Ph.D. Dissertation:

Determination of antioxidant and anti-microbial properties of extract extracted from red onion skin using masuration and ultrasonic methods

Red onion extract is rich in phenolic and flavonoid compounds, which are more abundant in the skin extract than edible parts. The aim of this study was to investigate the effect of solvent type and extraction method on antimicrobial effects and antioxidant properties of various onion skin extracts. For this study, after drying, onion skin extracts were obtained by maceration and ultrasonic methods using various solvents such as water, ethyl acetate, n-butanol, ethanol and methanol. The antimicrobial effects of the extracts were performed using the diffusion disc method and the determination of the minimum inhibitiory concentration (MIC), the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC) was evaluated using the micro-dilution brothmethod. Total phenol, total flavonoidscontents and their antioxidant activity were measured using DPPH free radical scavenging, reducing power and nitric oxide scavenging assays. The results showed that antimicrobial effects increasedby increasing the concentration of the extracts. In the maceration method, the highest growth inhibition zone in the highest concentration (400 ?l / ml) ofStaphylococcus aureus, Escherichia coli, Salmonella typhi, Aspergillus niger and Candida albicanswere recorded for ethyl acetate, n-butanol, ethyl acetate, n-butanol and ethyl acetateextracts with means of 17.67, 12.33, 12.00, 24.33 and 11.67 mm, respectively. Evaluation of antioxidant properties showed that ethyl acetate extract yielded the highest total phenol and total flavonoidscontents with an average of 433.95 mg GAE/g of extract and 29.59 mg QE/g of extract. Also, the highest DPPH scavenging activity and reducing power was related to methanolic and ethyl acetate extracts, respectively. The highest nitric oxide scavenging activity was recorded at a concentration of 100 ?g/ml for ethanolic extract (28.38%), at concentrations of 200 to 800 ?g/ml for aqueous extract (27.96- 33.72%) and at a concentration of 1600 ?g/mlfor ethyl acetate extract (40.18%). In the ultrasonic method, the maximum growth inhibition zone for Staphylococcus aureus, Escherichia coli, Salmonella typhi, Aspergillus niger, and Candida albicans at a concentration of 400 ?l/ml was recorded for ethyl acetate extract with averages of 24.00, 16.00, 18.33, 24.33 and 19.67 mm, respectively. Evaluation of antioxidant properties showed that the extraction by ethyl acetate yielded the highest total phenol and total flavonoidscontents with an average of 439.45 mg GAE/g of extract and 33.44 mg QE/g of extract, respectively. Also, the highest DPPH scavenging activity, reducing power and nitric oxide scavenging activity was observed for ethyl acetate extract. Comparison of the effect of the extraction method on the antimicrobial effects of the extracts showed that at high concentrations, ethyl acetate extract had the highest inhibitory effect. Also, the highest antioxidant activity was observed for extracts obtained by ultrasonic method. Based on the results of the present study, extraction by ethyl acetate solvent using ultrasonic method had the best yield for antimicrobial effects and antioxidant activity. Also, in a part of the present research, the effect of aqueous extract of red onion skin obtained by ultrasonic method on the quality of chicken sausage during the storage period was evaluated. For this purpose, after preparing sausage dough based on the initial formulation, the final sausages were prepared based on the studied treatments including (1) control (sausage without extract), (2) sausage with industrial antioxidant (sodium erythorbate at the rate of 500 mg/kg), (3) sausage with red onion extract at the rate of 250 mg/kg, (4) sausage with red onion extract at the rate of 500 mg/kg and (5) sausage with red onion extract at the rate of 750 mg/kg. Physicochemical tests, colorimetry, the measurement of cooking properties and microbial index were performed on the sausage samples in three replications on the first, seventh and fourteenth days of refrigerated storage. Examining the values obtained for pH during the 14-day storage period showed that the change trend of this parameter is sinusoidal and the interaction effect of treatments and storage time on the pH value of sausage samples was significant. It is worth noting that the pH value of the samples decreased as storage time increased. The results showed that the use of sodium erythorbate and the extract decreased L* (lightness) of sausage samples and even increasing the concentration of the extract resulted in a decrease in the value of this parameter. Also, the use of sodium erythorbate and different concentrations of red onion extract decreased a* and changed the color of samples to green. The results of the mean comparison showed that the use of sodium erythorbate increased b* and yellowness in the samples compared to the control. On the other hand, the use of red onion extract and increasing its concentration caused a decrease in b* and the yellowness in the samples. The results showed that the use of sodium erythorbate increased cooking losses (CL), while the use of onion extract decreased this parameter compared to the control, and the percentage of cooking losses also decreased when the concentration of the extract increased. The results obtained from the shrinkage test or diameter reduction (DR) of the samples showed that the use of sodium erythorbate and different concentrations of the extract decreased this parameter, and the amount of DR decreased as the concentration of the extract increased. The results of the present study showed that treatments containing industrial antioxidants and different consentrations of the extract had significantly lower TBARS number compared to the control, and this trend was also observed during the storage period. The results showed that the application of sodium erythorbate and especially red onion extract had a positive and increasing effect on free radical inhibitory activity and a significant difference was observed between these treatments and the control. Based on the obtained results, there was no significant difference between control and other treatments in terms of fat, protein and moisture content. On the other hand, the analysis of the results showed that the use of industrial antioxidants and different concentrations of red onion extract caused a significant increase in the amount of ash in the sausage samples prepared from these materials. The trend of changes in the total count of microorganisms during the storage period indicated an increase in the total microbial count of the treatments from 1 to 14 day of storage. The general trend of changes showed that the use of red onion skin extract and increasing its applied concentration caused a decrease in the total microbial count in chicken sausage samples containing different concentrations of the extract. Also, the use of sodium erythorbate resulted in a decrease in the microbial index of the sausage samples prepared from this combination compared to the control

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