BIOSURFACTANTS AND BIOPOLYMERS 465 exploring sustainable extraction processes involving microbial or enzymatic treatment (8,98–103). The substitution of strong alkaline treatments by enzymatic treatment resulted in reduced energy and water consumption, whereas microbial treatment for the deprot- einization step recorded enhanced chitin recovery (99). Khanafari et al. (8) compared and characterized the chitin obtained by chemical and biological extraction methods from shrimp shells. Their studies revealed that microbial extraction resulted in enhanced pres- ervation of chitin structure compared with the chemical method. ALGI NATE Algi nates are another group of natural linear polysaccharides that have garnered a lot of scientifi c interest in recent years because of their application in the cosmetic, food, textile, and pharmaceutical industries as a stabilizer, thickener, or fi lm-forming agent. They mainly consist of varying ratios of β-D-mannuronate (M) and α-L-guluronate (G) (Figure 8) which are linked through 1-4 glycosidic bonds. The amount of M and G units depends on the biopolymer source (9). Currently, commercial alginate is sourced from marine brown algae (seaweed). This biopolymer is naturally present in the cell wall of these marine macroalgae. In particular, alginate is primarily sourced from a group of seaweed called kelp (103,104). Algina te salts found in the algal cell walls are transformed to insoluble alginic acid by acidifi cation. Sodium alginate is then extracted by treating with sodium hydroxide solution. Figure 7. Che mi cal structure of chitosan. Figure 8. Che mi cal structure of alginate.
JOURNAL OF COSMETIC SCIENCE 466 Seaweed residue is separated from this solution by fi ltration, and fi nally, sodium alginate is precipitated by the acidifi cation of sodium alginate solution using dilute hydrochloric acid (105). The fi ltration step of alginate extraction requires large quantities of water, making the need for a more sustainable process or source for alginate production a neces- sity (104). In addition, as the demand for alginate increases, the macroalgal community, which is the main resource for alginate, is fast declining. This in turn has a negative impact on marine biodiversity in addition to other ecological and economic consequences (9,103). This growing concern over the harmful effects of excessive seaweed harvesting has paved the way for research on certain bacterial species such as Azotobacter and Pseudomonas as al- ternative sources for alginate production. The mutant strain of Azotobacter vinelandii has been extensively explored as it has the ability to produce greater quantities of the biopolymer (84,106,107). Furthermore, the excellent mechanical stability and wider pore size distri- bution of alginate produced by bacterial fermentation have made bacterial sources all the more favorable. Bacterial alginate also showcased better rheological properties, making it ideal for the cosmetic industry (84,106,107). PECTIN Pectin is a polysaccharide found in abundance in the cell wall and middle lamellae of many plants. It is a complex molecule and has D-galacturonic acid as its main monomeric unit linked by α-1→4 glucuronosyl links (Figure 9). These linkages may be interspersed with L-rhamnose units (108,109). This biopolymer has found itself a market within the beauty industry as a texturizer. A major portion of commercial pectin is derived from citrus peels and apple pomace (110). The proc esses involved in extracting pectin from plant material can be broadly classifi ed into raw material pretreatment, extraction, and post-extraction. The extraction stage involves an acid hydrolytic process at high temperatures which generates large amounts of acid wastewa- ter. This process also consumes a lot of energy as it requires heating for extended time periods, further resulting in long extraction times (10,111). Researchers have been studying various alternative approaches for extracting pectin that would help provide better yield with low solvent and energy consumption. One popular method is the enzyme-assisted extraction where certain enzymes such as cellulases and proteases, which can degrade the various constituents of the cell wall, catalyze the reactions, thus reducing the amount of solvent required while Figure 9. Chemi c al structure of pectin.
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