# Physicochemical, Functional, and Antioxidative Characteristics of Oyster Mushrooms
## 5 Biological and Industrial Value of Multi-Coloured Oyster Mushrooms  
In addition to the commonly grown oyster mushroom (_P. ostreatus_), there are vibrantly coloured varieties such as the pink oyster mushroom (_P. djamor_) and golden oyster mushroom (_P. citrinopiletatus_) (Figure 1). These species stand out not only for their vibrant colours but also for their rich nutritional and bioactive profiles. Both types are known for their high levels of antioxidants, essential amino acids, and immunomodulatory polysaccharides, making them valuable as functional foods. Their unique chemical composition offers potential health benefits, including antimicrobial, antioxidant, and cytotoxic properties, contributing to their growing popularity in both culinary and health applications [19,50]. Pink oyster mushrooms have significant biological value due to their bioactive compounds and nutritional profile. Studies have found high antioxidant activity in _P. djamor_, primarily related to its phenolic compounds and \(\beta\)-glucans, which play a role in immunomodulation and free radical scavenging. Polysaccharides extracted from this species have also demonstrated cytotoxic properties against cancer cell lines, suggesting potential as a functional food or nutraceutical. _P. djamor_ is also known for its antimicrobial properties, effective against both Gram-positive and Gram-negative bacteria, further enhancing its health benefits [51; 52; 53]. Golden oyster mushrooms (_P. citrinopileatus_) are renowned for their rich content of essential nutrients and bioactive molecules, including flavonoids and carotenoids, contributing to their antioxidant capacity. This species is particularly effective at mitigating oxidative stress, making it valuable in diets to reduce the risk of chronic diseases such as cardiovascular disease. Moreover, its nutritional value includes a good balance of essential amino acids and minerals, making it an excellent dietary supplement for various population groups [57; 58]  
These results highlight the potential of oyster mushrooms not only as culinary delicacies but also as valuable components of dietary regimens that promote health. The colour of the fruit bodies of _P. ostreatus_ mushrooms is due to some substances that may play an essential bioactive and health-promoting role in the human body (such as carotenoids and flavonoids). It may also be a source of colour substances used in industry, such as melanins, azaphylones, and polyketides [59]. Studies indicate that the colour of the _P. salmonestramineus_ or _P. djamor_ mushrooms, commonly known as pink oyster mushroom varieties, comes from the presence of a pink protein pigment (pink chromoprotein), for which the sequence of amino acid residues has been determined. It has been confirmed that this molecule is a protein with a molecular weight of 23.712 kDa and an isoelectric point of 7.505. Pink chromoprotein also exhibits the ability to oligomerize into dimeric forms and the property of glycation in the Ser6 residue. It is also indicated that the pink chromoprotein's amino acid residues Leu5, Leu8, Lys211, Ala214, and Gln215 bind the prosthetic group to the protein [60]. It is suggested that the identified pink chromoprotein is a melanosomal protein and probably plays a key role in melanogenesis and melanin polymerization in the cells of the mushroom cap and spore structures. For this reason, melanin in the fungal cells plays an essential role in mycelium colour adaptation to the environment and in protection against the harmful effects of ultraviolet (UV) radiation [60]. HPLC analysis indicated that melanin in oyster mushrooms (primarily located in the cell wall) is a mixture of eumelanin and pheomelanin, and differences in the amounts and relative proportions of eumelanin to pheomelanin determine the high colour variation of oyster mushroom caps [61]. An additional property of the pigment derived from the pink oyster mushroom (_P.