Antioxidant and antibacterial properties of borage (Echium amoenum L.) and hollyhock (Althaea rosea var. Nigra) extracts obtained through soaking and ultrasonic-assisted extraction methods

Abstract

This study aimed to investigate antimicrobial and antioxidant activities of borage (Echium amoenum L.) and hollyhock (Althaea rosea var. Nigra) extracts. The extracts were obtained through soaking and ultrasound- assisted methods using water or methanol as a solvent. The total phenols and flavonoid, anthocyanin content, free radical scavenging activity, ferric reducing antioxidant power, and antibacterial capacity of the extracts were determined. Phenolic acids were identified using the HPLC chromatogram. It was found that the ultrasound-assisted extraction was more efficient compared to the soaking method. The results showed that in the TPC, anthocyanins, and the FRAP tests, the highest amount was related to the samples extracted using the ultrasound- assisted method with water as solvent. The highest amount of TFC was obtained through a soaking method using methanol as the solvent. Anti- radical activity of the samples indicated that using water as a solvent in the optimum method resulted in a higher antioxidant activity. Furthermore, bacterial alpha amylase inhibition test signified that the inhibitory effect was boosted by increasing the extract concentration. The HPLC analysis of the borage and hollyhock extracts revealed that gallic acid and Syringic acid were the most prominent phenolic compounds. Generally, the results showed a good antibacterial property against Staphylococcus aureus for borage and hollyhock extracts. The results give us valuable insight into the potential therapeutic and medicinal applications of borage and hollyhock as a natural preservative to improve immunity.

Keywords

• natural extracts
• soaking method
• ultrasound-assisted extraction
• polyphenols