Studies on the Antioxidant Effect of Rosemary Extract in Corn Oil

 Abstract: In this paper, the optimal additive amount of homemade rosemary extract in corn oil was investigated under accelerated storage conditions at 60 ℃ with peroxide value (POV) and malondialdehyde content as the indexes, and the effects of the same additive amount were compared with those of the same models of products from three companies, natural and synthetic antioxidants in corn oil. The results showed that the optimum amount of homemade rosemary extract in corn oil was 0.2‰, which had the best antioxidant effect among the same types of products, and was significantly better than VE, BHA and BHT, but weaker than tea polyphenols and TBHQ.

 

Oils and fat-rich foods are easily oxidized during storage, which reduces their nutritional value and even produces toxic substances, and the addition of antioxidants can effectively inhibit their oxidation [1]. However, synthetic antioxidants such as BHT, TBHQ, etc., although more effective, have certain toxicity and even carcinogenic effects [2,3]. As a natural antioxidant, rosemary extract has the advantages of safety, high efficiency and high temperature resistance [4-6].

 

Rosemary is a perennial evergreen shrub of the Labiatae family native to the Mediterranean region, and was introduced into China by the Institute of Botany, Chinese Academy of Sciences in 1981. At present, there have been a lot of studies on the application of rosemary extract in food, but the antioxidant effect in corn oil has not been reported. In this paper, we investigated the optimal amount of rosemary extract added to corn oil at 60 ℃ by using POV and malondialdehyde content as indexes. A systematic comparison was made with the same models of products from three companies in the market, and with the effects of commonly used synthetic and natural antioxidants in corn oil at the same dosage level, which is of great significance for the application of rosemary extract in fats and oils.

 

1 Materials and Methods

 

1.1 Raw materials and reagents

Rosemary Extract (30% of Sage, laboratory made and purchased from companies A, B and C), Corn Oil (Nanhai Oils and Fats Industry Co., Ltd.).

Potassium iodide, sodium thiosulfate, soluble starch, trichloroacetic acid, disodium ethylene diamine tetraacetic acid, thiobarbituric acid, glacial acetic acid, trichloromethane, all of the above reagents were analytically pure; 1,1,3,3-tetraethoxypropane (Tokyo Nisei Kogyo Co., Ltd., Tokyo, Japan); 98% tea polyphenols (Chaozhou Yilong Plant Technology Co., Ltd., Chaozhou, China); VE (Germany, MERCK Company); BHA, BHT, VE (MERCK, Germany); BHA, BHT, TBHQ (Guangyi Food Additives Co., Ltd.).

 

1.2 Instruments and equipment

PL-203 electronic balance (METTLER TOLEDO INSTRUMENTS CO., LTD.), DF-101S water bath (Gongyi IYUHUA INSTRUMENTS CO., LTD.), U-3010 spectrophotometer (Hitachi High-Technologies Co., Ltd., Japan), DL-5-B centrifuge (Shanghai ANTING SCIENTIFIC INSTRUMENTS FACTORY), ultrasonic wave (Shenzhen Heboda Ultrasonic Equipments Co., Ltd.), DHG-9070 electric heating constant temperature blower drying box (Shanghai Qixin Scientific Instruments Co., Ltd.). （DHG-9070 Electrothermal Constant Temperature Drying Box (Shanghai Qixin Scientific Instrument Co., Ltd.).

 

1.3 Experimental Methods

1.3.1 Sample pre-treatment

Weighing 0, 15, 30, 45, 60, 75 mg of rosemary extract in turn, adding 150 g of corn oil and ultrasonicating for 15 min, the rosemary extract was fully dissolved into corn oil, and the oil samples containing 0, 0.1‰, 0.2‰, 0.3‰, 0.4‰, 0.5‰ of rosemary extract were prepared. Then the oil samples were evenly divided into three 100 mL triangular bottles and put into a 60 ℃ blast drying oven, and the samples were taken every 3 d to determine the POV and malondialdehyde content in the corn oil.

30 mg of rosemary extract, VE, tea polyphenols, BHA, BHT and TBHQ were weighed sequentially and added into 150 g of corn oil, and ultrasonicated for 15 min, so that the antioxidants were fully dissolved into the corn oil, and the oil samples with antioxidant content of 0.2‰ were prepared. Then the samples were evenly divided into three 100 mL triangular bottles and placed into a 60 ℃ blast drying oven, and the samples were taken every 3 days to determine the POV and malondialdehyde content in corn oil.

 

1.3.2 POV measurement

In the early stage of oxidation, the oil mainly produces hydroperoxides, and the determination of POV can reflect the degree of oxidation of the oil in the early stage of oxidation.The method of determining POV refers to the titration method of GB/T5009.37-2003, and the sampling volume of corn oil was 1 g at the early stage of the experiment, and the sampling volume was reduced appropriately as the value of POV was gradually increased with the progress of the experiment.

 

1.3.3 Plotting of malondialdehyde standard curve and determination of its content 1.3.3.1 Determination of malondialdehyde content

The hydroperoxides generated in the early stage of oxidation are extremely unstable, and will be further decomposed to produce malondialdehyde and other small molecules, so the change of malondialdehyde content can reflect the degree of oxidation in the late stage of the oils and fats. For the determination of malondialdehyde content, refer to GB/T5009.181-2003, the sampling volume of corn oil in the early stage of the experiment was 3 g, and the dosage of TCA mixture was 15 mL, and the sampling volume was reduced appropriately with the progress of the experiment due to the gradual increase of malondialdehyde content.

