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.

Enzymatic browning, catalysed by the enzyme polyphenol oxidase in fruit and vegetables, limits the efficient use of natural resources and promote food waste. Plums are a popular fruit with consumers around the world and are considered an important raw material in the food industry. Plums are very susceptible to enzymatic browning due to their high phenolic compound content and climacteric nature. The aim of this study is to purify the polyphenol oxidase enzyme from Sarali plum (Prunus domestica) and to determine its biochemical properties, kinetic parameters, pH and thermal stability and inhibition. In this study, polyphenol oxidase enzyme was purified 22.54-fold by affinity chromatography using Sepharose-4B-l-Tyr-p-amino benzoic acid affinity gel. The purity and molecular mass of the enzyme were determined by SDS-PAGE and non-denaturing PAGE (native PAGE). The molecular mass of the enzyme was estimated to be 72.44 kDa by SDS-PAGE. The enzyme was confirmed as PPO by native PAGE as a single band. Kinetic characterization studies were conducted for both catechol and 4-methyl catechol substrates. The optimal pH and temperature for both substrates were found to be 7.0 and 20 °C, respectively. The thermal stability of PPO was investigated, and it retained about 90% of its activity for 90 min at 4 °C. The determination of K_M and V_max was carried out using the Lineweaver–Burk plot. The substrate specificity (V_max/K_M) values for catechol and 4-methyl catechol were determined as 790.91 ± 37.34 and 492.06 ± 13.75 respectively. The enzyme exhibited the best activity towards catechol substrate. IC₅₀, K_i constant and inhibition types were determined for various anti-browning agents on PPO enzyme. Ascorbic acid, l-cysteine, citric acid, salicylic acid and tartaric acid effectively inhibited PPO activity.

Enzymatic treatment systems play a significant role in the removal of phenolic pollutants from water, and naturally occurring clay minerals such as Turkish Green Clay (TGC) offer effective and environmentally friendly support materials for enzyme immobilization. In this study, polyphenol oxidase (PPO) was partially purified 10.70-fold with a yield of 15.21% from the zeferan peach ( Prunus persica L.) cultivar using the cold acetone precipitation method. Enzyme was immobilized onto TGC, and immobilization was confirmed by scanning electron microscopy (SEM). The immobilization yield was calculated as 37.26% based on activity measurements before and after immobilization. Both free and immobilized PPO exhibited an optimum pH of 7.0 and an optimum temperature of 30 °C. Kinetic analysis revealed K _m and V _max values of 2.13 mM and 1250.00 EU.mL ⁻¹ .min ⁻¹ . for the free enzyme and 1.0 mM and 1111.11 EU.mL ⁻¹ .min ⁻¹ . for the immobilized enzyme, indicating an increased affinity toward 4-methylcatechol upon immobilization. The immobilized enzyme exhibited superior thermal and pH stability compared to the free enzyme. Storage stability was evaluated at 4 °C for 15 days by measuring residual activity at 24-h intervals. After 15 days, the immobilized enzyme retained 69.75% of its initial activity, whereas the free enzyme maintained only 23.41% of its original activity. To assess the potential of the immobilized polyphenol oxidase for water treatment applications, phenol solutions at concentrations of 4, 8, 15, and 20 mg/mL were prepared and subjected to removal studies. The immobilized PPO eliminated phenol by 95.14%, 47.95%, 18.01%, and 11.7%, respectively. These results demonstrate that the immobilized enzyme is highly effective at removing phenol, particularly at low concentrations, and highlight its promise as an environmentally friendly biocatalyst for the treatment of phenol-contaminated water.