Simple addition of a minute quantity of non-toxic mustard oil in water/oil/water (W/O/W) double emulsion led to a porous morphology at the surface as well as in the interior of the biodegradable PLGA (Poly(l-lactide-co-glycolide)) microparticles. An attempt was made to understand the mechanism of pore formation by analyzing optical micrographs and SEM images in addition to solution viscosity of organic phase and interfacial tension values between organic and aqueous phases. The origin of surface porosity was thought to come from the inclusion of inner water droplet, stabilized by heteroaggregation of mustard oil and PLGA chains along with PVA (polyvinyl alcohol), to the solidifying polymer skin. The surface pores did not arise in absence of mustard oil. The encapsulation and release of antibacterial active (benzoic acid) from porous PLGA particles was studied in PBS buffer (pH 7) at 37 °C for 60 days. The release profiles were well-controlled in nature, and found to be influenced by surface porosity of the particles that can be manipulated by varying the amount of mustard oil. The release mechanism can well be explained with the help of power law model. Strikingly, in liquid medium, porous particles were found completely suppressing the growth of Escherichia coli and Staphylococcus aureus for a prolonged period of 60 days. The strong antimicrobial activity (100% inhibition of bacterial growth) in porous particles can be linked to the enhanced surface area due to the formation of micro/nano pores which accelerate the hydrolytic degradation of PLGA to release lactic acid/glycolic acid (antibacterial) in addition to encapsulated antibacterial (benzoic acid). In a food model system, the shelf life of the water melon juice was also found to be enhanced by suppressing the growth of the natural microbes in comparison to control.
Keywords: Antibacterial; Biodegradable polymer; Double emulsion; Food preservation; Mustard oil; Porous microparticles.
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