Zein self-assembled nanoscale structures for microencapsulation.

Nanotechnology is a broad interdisciplinary area of research that has the potential to affect virtually all disciplines. The use of nanotechnology in the context of food must address such issues as toxicity, regulatory restrictions, cost and scalability. Research is ongoing on a number of fronts, including characterizing and understanding nanoscale structures and phenomena pertinent to food systems, the synthesis and fabrication of nanoscale structures for food applications, nanosensors for detecting pathogens and chemicals, engineering packaging materials with embedded or grafted nanoscale structures and materials, the impact on nanoscale systems during food processing, and the effects of incorporated nanoscale systems on food functionality and safety.

Flavor encapsulation is always of interest to the food industry. Zein is an excellent film former and has been used for flavor encapsulation. Preliminary research has shown that zein forms self-assembled nanoscale structures that might be used as carriers to encapsulate flavors and bioactive compounds.

Scientists at the University of Illinois wanted to investigate the effect of surface and media polarity on the morphology of zein self-assembled structures. They also examined the effect of zein extraction.

Gold-coated glass slides were modified by depositing on them a self-assembled monolayer (SAM) of either carboxylic acid terminated thiol (COOH(CH2)10SH) or methyl-terminated alkanethiol (CH3(CH2)7SH). Zein was dissolved in 75% 2-propanol. The investigators adjusted the pH to 3.5 with chloroacetic acid.

Zein solutions were made to flow over the SAM surfaces for adsorption purposes. Then they were rinsed with distilled water or 75% 2-propanol. The researchers characterized the surface topography of zein deposits using atomic force microscopy. They observed hollow tubules for zein adsorbed on carboxyl-ended surfaces when these were rinsed with distilled water. The tubules were 35 nm high and 200 nm in diameter.

The scientists found that surface roughness increased significantly (from 2 nm to 7 nm) after zein nanotubules were formed. No tubules were found at other experimental conditions. Zein adsorbed to methyl-ended SAMs formed large grains, about 200 nm in diameter. The surfaces were highly uniform and had lower roughness value (~1.9 nm). Surfaces rinsed with 75% 2-propanol appeared to have few features. The zein formed nanoscale hollow tubules when adsorbed to carboxyl ended surfaces. The tubes had well-defined structures and could be used in microencapsulation processes.

Further information. Graciela Padua, Department of Food Science and Human Nutrition, 382L Agricultural Engineering Sciences Building, University of Illinois, 905 S.Goodwin Ave., Urbana, IL 61801; phone: 217-333-9336; fax: 217-333-9329; email: gwpadua@express.cites.uiuc.edu.