## 4 Concurrent Development of Value-Added Products Beneficial to Human and Animal Health  
Microalgae produce several products for use as raw materials for food, cosmetics, animal feed, fish feed, biofuels, and other value-added products. Many types of antioxidants, carotenoids, polymeric enzymes, lipids, natural dyes, polyunsaturated fatty acids, peptides, toxins, and sterols can be produced from different types of microalgae, which are used in a range of industrial products. Natural dyes are also produced for use in the pharmaceutical industry. Microalgae also produce acetyl acids, beta-carotene, agar, agarose, alginates, and carrageenan, which are used as viscosity-modifying agents in medicines and foods, as well as polyunsaturated fatty acids and lutein, which are used to treat degenerative diseases.  
In particular, marine microalgae may produce polyunsaturated fatty acids (PUFAs), which are useful in disease treatment and/or production of food. Large volumes of oils and fats containing long-chain omega-3 and omega-6 fatty acids (LC-PUFAs) can be produced by a number of microalgae species. Human nutrition and health, especially for the mental and physical development of infants, depend on LC-PUFAs.  
Microalgae create sterols, which help in cardiovascular disease treatment. In particular, it is reported that spirulina produces clionasterol, which protects vascular cells. Microalgae produce many antioxidant compounds, such as astaxanthin, beta-carotene, dimethylsulfoniropropionate, mycosporins, and some other carotenoids, which protect the organism from various diseases, aging, and oxidative stress. In recent years, with the introduction of probiotic supplements, microalgae have been investigated more intensively in the diet in relation to their benefits for human health. When comparing the quality of proteins, microalgae biomass excels over vegetables, rice, and wheat, but is diminished in relation to milk and meat. Of a wide range of microalgae that produce bioactive compounds for commercial purposes, the most important are _Dunaliella_, _Haematococcus_, _Nammochloropsis_, _Chloerella_, and _Chlamydomonas_, and the cyanobacterium _Spirulina_. Several species of spirulina, such as _Spirulina platensis_ and _Spirulina maxima_, are grown commercially, due to their protective or therapeutic role in the immune system, arthritis, anemia, cardiovascular disease, diabetes, and cancer. In addition, lactic acid bacteria in the gastrointestinal tract also increase, resulting in an improvement in the hormonal system.  
_Chloerella_ microalgae produce biomass that is rich in protein (51-58% dry weight), carotenoids, and various vitamins. _Chloerella_ is also used to produce _Chloerella_ growth factor, which improves the growth of lactic bacteria in the body and acts as a growth factor for intestinal bacteria. Many positive health effects from the use of _Chloerella_ are recorded, such as increasing the level of hemoglobin, lowering blood glucose and cholesterol, and hepatocytes action. _Chloerella_ species produce metabolic products that can activate the immune system and stop _Candida albicans_ and _Listeria monocytogenes_ from growing. _Chloerella_ extracts are also used in mammals to produce splenocytes and cytokines and to activate other immune responses.  
_Dunaliella_ microalgae (especially _D. salina_) are rich in lipids and proteins, glycerol, and beta-carotene, and have particular growth potential in brackish waters. Carotenoids produced by both _Dunaliella_ and _Spirulina_ species are more effective against cancer cells compared to beta-carotene.  
In China, _Nostoc sphaeroides_ has been used in traditional medicine to treat diarrhea, hepatitis, and hypertension. _Muriellosis_ sp. also produces a high level of carotenoids, such as lutein used to treat degenerative diseases. The cyanobacterium _Nostoc_. has been a food source since 2000 in China and is considered healthy in China, Korea, and Japan due to its high protein content [21].