Zein, the primary storage protein found in corn (maize) grain, forms nanoparticles on a carbonate scaffold under anti-solvent conditions. These zein nanoparticles may be useful for drug delivery systems but the instability and digestibility of the particles limits their potential use. Tannins are high molecular weight polyphenols made by a variety of plants in leaves, fruits, flowers and roots. Tannins characteristically interact with protein by phenol-peptide hydrogen bonds and hydrophobic interactions. The two classes of tannin are hydrolyzable tannin (HT) and condensed tannin (CT, also known as proanthocyanidin). HT is made of galloyl groups linked with ester bonds to a core sugar, while CT is made of flavan-3-ol groups linked with carbon-to-carbon bonds. In earlier studies, the HT known as tannic acid was used to crosslink and stabilize zein nanoparticles. Condensed tannin has not been applied to nanoparticle synthesis. We coated zein nanoparticles with CT from cocoa bean, grape seed, or sorghum grain. Sorghum tannin (dp = 16) and cocoa tannin (dp = 4) are made up of (epi)catechin subunits and were quite pure. The grape seed extract contained monomeric flavan-3-ols as well as CT (dp = 4.5) comprising mixed subunits of (epi)catechin, (epi)gallocatechin and some 3-O-gallate esters. Digestibility was assessed in vitro with chymotrypsin using SDS-PAGE to monitor loss of the protein. Preliminary results showed that sorghum grain CT most effectively prevents digestion, with less protection by grape seed extract and much less by cocoa CT. We hypothesize that chain length and CT subunit composition both influence their interaction with the zein nanoparticles. Additional work with other CT might allow us to eventually tune the nanoparticle properties by using different tannins to achieve desirable properties.
Author(s): Jules Jefferson, Sadeepa Mallikarachchi, Ann E. Hagerman
Advisor(s): Ann E. Hagerman, Department of Chemistry and Biochemistry
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