropionic acid substrates were determined in separate experiments. For all three substrates, the optimum pH was 7.0, while the optimum temperature was 20 °C. The catalytic efficiency ratio (V_max/K_m) was employed to assess the substrate specificity. Since the highest V_max/K_m ratio reflects the greatest substrate affinity, 4-methylcatechol was identified as the substrate with the highest affinity for sickleweed PPO based on these values. pH stability and thermal stability were examined in the presence of 4-methylcatechol. The inhibitory effects of widely used antibrowning agents, sodium metabisulphite, citric acid, and ascorbic acid, on PPO activity were investigated. The results show that ascorbic acid was the most efficient inhibitor.