Optimization of Extraction of Phenolic Compounds with Antimicrobial Properties from Origanum vulgare

Taja Žitek,Andrej Golle,Dragana Borjan,Željko Knez,Maša Knez

doi:10.3390/pr9061032

Abstract

Oregano (Origanum vulgare) is considered to be a good and cheap source of phenolic compounds with favorable biological activities, especially antimicrobial and antioxidant properties. Hypothesis/Purpose: The current work explored the optimization of the process conditions of solid–liquid extraction from Origanum vulgare to obtain extracts with high antimicrobial activity. We investigated which parameters promoted different efficiencies, leading to the maximum extraction of phenols and the consequent highest level of biological activity. Design-Expert Pro 11 was selected to design and analyze the experiments. The extracts were obtained by maceration as a simple method to recover value-added compounds from plant material, and supercritical fluid extraction was carried out as a green method with a high selectivity to obtain the compounds of interest. Pressure, temperature, and time were varied to obtain extracts with high antioxidant and antimicrobial activity. According to the results obtained using Design-Expert, the optimal conditions for maceration were at a temperature of 83 °C. The 1,1′-diphenyl-2-picrylhydrase method was used for the determination of antioxidant potential, while microdilution methods were used to determine the antimicrobial potential with regard to Staphylococcus aureus, Escherichia coli, and Candida albicans. A level of antioxidant activity of 87.21% was achieved. Supercritical fluid extracts showed higher antioxidant activity at a higher temperature of 60 °C and higher pressure of 25 MPa, although the results at 40 °C and 25 MPa were similar. The lowest minimum inhibitory concentration (MIC) values were 0.147 mg/mL for S. aureus, 0.728 mg/mL for E. coli, and 0.311 mg/mL for C. albicans. Overall, the optimal conditions for supercritical fluid extraction were 25 MPa and 40 °C. On the other hand, amounts of 0.208 mg/mL for S. aureus, 1.031 mg/mL for E. coli and 0.872 mg/mL for C. albicans were obtained using maceration. The MIC values of extracts obtained by supercritical fluid extraction were comparable to the minimum inhibitory concentration values obtained by different conventional techniques, such as those of Clevenger and Soxhlet.

Highlights

Oregano (Origanum vulgare) is a culinary and medicinal herb from the mint or Lamiaceae family
Antimicrobial activity was examined using three different microorganisms, namely Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922) and Candida albicans (ATCC 60193), all added to Mueller-Hinton broth (MH) obtained by National Laboratory for Health, Environment and Food
Supercritical fluid extraction was carried out to compare the antioxidant activity, since the implementation required a much lower temperature, which would significantly reduce the costs of production at higher volumes

Summary

Introduction

Oregano (Origanum vulgare) is a culinary and medicinal herb from the mint or Lamiaceae family. The chemicals that give the herb its unique and pleasant smell are thymol, pinene, limonene, carvacrol, ocimene, and caryophyllene. It adds flavor, can inhibit the growth of microorganisms, and may have several health benefits [2,3,4]. Oregano contains polyphenolic compounds (acacetin, apigenin, diosmetin, herbacetin, hispidulin, luteolin, naringin, quercetin, and rosmarinic acid [5,6,7]) that have multiple biological effects [7,8,9,10], including antioxidant and antimicrobial activity [3,4]. Oregano is a strong candidate for a natural food preservative because of its antioxidant and antimicrobial action, probably due to the presence of the diterpenes carvacrol and thymol, which have been extensively studied for their anti-bacterial and antioxidant properties [7,11]

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