## 1 Introduction  
Bioactive compounds from natural flora are an essential constituent of the nutraceuticalals pharmaceutical, which signifies the importance of identifying the appropriate method to extract these active components from the source material. These compounds are proved to have antioxidant, anti-diabetic, anti-mutagenic, anticancer, anti-inflammatory, and antimicrobial effects [1]. Extraction is the first step in obtaining these bioactive compounds from various biomaterials. The most traditional methods reported for the bioactive recovery, and still considered as a reference technique, are Soxhlet, cold maceration, boiling, and steam distillation [2]. New technologies are emerging to overcome these challenges, such as microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), and ultrasound-assisted extraction (UAE), as shown in Table 1. These technologies improve the extractability and recovery of bioactive compounds from various biomaterials, with many advantages such as higher extraction yield, shorter extraction time, and being operable at a lower temperature [3]. Moreover, the efficiencies of these methods depend on some critical parameters, such as a good understanding of the chemistry of bioactive and sample pre-treatment. All steps of extractions, from material pre-treatment (such as grinding, drying) to final extraction, are equally important and can affect the efficiency of the whole extraction process. A good number of researchers have studied the effect of different extraction parameters, such as extraction temperature, time, biomass percentage, material particle size, and solvent type on the extractability of various bioactives using conventional and non-conventional methods [4; 5; 6; 7; 8; 9; 10; 11; 12]. It is observed that reducing the material particle size usually has a significant effect on the efficiency of the extraction method used. The reduction of particle size by milling not only increases the diffusivity of the bioactive compounds, but also ruptures cell walls. Since particle size is one of the critical parameters affecting extraction [4; 5; 8], this might bring up the question of whether the extraction of bioactive compounds as reported by others was achieved through the extraction process or simply during sample pre-treatment (grinding). _Leptospermum scoparium_ (Manuka) is a tree that belongs to the family of Myrtaceae. It is a small indigenous tree grown widely throughout most of New Zealand. Maori people have used the bark, leaves, seeds capsules, and flowers of this tree for therapeutic preparation [13]. Manuka oil that is present in the cellular structure of Manuka leaves is high in bioactive compounds. There are three main chemo types of _Leptospermum scoparium_ available in New Zealand: (i) _Leptospermum_, high in triketones in the North Island \"East Cape\" and Marlborough Sounds, (ii) _Leptospermum_, high in monoterpene in North Island and West Coast, (iii) _Leptospermum_, high in sesquiterpene, grown around New Zealand [13]. Steviol glycoside is a sweetener present in _Stevia rebaudiana_ leaf, an herb cultivated originally in South America (Paraguay and Brazil). It has been used as a sweetener and for medicinal preparations by indigenous Paraguayan people for many centuries [14]. The Stevia plant, which belongs to the family of Asteraceae, is a perennial sub-tropical plant, grown during spring to summer. Today, Stevia is cultivated successfully in many countries around the world, such as Mexico, Canada, Hawaii, Spain, the UK, Italy, Czech Republic, Malaysia, Singapore, South Korea, Japan, Thailand, India, and Indonesia [15], and even in home gardens. Stevia is usually used as a zero-calorie sweetener containing a mixture of diterpene compounds. Commercial sweet glycosides product has about 80% stevioside, 8% rebaudioside A, 0.6% rebaudiosideC, and other glycosides in trace amounts [16].