Preparation of Highly Substituted Sulfated Alfalfa Polysaccharides and Evaluation of Their Biological Activity

Abstract

Alfalfa polysaccharides (AP) receive wide attention in the field of medicine, because of their anti-inflammatory property. However, AP has high molecular weight and poor water solubility, resulting in low biological activity. We wanted to obtain highly bioactive alfalfa polysaccharides for further research. Herein, we successfully synthesized highly substituted sulfated alfalfa polysaccharides (SAP) via the chlorosulfonic acid (CSA)-pyridine (Pyr) method, which was optimized using response surface methodology (RSM). Under the best reaction conditions, that is, the reaction temperature, time, and ratio of CSA to Pyr being 55 °C, 2.25 h, and 1.5:1, respectively, the maximum degree of substitution of SAP can reach up to 0.724. Fourier transform infrared spectroscopy also confirmed the existence of sulfonic acid groups on SAP. Despite the increased average molecular weight of SAP, its water solubility is improved, which is beneficial for its biological activity. Further in vitro results showed that SAP exhibited better antioxidant activity and antibacterial ability than AP. Besides, the former can efficiently enhance the viability of oxidatively stressed intestinal epithelial cells compared with the latter. Furthermore, SAP has the potential to inhibit obesity. It is concluded that sulfation modification could improve the antioxidant, antibacterial, bovine intestinal epithelial cells’ proliferation-promoting, and the obesity inhibition abilities of AP. The improvement of AP biological activity may provide references for the utilization of plant extracts that have weaker biological activity.

Physicochemical properties and biological activities of litchi glycans with different molecular weights

“…The active groups of glycans were closely related to their bioactivities. For example, the existence of sulphonic acid groups in alfalfa polysaccharide was beneficial for its biological activities, such as water solubility, antioxidant activity and anti‐obesity (Li et al ., 2022). Xu et al .…”

“…The active groups of glycans were closely related to their bioactivities. For example, the existence of sulphonic acid groups in alfalfa polysaccharide was beneficial for its biological activities, such as water solubility, antioxidant activity and anti-obesity (Li et al, 2022). Xu et al also found that the sulphated modification of the polysaccharide from Sphallerocarpus gracilis increased its antioxidant effects on DPPH, hydroxyl, superoxide radical scavenging and ferric-ion reducing (Xu et al, 2016).…”

Modification, Structural Characterizations, and Biological Activities of Sulfated Polysaccharides: A Review

“…Therefore, to prepare sulfated derivatives with higher activity, orthogonal experiments, and response surface methodology (RSM) are usually used to optimize the preparation conditions of polysaccharides derivatives. [32][33][34] Nagpal et al [35] used CSA/Pyr reagent to synthesize sulfated derivatives of okra pectin with the DS ranging from 0.39 to 1.13, and optimized the reaction conditions via Box-Behnken Design (BBD) of RSM. The results show that the optimum reaction conditions of sulfated okra pectin were as follows: CSA/Pyr ratio of 0.28 and reaction time of 3.05 h. Compared with unmodified okra pectin, sulfated okra pectin has significantly enhanced anticoagulant and antimicrobial properties.…”

Chemical Modification, Characterization, and Activity Changes of Land Plant Polysaccharides: A Review

“…The proportion of sulfation reagents, reaction time, and reaction temperature are the main factors that affect the DS. The appropriate test conditions are generally explored by orthogonal or response surface design to obtain the desired DS [ 20 , 21 ].…”