TiO2 - casein polymeric composite films for food preservation

Project leaders

Cinzia Giannini, Maria Lidia Herrera

Agreement

ARGENTINA - CONICET - Consejo Nacional de Investigaciones Científicas y Técnicas

Call

CNR/CONICET 2015-2016

Department

Chemical sciences and materials technology

Thematic area

Chemical sciences and materials technology

Status of the project

New

Research proposal

The habits of the consumers have changed during the last decades toward more natural, healthy and high quality food. Nowadays, consumers prefer minimally processed foods, without additives or preservers, but maintaining the original sensorial quality. In this direction the design of non-toxic and even edible films to protect food, precluding the infection by microorganism, oxidation and changes in humidity, is a very promising alternative. Such demands are challenging for food scientists, who have to use newly developed technology for the design of novel and advanced materials. The principal function of edible films is to create a protective barrier against microorganisms and the diffusion of humidity, oxygen, flavors, oils, etc, between food and environment. Besides, the films are also used to preserve the integrity of food by providing certain mechanical protection. The role of the film can be extended by the incorporation of antioxidants antimicrobial agents, flavors and nutrients. Milk proteins are an appropriate material for the production of edible films due to its good nutritional value and several physical and chemical properties that make it suitable for packaging. Sodium caseinate (NaCas) is a water soluble polymer obtained by acid precipitation of casein. Caseinate films are resistant to thermal denaturalization and coagulation in a wide range of pH, temperature and ionic force. The incorporation of a homogeneously distributed solid phase is an alternative to improve mechanical and permeation properties of protein films. TiO2 is one of the favorite solid additives due to its thermal and chemical stability, and negligible toxicity.. Al-Sagheerand Merchant (2011), and Amin and Panhuis (2012), have shown that themechanical properties of chitosan improve after the incorporation of TiO2 particles. TiO2 coated SiO2 particles were used in the preparation of protein films made from whey protein isolated (WPI). TiO2 particles were dispersed by application of ultrasonic waves; high power was necessary to disperse the particles and increase the film strength. Lei O. and coworkers reported the preparation of WPI-NaCas protein films containing TiO2 particles with low water permeability and antimicrobial activity. High concentration of TiO2 decreases light transmittance increasing haze of the protein film. Recently, nanoparticles with a high aspect ratio, as nanofibers or nanorods, have been successfully used as reinforcement for different polymers. For example, incorporation of AlOOH bohemite nanorods to polyurethane based films leaded to a significant improvement of the fracture toughness. Biobased polymers, such as polymeric starch, modified by the incorporation of well dispersed carbon nanotubes, displayed improved mechanical properties (tensile toughness increased by 50%). ZnO nanorods were used as reinforcement in PVA polymeric fibers prepared by electrospinning. The good dispersion of the nanofillers displayed a crucial role in the improvement of the properties. Moreover, the alignment of the nanorods has an important role in determining the mechanical properties.The use of TiO2 nanoparticles grown with one preferential orientation (as fibers, tubes, nanorods) and its comparison with regular tridimensional TiO2 particles has not been deeply explored yet. As in the examples presented above, it is expected that 1D TiO2 particle (like fibers or tubes) may improve mechanical strength and diminish water permeability if the interaction between fibers and the polymer is strong enough. The effect of 1D TiO2 on permeability and mechanical properties of protein films may be incremented if the rods acquired preferential orientation, which can be obtained e.g. by attaching magnetic particles to 1D TiO2 and applying a magnetic field during film formation. Although such kind of films will not be edible it can be used as external protection for foods if food degree components are used as precursors. The synthesis of 1D TiO2 with magnetic properties has been studied by Cinzia Giannini and coworkers, and the results have been presented and discussed in several articles. The microstructure of the films has an important role in determining both mechanical and permeability properties. Either in the case of films prepared from oil containing emulsions or in TiO2-casein composites the effect of the oil or solid phase on the film microstructure should be determined. Changes in porosity, particle distribution and aggregation, produced during the transition from emulsion (or sol) to gel are the key to obtain a film with the desired properties. Several factors are involved in the determination of the microstructure; for example the relative proportion of casein to oil, or solid particles and also the gelification rate, which depends on the acidification rate. In this project caseinate based films will be prepared by casting and dip-coating (supported on Si wafers), with the aim to determine the effect of additive and synthesis conditions on the structure and final properties of the films.The film precursors will be emulsions containing an oil phase stabilized by NaCas. Some emulsions will contain TiO2 in the form of either spherical like nanoparticles or 1D structures. Gelification rate will be modified through changes in the acidification rate, which depends on the concentration of delta gluco-lactone (a slow acifier). In some cases, magnetic iron oxide nanoparticles will be attached to the 1D structures to provide some magnetic behavior to the combined particles. The structure of the films will be mainly studied by XRD, SAXS and WAXS, providing structural and morphological characterization. In the case of supported films (flat samples) grazing incidence SAXS/WAXS will be employed, allowing the investigation of a much larger sample volume, and thus higher sensitivity. Water permeability and mechanical strength will be determined as well, looking for the effect of the additives on these properties.

Research goals

Synthesis and structural characterization of composite films based on continuous phase polymeric casein with dispersed TiO2 as reinforcement and barrier against water and gases permeation. Principal application: food preservation.
Edible films to protect foods from germens and prevent de-hydration are a newly way to increase the durability of different industrialized or natural foods.
Caseinate films are suitable candidates due to their good nutritional properties. Caseinate films can be prepared from sodium caseinate dispersions or from emulsions containing caseinate and edible oils. Some functionalities can be incorporated by dissolution of nutraceutics in the oil phase. Appropriate gelification and drying of the dispersions or emulsions lead to the formation of rigid films. Mechanical and permeability properties of the films can be improved by incorporation of plasticizers and solid particles (for example TiO2). The aspect ratio of the particles,and the changes in porosity, particle distribution and aggregation, during emulsion (or sol) to gel transition, are the key to obtain a film with the desired properties. In this work we propose to thoroughly study the relationship between the aspect ratio of TiO2 nanoparticles on the microstructure of the films and on its mechanical and permeability properties.

Last update: 09/06/2025