Tannic acid-crosslinked casein films with modified material properties

ROQUE J. MINARI ; CECILIA I. ALVAREZ IGARZABAL; MATÍAS L. PICCHIO

Los Cocos

Simposio; XII Simposio Argentino de Polímeros - SAP 2017; 2017

Over the past few years, interest has grown for edible packaging materials as a replacement of traditional non-biodegradable plastic films driven by a societal desire for environmentally-friendly, biodegradable and sustainable packaging products [1]. Among the different natural sources, milk proteins are the most desirable hydrocolloids for the formation of edible films due to the high nutritional value, water solubility, and emulsification capability [2]. For instance, casein films can form a good barrier to oxygen and other nonpolar molecules, because casein provides polar functional groups (COOH-, NH2- and OH-) to the film matrix [3]. However, some deficiencies need to be solved before casein films can be widely commercialized, such as moisture sensitive and poor mechanical properties. Chemical treatments can be applied to modify the polymer network trough crosslinking of the polymer chains to improve protein film functionality. Some chemical agents used as crosslinkers include aldehydes, calcium salts, 3-aminopropyl triethoxysilane, among others [4]. Enzymes such as transglutaminase [5] and a natural cross-linking agent, genipin [6] have been investigated as crosslinking agents for casein films, but the high cost limits their further application. In this work, plasticized casein films were crosslinked in aqueous system using a simple plant-derived phenolic compound, tannic acid. FTIR analysis, high-resolution NMR technique, and rheological measurements confirmed the crosslinking reaction between casein amine groups and tannic acid. The influence of concentrations of the crosslinking agent on the mechanical properties, thermal stability, swelling kinetic, water vapor permeability, viscoelastic properties, and cytotoxicity were investigated in details. Moreover, SEM was applied to observe both, the surface and internal morphology of the crosslinked materials. The results showed that tannic acid was an effective crosslinking agent for casein protein and that the treated films presented improved physicochemical properties.