Desarrollo, caracterización y aplicaciones alimentarias de películas comestibles basadas en zeína de maíz

Resumen

Zein extracted from corn kernels is a globular protein classified as a prolamine, and characterized for its low solubility in water because of the hydrophobicity of its amino acids. In addition, it shows excellent coating and film forming ability. Edible films based on zein could be used as a barrier for mass transfer as well as for mechanical protection both as a coating in direct contact with food, or as a part of the packaging system. The final aim of the use of zein coatings and films is either the improvement of the food quality and the increase of food shelf-life or the simplification of the packaging system. This present study has been focused on the development and characterization of zein coatings, as well as in some food applications. Thus, the thesis has been divided in six chapters. Chapter 1, has been dedicated to a general introduction to edible films and specifically to films based on corn zein. Afterwards, a basic study on development and characterization of solutions and zein films was carried out (Chapter 2 and 3). Subsequently, three potencial food applications of zein coatings were studied(Chapter 4, 5 and 6). Basic Study. Zein films made exclusively from corn zein are rigid and very brittle, and then require the addition of plasticizers to have acceptable mechanical properties. In Chapter 2, the effect of different plasticizers (oleic acid, glycerol, polyethylene glycol) on the technological properties of solutions and films was evaluated. The results showed that barrier properties and functionality of films and coatings can be improved by manipulating the type and amount of plasticizer. The incorporation in the formulation of a mixture AO: PEG (50:50), allowed one to obtain zein films with enhanced functional properties and thus to increase the potential for practical applications. There is certainty that the functional properties of biopolymers could change over time. Taken it into consideration and in order to complete the characterization of zein films, in Chapter 3 the stability of the mechanical properties of zein films with different plasticizers during storage at different relative humidities was evaluated. It was shown that by using a mixture of plasticizers AO: PEG (50:50), a significantly improvement of the stability of the mechanical properties was achieved. Food applications In Chapter 4, it was assessed the protective effect of zein films against oxidative rancidity of foods rich in polyunsaturated fatty acid. Sunflower oil was used as a food model. It was found that the protective mechanism depended on the oxygen barrier properties. Results showed that the type and amount of plasticizer and storage relative humidity significantly affected its protective capacity. The most effective films were those prepared with the lowest concentration of glycerol, showing a protection similar to that exerted by an aluminum film. In Chapter 5, the application of zein coatings on minimally processed apples (var. Golden Deliciuos) caused significant changes in some technological properties of the samples during storage. Thus, the resistance to water vapor increased and the respiration rate decreased. It was found that the coating acted as a barrier to water vapor at different RHs and temperatures of storage. Finally, in Chapter 6, zein coatings were applied on raisins (var. Malaga) as dehydrated food model. The coated raisins were exposed to different RH for 15 days of storage. The results showed that the coatings acted as barriers to reduce water vapor loss (or uptake) during storage. In addition, coatings helped to maintain the mechanical properties of raisins. It was concluded that the zein coating as hydrophobic barrier increased the shelf-life of raisins.