 

1.3.3.2 Preparation of a standard curve for malondialdehyde

Weigh 31.5 mg of 1,1,3,3-tetraethoxypropane accurately, dissolve and dilute to 100 mL to obtain malondialdehyde standard stock solution, and store in the refrigerator. Pipette 10 mL of the above stock solution accurately, dilute to 100 mL, get the malondialdehyde standard use solution, put in the refrigerator for spare. Pipette 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 mL of malondialdehyde standard solution into a 25 mL cuvette, dilute it with water to 5 mL, then add 5 mL of thiobarbituric acid solution, and then operate according to the method of the sample determination. The standard curve was plotted according to the relationship between the concentration of malondialdehyde standard solution and the absorbance value, as shown in Figure 1.

The regression equation for the standard curve was obtained as: y=1.0178x-0.0157, R2=0.9996.

 

2 Results and analysis

2.1 Determination of the optimal additive level in corn oil

The effects of the homemade rosemary extract on the POV and malondialdehyde content of corn oil at different dosages are shown in Figures 2 and 3. From Figures 2 and 3, it can be seen that for the same dosage, the POV and malondialdehyde contents in corn oil increased significantly with time. For different dosage levels, the POV and malondialdehyde contents in corn oil showed a decreasing trend with increasing dosage at the same time. However, when the addition amount was higher than 0.2‰, the decrease of POV and malondialdehyde content was not obvious, and at this time, increasing the amount of rosemary extract had little effect on the POV and malondialdehyde content in corn oil. Therefore, it can be determined that the optimal amount of homemade rosemary extract in corn oil is 0.2‰. 2.2 Comparison of antioxidant properties in corn oils

 

2.2.1 Comparison with products of different companies

The effects of home-made and different companies' rosemary extracts on the POV and malondialdehyde content of corn oil are shown in Figures 4 and 5. As can be seen from Figures 4 and 5, both the home-made and different companies' rosemary extracts had significant inhibitory effects on the oxidation of corn oil. At day 12, the POV in corn oil was 153.43±0.92, 36.99±1.90, 97.21±2.95, 64.02±0.54, and 79.91±0.38 meq/kg for the blank, and for the rosemary extracts from the housemade, company A, company B, and company C, respectively, and the POV in corn oil was 0.9±1.92, 36.99±1.90, 97.21±2.95, 64.02±0.54, and 79.91±0.38 meq/kg for the housemade, company A, company B, and company C, respectively, relative to the blank. The inhibition rates of POV in corn oil were 76.0%, 37.1%, 58.5%, and 48.3% with the addition of homemade, Company A, Company B, and Company C extracts, respectively, compared to blank. At d 12, the

The malondialdehyde content in the blank was 2.34, 1.39, 1.73, and 1.44 times higher than that in corn oil with the addition of homemade, company A, B, and C rosemary extracts, respectively. Therefore, the homemade rosemary extract had the best antioxidant effect in the oils.

 

The antioxidant effect of different rosemary extracts in corn oil varied somewhat despite the same content of rhamnosus acid, probably due to differences in the composition and content of other antioxidant components. Studies have shown that rhamnoside is the most abundant and antioxidant component of rosemary [7]. However, there are some other components, such as rhamnetol, geraniol, and 7-methyl-epi-rosemarylphenol, etc. [8-10], which are not as strong as rhamnetol, but also inhibit the oxidation of corn oil to a certain extent.

 

2.2.2 Comparison with natural antioxidants

The antioxidant effects of the homemade rosemary extract in corn oil were compared with those of the natural antioxidants VE and tea polyphenols as shown in Figures 6 and 7. The antioxidant effects of rosemary extract in corn oil were comparable to those of tea polyphenols and significantly better than those of VE. At d 12, the POV of corn oil with VE was 4.02 times higher than that of the homemade rosemary extract, and the malondialdehyde content was 2.19 times higher than that of the homemade rosemary extract, but it was slightly weaker than that of tea polyphenols. Tea polyphenols were partially insoluble in the corn oil, and the dark red color of tea polyphenols had a certain effect on the color of the corn oil, while rosemary extract had a better solubility in the fat and had no obvious effect on its color. In summary, rosemary extract was more advantageous than tea polyphenols.

 

2.2.3 Comparison with synthetic antioxidants

A comparison of the antioxidant effects of the homemade rosemary extract with those of the commonly used synthetic antioxidants BHA, BHT and TBHQ in corn oil is shown in Figures 8 and 9. From Figures 8 and 9, it can be seen that the antioxidant effect of rosemary extract in corn oil was significantly better than that of BHA and BHT, and the POV and malondialdehyde content of corn oil with BHA was 4.08 times higher than that with homemade powder at day 12, but slightly weaker than that of TBHQ.

 

3 Conclusion

3.1 Homemade rosemary extract has good antioxidant effect in corn oil, and its oxidation degree was inhibited at the dosage of 0.2‰ in corn oil. Therefore, the optimum amount of homemade rosemary extract in corn oil can be determined as 0.2‰.

3.2 The antioxidant effect of homemade rosemary extract in corn oil was significantly better than that of natural antioxidant VE and synthetic antioxidants BHA and BHT, and slightly weaker than that of tea polyphenols and TBHQ at the same dosage level, so it can be a good substitute for synthetic antioxidants in oils and fats.

 

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