# Current Progress Regarding _Cordyceps militaris_, Its Metabolite Function, and Its Production
## 2 Biological Compounds of _C. militaris_
### Carotenoids  
Carotenoids, such as \(\beta\)-carotene, lycopene, lutein, and zeaxanthin, are responsible for the vivid yellow-orange hue of the fruiting bodies of various species of fungi, includingC. _militaris_, in which their presence was confirmed [18; 128]. In the aqueous extract of C. _militaris_, \(\beta\)-carotene was found at a concentration of 24.51 mg/kg, while lycopene was detected at 3.42 mg/kg [88]. Cordyxanthins are a novel class of carotenoids found in the fruiting bodies of C. _militaris_. They show better solubility in water and have unique chemical structures when compared to traditional carotenoids. Four types of cordyxanthins, including cordyxanthin I, II, III, and IV, have been identified in fruiting bodies of C. _militaris_, with respective concentrations of 0.289, 0.235, 0.401, and 0.175 mg/g. Using \(\beta\)-carotene as a standard, total _Cordyceps_ carotenoids were directly quantified at 447 nm. Carotenoids are powerful antioxidants due to their ability to efficiently quench singlet oxygen (\({}^{1}\)O\({}_{2}\)) [129; 130; 131; 132], which is attributed to their triplet energy levels being in close proximity to that of \({}^{1}\)O\({}_{2}\)[133; 134]. The \({}^{1}\)O\({}_{2}\)-quenching process is particularly efficient for carotenoids that have 11 conjugated double bonds [135], with an approximate rate constant of 10\({}^{10}\) M\({}^{-1}\)-s\({}^{-1}\). In addition to their antioxidant properties, carotenoids were observed to act as protective agents against ROS in eye-related disorders [136]. Lutein and zeaxanthin, two oxygen-containing carotenoids, are present in high concentrations in the eye lens and the macular region of the retina (yellow spot) [137]. Carotenoids possess anti-inflammatory properties by suppressing the activation of NF-kB [138; 139; 140; 141]. Apocarotenals, which are derivatives of carotenoids, possess electrophilic groups that can interact with cysteine residues of 1 kB kinase (IKK) and NF-kB subunits (p65), leading to inactivation of the NF-kB pathway [142]. Most carotenoids have demonstrated antiaging effects. For instance, an animal study showed that lutein can extend the lifespan and reduce the mortality rate caused by hydrogen peroxide and paraquat in _Drosophila melanogaster_[143], and further study indicated that lutein (at 0.5, 1.5, 5, and 15 uM) can mitigate the age-related decline in human skin cells [144]. Astaxanthin, another carotenoid, can also prolong the lifespan in wild-type and long-lived mutant age-1 _Caenorhabditis elegans_ when administered at a concentration of 0.1-1 mM [145]. That study suggested that carotenoids partially modulate insulin-like growth factor (IGF)-1 signaling by increasing _DAF-16_ gene expression and decreasing the mitochondrial production of ROS. Beta-carotene, a commonly found carotenoid derivative, also exerts antiaging effects by downregulating the expression of lysine acetylcholinesterase 7 (_KAT_7), while _KAT_7 is a histone acetylcholinesterase transferase gene known to be a driver of senescence [146]. Some research examined the antimicrobial effects of carotenoid pigments in _Rhodotorula_ against two food-borne bacterial strains, _Staphylococcus aureus_ ATCC 25,923 and _Salmonella typhimurium_ ST38 [147]. Another study indicated that a wide range of antimicrobial activities against _Escherichia coli_, _Staphylococcus aureus_, _Bacillus subtilis_, _Saccharomyces cerevisiae_, and _Rhizopus oryzae_ were exhibited by the methanol extract of carotenoids, as evidenced by the disc diffusion method and minimum inhibitory concentration (MIC) determination, with inhibition zones ranging 8.97-19.47 mm and MICs ranging 18.75-140 ug/mL [148]. Antiapoptotic properties were demonstrated in some carotenoids. Lycopene, for instance, is capable of preventing the loss of such antiapoptotic proteins as Bcl-2 and Bcl-xL [149; 150], as well as inhibiting proapoptotic proteins like Bax under neurotoxic conditions [151; 149].