Examination of the effect of different cooking methods on the antioxidant capacity and phenolic compound content of kaldirik plant (trachystemon orientalis (L.) G. don)

There are many plants rich in antioxidant capacity and phenolic compounds in nature. Cooking methods applied to make plants consumable change the antioxidant capacity and phenolic compound content of the plant. Kaldirik is a plant found and consumed in the Black Sea region. In this study, it was aimed to investigate the effect of different cooking methods on the antioxidant capacity and phenolic compound content of kaldirik plant. Kaldirik plant (Trachystemonorientalis (L.) G. Don) grown in Rize province in the Eastern Black Sea region and collected in May 2021 was included in the study. The collected kaldirik plant was transferred to the Rize Recep Tayyip Erdogan University Central Research Laboratory and cleaned. Six different cooking methods, including boiling (5, 10, and 15 mins.), roasting (5, 10, and 15 mins.), microwave cooking (3, 5, and 7 mins.), pressure cooking (3, 5, and 10 mins.), steam cooking (5, 10, and 15 mins.) and sous vide (vacuum cooking) (15, 30, and 45 mins.), were applied to the kaldirik plant, and three different cooking times were tried separately for each cooking method. While the Folin-Ciocalteau method was used to determine the total phenolic content of raw and cooked kaldirik plants, the Iron (III) Ion Reducing Antioxidant Capacity (FRAP) method, the Copper (II) Ion Reducing Antioxidant Capacity (CUPRAC) method, and the DPPH Radical Sweeping Capacity method were used to determine the antioxidant capacity. Phenolic compound content was determined using High Performance Liquid Chromatography (HPLC). Since the total phenolic content and antioxidant capacity values are calculated on dry matter, the calculations of all samples were made on dry matter. Three parallel replications were made for the results and the averages were taken. The total phenolic content of the raw caldiric plant was determined to be 4.83±0.32 mg gallic acid equivalent/g dry matter. While the CUPRAC value of the raw kaldirik plant was found to be 138.86±5.17 mmol Trolox/g dry matter, the FRAP value was found to be 44.74±0.59 μmol FeSO4.7H2O/g dry matter. It was revealed that the total amount of phenolic substances, FRAP and CUPRAC values increased in roasting, microwave cooking and sous vide methods compared to raw kaldirik plant (p<0.05). In steam cooking, on the contrary, it was determined that the total amount of phenolic substances, FRAP and CUPRAC values decreased with the prolongation of the cooking time (p<0.05). The DPPH• radical sweeping capacity of the raw kaldirik plant was determined to be 0.43±0.33 mg/mL. It was determined that the highest total phenolic content and antioxidant capacity belonged to the kaldirik plant, which was roasted for 15 minutes, while the lowest total phenolic content and antioxidant capacity were found to belong to the kaldirik plant that was steamed for 15 minutes. In terms of phenolic compound content, new phenolic compounds (protocatechuic acid and p-coumaric acid) were revealed in all cooking methods except steam cooking, compared to raw plant. A highly significant correlation was found between antioxidant determination methods and total phenolic substance content (p<0.05). As a result, it was determined that the best cooking method and time for the kaldirik plant in terms of total phenolic substance content and antioxidant capacity was roasting for 15 minutes. In future studies, the bioavailability, metabolism and absorption of antioxidant and phenolic compounds can be evaluated, supported by human and animal studies. Key Words: Kaldirik Plant, Cooking Methods, Antioxidant Capacity, Phenolic Component