Emulsification efficiency of adsorbed chitosan for bacterial cells accumulation at the oil-water interface.

The use of bacterial cell or biocatalyst for industrial synthetic chemistry is on the way of significant growth since the biocatalyst requires low energy input compared to the chemical synthesis and can be considered as a green technology. However, majority of natural bacterial cell surface is hydrophilic which allows poor access to the hydrophobic substrate or product. In this study, Escherichia coli (E. coli) as a representative of hydrophilic bacterial cells were accumulated at the oil-water interface after association with chitosan at a concentration range of 0.75-750 mg/L. After association with negatively charged E coli having a ζ potential of -19.9 mV, a neutralization of positively charged chitosan occurred as evidenced by an increase in the ζ potential value of the mixtures with increasing chitosan concentration up to +3.5 mV at 750 mg/L chitosan. Both emulsification index and droplet size analysis revealed that chitosan-E. coli system is an excellent emulsion stabilizer to date because the threshold concentration was as low as 7.5 mg/L or 0.00075% w/v. A dramatic increase in the surface hydrophobicity of the E. coli as evidenced by an increase in contact angle from 19 to 88° with increasing chitosan concentration from 0 to 750 mg/L, respectively, resulted in an increase in the stability of oil-in-water emulsions stabilized by chitosan-E. coli system. The emulsion was highly stable even the emulsification was performed under 20% salt condition, or temperature ranged between 20 and 50 °C. Emulsification was failed when the oil volume fraction was higher than 0.5, indicating that no phase inversion occurred. The basic investigation presented in this study is a crucial platform for its application in biocatalyst industry and bioremediation of oil spill.

Bacteria interface pickering emulsions stabilized by self-assembled bacteria-chitosan network.

An oil-in-water Pickering emulsion stabilized by biobased material based on a bacteria-chitosan network (BCN) was developed for the first time in this study. The formation of self-assembled BCN was possible due to the electrostatic interaction between negatively charged bacterial cells and polycationic chitosan. The BCN was proven to stabilize the tetradecane/water interface, promoting formation of highly stable oil-in-water emulsion (o/w emulsion). We characterized and visualized the BCN stabilized o/w emulsions by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). Due to the sustainability and low environmental impact of chitosan, the BCN-based emulsions open up opportunities for the development of an environmental friendly new interface material as well as the novel type of microreactor utilizing bacterial cells network.

Turning hydrophilic bacteria into biorenewable hydrophobic material with potential antimicrobial activity via interaction with chitosan.

Alteration of a bacteriocin-producing hydrophilic bacterium, Lactococcus lactis IO-1, into a hydrophobic material with potential antimicrobial activity using chitosan was investigated and compared with five other bacterial species with industrial importance. The negatively charged bacterial cells were neutralized by positively charged chitosan, resulting in a significant increase in the hydrophobicity of the bacterial cell surface. The largest Gram-positive B. megaterium ATCC 14581 showed a moderate response to chitosan while the smaller E. coli DH5α, L. lactis IO-1 and P. putida F1 exhibited a significant response to an increase in chitosan concentration. Because L. lactis IO-1 is a good source for natural peptide lantibiotic that is highly effective against several strains of food spoilage organisms and pathogens, hydrophobic material derived from L. lactis IO-1 and chitosan is a promising novel material with antimicrobial activity for the food and pharmaceutical industries.