POMEGRANATE SEED OIL-LOADED PARTICLES OF THE ZEIN CROSS-LINKED WITH CITRIC ACID

Zein was cross-linked chemically with citric acid in the presence of sodium hydroxide as the reaction catalyst. Water was then used to desolvate the zein and generate core-free or pomegranate seed oil-loaded particles. Mean size of the particles obtained from noncross-linked and cross-linked zein was 350 and 246nm, respectively. Cross-linking reaction caused an increase in the oil encapsulation efficiency. Scanning electron microscopy revealed the spherical morphology of particles. Fourier transform infrared (FTIR) spectroscopy confirmed the occurrence of chemical linkages between citric acid and zein. As well, it suggested that oil entrapment inside the zein particles was merely physical. Particulation of zein increased the upper limit of the glass transition phenomenon of biopolymer from 78C to approximate to 120C. The glass transition temperature (Tg) was also affected by the cross-linking of zein and oil encapsulation. The amount of encapsulated oil released from particles via the peptic hydrolysis was lower for the cross-linked sample. Practical ApplicationsMany biologically active ingredients including the pomegranate seed oil are extensively susceptible to oxidation, as well as, some are hydrolyzed considerably by enzymes leading to diminished bioactivity. Encapsulation of these hydrophobic cores within sub-micron zein particles generated via desolvation with water (an easily scale-up able method) leads not only to increased oxidative stability but also the wider application of core in aqueous foods. Citric acid-mediated cross-linking of zein molecules before the desolvation stage increased considerably the gastric digestion stability of particles, which assures that the encapsulated core may pass the stomach without being hydrolyzed with pepsin or acid. The particles prepared from the cross-linked zein were also more heat resistant. This suggested that the particles can be heat-treated to higher temperatures in food processing practices.