*2.3. Carbohydrates*

Carbohydrates, which include mono-, oligo- and polysaccharides, are considered an important and irreplaceable source of energy necessary to support di fferent functions of the human body and its physical activity [32]. Of these, algal polysaccharides such as alginates, carrageenan, fucoidan, and laminarin, were found to exhibit a wide spectrum of biological activities, amongs<sup>t</sup> which the antioxidant, antithrombotic, anti-inflammatory, and neuroprotective activities are the most studied [33]. Additionally, the nondigestible oligosaccharides can act as prebiotic agents gaining increased attention due to their positive influence on the gu<sup>t</sup> flora [34–36]. The qualitative di fferences of the sugar backbone, the molecular weight, and also the sulfation degree vary the pharmacological e ffects of algal carbohydrates [37].

In general, edible seaweeds present a variable carbohydrate content. Reported to fresh weight, carbohydrates levels vary from 4.1/100 g wet weight in *Ulva* sp., to 13.1/100 g wet weight in species *Ascophyllum nodosum*, with species *Laminaria digitata* having a content of 9.9/100 g wet weight [3]. Furthermore, the *Undaria pinnatifida* species contains carbohydrates in a content of 9.14% [38]. Related to dry matter, the total carbohydrate concentrations in the seaweed species represent up to 76% of their dry weight. In this sense, species such as *U. pinnatifida* contains between 45 and 52% total carbohydrates. A high content of carbohydrates can be also found in *Saccharina japonica* brown algae (51.9% of dry weight), *Gracilaria chilensis* red algae (66.1% of dry weight), and *Ulva compresa* green algae (48.2% of dry weight) [17,39,40].

According toliterature data, the sulfated polysaccharides represents one of themain constituents [41,42]. The highest contents are found in genera such as *Ascophyllum*, *Porphyra*, and *Palmaria*. Additionally, species *Kappaphycus alvarezii* and *Eucheuma spinosum* present a content of polysaccharides up to 56 and 40%, respectively [43]. Carrageenans are one of the major constituents of red seaweed cell walls representing 30 to 75% of the algal dry weight. Ulvans are the major constituents of green seaweeds cell walls representing 8 to 29% of the algal dry weight. Alginates and fucans are the major constituents of brown seaweeds cell walls representing between 17 and 45%, respectively 5 to 20% of the algal dry weight. Furthermore, brown seaweeds contain laminarin up to 35% of the algal dry weight [44]. Porphyran, a linear sulfated polysaccharide, was found to be one of the main components isolated from *Pyropia yezoensis* (edible red alga cultivated and consumed mainly in East and Southeast Asia) [45]. Considering the applicability in the food industry, seaweed polysaccharides such as agar, alginates, and carrageenan are the most important and economically feasible obtained products due to their rheological gelling and thickening properties [17].
