**6. Biotechnological applications**

Cryptophytes are cells with unique biochemistry; for example, it has a high and balanced content of PUFA (ALA, SDA, EPA, DHA) [21, 22], phytosterols, carbohydrates [21], and fluorescent pigments PBPs. Each of these compounds has effects on health [21, 22, 83, 120], giving them a wide variety of potential applications in food, cosmetics, pharmaceuticals, medicine, immunology, as well as for scientific research [116]. There are many patents for these applications, but most are related to fluorescent properties of PBPs [121].

The food and beverage industries have increased attention to natural pigments from microorganisms, especially aquatic products from macro and microalgae [21]. This trend is predicted to continue in the future due to increasing consumer health consciousness of potential and known harmful effects of synthetic compounds. Other advantages are stability, considering temperature, pH, osmolarity, low reactivity [122–124], and the health-promoting effects from another point of view [121]. An advantage is that the market for cyanobacteria and their PBPs (mainly *Arthrospira*, *Anabaena*) and red alga (*Porphyridium* and *Galdieria*) has been established. For PBPs and their products, in 2010, it was estimated to be around US\$60 million [125]. Another critical factor for industries is the stability of PBPs, they showed good range of stability between pH 5–10 and between −20 and 80°C, and it could be prolonged by adding preservatives [124]. The blue (PCY) and red (PER) pigments that Cryptophytes provide is attractive to the food and cosmetic industries [21]. Some of their uses are in chewing gum, desserts, candies, dairy products, ice cream, soft drinks in different presentations (aqueous and alcoholic), and cosmetics like lipstick and eyeliners [116, 119, 126, 127]. Some applications like food and cosmetics do not need high purity, thus semi-purified pigments are an attractive option since they are less expensive than highly purified pigments, that are needed for using them as molecular markers. The purity is measured by the ratio of the maximum pigment absorbance divided by its absorbance at 280 nm; for food, a ratio of ≥0.7 is accepted, a reagent grade is ~3.9, and analytical grade ≥4.0 [117], that is the reason why PER is expensive and sold anywhere from US\$200 to US\$100,000/kg.

In regards to the effects of PBPs, some are related to their antioxidant potential [119, 128, 129] as they are natural ROS scavengers, have anti-inflammatory [130, 131], and anti-aging properties [119, 128, 129]. Other protective effects of PBPs are located in mitochondria membrane from ROS stress, which could maintain cellular viability and proliferation [131, 132] in different health problems. PCY also has a pro-apoptotic effect in different cancer cell lines and is an inhibitor of COX-2 enzyme, which converts arachidonic acid to prostaglandins and plays a crucial role in tumor progression and chemical resistance, and the PGE2, which participates in promoting angiogenesis [132]. PCY has been observed as an inhibitor of viral protease activities (i. e. SARS-CoV-2) [133, 134], which could mean antiviral protection. The anti-diabetes activity of phycocyanobilin could be due to the inhibition of NADPH oxidase and the protective effects against human lymphatic endothelial cells apoptosis, which also explains its neuroprotective effects [135].

PBPs play an essential role in fluorescent-based detection systems, like with flow cytometry, epifluorescence, and confocal microscopy for fluorescent immunoassays like protein electrophoresis [136], immunophenotyping; they can also be used as selective markers of specific biological structures, i.e., arterial wall thickness, atherosclerotic plaque, luminal boundaries and to better delineate tumors mass outlines and such other fluorescent studies [121, 137]. Spectral properties, such as excitation and emission at the red end of the spectrum and diminished interference from biological matrices give it considerable stability for quenching compared to other biological

compounds. In addition, PBPs have high water solubility with minimal interaction with other substances, and the ease of binding to antibodies by conventional cross-linking reagents, have made these fluorochromes unique and superior to other products, i.e. for medical tagging [137–139]. All of this is motive for developing new biotechnological processes and products, and the commercialization of new patents is still a goal in the near future.
