## 1 Introduction  
_Arthrospira_ species, commonly known as spirulina, are blue-green photosynthetic microorganisms classified as non-toxic edible cyanobacteria [1]. Known for their rich nutrient profile, including proteins, vitamins, and minerals, _Arthrospira_-derived products have attracted significant attention as a healthy and functional food ingredient [2]. In particular, the water-soluble photosynthetic pigment C-phycocyanin (C-PC) in _Arthrospira_ cells is a major bioactive component that has been extensively studied for its diverse physiological activities, including antioxidant, anti-inflammatory, and immune-enhancing effects [3, 4]. Moreover, its excellent biocompatibility, non-toxicity, and unique color make it widely used in the food, cosmetics, and biomedical industries [3, 4]. Among naturally occurring blue pigments, C-PC is considered the most suitable for application in the food industry [5]. In recent years, the US Food and Drug Administration granted GRAS (Generally Recognized As Safe) status to C-PC extracted from _Arthrospira_ spp. as a blue pigment in confectionery and chewing gum. However, as a protein-based compound, C-PC exhibits low stability under light, heat, and acidic conditions because of protein denaturation, limiting its industrial applicability [5, 6]. C-PC is composed of \(\alpha\) and \(\beta\) subunits joined together to form the minimum building block, a monomer, which further assembles into \((\alpha\beta)_{3}\) trimers and then \((\alpha\beta)_{6}\) hexamers to form higher-order structures [7]. Generally, food-grade purity C-PC exists as a hexamer [8], but under conditions that do not allow it to maintain a stable structure, it dissociates into trimers, monomers, and monomeric subunits or enters into protein aggregation and easily loses its color [9]. Among the many factors that affect C-PC stability, heat is known to have the greatest impact [8, 10]. Many studies have focused on the addition of various additives to increase stability against heat [11]. Although treating C-PC with additives can be a cheap and attractive option, it is essential to use additives with low toxicity, and they sometimes impart unacceptable flavors to the food product [11]. To address this limitation, previous studies have proposed extracting the chromophore phycocyanobilin (PCB), which is responsible for the blue color [12]. PCB can be obtained by cleaving molecules from phycobiliproteins present in _Arthospira_ spp. PCB, an open-chain tetrapyrrole prosthetic group, which is separated from the apoprotein of C-PC and can serve as a stable blue pigment even under strong light, acidity, and high temperatures [13]. In addition to its enhanced stability, PCB exhibits physiological activities, including antitumor, antioxidant, and anti-inflammatory effects, which confer significant commercial potential for applications in the pharmaceutical, cosmetic, food, and healthcare industries [14, 15, 16]. Methanol is commonly used to obtain this appealing natural blue pigment from C-PC [17]. Although methanol extraction may be effective in maximizing the yield of PCB [18], its use in industrial applications is limited because of the need for the complete removal of residual solvents, extensive purification processes, and safety validation. According to the Toxic Release Inventory (TRI) of the US Environmental Protection Agency (EPA), methanol is classified as a solvent that is generally harmful to both the environment and human health, necessitating measures to maximize recovery or minimize emissions in industrial settings [19]. In contrast, ethanol, a 'green solvent,' is excluded from the TRI. It is a non-toxic, food-grade, and environmentally friendly solvent, making it a suitable alternative to methanol for industrial applications [20]. Efforts to use ethanol for PCB extraction have been discussed in several studies [12, 13].