The aim of this study was to investigate the effects of ultrasound with different frequency modes on the chemical structure, chain conformation, and immune activity of lentinan from Lentinus edodes; the structure–activity relationship of lentinan was also discussed. The results showed that, compared with original lentinan (extracted using hot water), although ultrasonic treatment did not change the monosaccharide composition and main functional groups of lentinan, it significantly changed its chain conformation. Especially at 60, 40/60, and 20/40/60 kHz, according to atomic force microscopy and solution chain conformation parameters, lentinan transformed from a rigid triple-helix chain to a flexible single-helix chain, and the side-chain was severely broken. Under this condition, lentinan had the worst immune activity. However, at 20/40 and 20/60 kHz, the rigid triple-helix chain transformed into a loose and flexible triple-helix chain, showing the strongest immune activity. These results indicated that dual-frequency ultrasound had significant effects on the conformation of lentinan, and the conformation characteristics of polysaccharide chain such as spiral number, stiffness and flexibility, and side-chain played an important role in immune activity. This study shows the great potential of ultrasound with different frequency modes in carbohydrate food processing, which may have important reference value and practical significance.

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Environmental regulations not only benefit environmental improvement but may also have a potential employment dividend, which is important for sustainable economic development. Based on the provincial panel data of China from 1997 to 2019, the spatial Dubin model is used to analyze the spatial spillover effects of environmental regulation on employment. From the findings, there is a significant spatial agglomeration characteristic in the employment scale. The environmental regulation positively influences the local employment scale, while there is a negative spatial effect on employment in neighboring regions. With regards to the regional heterogeneity analysis, environmental regulation has a spatial negative correlation with employment in coastal areas and less polluted areas. Additionally, in inland areas and less polluted areas, environmental regulation has a significant positive impact on the employment scale. Meanwhile, market-based environmental regulation has the potential to expand the employment scale in local and neighboring areas, while command-and-control environmental regulation impacts negatively on employment in neighboring areas. This study found that environmental regulation has an employment dividend. These findings reveal the spatial dependence between environmental regulation and employment, which will help policy makers consider the environmental and employment effects of environmental regulation more comprehensively. Therefore, the government should formulate targeted policies under regional differences to promote high-quality employment and construct a multiple governance environmental regulatory system.