# Anti-Yeast Synergistic Effects and Mode of Action of Australian Native Plant Essential Oils  
[PERSON]  
1 ARC Industrial Transformation Training Centre for Uniquely Australian Foods, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Indooroopilly, Brisbane, QLD 4068, Australia; [EMAIL_ADDRESS] (F.  
In recent years, EOs have been studied for their antimicrobial properties against bacteria, fungi and viruses. However, little is known about their efficacy when compared to synthetic food preservatives, their activity against weak-acid resistant yeasts and mode of action [6; 7; 8; 9; 10]. Yeasts are well-known for their positive contributions in the production and development of various foods and beverages. However, some species of yeasts cause negative effects by spoilage [11]. These yeasts can grow in an environment that has a low water activity, low pH, high concentration of sugar/salt, cold temperatures and are able to resist and survive within the legally permitted levels of synthetic preservatives, which creates a real challenge to the food and beverage industries [6; 12; 13]. The scientific literature shows numerous studies referring to the emergence of spoilage yeast resistant to weak-acid preservatives such as acetic acid, benzoic acid, sulfur dioxide and sorbic acid [6; 12; 13]. Almost every food industry that manufactures acid beverages was exposed to one or more occasions of great economic losses due to yeasts that are resistant to weak-acid preservatives [14]. A great example of the seriousness of this challenge is when yeasts spoiled about 300,000 bottles of orange-based carbonated beverages from one of the manufacturers in Europe [6]. The observed increased resistance is a \"wake up call\" to look for alternative solutions, and the food industry is interested in exploring the utilization of natural antimicrobial compounds as an alternative pathway to control this spoilage problem [15]. In addition, the pharmaceutical industry is also focusing on incorporating natural products in medications, where about 28% of all the newly approved drugs were derived from either natural or derivatives of natural compounds [16; 17]. The rich Australian indigenous flora contains a variety of plants that are abundant in EOs and phytochemicals with promising biological activities. Three commercially produced plants, Tasmanian pepper leaf (TPL) (_Tasmannia lancelata_), lemon myrtle (LM) (_Backhousia ctiridorora_) and anise myrtle (AM) (_Syzygium anistatum_) are known to possess antimicrobial activities. TPL belongs to the Winteraceae family and is located in forested regions in Tasmania, Victoria and north to the Blue Mountains [18]. Polygidal, sesquiterpene dialdehyde, is reported to be the major bioactive compound (37% to 64%) in TPL EO contributing to its antibacterial and antifungal activities [18; 19; 20; 21; 22]. TPL is utilized commercially in food products as a flavoring, seasoning, coloring and preservative agent [23; 24; 19]. LM is a member of the Myrtaceae family and grows in the subtropical rainforests of central and southeast regions of Queensland, Australia spreading along the coastal regions from Brisbane to Cairns [25]. LM EO was first steam distilled in 1890 and is used as a flavoring agent in food and beverage systems, cosmetic products, fragrances and aromotherapy [26; 27; 28; 29]. The antimicrobial properties of LM are due to its predominant compound (82% to 91%) citral, a monoterrene aldehyde [30]. Anise myrtle is a rare Australian native plant found in the moist rainforest areas located in the Bellingen Valley of northeast New South Wales and some nearby parts of Queensland [31]. Its leaves are used as an herb either fresh or as ground powder to provide anised flavors in Australian cuisines, and its EO is utilized in cosmetic products, alcoholic beverages and in the pharmaceutical industry [32]. EO of AM consists of anethole (94.97%) and its isomer methyl chavicol (4.43%), known as estragole, which contribute to the antimicrobial property [33].