# Enzymatic Degradation of _Gracilariopsis lemaneiformis_  
Polysaccharide and the Antioxidant Activity of Its Degradation Products  
Tian Fang  
Xiaoqian Zhang  
(\(1\to 4\))-linked 3,6-anhydro-L-galactose units [9]. Notably, the physiochemical properties of GLP might vary with the difference of its sources, extraction, and purification method [10]. Our previous research prepared GLP by the traditional method of hot-water extraction and obtained a polysaccharide with Mw of 123.06 kDa and sulfate content of 9.24% [7]. Studies on in vitro antioxidant activity of GLP indicated that the GLP had strong hydroxyl radical scavenging activity [11] and could protect human kidney proximal tubular epithelial cells (HK-2) from oxidative stress-mediated damage [12]. However, the biological activities of polysaccharides are closely associated with their primary structures, such as monosaccharide composition, sulfate and uronic acid contents, and molecular weight (Mw) [13; 14]. The bioavailability and bioactivity of polysaccharides with high Mw can be restricted because of their high viscosity, poor solubility, and difficulty in penetrating the cell membrane [15]. The bioactivity of natural polysaccharides can be improved through degradation, which can alter the physicochemical properties of a polysaccharide, such as molecular weight, sulfate content, and solubility [16; 17]. The repair abilities of degraded low-molecular-weight seaweed polysaccharides were stronger than that of the undegraded polysaccharide on oxalate-induced damaged HK-2 cells, and a positive correlation was found between -SO\({}_{3}\)H content and repair ability [18]. Similarly, ultrasonic degradation decreased the molecular weight of _P. yezenesis_ polysaccharides and enhanced its superoxide and hydroxyl radical scavenging abilities [19].  
Degradation methods influence the structures and activities of polysaccharides. Physical, chemical, and biological methods have been widely used in polysaccharides degradation. Biodegradation methods, particularly enzymatic degradation, can specifically break glycoside bonds and yield homogeneous products in a mild manner. According to [PERSON] et al. (2006) [20], the enzymatic degradation of polysaccharides is the best option for large-scale oligosaccharidesacharide production and oligosaccharidesacharides with desired molecular weights may be obtained through enzymatic hydrolysis. Effects of hydrochloric acid, ultrasonic-assisted hydrochloric acid, and \(\alpha\)-amylase degradation on _Passiflora edulis_ Sims peel polysaccharides were investigated, and the results showed that enzymatic degradation could yield products with strong antioxidant activities and cause minimal damage to the triple helix structures of polysaccharides [21]. Previous studies have degraded GLP by chemical method with H\({}_{2}\)O\({}_{2}\), citric acid, or vitamin C [12; 22]. However, to our knowledge, the effect of enzyme degradation on the antioxidant activities of GLP is scarcely addressed.  
The aim of this study was to improve the physicochemical properties of GLP and obtain polysaccharides with better antioxidant activity. Five carbohydrates, namely, pectinase, glucoamylase, cellulase, xylanase, and \(\beta\)-dextranase, were used for the first time to degrade GLP, and degradation conditions (time, temperature, pH, and enzyme dosage) were optimized through the in vitro chemical assays of antioxidant activities (hydroxyl radical scavenging activity, 1,1-diphenyl-2-trinitrophenyl hydrazine (DPPPH) radical scavenging activity, reduction capacity, and total antioxidant capacity) of enzymatic hydrolysates. Moreover, human fetal lung fibroblast 1 (HFL1) cells are ideal models for studying antioxidant activity [23]. Thus, the antioxidant activities of three degraded polysaccharides obtained under optimal conditions were evaluated with HFL1 cells at the cellular level.