**1. Introduction**

*Buchanania obovata* Engl. is a native Australian tree that grows in the northern parts of Australia in Western Australia and the Northern Territory [1]. It produces a small green fruit known as the green plum which is eaten by Indigenous Australians. As a food it is eaten straight from the tree or with the flesh and seeds mashed into a paste, and is a favourite with children [2,3].

The *B. obovata* plant is in the family Anacardiaceae, which also contains the mango (*Mangifera indica*), cashew apple (*Anacardium occidentale*) and pistachio nut (*Pistacia vera*) [4].

The green plum was selected to be in this study because it is commonly eaten as a food and parts of the tree are used as bush medicine by Australian Aboriginal people. Leaf ribs, young stems, and the inner bark from young branches and older stems are used as bush medicine for their antiseptic and analgesic qualities to treat toothache, skin conditions and infections, and as an eye lotion [5,6].

Other native Australian foods have good nutritional and functional properties. The Kakadu plum (*Terminalia ferdinandiana*) has very high levels of ascorbic acid, high antioxidant capacity [7,8], and strong antimicrobial activity, enabling it to be used as a natural preservative for the commercial dipping of prawns in Queensland, Australia [9]. It is increasingly being used for its functional properties and is

currently used in food and beauty products [10]. Davidsons plum (*Davidsonia pruriens* F. Muelli) has shown vitro anti-proliferative activity against a variety of cancer cells [11] and can be used as a natural preservative in meat [9].

Synthetic antioxidants like butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) and propyl gallate are commonly used in food products, but have been associated with carcinogenic and toxic effects [12]. Risk perceptions of chemicals in foods cause people to prefer natural foods [13]. A total of 84% of people in the 2017 Eurobarometer survey said they are worried about the impact of chemicals present in everyday products on their health [14]. The food industry is increasingly trying to replace synthetic antioxidants with natural ingredients that are safer. There is interest in the use of foods that inherently contain bioactive compounds with these properties and can be used as food additives and ingredients [15].

This study seeks to determine the functional properties (antimicrobial and antioxidant) of the green plum flesh and seed and the components that give it these properties. This is the first study of this kind on the green plum and will give an understanding for its potential use as both a food and as a functional ingredient in food processing.

#### **2. Materials and Methods**
