## 4 Factors Regulating Mushroom Polysaccharide Synthesis  
Monosaccharide composition/combinations significantly affect PS bioactivity. Increasing research attention has been paid to regulation of synthesis of PS with stronger bioactivities. Variability in monosaccharide composition/combinations among mushroom PSs may result from strain variations, developmental stage, culture method and conditions, medium composition, extraction method, and even drying method [60; 75; 76; 77; 78; 79]. In industrial-scale operations, submerged fermentation procedures have been successfully applied for mushroom cultivation during the past two decades. Submerged culture has advantages over traditional solid-state culture in terms of higher mycelian biomass production of bioactive metabolites in a compact space, shorter times, and reduced contamination [75; 80]. This is a useful alternative approach for efficient production of IPS and EPS.  
Structural parameters (monosaccharide composition, degree of branching, molecular weight, molecular weight distribution, chain conformation) are affected by the fermentation medium [81; 82]. Among the various nutrients present in the culture medium, carbon source is an important factor determining the monosaccharide content of PS. In a study by [PERSON] et al., the use of sugar as a carbon source was associated with an excess of the same monosaccharide in _G. lucidum_ EPS. With mixed carbon sources, the main containing monosaccharides of _G. lucidum_ EPS were Glc, Gal, and Man, and the combined mole percentage of EPS monosaccharides was the same as carbon sources used in culture medium. [16]. In _Pleurotus pulmanarius_ submerged culture, each EPS sample had Man, Gal, and Glc as major monosaccharide components. Water-insoluble polysaccharides (IEPS) fractions obtained from Glc- and Xyl-based culture media (termed IEPS-GlcNAc and IEPS-Xyl, respectively) contained Glc as the sole monosaccharide component. Surprisingly, these glucans were not isolated from Gal- and Ara-based culture media [83]. In _Paecilomyces hepiali_, a high percentage of Man in EPS was observed under Glc carbon source, and a high percentage of Glc was observed under Man carbon source [63]. These findings indicate that monosaccharide composition and mole percentages of PS are determined by carbon source in mushroom submerged culture. In a study of _Cordyceps sinensis_ CS-HK1 mycelil cultures, the monosaccharide composition of EPS isolated on different days varied according to carbon source. The monosaccharides Glc, Gal, and Man were found in all EPS samples, with Glc being the major component (50-75% of total). The addition of Gal or Man to the culture medium resulted in no notable increase (in some cases, even a slight decrease) in their content in EPS [84].  
In a study of _Tuber melanosporum_ by [PERSON] et al., the addition of metal ions to culture medium affected IPS and EPS biosynthetic pathways. Gal, Glc, and Man were the major monosaccharides in both IPS and EPS. The addition of Mg\({}^{2+}\) resulted in a maximal Man content (27.6%) in IPS, but no significant change in Gal or Glc content in IPS or EPS. Both IPS and EPS were acidic hetero-PSs containing Man, Gal, and Glc [81]. The metal ions may be a cofactor in enzymatic reactions in the PS biosynthesis pathway and alter some key enzyme activities, which lead to different molar ratios of the monosaccharide components [81]. Alternatively, addition of metal ions is an effective method to regulate the structural properties of polysaccharide.