# Phenolic Profiling of Five Different Australian Grown Apples
## 1 Introduction  
Apples (_Mulus domestic_) are widely grown and consumed fruits. In 2018, apple production across the globe was 86 million tonnes, mainly from China, America and New Zealand, whereas the apple production in Australia was over 2.6 million tonnes [1]. Apples are usually supplied to the market in the form of fresh fruit or processed products, including dried apples, apple cider, apple juice and sauce [2]. Apples are enriched with bioactives compounds [3], vitamins (water and fat soluble) and minerals like calcium, potassium and phosphorus [4]. These compounds are required by the human body to perform various functions like strengthening of the bones, building muscles, filtering out waste [3], and have positive health benefits against several chronic diseases, including type 2 diabetes, asthma and rheumatoid arthritis [5]. The varieties of apples are due to the difference of agroclimatic regions and zones, cultivation practices, nutritional composition and sensory characteristics [6]. Royal Gala, one of the variety of apples having bright shiny red colour, with stripes ranging from straw yellow to amber orange, has a sensory profile that is sweet, soft, crunchy and slightly acidic [7, 8]. Pink Lady is a variety that has been originated from a cross between 'Golden Delicious' and 'Lady Williams', known for its sweet taste, firmness and possesses a scald-free surface [6]. A consumer panel in New Zealand appreciated the Pink Lady variety for its dense flesh, excellent crispness, juiciness, good sugar-acid balance and sweet flavour [9]. The Red Delicious variety when compared to the previous two varieties has a darker crimson red surface with traces of yellow and orange [10]. The physicalcharacteristics of Red Delicious is an elongated form with a thick peel, grainy and tender with a melting texture, usually exhibiting small but evident humps on the skin surface [11]. While different varieties exhibit different appearances, taste and shapes, apples have one common characteristics, which are the high concentrations of phenolic compounds that exhibit high antioxidant potential [12]. Phenolic compounds are important plant secondary metabolites which exhibit excellent abilities to reduce and eliminate free radicals thereby providing antioxidant and anti-lipid peroxidation properties [13; 14]. The phenolic compounds exhibiting antioxidant potential have made the food and nutrition market interested in phenolic compounds, thus replacing the existing chemical anti-oxidation ingredients in food to increase the nutritional value and health benefits [14]. One of the polyphenol mechanisms is the removal of free radicals by supplying hydrogen atoms or separate electrons from the phenol group and eliminating related enzymes, thereby preventing the production of free radicals and their intermediate products [15]. Additionally, phenolic compounds can react with metal ions to inactivate the Fenton reaction [16]. The antioxidant potential are often determined by using a series of different in vitro spectrophotometric-based assays including the total antioxidant capacity (TAC), 2,2\({}^{\prime}\)-azino-bis-3-ethylbenzothazoline-6-sulfonic acid (ABTS) assay, the ferric reducing ability of plasma (FRAP) and 2,2\({}^{\prime}\)-diphenyl-l-picrylhydrazyl (DPPH) [17]. Liquid chromatography coupled with mass spectrometry (LC-ESI-QTOF-MS/MS) is an effective tool used for the identification and characterisation of phenolic compounds. High pressure liquid chromatography (HPLC) combined with photodiode array detector (HPLC-PDA) is used for the quantification of the phenolics [18; 19]. According to a previous study, few phenolic compounds have been identified in apples through HPLC and LC-ESI-QTOF-MS analysis including flavonols (catechin), dihydrohalcones (chlorogenic acid), phenolic acids and anthocyanins [20]. Although there are many studies that have isolated and identified phenolic compounds in different apples, only a few have focused on Australian grown apples.