Investigation of oxidation parameters and some quality properties of sunflower oil depending on bleaching earth type and deodorization temperature

The cultivation of sunflower (Helianthus annuus) in Türkiye is predominantly carried out in the Thrace and Central Anatolia regions. Sunflower oil, extracted from sunflower seeds, is widely preferred by consumers due to its neutral flavor and odor, high linoleic/oleic acid content, and long shelf life. According to 2023–2024 data, Türkiye's annual domestic consumption of sunflower oil is approximately 1.39 million tons, with exports reaching nearly 1.1 million tons. Crude sunflower oil, which is not suitable for direct consumption due to high free fatty acid (FFA) content, unpleasant taste and odor, short shelf life, and microbiological risks, must undergo a series of refining processes to become suitable for consumption. These processes reduce FFA levels and remove impurities from the oil. Determining the appropriate industrial-scale refining parameters is essential to make sunflower oil ideal for end-users. The effects of earth types used during the bleaching stage and temperature parameters applied during the deodorization stage in the refining of sunflower oil were investigated in industrial-scale systems through the thesis study conducted. During the bleaching stage, two types of earth were used: acid-activated (AAT) and neutral (NT). Following bleaching, the effects of deodorization at 215°C, 225°C, and 235°C were evaluated. To assess key chemical quality parameters of the oil, analyses such as free fatty acidity (FFA), peroxide value (PV), p-Anisidine value (AV), TOTOX value, and conjugated dienes were conducted. Antioxidant capacity was determined by measuring total phenolic content using spectrophotometric methods and quantifying α- and β-tocopherol as well as α-tocotrienol via high-performance liquid chromatography (HPLC). Fatty acid methyl esters were identified using gas chromatography (GC). The refining process led to significant improvements in fundamental quality parameters such as FFA. The FFA content in crude oil, initially measured at 0.61% (as oleic acid), was reduced to as low as 0.04% in samples treated with acid-activated bleaching earth. Reductions in PV and AV values after refining indicated decreased oxidative degradation. The lowest TOTOX values were observed in samples processed with AAT and deodorized at 225–235 °C. In terms of physical stability, cold test results showed that only crude oil exhibited turbidity, while refined samples remained visually clear. Analyses related to antioxidant properties revealed that the total phenolic content reached up to 45.27 mg GAE/100 g in oils refined with NT at 235 °C, indicating that certain refining conditions can effectively minimize antioxidant loss despite high processing temperatures. Although some loss of tocopherols and tocotrienols occurred due to thermal and chemical exposure during refining, the highest total levels were preserved in samples processed with AAT and deodorized at 235 °C. The fatty acid composition, including saturated, monounsaturated, and polyunsaturated fatty acids, did not show statistically significant variation throughout the process, suggesting that the applied refining conditions did not adversely affect these components. On average, the samples contained 11.4% saturated, 28.5% monounsaturated, and 60.1% polyunsaturated fatty acids. All quality parameters remained within the permissible limits defined by the Turkish Food Codex (2012/29) and Codex Alimentarius (CXS 210-1999). Among the tested refining parameters, the combination of acid-activated bleaching earth and 235 °C deodorization yielded the most favorable outcomes.