## 1 Introduction  
Nanoemulsions are metastable colloidal dispersions that consist of one dispersed liquid in the form of small spherical droplets, with diameters between 10 and 500 nm, within another immiscible liquid [1]. A significant advantage of nanoemulsions is the high resistance to structural changes, such as flocculation, coalescence, and gravitational separation [2]. Additionally, nanoemulsions are excellent delivery systems for bioactive ingredients, improving their solubility, bioavailability, and bioaccessibility [3, 4]. Due to their stability, they are suitable for the protection of the incorporated bioactives from adverse environmental conditions and chemical degradation, retaining their physicochemical stability and sensorial properties [5]. One very important aspect for the successful nanoemulsion preparation is the selection of the appropriate emulsifier [6]. Emulsifiers are surface-active compounds that facilitate the emulsion formation and promote their stability. While various synthetic emulsifiers, such as sucrose esters and sorbitan esters, and their ethoxylates are commonly used, the increased consumer demand for natural ingredients is driving efforts to replace synthetic surfactants with natural alternatives such as proteins and carbohydrates [7,8]. Microalgal proteins are high-potential non-animal alternatives for industrial applications for food products [9]. _Chlorella_ spp. are photosynthetic microalgae known for their high protein content (51-58% on dry basis); they also contain 14-22% polyunsaturated fatty acids, 12-17% carbohydrates, 0.4% fibers, 0.5% carotenoids, and 5.5% chlorophylls [10]. Among microalgae, _Auxenochlorella pyrenoidosis_ (formerly known as _Chlorella pyrenoidosis_) stands out due to its high protein content and quality. Specifically, _A. pyrenoidosis_ proteins contain all the essential amino acids, while, based on the essential amino acid index, they have higher nutritional value compared to soy proteins. Additionally, _A. pyrenoidosis_ proteins are ideal for applications in food products due to their functional and emulsifying properties, such as good water- and oil-holding capacities (3.1 mg water/mL and 2.1 mg oil/mL), high emulsifying capacity (2600 mL oil/g protein), and higher emulsion stability compared to synthetic surfactants (77%) [11,12]. To utilize these biofunctional proteins, they must be recovered from the intracellular space. However, due to the rigidity of _A. pyrenoidosis_ cell walls, effective cell disruption methods are required to recover the proteins without degrading them. This can be achieved by applying enzymatic hydrolysis (EH) or nonthermal technologies such as pulsed electric fields (PEF), bead milling (BM), ultrasounds (US), and high-pressure homogenization (HPH) [13,14]. The EH leads to the enhancement of intracellular protein recovery via the application of hydrolytic enzymes for the degradation of specific components of the cell wall of microalgae, such as polysaccharides, proteins, and hemicellulose. Main disadvantages of EH are the high cost and the selectivity of the enzymes. Pulsed electric fields are based on the exposure of cells to high-intensity electrical fields, resulting in the formation of pores on the cellular membranes (electroporation). Pulsed electric fields processing stands out for the low energy requirements and the high extraction selectivity, but the level of the cell disruption of microalgae with rigid cellulose-composed cell walls is relatively low. Bead milling achieves cell disruption via the beads collision with cells in a high-speed spinning system. While it is characterized by high cell disruption rates and high protein recovery efficiency, bead milling requires relatively high energy and leads to non-selective extraction. US technology is based on the cavitation phenomenon, which occurs in liquid media due to the propagation of ultrasound waves, leading to protein extraction enhancement. However, US also has high energy requirements and is not suitable for microalgae with rigid cellulose-based cell walls [15].