## 1 Introduction  
Konjac glucomannan (KGM) is a water-soluble polysaccharide originated from the plant tuber of _Amorphorphallas konjac_. The polysaccharide chain of KGM is composed of 1.4-linked \(\beta\)-d-mannopyranose and \(\beta\)-d-glucopyranoside backbone with a mannose and glucose molar ratio of 1.4 to 10 [1; 2; 3; 4]. KGM is widely used in pharmaceutical, biotechnological, fine chemical, and other fields because of its excellent biocompatibility and biodegradable activities [5]. Moreover, it is recognized as a promising dietary fiber supplement and functional food for gut health, body weight management, and type 2 diabetes treatment [6; 7; 8; 9; 10]. However, native KGM has a very limited range of functionality. Therefore, its modifications attracted increasing attention for expanding its functions and applications [11].  
Chemical and physical methods are frequently applied to modify KGM [11]. Sulfated KGM was shown to have potent anti-human immunodeficiency virus (HIV) activity and moderate blood anticoagulant activity [12]. Oxidized KGM and its acidolysis products exerted immune responses to _Schizophotax preanti_ infected by _Aeromonas hydrophila_[13]. Consumption of depolymerized KGM has been shown to enhance wound healing for mice [14]. Acid-hydrolyzed KGM exhibited a greater prebiotic effect on the modulation of cecal and fecal microflora than did original KGM in mice [15].  
On the other hand, physical methods such as \(\gamma\)-irradiation, ultrasonication (US), and extrusion were used to modify KGM. Degraded KGM prepared by \(\gamma\)-irradiation was demonstrated to be more effective in protecting the LO2 cell line (human hepatic cell line) against H\({}_{2}\)O\({}_{2}\)-induced oxidative damage [16]. US-degraded KGM had stronger protective effects on _Bifidobacteria_ against antibiotic damage [17]. Extrusion modification was able to reduce the molecular weight, water absorption index, and viscosity of KGM [18].  
As sonochemistry is used in several chemical, physical, and biological processes [19], ultrasonic (US) treatment was effective for partial degradation of polymer compounds, reducing the molecular weight and viscosity but not causing any significant changes in the chemical nature [20]. It has been widely explored for the modification and partial degradation of carbohydrate polymers including various natural polysaccharides [20; 21]. Sonication usually breaks polymer chains at the center point or at the structurally weakest points. The polymer at a high molecular weight or with a longer chain is degraded more rapidly by US. A linear polymer chain was found more easily degraded with US than branched ones [22]. The degradation kinetics can be fitted to either a midpoint chain scission model or a random chain scission model [23].  
A previous study of our group showed the effects of power ultrasound on the molecular weight and rheological properties of KGM [24]. Based on this, the aim of the present study was to further investigate the effects of US treatment on the solution properties of KGM, particularly its conformation characteristics and microstructure in water. The effects of US treatment on the bioactivity of KGM have rarely been reported except the studies reported by [PERSON] et al. and [PERSON] et al. [17; 25], the influence of US degradation on the antioxidant activity of KGM was evaluated using in vitro assays. The investigation will be helpful for a better understanding of the degradation mechanisms and the effects of US on the functional properties of KGM.