## 1 Introduction  
Citrus fruits are members of the _Rutacene_ family, comprising 1600 species and 150 genera [1]. They are important horticultural crops that contribute to human diets globally [1, 2]. Mandarin is a juicy fruit with a globular to oblate shape and deep- to reddish-orange skin, representing an easy peeling group of citrus variety. Mandarin fruit consists of peel (pericarp) and pulp (endocarp). The endocarp is the flesh of mandarin fruits, typically containing 3-7 seeds and nine to 14 easily detached segments [3]. The peel or pericarp can be divided into an outer, orange coloured part, called exocarp or flavedo, and the inner colourless part, which is called mesocarp or albedo (Figure S1). Some of the components contained in the exocarp, such as paraffin waves, essential oils, fatty acids, and pigments, have a critical role in protecting the fruitsagainst insects and excessive sunlight exposure [1]. These compounds, especially the phenolic acids and flavonoids, also show diverse health benefits, including anticancer [4; 5], antioxidant [4; 6; 7], anti-inflammatory [4], and antibacterial activities [4; 7; 8]. Mandarin peel is a rich source of essential oil and pectin, which are used in pharmaceutical and food industries to deliver substantial economic value [9; 10; 11]. However, the peel is normally discarded as a by-product during fruit consumption and juice processing. Mandarins are strongly characterized by their pleasant flavour and high nutritional values and, therefore, have been well accepted by consumers. Mandarins have been manufactured into a wide range of products, including natural juices, jellies, candies, and syrup [1], in addition to its consumption as fresh fruit. Recently, there is a growing interest in the development of healthy functional foods while using natural substances. A number of research have been conducted to fortify food products with mandarin-derived bioactive components as the consumer trend moves toward the use of fruit in functional food products. For example, mandarin peel was added in biscuits dough in order to improve the nutritive value and strengthen the antioxidant properties [12]; mandarin low pulp juice has been successfully incorporated into an apple snack by vacuum impregnation technology [13]. Nowadays, functional ingredients in a dry format are in better market demand. Removing the water content in fruits could reduce quality loss that is induced by enzymatic hydrolysis and microbial growth while ensuring shelf-life stability during storage and transportation [14]. Furthermore, this will make the fruit product available all year round, overcoming the issue of seasonality. For mandarin fruits, they are more perishable than other citrus varieties, as their sensorial acceptability deteriorates quickly after fruit harvesting [1]. However, making fresh mandarins into powder forms could be an effective way to maintain their nutritional and sensorial values. On the other hand, spray drying has long been used as an efficient way to produce powders from fruits [15; 16]. It has many advantages, including the ease of operation and scale up for commercialisation, which offer lower cost and higher throughput when ompared to other drying techniques. Moreover, it produces powders with good flowability and stability [17]. In the last few decades, advancement in the spray drying technique has enabled the application of this method into a broad range of industries. The microfluidic-jet (MFJ) spray drying, as illustrated in Figure 1, is one of the successful attempts made by [PERSON] et al. in 2007 [18], aiming to manufacture particles with a uniform size with identical morphology. To date, the spray drying of mandarin juices has been reported [19; 20], but the application of MFJ spray drying technique has obviously not been explored. Furthermore, it is noted that previous studies have been focused on either the flavour or nutrient profile of the mandarin pulp juices during processing, or the utilisation of mandarin peels as a source of bioactive ingredients.