## 1 Introduction  
Oil-in-water (O/W) emulsions are basic constituents of many products in industries such as beverages, cosmetics, drug delivery, foods, nutraceuticalals, and personal care products [1, 2, 3]. Kinetic instability of O/W emulsions can be ascribed to the presence of positive free energy made available when dispersions are formed that allows colloids to separate through creaming, coalescence, flocculation, and sedimentation [2, 4]. Emulsifiers are materials that kinetically stabilize emulsions by coating the O/W interface by generating repulsive forces that hinder oil globules aggregation [2, 5]. The food industry has legally approved the use of several food-grade emulsifiers, however, costs, ease of use, and functionality make it difficult for food scientists to select the most proper emulsifier for an application [2, 6, 7]. The kinetic stability of O/W emulsion has been increased by adding emulsifiers, stabilizers, and biopolymers [2, 8, 9]. Food scientists have been faced with the challenge of formulating biologically nutritious semi-solid foods either as colloids, emulsions, gels, or simple solutions for individuals facing health challenges such as diabetes, obesity, or allergies [10, 11, 12]. These challengeshave been complicated because the biologically nutritious components tend to be immiscible with water [11; 12]. Researchers have therefore shifted focus to emulsifying methods that apply high-energy emulsification methods to deliver emulsions [2; 13]. Authors have reported the use of micro-emulsions and nanoemulsions to deliver different emulsion components [4; 14]. However, nanoemulsions are preferred in comparison to microemulsions because nanoemulsions can be stabilized with low emulsifier concentrations [4; 14]. Emulsifying methods apply systems that require high-pressure, microfluidics, rotors, or ultrasonic equipment [2; 13; 15]. These high-energy emulsifying methods use machine-driven devices that generate strong disruptive forces that fragment the dispersed phase and result in small oil globules [2; 16]. Authors have proposed ultra-sonication which involves shearing the interface between oil and water globules to form stable dispersions at low frequencies [10; 11; 12]. Authors have reported that an emulsion can attain stability when its particle size is reduced [8; 17]. The literature established that the lower the particle size the more stable an emulsion becomes [8; 18; 19]. Response surface methodology (RSM) a multivariate statistical method has been commonly used to optimize food processing techniques [20; 21]. RSM is a regression-based analysis that fits mathematical models, such as linear, square, or quadratic polynomial functions, and other models, to the experimental response observed in the experiment by applying multivariate statistical analysis [20; 22; 23]. The RSM strategy establishes relationships between input factors and responses with the aid of a mathematical model, deals with hindrances of optimizing with sole parameters, and provides an efficacious way to formulate emulsions in a mixture design [13; 23]. Mixture designs are statistical experimental designs derived from mixture components [24] where constraints are placed on the concentration of the dependent variables used [25; 26; 27]. The nucilage secreted from the fish skin when fish are stressed is a waste that contains elements such as carbohydrates, enzymes, lipids, metabolites, proteins, and water [24; 28; 29]. Several authors have established that vital enzymes and proteins have been identified in fish skin nucilage which is responsible for its natural defense [28; 29; 30]. These include antimicrobial peptides (AMP), glycoproteins, immunoglobulin, lectins, lysozyme, mucins, complement proteins, proteases, transferrins, and various other antibacterial proteins and peptides [28; 29; 30]. The skin of fish contains goblet and paneeth cells which play a focal role in defending the fish by producing humoral immune factors and mucins [28; 29; 30].