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Background and purpose: In recent years, the use of natural substances such as essential oils and extracts has been emphasized in place of chemical preservatives in the food industry. green walnut skin is an agricultural waste that, due to its phenolic compounds, can be considered as a natural combination containing biological properties, and it reduces many of the incurable diseases and prevents the oxidation of lipids and is used as antimicrobial factors. In this study, the content of phenolic compounds, antioxidant and anti - bacterial properties of methanolic extracts of green walnut skin was investigated.
Materials and Methods: Extraction was carried out using both soaking and soxhelt methods in  60% and 80% methanol solvent. The amount of phenolic compounds of the extract was determined by spectrophotometric method.
The anti-radical activity of the extract was evaluated by DPPH radical inhibitory test. Antibacterial activity of the extract was investigated by disc diffusion method against Salmonella typhimurium, Shigella dysentery and Listeria monocytogenes. Collected data were analyzed using SPSS software and Duncan test.
Results: The total phenol content for soaking and soxhlet methods was respectively 17.81 and 89.07, according to Gallic acid equivalent, based on mg / g of sample. EC50 amount of green walnut skin was 0.15 mg / ml. The  Remarkable antimicrobial activity was observed against all studied bacteria. MIC was between 1.625 and 1.25 and MBC between 1.2 and 2.5 mg / ml.
Conclusion: The results of this study showed that methanolic extracts of green walnut skin are a potential source of bioactive compounds with antioxidant and antimicrobial properties that can be used in the food and medicine industry to protect human health.
 

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One of the ways to prevent the oxidation of oils and fats is the addition of antioxidants, but since synthetic antioxidants may have adverse effects on the body, they are gradually removed from the list of antioxidants. Therefore, it is necessary to produce and produce natural varieties. Therefore, the aim of this study was to investigate the possibility of using natural extract extracted from Carduus pycnocephalus L. to prevent oxidation of soybean oil and compare it with essential oil. In this study, the extraction process was performed by ultrasound technology with 3 factors of 3 levels including concentration (200, 500 & 800 ppm) time (10-30 minutes) and temperature (55-35°C) by response surface methodology. To investigate the antioxidant effect of different concentrations of extracts on oxidative stability of soybean oil, peroxide value and thiobarbituric acid reactive index were used. The optimization results showed that the optimum conditions were: temperature 48.483 ° C and time 299. 201 min and concentration of 594.745 ppm. According to the optimization results of free radical scavenging and Folin compounds were reported 32.537% and 40.378%, respectively. The results of oxidative stability of oil showed that both extracts and essential oils were effective in preventing oil oxidation. Also, the type of extracted material was related in two ways. Since the extract has the most antioxidant effects in the oil and is more effective than the essential oil in the oil, it can be a good alternative to synthetic antioxidants in frying oils.