In this work, the biosurfactant produced by a Bacillus subtilis strain isolated from crude oil samples was characterized and its properties compared with commercially available chemical surfactants. The purified biosurfactant production yield (Y(P/X)) was 0.20 g/gcell dry weight. The surface tension (29.0 mN/m) and critical micelle concentration (40 mg/l) were found to be similar to the values previously reported for surfactin. Temperature and pH stability of the biosurfactant were also evaluated. The biosurfactant was exposed to different temperatures (20, 37 and 46°C) during two weeks and was found to be as stable as the commercial chemical surfactants Glucopone(®)215, Glucopone(®)650, Findet(®)1214N/23 and linear alkylbenzene sulfonates (LAS). Moreover, the biosurfactant subjected to 121°C for 20 min did not exhibit a significant loss of surface activity. Contrary to the commercial chemical surfactants that were found to be stable over a wide range of pH (3.0-10.0), the biosurfactant was unstable precipitating at pH values below 5.0. The emulsification indexes showed that the biosurfactant possesses equal or superior capacity to form emulsions with n-hexadecane as compared to the commercial chemical surfactants. Moreover, the anti-adhesive activity of the biosurfactant and commercial chemical surfactants was evaluated. The biosurfactant showed some activity against Staphylococcus aureus and Escherichia coli. Nevertheless, no particular trend or special effect could be assigned to the use of commercial chemical surfactants as anti-adhesives. Results gathered in this work suggest that the biosurfactant recovered from B. subtilis EG1 constitutes an interesting alternative to the commercial chemical surfactants with potential use in several industries.
Olive mill waste (OMW) creates a major environmental problem due to the difficulty of further waste processing. In this work we present an approach to give OMW added value by using it for the production of biosurfactants. Two bacterial species, Pseudomonas aeruginosa and Bacillus subtilis, were grown with OMW as the sole carbon source. Glycerol and waste frying oil were used as comparative carbon sources. B. subtilis produced surfactin (a lipopeptide) at a maximum concentration of 3.12 mg/L with 2% w/v of OMW in the medium, dropping to 0.57 mg/L with 10% w/v of OMW. In contrast, P. aeruginosa produced 8.78 mg/L of rhamnolipid with 2% w/v OMW increasing to 191.46 mg/L with 10% w/v OMW. The use of solvent-extracted OMW reduced the biosurfactant production by 70.8% and 88.3% for B. subtilis and P. aeruginosa respectively. These results confirm that OMW is a potential substrate for biosurfactant production.
The scientific network of the surfactants and related subjects has been analyzed with the CoPalRed © knowledge system. The actors studied have been countries, research centers and laboratories, researchers, and journals. The thematic map of the major research areas has been established. Most of the research areas, and those that have the greatest representation in terms of number of documents, are related to physics and chemistry. However, biochemistry and cell biology, medicine (pediatrics and pulmonary physiology), and, to a lesser extent, veterinary medicine and food science and technology are also noteworthy in the field of surfactants, which presents a markedly multidisciplinary profile.
The bibliometric laws of Zipf, Bradford, and Lotka, in their various mathematical expressions, frequently present difficulties in the fitting of empirical values. The empirical flaws of fit take place in the frequency of the words, in the productivity of the authors and the journals, as well as in econometric and demographic aspects. This indicates that the underlying fractal model should be revised, since, as shown, the inverse power equations (of the Zipf-Mandelbrot type) are not adequate, as they need to include exponential terms. These modifications not only affect Bibliometrics and Scientometrics, but also, for the generality of the fractal model, apply to Economy, Demography, and even Natural Sciences in general.
By the information system of CoPalRed© and with the treatment of 63,543 bibliographical references of scientific articles, the field of surfactants has been analysed in the light of the Unified Scientometric Model. It was found that the distributions of actors (countries, centres, and research laboratories, journals, researchers, key words of documents) fit Zif's Unified Law better than the Zipf-Mandelbrot Law. The model showed an especially good fit for relational indicators such as density and centrality. Using the Unified Bradford Law, the three zones fit were: core, straight fraction, and Groos droop. The fractality index was used to verify that Science can present fractal as well as transfractal structures. In conclusion, the Unified Scientometric Model is, for its flexibility and its integrating capacity, an appropriate model for representing Science, joining nonrelational with relational Scientometrics under the same paradigm.
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