Ultrasound enhanced production and antioxidant activity of polysaccharides from mycelial fermentation of Phellinus igniarius

In this study, a novel flat-plate ultrasound technology was developed to stimulate polysaccharides production from Phellinus igniarius mycelial fermentation. Three-factor-three-level Box-Behnken design was used to optimize ultrasonic treatment time, duty cycle time and culture time for a high yield of P. igniarius polysaccharides (PIPS). Optimal conditions were found to be ultrasound treatment time 65 min, duty cycle time 25 s, and culture time 3.8 d that gave a maximum PIPS yield of 1.8002 g/L, which increased ∼22.64% compared with the control (without any ultrasound). PIPS mainly contained low-molecular weight (MW) polysaccharides (3.1 kDa, 80%) composed of glucose, rhamnose and mannose in a molar ratio of 11.0:14.0:1.0. PIPS with higher carbohydrate and uronic acid contents exhibited strong antioxidant activities in vitro. Laser scanning confocal microscope (LSCM) observations suggested that ultrasound could change the morphology and structure of P. igniarius mycelium, and accelerate the transfer of nutrients and metabolites.