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. 2023 Jan 24;23(1):2.
doi: 10.1186/s12896-022-00772-4.

Production of rhamnolipid biosurfactants in solid-state fermentation: process optimization and characterization studies

Shima Dabaghi  1 , Seyed Ahmad Ataei  2 , Ali Taheri  3
Affiliations

Production of rhamnolipid biosurfactants in solid-state fermentation: process optimization and characterization studies

Shima Dabaghi et al. BMC Biotechnol. .

Abstract

Background: Rhamnolipids are a group of the extracellular microbial surface-active molecules produced by certain Pseudomonas species with various environmental and industrial applications. The goal of the present research was to identify and optimize key process parameters for Pseudomonas aeruginosa PTCC 1074s synthesis of rhamnolipids utilizing soybean meal in solid state fermentation. A fractional factorial design was used to screen the key nutritional and environmental parameters to achieve the high rhamnolipid production. Response surface methodology was used to optimize the levels of four significant factors.

Results: The characterization of biosurfactant by TLC, FT-IR and H-NMR showed the rhamnolipids presence. In the optimum conditions (temperature 34.5 °C, humidity 80%, inoculum size 1.4 mL, and glycerol 5%), the experimental value of rhamnolipid production was 19.68 g/kg dry substrate. The obtained rhamnolipid biosurfactant decreased water's surface tension from 71.8 ± 0.4 to 32.2 ± 0.2 mN/m with a critical micelle concentration of nearly 70 mg/L. Additionally, analysis of the emulsification activity revealed that the generated biosurfactant was stable throughout a broad pH, temperature, and NaCl concentration range.

Conclusions: The current study confirmed the considerable potential of agro-industrial residues in the production of rhamnolipid and enhanced the production yield by screening and optimizing the significant process parameters.

Keywords: Agro-industrial residues; Biosurfactant; Optimization; Response surface methodology; Solid-state fermentation.

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Conflict of interest statement

The authors have no competing interests to declare that are relevant to the content of this article.

Figures

Fig. 1
Fig. 1
A Kinetics of rhamnolipids production: non-optimal conditions (solid line—▲— and optimal conditions (dash line–––), B Surface tension values (mN/m) versus rhamnolipid concentration (mg/mL)
Fig. 2
Fig. 2
Response surface plots for rhamnolipid production: A interaction of temperature and inoculum size, B interaction of temperature and humidity, C interaction of inoculum size and humidity, D interaction of temperature and glycerol concentration, E interaction of inoculum size and humidity, F interaction of humidity and glycerol concentration
Fig. 3
Fig. 3
FT-IR spectrum of rhamnolipid showing the following vibrations: O–H stretching (3409 cm−1), C–H stretching asym. (2922 and 28,563 cm−1), C=O stretching (1650 cm−1), C–H deformations (1453, 1238 and 808 cm−1), C–H/O–H deformation (1386 cm−1), C–O stretching (1048 cm−1), α-pyranyl II sorption band (832 cm.−1)
Fig. 4
Fig. 4
1H-NMR spectrum of produced biosurfactant by Pseudomonas aeruginosa PTCC 1047
Fig. 5
Fig. 5
Stability studies of rhamnolipid under different temperature (A), pH (B), and salinity (C)
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