BIOSURFACTANTS AND BIOPOLYMERS 473 stress to evaluate the thixotropic properties of carboxymethyl cellulose. Carboxymethyl cel- lulose solutions showed excellent thixotropic behavior. Furthermore, this time dependence of viscosity increased at greater carboxymethyl cellulose concentrations. This was explained by the different rates of disentanglement and re-entanglement of the polymer chains when a shear is applied (162). Because of its thixotropic behavior, carboxymethyl cellulose has found widespread use in cosmetic products such as nail polish. Studies on the rheological effects of biosurfactants are few. One study carried out by Abbas et al. (163) discussed the rheology of the biosurfactant synthesized by Pseudomonas aeruginosa—in other words, RLs from food industry by-products. Rheological measure- ments were carried out using viscosity-shear, strain, and frequency sweep tests. The bio- surfactant displayed a linear viscoelastic region of less than 1% on carrying out the strain sweep test. The viscosity tests revealed shear thinning behavior, and the frequency sweeps revealed a dominant storage (G′) modulus throughout the range, where the modulus was frequency dependent. When the sample was subjected to a constant shear rate, it displayed thixotropic behavior with respect to time. A nother study by Jain et al. (164) studied the rheology of biosurfactant produced by an alka- line environment preferring bacterium Cronobacter sakazakii which was extracted from waste- water polluted by oil. This biosurfactant is a heteropolysaccharide–protein complex which is also emulsifying in nature. Viscosity measurements were carried out for the sample. The fl ow sweep revealed that the biosurfactant was a pseudoplastic, or, in other words, it was shear thin- ning in nature. The viscosity was 0.429 Pa/s at 0.01 1/s shear rate and decreased from there onward with an elevation in the shear rate. Another biological emulsifi er produced from Halomonas eurihalina also displayed similar pseudoplastic behavior (165). F inally, Xu and Amin (15) carried out mechanical rheometry to study the effect of RLs on sodium lauryl ether sulfate and CAPB—which are common synthetic surfactants. The addition of RLs to the SLES/CAPB system lowered the viscosity at low shear rates. The viscoelastic behavior was Maxwellian—where before crossover, the loss modulus (G″) was dominant. As more RLs were added, the crossover shifted to shorter relaxation times, which is always inversely proportional to the frequency. Micro rheological tests were also performed to understand the rheological properties of the ternary system at higher frequencies. From the tests, one could construe that with the addition of RLs, the long micelles broke into shorter micelles because of weaker entanglements. This explained the reduction in viscosity. Fu rther research on biosurfactant and bioemulsifi er effects on rheology would make for an interesting long-term study on the development of novel rheological textures in cosmet- ics and cosmeceuticals. FU TURE TRENDS AND CHALLENGES Sh ifting into the realm of sustainability has become a necessity for the sustenance of cos- metic companies. This transition, although advantageous in terms of environmental consid- erations, comes with its own challenges. The most consequential challenge that is faced in today’s market scenario is the existence of a supply–demand paradox, where low demand has led to diffi culty in quelling market prices of green cosmetic commodities. This can be addressed by systematically increasing the percentage of sustainable ingredients in cosmetic formulations and continually funneling these into the market for consumer accep-
JOURNAL OF COSMETIC SCIENCE 474 tance. Growth in consumer acceptance is also heavily dependent on the performance prop- erties of green cosmetics. Their performance can be engineered by exploring interactions between traditional surfactants and polymers, and their bio-based alternatives which have been discussed extensively in this article. Furthermore, biosurfactants and biopolymers can be rheologically modifi ed and explored as discussed by Xu and Amin (15). This is a scarcely investigated area which presents researchers with a plethora of opportunities. To day, there is a highly anticipated evolution transpiring across the entire product life cycle of the cosmetics industry—right from sourcing raw materials for commercial-scale production—all the way up to fi nal market appeal. From a scientifi c standpoint, the design stage of cosmetics is a key factor in incorporating sustainability into the product life cycle. The design stage should address the principles of green chemistry and green engineering, which calls for studying fundamental molecular properties and transformations. On the consumer end, with evolving demands and industry regulations, there is a need for high- throughput and high-output research in the formulation space. This can be achieved by introducing automation platforms to the formulation process. Automation can meet the large volume requirement for customization techniques and can provide companies with fl exibility in formulation without time and cost constraints, and can hence enable more iterative investigation into structure, property, and performance. In the coming years, it is inevitable that with research in this fi eld picking up pace, there will be a complete metamorphosis of the cosmetics industry into a model that is highly sustainable and automized. RE FERENCES ( 1 ) V. Dimitrova, M. Kaneva, and T. Gallucci, Customer knowledge management in the natural cosmetics industry, Ind. Manag. Data Syst., 109, 1155–1165 (2009). ( 2 ) J. Zimmerman, P. Anastas, H. Erythropel, and W. Leitner, Designing for a green chemistry future, Science, 367, 397–400 (2020). ( 3 ) S. Srivastava, Green supply-chain management: a state-of-the-art literature review, Int. J. Manag. Rev., 9(1), 53–80 (2007). ( 4 ) P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice (Oxford University Press, Oxford, England, 1998). ( 5 ) I. M. Banat, S. K. Satpute, S. S. Cameotra, R. Patil, and N. V. Nyayanit, Cost effective technologies and renewable substrates for biosurfactants’ production, Front. Microbiol., 12(5), 697 (2014). ( 6 ) D. K. F. Santos, Y. B. Brandão, R. D. Rufi no, J. M. Luna, A. A. Salgueiro, V. A. Santos, and L. A. Sarubbo, Optimization of cultural conditions for biosurfactant production from Candida lipolytica, Biocatal. Agric. Biotechnol., 3, 48–57 (2014). (7 ) D. K. F. Santos, R. D. Rufi no, J. M. Luna, V. A. Santos, A. A. Salgueiro, and L. A. Sarubbo, Synthesis and evaluation of biosurfactant produced by Candida lipolytica using animal fat and corn steep liquor, J. Petrol. Sci. Eng., 105, 43–50 (2013). (8 ) A. Khanafari, R. Marandi, and S. Sanatei, Recovery of chitin and chitosan from shrimp waste by chemical and microbial methods, Iran. J. Environ. Health Sci. Eng., 5(1), 1–24 (2008). (9 ) I. D. Hay, Z. Ur Rehman, M. F. Moradali, Y. Wang, and B. H. Rehm, Microbial alginate production, modifi cation and its applications, Microb. Biotechnol., 6(6), 637–650 (2013). (1 0 ) R. Gentilini, S. Bozzini, F. Munarin, P. Petrini, L. Visai, and M. C. Tanzi, Pectins from aloe vera: extraction and production of gels for regenerative medicine, J. Appl. Polym. Sci., 131(2), 2014. doi: 10.1002/app.39760. (11) S. Raposo, A. Salgado, G. Eccleston, M. Urbano, and H. M. Ribeiro, Cold processed oil-in-water emulsions for dermatological purpose: formulation design and structure analysis, Pharmaceut. Dev. Technol., 19, 417–429 (2014). (12 ) J. Beerling and A. Sahota, “Green standards, certifi cation and indices,” in Sustainability: How the Cosmet- ics Industry is Greening up, A. Sahota. Ed. (John Wiley & Sons, London, United Kingdom, 2014).
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