## 4 Chemical Aspects of Ulvan from _Ulva_ sp. ### Chemistry and Physicochemical Properties  
Ulvan mainly consists of cellulose, xyloglucan, and glucuroran with other various types of sugars. It has a low content of mannose, galactose, and arabinose [10; 21]. Ulvan is mainly built on a repetitive sequence of disaccharides that consist of rhamn sulfate, uronic acid, iduronic acid, or xylose. The two main repeating disaccharides are aldobiuronic acids, which are designated as type A ulvanobiuronic acid 3-sulfate (A\({}_{3S}\)) and type B ulvanobiuronic acid 3-sulfate (B\({}_{3S}\)) (Figure 2) [2; 3; 22]. In addition to the polysaccharide content, there are also other contents such as protein around 1-3% and fatty acids less than 1% [10; 22; 23]. The physicochemical properties of the active components contained in ulvan--hydration, polarity, swelling, and viscosity--are related to stability and physiological effects. These properties will depend on the extraction process. Ulvans from _U. pertusa_ and _U. rigida_ show a multimodal distribution by gel permeation chromatography. In addition, the major fraction of ulvans are distributed as a single polydispersed population on gel permeation chromatography. The polymolecularity was due to linear xyloglucan structure of ulvans [24; 25]. Ulvan extracted from _U. lactuca_ contains polysaccharides that can be used as natural fibers or matrix; they can also be modified for other purposes, including as part of a composite [26]. Ulvan is also used as a substitute for Avicel, a polymer that contains cellulose. Ulvan has the same characteristics as Avicel in terms of thermal stability (degradation at 360-365 \({}^{\circ}\)C) [21]. Ulvan has a soluble fiber content of around 15.8% and an insoluble fiber content of 24.2%; the total fiber content is around 36.6-44.6% [27]. In a study conducted by [PERSON] et al., ulvan extracted using alcohol at pH 1-2 and a drastic temperature (80-90 \({}^{\circ}\)C) produced 20.37-23.60% uronic acid and 20.09-29.12% sugars. A reduction in molecular weight was influenced by a more acidic pH and altered extraction time [22; 28; 29]. The process of dissolving the fiber is influenced by pH: At pH 3, the insoluble fiber content is around 5.5%, while at pH 7, the insoluble fiber content is 7.5%. The pH also affects the zeta potential: the higher the extraction pH, the lower the zeta potential produced (with a range of \(-\)15 to \(-\)35) [10]. Ulvan has a low viscosity [22]. When analyzing the distribution of macromolecules using high performance size exclusion chromatography (HPSEC), there are two main distributions: population A, with a molecular weight of \(7.21\times 10^{2}\) kDa; and population B, with a molecular weight of \(2.25\times 10^{2}\) kDa. Some studies  
Figure 2: Structures of two main repeating disaccharides, type A ulvanobiuronic acid 3-sulfate (**A\({}_{3S}\)**) having repeating \(\beta\)-D-glucuronic acid (1\(\rightarrow\)4)-\(\alpha\)-L-rhamnose-3-sulphate units, and type B ulvanobiuronic acid 3-sulfate (**B\({}_{3S}\)**) having repeating \(\alpha\)-L-iduronic acid (1\(\rightarrow\)4)-\(\alpha\)-L-rhamnose-3-sulphate units. stated that the differences in molecular weight was due to selection of the extraction method and parameters [22; 30]. Based on several parameters, ulvan content is markedly degraded at 360 \({}^{\circ}\)C [29]. Ulvan extracted has a moisture content > 90% [21]. Another study stated that a film with _U. lactuca_ polymer is stable between -50 to 250 \({}^{\circ}\)C [10]. Yields resulting from acid extraction decrease when constant pH and temperature are used. Yields will increase with increasing extraction pH at a constant temperature [22]. The polysaccharides in ulvan have a strong ligand bond, a factor that may provide a therapeutic effect [31]. Ulvan can be employed in various fields, one of which is pharmaceutical formulation. Ulvan can be used as a polymer because of its high polysaccharide content [29].