Abstract: The cell free filtrate of Flammulina velutipes (FV-CFF) obtained by two-stage fermentation was used for the synthesis of silver nanoparticles (AgNPs) and their effects were studied. The results showed that FV-CFF acted on AgNO3 to produce stable brown AgNPs solution, and AgNPs production was increased with pH elevation. The reducing power of FV-CFF on AgNO3 was significantly inhibited at pH<5, but exhibited a linear growth trend within the pH range of 5-11. The kinetic curve of AgNPs synthesis was acquired by determining AgNPs generation using FV-CFF at normal pH (7.22) and pH 11, respectively. The effect of freezing and thawing was also compared by calculating the formation kinetic curve. The apparent activation energy (Ea) obtained was 98.96 kJ/mol (pH 7.22, initial), 106.725 kJ/mol (pH 7.22, thawed), 119.82 kJ/mol (pH 11, initial), 80.21 kJ/mol (pH 11, thawed), respectively. The results of composition and reducing power determination showed that although freeze-thaw could remove a mass of proteins and carbohydrates in FV-CFF, it had a relatively low effect on reducing power. However, the increasing pH could significantly improve the reducing power of FV-CFF, and the maximum absorption wavelength and particle size of synthesized AgNPs were also significantly reduced at pH 11. The present results will be contributed to further analysis of AgNPs synthesis mechanism by F. velutipes.
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