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Title: Control-release of antimicrobial sophorolipid employing different biopolymer matrices

Author
item Solaiman, Daniel
item Ashby, Richard - Rick
item Zerkowski, Jonathan
item KRISHNAMA, ANUSHA - Long Island University
item VASANTHAN, NADARAJAH - Long Island University

Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2015
Publication Date: 7/10/2015
Citation: Solaiman, D., Ashby, R.D., Zerkowski, J.A., Krishnama, A., Vasanthan, N. 2015. Control-release of antimicrobial sophorolipid employing different biopolymer matrices. Biocatalysis and Agricultural Biotechnology. DOI: 10.1016/j.bcab.2015.06.006.

Interpretive Summary: Sophorolipids (SLs) are biobased surfactants produced by yeast. SL is a highly desired substitute for petroleum-based surfactants because it can be produced using renewable agricultural (by-)products in fermentation tank and is environmentally friendly to aqueous ecosystem. Potential commercial value of SL derives mainly from its use as an active ingredient in washing solutions and cleaning products and as an antimicrobial agent to inhibit growth of bacteria in consumer products. Research is lacking, however, on the use of SL in polymer film such as in food packaging and consumer products in bandage or adhesive-strip forms. In the present work, we incorporated SL into three different types of well-known biodegradable plastics called PLLA (poly(L-lactic acid)), PCL (poly(epsilon-caprolactone)), and PHB (poly(hydroxybutyrate)). We then compared their properties in terms of bacterium-killing potency, the extent of SL release into water, and the melting/re-solidifying (i.e., crystallization) characteristics. Our study showed that different bioplastics can be used to manipulate antibacterial potency, extent of SL release, and the physical properties of SL-embedded biopolymers. The results lay down important groundwork toward expanded use of SL in solid materials such as bioplastics.

Technical Abstract: Sophorolipid (SL) purified from fermentation broth of Candida bombicola grown on oleic acid and glucose substrates was embedded at 0, 9, 17, and 29% (%-total weight of final product) in solvent-cast films of poly(L-lactic acid) (PLLA), poly(epsilon-caprolactone)(PCL), and poly(hydroxybutyrate)(PHB). Growth-inhibition activity of the SL-biopolymers against Propionibacterium acnes, a causative agent of acne vulgaris skin condition, is dependent on the SL contents of the films; the degree of inhibition as determined from the width of the zone of inhibition in agar-plate assays follows the order of SL-PCL > SL-PLLA > SL-PHB. The release of SL from the films into aqueous medium after a 4-d shaking at 25 deg C showed that SL-PLLA (30.1 +/- 1.7 wt-% SL released) most readily released the embedded SL, followed by SL-PHB (11.4 +/- 4.3 wt-%) and SL-PCL (4.3 +/- 1.4 wt-%). Thermal and physical properties as determined by differential scanning calorimetry showed that SL decreases the heat of fusion (delta H) and the melting temperature (Tm) of the biopolymers, indicating for the first time its usefulness as a plasticizer to prevent crystallization. In summary, the study shows the feasibility of controlling the release of antimicrobial SL by varying the type of biopolymer used, with the added advantage of SL functioning as a plasticizer to improve the physical properties of the film.