Ultrasound-assisted extraction of polysaccharides from Ganoderma lucidum sprout: process, physicochemical properties,...

The young sprouts pruned to ensure optimal growth of Ganoderma lucidum, called Ganoderma lucidum sprouts (GLS), are often discarded as waste despite being rich in polysaccharides (GLSP). Therefore, an ultrasonic-assisted extraction (UAE) method for GLSP was developed and optimized via entropy weight method-response surface methodology (EWM-RSM) considering yield, activity, and energy consumption with energy consumption treated as a negative indicator. Energy consumption and related greenness metrics were subsequently incorporated into the AGREEprep assessment, which evaluates sample preparation greenness across ten principles. The physicochemical properties, including thermal stability and functional groups, and in vitro activities were characterized. The results showed that the optimal conditions of UAE were as follows: power 280  W, liquid-to-material ratio 38:1 mL/g, ultrasonic time 27.5  min, and temperature 47°C. At this time, the extraction rate was 2.22% and the energy consumption was 0.292 Wh/sample. The AGREEprep evaluation confirmed that this extraction process is environmentally friendly and highly green. UAE had higher purity and better thermal stability compared with microwave-extraction and thermal reflux extraction, along with a yield increase of 24.02% and 47.02%. Infrared spectroscopy analysis further showed that UAE did not change the basic chemical skeleton of the polysaccharide, but there was a significant difference in the pyranose ring peak area. In addition, UAE performed better in terms of ABTS⁺ radical scavenging activity, hydroxyl radicals, total reducing power and nitrite scavenging activity. This UAE process provides a theoretical foundation and fresh perspectives on the effective extraction of GLSP and the high-value application of GLS.