BIOSURFACTANTS AND BIOPOLYMERS 463 involves the addition of mannopyranosyl residues to phosphatidylinositol (71). Alasan is an anionic alanine comprising bioemulsifi er obtained from Acinetobacter radioresistens, a species of bacteria which has a resistance toward radiation (72). Alasan is a complex of the α-amino acid alanine, polysaccharides, and proteins (73). B IODEGRADABILITY B iosurfactants have been long used to treat contaminated media such as water and soil. The amphiphilic nature of biosurfactants enables hydrophobic compatibility, where pollut- ant substrates such as hydrocarbons easily associate into the microbial cells. The mecha- nism of biodegradation was studied by Urum and Pekdemir (74), where it was discussed that biosurfactants followed different biodegradation mechanisms depending on their molec- ular masses. Biosurfactants containing lower molecular mass act in two ways, namely, (i) mobilization and (ii) solubilization (75). Mobilization takes place when the biosurfac- tant’s concentration is lower than the critical micelle concentration (CMC). In this mech- anism, biosurfactants act on the interface between the hydrophobic pollutant and surface by reducing interfacial tension which allows for easier removal of the pollutant. Solubili- zation occurs for concentrations that are greater than the critical micellar concentration. This mechanism involves the formation of thermodynamically stable micellar structures which encompass the hydrophobic pollutants. Biosurfactants of higher molecular masses carry out biodegradation by emulsifi cation of pollutants (76). C ameotra and Singh (77) outlined the uptake of hexadecane by RLs. RLs increased the surface area of the pollutant by breaking it down into smaller particles of 0.22 μm. The microbe engulfed the droplets and slowly began to render the hydrocarbon into its cellular phase by breaking it down metabolically. In addition to RLs, trehalose lipids have been important for soil bioremediation, and it has been proposed that they could also be useful in the treatment of wastewater through micelle formation (78). SLs have been used to degrade open and closed chain hydrocarbons in controlled conditions this was tested in particular for soil bioremediation. It exhibited superior biodegradation capabilities for pollutants such as n-hexadecane, 2-methylnaphthalene, diesel, gasoline, and kerosene (79). There have been several studies of the effect of biosurfactants on n-alkanes such as octadecanes, polyaromatic hydrocarbons, oils, and hydrocarbon residues however, studies on complex hydrocarbon mixtures are scarce. To study the effect on unresolved complex mixtures, Nievas et al. (75) collected marine ship waste known as oily bilge waste, which is a mix- ture of seawater and hydrocarbon residues, and studied the effect of a symbiotic microbial system on its degradation by emulsifi cation. The positive effect of reduction on the com- plex mixture was around 58%. Ap art from their key roles in biodegradation of pollutants, biosurfactants are themselves easily biodegradable. Mohan et al. (80) investigated the biodegradability of RLs under aerobic, anaerobic, and nitrate- and sulfate-reducing conditions. The study revealed that RL was biodegradable against all four conditions with a soluble chemical oxygen demand effi ciency percentage of 74 under aerobic conditions, 47.2 under anaerobic conditions, 34.2 under sulfate-reducing conditions, and 24.6 under nitrate-reducing conditions. Bio- surfactants are also low in toxicity when compared with synthetic surfactants. Within biosurfactant classifi cations, environmental toxicity can vary with the type of strain that they are sourced from, for example, glycolipids synthesized from Rhodococcus ruber exhibits a
JOURNAL OF COSMETIC SCIENCE 464 toxicity 10 times lower than that of TL (synthesized from R. erythropolis) and 13 times lower when compared with RLs (synthesized from Pseudomonas aeruginosa) (79). Th e aforementioned evidence concludes that biosurfactants display several environmen- tally positive functionalities. There is a strong need for process optimization and feasible production of biosurfactants to commercially adapt them. BI OPOLYMERS Po lymers fi nd widespread use in beauty and personal care products, and a majority of these polymers are synthetic and nonbiodegradable. As a result of its widespread use across the industry, an alarming amount of polymer waste is being generated (81). In response to this increased awareness regarding the toxic effects of certain polymers, various biopoly- mers such as chitosan, alginate, and xanthan gum, and several other polysaccharides have been extensively explored as potential alternatives to the traditionally derived polymers (82–85). Bi opolymers are polymeric biomolecules derived from plants and microorganisms (86). They can be produced or sourced in different ways. Most biopolymers are found in abun- dance in nature and are extracted from plants, algae, or other microorganisms. Examples of such biopolymers include alginate and chitosan. Other methods of production are in vitro synthesis of biopolymers with isolated enzymes and through fermentation (87). Poly- saccharides, also known as carbohydrates, are agro-based polymers. Some of the most common polysaccharides include cellulose, chitin, alginate, xanthan gum, and pectin. CH ITIN AND CHITOSAN Ch itin or poly(β-(1→4)-N-acetyl-D-glucosamine) is one of the most abundant polysac- charides present in nature second to only cellulose. Chitin is primarily extracted from the outer shells of crustaceans such as shrimps, crabs, and squids or the cell wall of fungi and yeast (88). However, at present, chitin is primarily sourced from the outer shells of crabs and shrimps. Thus, this biopolymer is essentially produced by recycling or processing biowastes from marine food industries (89). Chitosan is one of the most signifi cant de- rivatives of chitin obtained by the deacetylation of chitin. On deacetylation, the acetyl groups of chitin are substituted by primary amino groups, resulting in the formation of chitosan (Figure 7) (90). Although chitin is found in abundance in nature, the main natural source of chitosan is limited to certain fungi such as Mucoraceae (91). Pazo et al. (92) reported that crustaceans make up nearly 7% of the marine waste in oceans. Thus, discarded marine biomass has great potential for the production of chitin and chitosan. The waste shells consist of chitin along with various proteins and inorganic salts. As a result, the extraction of chitin from marine waste includes two steps—mainly deproteinization and demineralization. These processes may be achieved by many methods. The most common and conventional method involves chemical treatment. However, this route requires strong alkali and acids at extreme temperatures in addition to high energy consumption and effl uent production (93–96). Furthermore, the extraction of chitin by chemical means only results in a 10% recovery of the raw material (97). This has led to a desire for the optimization of chitin production and the effi cient use of shell waste by
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