Synthesis of some biobased surfactants, and their functionalities as emulsifiers and antimicrobial agents.
Biobased surfactants, which are biochemicals derived from biological resources via various methods like enzymes and microbial fermentation, can achieve similar application functionality to petroleum-based surfactants. The conventional surfactants could face challenges in terms of limited fossil fuel availability, harsh processing conditions, low biodegradability and high aquatic toxicity. Biobased surfactants, on the other hand, can address some of these challenges; however, they also have their own challenges, for example, lower yield and production rate compared with conventional surfactant production method.
The overall goal of this work was to investigate the synthesis of specific biobased surfactants and evaluate their functionalities for potential food applications. This was accomplished by 1) optimizing the synthesis condition for glucose-fatty acid esters and evaluate their emulsification properties, 2) exploring the antimicrobial performance of some biobased surfactants and elucidate their mechanisms, and 3) exploring the emulsion-stabilizing effect of microbial biosurfactants and the emulsions’ antimicrobial properties.
The method explored to synthesize glucose fatty acid esters biobased surfactants using lipase with the substrates of glucose of fatty acids. The emulsifying and antimicrobial properties of the glucose-fatty acid esters and two microbial biosurfactants - surfactin and fatty acyl glutamic acid (FA-glu) were also investigated. It was found that the conversion percentages of fatty acids and rates of reaction depended on the reaction substrate concentration the reaction medium. The glucose-fatty acid esters demonstrated some emulsification capabilities, but weaker than commercial sucrose esters compared. One of the glucose esters, glucose laurate inhibited growth of E.coli O157:H7, Listeria monocytogenes and Salmonella Enteritidis during 24 h at the concentration of 6.5 mg/mL. The microbial biosurfactant FA-glu inhibited pathogens from growing at the concentration of 25 mg/mL; the mechanism of inhibition was the disruption of bacterial cell membrane by FA-Glu.
Surfactin, FA-glu and two other common food emulsifiers (lecithin and Tween 80) were also studied for their ability to stabilized nano- and coarse emulsions containing cinnamaldehyde (CM) and the emulsions’ inhibition effect on pathogens. Although the minimum inhibitory concentrations were not reduced compared with non-emulsified CM, the dispersion of the CM in the emulsion strengthened the inhibition of pathogens at sub-minimum inhibitory concentrations. There was no definite relationship between the emulsion droplet size and antimicrobial effect.
In summary, our study provided important information on some biobased surfactants for their use in food and agriculture industries as the potential “clean label” emulsion and/or antimicrobial ingredients.