The effect of the use of natural antioxidants (thyme and ginger oleoresin) on the physical, chemical and sensory properties of sesame oil.

Introduction: Sesame oil is one of the most important edible oils, which is prone to oxidation spoilage due to its relatively high unsaturation. Oxidative stability is one of the important and effective factors for oil storage, especially in long-term storage conditions, high temperature, oxygen, light, or the presence of some pollutants. Oxidation in oils causes unpleasant smell, taste and color change. The free radicals resulting from the spontaneous oxidation reaction of fats, having single electrons, are very reactive and cause a lot of damage to biological molecules such as proteins, lipids, nucleic acids and carbohydrates, which by using Oils can be protected from synthetic or natural antioxidants. New reports indicate that synthetic antioxidants are harmful to human health, so attention has been focused on natural antioxidants, of which spices and aromatic plants such as ginger and thyme are good sources. they go Aromatic plants and spices contain essential oils and oleoresins, the health-giving and antioxidant effects of these compounds have been mentioned in various studies (Sirnivasan, 2017). In addition to healing properties, plant extracts also have good antioxidant properties and their use can play a multi-purpose role in the food system containing fat. Therefore, the use of natural materials instead of synthetic materials, which, in addition to increasing the shelf life, also increases the nutritional value of the product, can play an important role in consumer nutrition. Essential oils, oleoresin extracted from different plant species, including all kinds of spices (ginger, pepper, cinnamon, cardamom, thyme, etc.) and aromatic vegetables such as basil and mint, which contain volatile aromatic compounds with polyphenol There are many substances with antioxidant and antimicrobial properties. Essential oils are generally liquid at room temperature and their solubility is low compared to fats, alcohols, organic solvents and other solutions. Hydrophobicity is low in water (Al-Esbahani et al., 2015). Although water distillation and steam distillation as well as solvent extraction method are the most applicable methods on an economic scale to extract essential oils, several extraction technologies New methods including extraction with supercritical fluid, using ultrasound (Garcia, 2004) and extraction with the help of microwaves are known as new industrial methods and have been developed as alternatives to traditional methods. Ginger is one of the important medicinal plants. and it is also used as a seasoning in the food industry. The presence of antioxidants in ginger cleans free radicals. Gingerol is the most important constituent of ginger, which is responsible for Create flavor in this plant. According to the variable amount of ginger essential oil, which the medicinal value of ginger depends on, varieties of ginger that have more than 1.5% essential oil have medicinal value (Sirnivasan, 2017; Bayala et al., 2014). The main ingredients of ginger are sugars, fats, oleoresin, and burning aromatic compounds. The special taste of ginger is due to volatile oils (essential) and compounds such as zingerone, shogaols and gingerols (Sirnivasan, 2017). Generally, the zingeron, gingerol and shogaol (or shagoal) parts of ginger are called its oleoresin part (Sirnivasan, 2017). According to the mentioned contents and the use of antioxidant as a solution to prevent the progress of oxidation in all kinds of edible oils by extracting the oleoresin of these two plants and adding it to sesame oil, it can be expected that the oleoresin present in these vegetable extracts compared to industrial antioxidants, increase the oxidative stability of sesame oil.
Material and Method: In the present study, Thyme and ginger plants were procured in dry form from the local market of Tabrizand then they were made into powder form by TS-1400 laboratory mill (28000 rpm and 2600 w) for conducting experiments. Sesame oil was also prepared in raw and unrefined form from oil extraction under a press (Tabriz).
Oleoresin extraction from ginger and thyme:
After separating the impurities, ginger and thyme were ground and passed through sieve number 40. Then 25 grams of ginger or thyme powder was poured into a cellulose thimble and placed in a Soxhlet apparatus. Then oleoresin was extracted using methanol solvent. The extraction was done at a temperature higher than the boiling temperature of the solvent (65 degrees Celsius) and continued until the extraction was complete. Then the solvent was removed using a rotary evaporator. Then the extracted oleoresin was cooled and stored in the refrigerator for further tests (Sidi et al. 2015). Next, oleoresin prepared from thyme and ginger at a concentration of 300 ppm was added to sesame oil, and in another experimental treatment, industrial alpha-tocopherol was added to the same sesame oil as an industrial antioxidant, and at the end of the antioxidant power of these two oleoresins together and were compared with the control sample (containing the industrial antioxidant alphatocopherol). The shelf life of sesame oil was considered to be 45 days and sampling was done every 10 days and the last sampling was done with a time interval of 15 days.
