## Biomedical Applications
### Antioxidant Activity  
Antioxidants can be obtained from animals and plants, including _U. lactuca_. This alga has an anti-radical capacity by inhibiting lipid peroxidation and increasing the activity of antioxidant enzymes. Studies have reported that the strong antioxidant activity of ulvan correlates to the degree substitution of sulfate groups along the polymeric backbone [106]. In 2019 and 2020, several sources of ulvan from _Ulva_ sp were found to have an antioxidant effect; they include _U. lactuca_, _U. australis_, _U. rigida_, and _U. olnoi_[48; 107; 108]. The antioxidant capacity of ulvan has been measured using various in vitro systems such as 2,2-diphenyl-2-picryl hydrazine (DPPH) radical scavenging, superoxide scavenging, ferric reducing antioxidant power (FRAP), hydroxyl radical scavenging, and lipid peroxidation inhibition assays. Sulfate content and molecular weight have been reported to play an important role in the antioxidant effects of ulvan from _Ulva_ sp. [68; 75; 76; 79; 109]. The DPPH assay is the fastest method to measure antioxidant ability, compared to other methods that are also commonly used, namely reducing power and superoxide anion radical scavenging activity [76; 102; 107; 108; 110; 111]. Notably, using more than one method to assess antioxidant activities increases the accuracy of the results. Several studies have compared methods to determine which is more sensitive. Among DPPH, oxygen radical absorbance capacity (ORAC), FRAP, and \(\beta\)-carotene linoleic acid bleaching methods, ORAC was most effective for observing changes in peroxide formation [77; 78]. The antioxidant power of ulvan has been compared with other molecules, such as BHA, BHT, andtocopherol. While the percent of ulvan inhibition (54.9%) was lower than BHA (73.20%) and BHT (69.40%), the differences were not statistically significant [112]. Based on research conducted for antioxidant testing, it is known that ulvan from _Ulva_ sp has antioxidative ability, as evidenced by the comparison of several methods described above. Products from experimental animals have also been used to assess the antioxidant activity of ulvan, including erythrocyte-based and 2,2-azobis(2-amidinopropane)dihydrochloride (AAPH) assays [80; 81]. Ulvan reduces ROS production by AAPH and attenuates lipid peroxidation, evaluated by thiobarbituric acid reactive substances (TBARS), according to erythrocyte-based assays [80]. Ulvan's antioxidant mechanism involves sulfate and low-molecular-weight polysaccharides [31; 83; 113]. The latter inhibit cholinesterase and have neuroprotective potential [4]. Components of oligosaccharides can increase glutathione peroxidase (GSH), superoxide dismutase (SOD), catalase (CAT), telomerase, and total antioxidants and decrease the level of malondialdehydedehyde [27; 114]. For ulvan, the IC\({}_{50}\) for radical activity is 623.58 \(\mu\)g/mL and the IC\({}_{50}\) for superoxide anion scavenging is 785.48 \(\mu\)g/mL. Other components in _U. lactuca_ with antioxidant activity are pigments (chlorophyll, carotenoids), essential oils, and low-molecular-weight polysaccharides [76]. The extraction procedure also affects the antioxidant effect produced by ulvan. This is related to the polarity of the solvent used to extract components that have antioxidant activity. The percentage of inhibition produced from methanol extract is higher than the percent inhibition of the water extract [115]. Furthermore, enzymatic extraction provides higher percent inhibition compared with acid extraction [22]. Besides in vitro antioxidant tests, animals can be exposed to radicals, such as thiacloprid, and then treated with an extract [5; 6]. In hypercholesterol mice, ulvan reduces oxidative stress by increasing the activity of antioxidant enzymes (110% for CAT, 77% for GPx, and 23% for SOD) and the level of nonenzymatic antioxidants (GSH). These changes limit the consequences of damaging macromolecules by minimizing lipid peroxidation and protein oxidation [6].