The effect of the extraction method on the antibacterial activity of white mulberry extracts.

Introduction: The Polish cultivar of white mulberry (Morus alba L.) “Żółwińska wielkolistna” is a source of many bioactive substances with a wide spectrum of activities. The leaves of the plant are considered to be a raw material richest in bioactive substances. The unique properties of the plant are primarily due to polyphenols, in particular flavonoids, including: rutin, albanon, kuwanone, which make it possible to use white mulberry as an agent with a wide spectrum of activities, from anti-inflammatory, diaphoretic, antioxidant to antimicrobial. Objective: The aim of the study was to determine the effect of the method of extracting substances from dried white mulberry leaves on the antibacterial activity of the obtained extracts. Four extraction methods were used to obtain the extracts, and then their antimicrobial activity against selected Gram-positive and Gram-negative bacteria was determined. Methods: Mulberry leaves were collected in September 2021 from an ecological plantation located at the Experimental Station, Institute of Natural Fibers and Medicinal Plants in Poznań – National Research Institute in Pętkowo. Leaves were dried at 60°C for 12 hours, then laboratory analyses were performed. The extraction was carried out by the following methods: 1.) carbon dioxide extraction, 2.) carbon dioxide extraction using a cosolvent, 3.) maceration with carbon dioxide extraction using a cosolvent, 4.) solvent extraction. Then, the antimicrobial activity of the obtained extracts against selected strains of Gram-positive and Gram-negative bacteria was determined. MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) were determined. Results: As a result of the conducted research it was found that there are differences in the antibacterial activites of extracts from dried white mulberry leaves depending on the extraction method used. The highest antibacterial activity both against Gram-positive and Gram-negative bacteria was shown by extracts obtained using a supercritical carbon dioxide extractor without the use of cosolventa, with more effective growth-inhibiting and bactericidal effects observed against Gram-positive bacteria compared to Gram-negative bacteria. Conclusions: Extracts obtained from dried leaves of white mulberry (Morus alba L.) of the Polish variety “Żółwińska wielkolistna” have antibacterial properties. This leads to the possibility of using white mulberry in herbal medicine and pharmacology as an antimicrobial agent. [ABSTRACT FROM AUTHOR]