Measurement of peroxide index
peroxide value was calculated in terms of milliequivalents of oxygen per kilogram of oil based on the following formula (Iranian National Standard 4179). P=(1000×N×V)/W
V = amount of sodium hyposulfite consumed in mL, N = normality of sodium hyposulfite solution, W = oil weight in gr, P = peroxide value in milliequivalents of oxygen per Kg of oil
Total phenol content
In this research, the method of Singleton and Rossi (1965) was used with a slight modification to measure the amount of total phenol. First, the amount of 200 microliters of the diluted sample was mixed with the amount of 0.1 ml Folin-Ciocaltio reagent and kept at room temperature for 8 minutes. Then 0.8 ml of sodium carbonate solution (7.5%) was added to the above mixture and after 30 minutes of storage at ambient temperature, the absorbance of the samples was read at the wavelength of 765 nm. The equivalent concentration was obtained by placing the absorbance in the standard curve. The results were reported as gallic acid equivalent in 100 ml of sample (mg of gallic acid per liter).
The antioxidant activity of the oil samples was measured based on their ability to inhibit 2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. For this purpose, a methanol solution of DPPH with a concentration of 0.1 mM was first prepared. 0.1 ml of sample solution was mixed with 3.9 ml of DPPH solution. The absorbance of the samples was read after 20 minutes at a wavelength of 517 nm using a spectrophotometer.(Teminago et al. 2005).
Free radical inhibition percentage=(absorption control-absorption sample)/(absorption control)×100
Sensory evaluation for the attributes of taste, smell, color and overall acceptance was done by 10 semi-trained sensory evaluators using a 5-point hedonic test. A score of zero was considered for unacceptable quality,
The statistical technique of this research in the inferential part includes two-way ANOVA. The statistical software SPSS (version 19) was used for the desired statistics. 5% p-value was used to evaluate the significance level and the obtained results were analyzed based on the completely randomized block design during the storage period of 45 days.
Results and discussion: The amount of peroxide index increased significantly during the storage period. The lowest amount of this index after 45 days was related to samples containing alpha-tocopherol and 300 ppm oleoresin of thyme and ginger. According to the obtained results, it was found that with the simultaneous use of two oleoresins in oil samples containing two essential oils of thyme and ginger, the amount of total phenol also increased, which could be related to the presence of abundant phenolic compounds in both ginger and thyme oleoresins. be The inhibition percentage of free radicals of all oil samples significantly decreased during 45 days of storage. The highest inhibition percentage of these radicals was related to the sample containing alpha-tocopherol, and then the sample containing 300 ppm oleoresin of thyme and ginger together had the highest inhibition percentage. The relatively high antioxidant effect of thyme essential oil is due to the presence of phenolic compounds thymol and carvacrol in its essential oil, followed by monoterpenes terpinolene and hydrocarbons such as gamma-terpinene. Also, due to the fact that thymol is the main substance of thyme essential oil and this substance reacts with oxidant compounds in a short period of time, therefore, within 20 minutes, the essential oil of the plant shows a good antioxidant effect (Sharififar et al. 2007). The results of sensory evaluation showed that the addition of antioxidants to oil did not cause any specific changes in the parameters related to sensory evaluation.
Conclusion: According to the obtained results, it can be stated that with the use of two oleoresins of thyme and ginger in the oil samples, the amount of total phenol also increased, which could be related to the presence of phenolic compounds in the oleoresins of ginger and thyme. be The addition of antioxidants to the oil did not cause any specific changes in the sensory evaluation parameters. In general, it can be concluded that thyme and ginger oleoresins can be used as natural antioxidants to inhibit the oxidation of edible oils, including oils containing high amounts of omega-6 and omega-3.oleoresin of various essential oils (ginger and thyme) can be used as a natural antioxidant to inhibit the oxidation of edible oils, including sesame oil.