## 3 Discovering Polysaccharides in Africa
### A Focus on Bioactive and/or Functional Polysaccharides from Arid and Semi-Arid Lands
#### 3.3.3. Opuntia  
_Opuntia_ genus has over 181 species (Cactaceae family). This intriguing genus are widespread in dry, arid, and rocky pastural zones across the Mediterranean area but also North and South Africa [142]. _Opuntia ficus-inducing_ (OFI) is probably one of the most species studied and described in the literature for its content in polysaccharides, associated to functional properties [143]. Hemicellulosic polysaccharides were isolated from the seeds of OFI prickly pear fruits by alkaline extraction [144]. Six fractions of water non-soluble and water-soluble polysaccharides were thus obtained and were mainly composed of Xyl with minor quantities of Glc and Ara. Uronic acid amounts were variable depending on the fractions. Both water-soluble and water non-soluble xylans had unique non-reducing end of 4-O-Me-Glc, for every 11 to 14 and 18 to 65 Xyl units, respectively [145]. Secondly, two major xylans CASF1 and HASF1 were extracted by sequentially cold and hot alkali treatments, respectively, from depetimented cell walls material of seed endosperm.  
Interestingly, a fucosylglucuronoxylan was characterized in CASF1 and consisted of a \(\beta\)-(1,4)-D-Xyl\(p\) main chain, with 4-O-Me-GlcNAc and Fuc\(p\) residues attached to the second and third carbon of Xyl\(p\). HASF1 was fully composed of Xyl units with a backbone made of \(\beta\)-(1,4)-D-Xyl\(p\)[144]. Besides, polysaccharides extracted from skin, peeled or total OFI fruits were also studied in many reports. On one hand, [PERSON] et al. highlighted the presence of arabinidactan type I. It was mainly composed of Gal and Ara with a molar ratio of 6.3:3.3, with some traces of Glc, Rha and Xyl, but no uronic acids [146]. The backbone was described as a \(\beta\)-(1,4)-linked D-Gal\(p\), with sidechains of mono-l-Araf residues or di-l-Araf linked in \(\alpha\)-(1,5). Besides, another acid soluble pectin (ASP) was obtained after sequential hot water and hot EDTA extraction from skin of OFI. Acid extraction yielded 8.7% of ASP, including a considerable amount of GalA (50.7%), in addition to variable rates of neutral sugars, including Rha, Gal, Glc, Ara and Xyl (12.5%, 10.8%, 2.9%, 1.2% and 0.8%, respectively) [147]. Three main fractions called ASP1, ASP2 and ASP3 were studied. The results revealed that the first one was a linear \(\beta\)-(1,4)-galactan. The main chain of the second fraction was made of an alternation of homogalacturonan blocks and disaccharide units [\(\rightarrow\)2]-\(\alpha\)-\(\iota\)-Rha\(p\)-(1\(\rightarrow\)4)-\(\alpha\)-d-Gal\(p\)A-(1\(\rightarrow\)). Lateral chains of \(\beta\)-(1,4)-galactan have been connected to Rha residues in position \(O\)-4. The third fraction ASP3 was composed of homogalacturonan blocks, i.e., \(\alpha\)-(1,4)-d-GalA, and rhamnogalacturonan units, i.e., [\(\rightarrow\)2]-\(\alpha\)-L-Rha\(p\)-(1\(\rightarrow\)4)-\(\alpha\)-D-Gal\(p\)A-(1\(\rightarrow\)) [147]. On the other hand, extraction of peeled fruits allowed to obtain 3.8% of mucilage which was described as some heterogeneous polysaccharides with 23.4% of GalA and no trace of proteins. Neutral sugars included Ara, Rha, Xyl and Gal residues with molar ratios around 1.0:1.7:2.5:4.1 [148]. Additionally, [PERSON] et al. [149] obtained 0.65% of a water-soluble polysaccharide through hot soaking of peeled OFI (L.) Miller. This homogeneous polysaccharide presented a positive optical rotation value and an approximate average molecular weight of 360 kDa. It was highly rich in neutral sugar (more than 80% \(w/w\)) and exclusively composed of Glc. The backbone was made up of \(\alpha\)-(1,4)-D-Glc\(p\), while side chains were attached through (1,6)-linkages [149]. Lastly, [PERSON] et al. obtained three pectic fractions from whole clades of OFI [103]. The results showed that all pectin fractions were mainly composed of GalA with ratios close to 66.6%, 44.3% and 81.1% for water-soluble, chelating-soluble, and acid-soluble pectin, respectively.