Effect of thyme and ginger metanoic extraction on the oxidative stability of sunflower oil

Due to unsaturated fatty acids of GSO, is exposed to various types of chemical reactions, including enzymatic reactions and lipid oxidation. In this regard, the use of antioxidants for increasment the resistance of the oil to oxidation, is essential. Due to the poor nutritional and cancerous effects of these compounds and the consumer's desire to use natural compounds, the use of natural antioxidants is considered by researchers instead of industrial antioxidants. Spices (ginger, pepper, cinnamon, cardamom, thyme) and aromatic vegetables such as basil and peppermint with essential oils (EOS) containing multiple polyphenols with anti-oxidant and anti-microbial properties are a good source of natrul antioxidant (Teixeira et al., 2013; Srinivasan, 2017). Ginger is an important medicinal herb and has several properties, including anti-nausea, cardiovascular, antibacterial, liver anti-inflammatory, lowering blood cholesterol stimulates brain circulation and stimulates digestion. The presence of antioxidants in ginger causes the removment of free radicals from oil. Thyme is the other valuable herbs with high antioxidant and antimicrobial activity and is one of the world's best herbs in terms of high levels of antioxidants. The phenolic antioxidants in thyme, eliminate free radicals and prevent oxidative stress in all body systems. In spite of studies on the use of phenolic compounds in oxidation stability of oils, the use of ginger and thyme EOS in combination, as a natural antioxidant has not been investigated for the stability of grape seed oil. By extracting these phenolic compounds and adding to grape seed oil, it can be expected that the oleoresin in these plant extracts, in comparison to industrial antioxidants, increases the oxidative stability of grape seed oil. Methods Extraction of phenolic compounds from ginger and thyme 25 g of powdered ginger or thyme was placed in a cellulose ring of suksele apparatus. Then their phenolic compounds were extracted using methanol solvent. Extraction was done at a temperature higher than boiling point of solvent (65 °C) and continued until extraction complete. The solvent was removed using a rotary evaporator and the extracted compounds was stored for further experiments in the refrigerator (Seidi Damyeh and Niakousari, 2015). Different types and concentrations of metanoic extraction were added to GSO (Table 1) and experiments was done during 45 days of storage. Table 1 Number Timar 1 Control sample (grape seed oil without antioxidant) 2 GSO+ α-tocopherol (200 ppm) 3 GSO+ ginger phenolic compounds (300 ppm) 4 GSO+ thyme phenolic compounds (300 ppm) 5 GSO+(ginger+thyme) phenolic compounds (300 ppm) Experiments The properties of sunflower oil including acidity, peroxide and tiobarbioturic acid (TBA) indices, total phenol and antioxidant activity were studied during 45 days of storage. Statistical Analysis The results were analyzed using completely randomized blocks during 45 days of the storage time. One-way ANOVA and Duncan’s mean comparison tests were used at 5% significance (p < 0.05). Results and discussions Acidity acidity of the all samples increased significantly during the 45 days of storage (p < 0.05). The sample contained 300 ppm of (thyme and ginger) phenolic compounds on the 45th day had the lowest acidity and the highest acidity was observed in the sample without antioxidants (control sample). GSO containing two species of thyme and ginger had fewer amounts of FFA and were able to prevent oxidation, resulting in less acidity, Peroxide index The rate of peroxide index increased significantly during the 45 days of storage. In all days, the control sample had the highest amount of peroxide because the presence of antioxidants in different samples caused the peroxide to be neutralized and consequently reduced its amount and against the lowest index after 45 days of the sample. TBA index In all samples, the level of TBA index increased significantly, while the lowest amount of the index after 45 days of storage was related to the sample containing α-tocopherol and the sample containing 300 ppm of thyme metanoic extraction. It should also be noted that no significant difference was found between them. In the case of other treatments, it can be stated that the highest level of this index is related to the control sample without any antioxidants. TBA index shows the amount of secondary oxidation products, especially aldehydes. Total phenol Over time, Total phenol (mg of gallic acid per liter) of oil samples containing different concentrations of antioxidants has been significantly reduced in all samples. According to the results, it can be stated that with increasing concentrations of phenolic compounds in oil samples, the total phenol content also increased. This can be attributed to the presence of phenolic compounds in both essential oils of thyme and ginger. Phenolic compounds play an essential role in antioxidant activity due to the presence of hydroxyl groups in their structure and their ability to donate hydrogen to the free radicals. Conclusion The results showed acidity of the samples increased during storage. Peroxide value and TBA of sunflower oil samples were significantly increased during storage. The lowest amount of these indices after 45 days was related to the samples containing α-tocopherol and 300 ppm mixture of ginger and thyme, respectively. The total phenol also was increased by increasing the concentration of extract which can be due to the presence of phenolic compounds in the ginger and thyme extracts. The radical scavenging activity of all samples was decreased during storage. The highest antioxidant activity was related to the samples containing α-tocopherol and then those containing 300 ppm of ginger +thyme extract In general, it can be concluded that the metanoic extraction of ginger and thyme can be used as a natural antioxidants in the edible oils to prevent their oxidation.