Atomic force microscopy applied to food rheology. Interface operating forces, electrical double layers present in charged interfaces and structure of water layers adjacent to biomolecules among other concepts, constitute the basis for understanding a wide variety of surface and soft matter properties in food processing, medicine, biotechnology and environmental sciences, to mention a few[Fragneto 2009]. On the other hand, although atomic force (AFM) is a widespread technique for the analysis of bio-related surfaces [Morris 2008], only a few groups in Chile have developed research on this field. Indeed, over the last five years our group has been studying the crystal growth mediated by organic molecules (Dermatan Sulfate, DS) by the use of this technique. Main achievements include surface charge measurements by colloidal probes and mechanical characterization of single DS molecules. Experimental work was carried out to elucidate the selective role of molecules treated with Dermatan Sulfated on step roughness, step density, and step speed and also evaluating step-step interaction as a function of DS concentration [Gonzalez 2009]. Further experiments employing suitable functionalized nanoparticles should provide notions for elucidating the role of functional DS groups in eliminating acute steps (see figure). Our expertise on gold functionalized nanoparticles of potential therapeutic applications, [Guerrero 2009*], will provide the methodological basis for this investigation.

Our proposal is to apply AFM for the study and understanding of food properties with the purpose of solving problems related to this area. Reviews on the field have pointed out promising directions [Kirby 1995, Shimori 2008*, Morris 2004*] (see for instance [Morris 2008] for experimental methods), some of which we intend to explore. For instance, in a tight interaction with Prof. Osorio´s group, we will use AFM to investigate polysaccharides which are mainly used as thickeners through the observation of relevant parameters in structural changes, aiming at providing valuable insight onto the mechanics and self-organization properties of these molecules. Optical and magnetic [Celedon, 2009*] tweezers will be developed to investigate the mechanical properties of single molecules of our interest.

-Wetting of fruit surfaces. To avoid bursting, and even cracking of the fruit cuticle, we propose to improve the mechanical properties of the surface by adding protective or edible films whose suitability requires knowledge of surface chemistry to improve/inhibit adhesion or wetability. In the same fashion, we will undertake studies of surface topology and interactions by AFM techniques. Dynamics of micro and nanodrops on top of such surfaces will be investigated. This study aims at producing relevant information for edible film optimization.

-Vesicles for micropackaging: Vesicles have been widely studied in the last ten years as model systems for drug delivery and mimicry of cellular agglomerates. A method for generating these structures is through the combination ternary lipids which result in enhanced giant unilamellar vesicles (GUVs). At the laboratory of BioPhysics we plan to mechanically test bilayered vesicles that incorporate biopolymers such as f-actin and tubulin to enhance vesicle wall properties. Addition of ligand proteins at the vesicle´s outer wall is also being considered for improving the membrane’s adhesion to specific targets. Another topic being addressed as an option for food innovation is the incorporation of functional natural products, such as phenolic compounds that act as natural antioxidants and also provide with antimicrobial activity [Manach et al, 2004]. The use of these compounds would not only provide protection towards cardiovascular diseases, age-related degenerative diseases and cancer, but would also generate a decrease in the use of artificial additives as antioxidants [Seeram, 2008; Wang, 2000]. Phenolic compounds are being targeted for the design of conventional food with additional health benefits (functional foods). Such value-added food is needed for dietary support to manage major oxidation-linked diseases. In this proposal, we will explore the potential of vesicles in selective encapsulation and delivery of phenolic compounds, antibiotics and proteins among others. The methodological aspects of this investigation will be optimized in collaboration with food groups.

-Bio mineralization based degradable films. Nanostructured materials not only add value to traditional materials but also enhance their mechanical strength, superconductivity, and ability to incorporate and efficiently deliver active substances into biological systems, food included, at low costs and with limited environmental impact. In addition, it is possible to incorporate sensing properties to the nanostructured packaging materials that, for example, change color in the presence of harmful microorganisms or toxins. Biomineralization-inspired nanocomposites are a promising class of new materials with nanoscale structure and that present morphology and interfacial properties which give them novel desirable characteristics. An example of this, is packaging material made out of potato starch and calcium carbonate that form lightweight foam material with increased toughness, good thermal insulation properties, and biodegradability (see [Moraru, 2003]. Our expertise in biomineralization is a source of inspiration for producing micro- and nanocomposites biomimetically, and will set the basis for scaling our research efforts towards the design, characterization and production of novel nanocomposite material for food packaging and technology (see [Arias, 2007; Arias, 2008; Toro, 2007; Neira-Carrillo, 2007, Neira-Carrillo, 2008]). Nanocomposites will be designed by combining natural (i.e. starch, chitosan, cellulose) or synthetic polymers (i.e.polyethylene, polyesters) with calcium carbonate or other inorganic salts or oxides of different particle sizes and by using different compatibilizers when needed to produce variable films with taylored mechanical properties [Srinivasa, 2002; Rahmat, 2009]. This development of these structures will be carried out in collaboration with Prof. Guarda´s Group.