Optimization of sonication parameters to obtain food emulsions stabilized by zein: formation of zein–diutan gum/zein–guar gum complexes

BACKGROUND: Zein as a sole material is not suitable for technological applications since it is not flexible. A possible solution to extend the applications of zein is the formation of zein–polysaccharide complexes. As a first step, sonication parameters were optimized to obtain finer emulsions formulated with zein, rosemary essential oil as food preservative, and sunflower oil, by means of response surface methodology. After the formation of these guar– or diutan–zein complexes the rheological properties of these food emulsions were evaluated. RESULTS: An increase in sonication power, sonication time and cycles provoked a decrease in mean droplet size and a lack of recoalescence. The optimized emulsion was the starting point to form two different complexes: zein with diutan gum and zein with guar gum at different concentrations. Rheological properties as well as the microstructure observed by field emission scanning electron microscopy (FESEM) were analyzed. Interestingly, zein–guar gum complexes did not form a rheological gel; as a consequence, emulsions containing them seem to undergo a destabilization process with aging time. In contrast, emulsions formulated with zein–diutan gum presented a 3D network, observed by FESEM technique and proved by rheological measurements. CONCLUSION: While emulsions containing zein–guar gum complexes did not form networks to stabilize oil droplets, zein–diutan gum complexes did. This work brings to light the importance of the selection of polysaccharide used in food emulsions formulated with zein.