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Increased thermal stability of phycocyanin extracted from Spirulina platensis by cysteine addition during enzyme extraction

Spirulina (Spirulina platensis) is a cyanobacterium (blue-green algae) that is widely grown in alkaline brine lakes (Nege et al., 2020). Spirulina is nontoxic, contains polysaccharides, vitamins, minerals, unsaturated fatty acids, carotenoids, and phycobiliproteins, and is used as a food supplement (Lafarga et al., 2020; Sánchez et al., 2003). In addition to fibers and pigments, the biomass of spirulina consists of 55-70% protein, 3-9% fat, and 15-30% carbohydrates (Kay & Barton, 1991). Spirulina markedly differs from other microalgae because it contains large amounts of protein pigments called phycobiliproteins (Glazer, 1985), which are phycobilisomes attached to the thylakoid membranes of chloroplasts and auxiliary photosynthetic pigments that aggregate in cells (Arad & Yaron, 1992). Phycobiliprotein consists of three main components: phycoerythrin, phycocyanin, and allophycocyanin (Sonani et al., 2016). Among them, phycocyanin is a blue-colored natural pigment with various physiological activities (antioxidant, antibacterial, and anticancer activity); thus, it is a protein pigment that can also be used in the food industry as a bioactive substance (Kumar et al., 2014; Liu et al., 2016).