Mechanism of Action against Food Spoilage Yeasts and Bioactivity of Tasmannia lanceolata, Backhousia citriodora and Syzygium anisatum Plant Solvent Extracts.

Fahad Alderees,Dennis Webber,Nilesh Nirmal,Yasmina Sultanbawa,Ram Mereddy

doi:10.3390/foods7110179

Abstract

Bioactive properties of solvent extracts of Tasmannia lanceolata, Backhousia citriodora and Syzygium anisatum investigated. The antimicrobial activities evaluated using agar disc diffusion method against two bacteria (Escherichia coli and Staphylococcus aureus) and six weak-acid resistant yeasts (Candida albicans, Candida krusei, Dekkera anomala, Rhodotorula mucilaginosa, Saccharomyces cerevisiae and Schizosaccharomyces pombe). The antioxidant activities determined using DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging and reducing power assays. Quantification of major active compounds using ultra-high performance liquid chromatography. Extracts showed broad-spectrum antifungal activity against weak-acid resistant yeasts in comparison to the standard antifungal agents, fluconazole and amphotericin B. Dekkera anomala being the most sensitive and strongly inhibited by all extracts, while Escherichia coli the least sensitive. Polygodial, citral and anethole are the major bioactive compounds identified in Tasmannia lanceolata, Backhousia citriodora and Syzygium anisatum, respectively. Hexane extracts contain the highest amount of bioactive compounds and demonstrate the strongest antimicrobial activities. Methanol and ethanol extracts reveal the highest phenolic content and antioxidant properties. Fluorescence microscopic results indicate the mechanism of action of Backhousia citriodora against yeast is due to damage of the yeast cell membrane through penetration causing swelling and lysis leading to cell death.

Highlights

The market for soft drinks and fruit juices is increasing annually with the release of new beverage products, which are gaining popularity among consumers
There was a significant difference in yield between solvents used in extraction except for methanolic and ethanolic extracts of Tasmanian pepper leaf and ethanolic and water extracts of anise myrtle
Previous reports found that the nonpolar compounds, polygodial, citral and anethole, were the dominant compounds in the essential oil of Tasmanian pepper leaf, lemon myrtle and anise myrtle, respectively, which could be the main contributors to the reported antibacterial and antifungal property of these herbs [10,23,24,40,41,42]

Summary

Introduction

The market for soft drinks and fruit juices is increasing annually with the release of new beverage products, which are gaining popularity among consumers. This market expansion has increased the challenge of addressing spoilage problems [1]. Yeasts are the most common group of microorganisms responsible for spoilage of soft drinks and fruit juices due to their ability to withstand juice acidity and resist the action of weak-acid preservatives [1,2]. Beverage industries are focusing on the application of novel antimicrobial agents derived from plant sources as an alternative solution to address beverage spoilage caused by weak-acid resistant yeasts [3]. Tasmanian pepper leaf (Tasmannia lanceolata), lemon myrtle (Backhousia citriodora) and anise myrtle (Syzygium anisatum) are three Australian native herbs in commercial production and there is a growing interest in their bioactive properties and assessing their potential applications as functional ingredients in the beverage industry [4].

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