Location: Dairy and Functional Foods
Title: Casein films: effects of formulation, environmental conditions, and addition of citric pectin on the structure and mechanical properties Authors
Submitted to: Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2014
Publication Date: N/A
Interpretive Summary: Thin films made from casein, a milk protein, have excellent potential for food packaging applications because they are strong and form excellent barriers to oxygen to shield air-sensitive foods from oxidation. Casein films are soluble in water and can be eaten along with the food, which is ideal for single-serve pouch applications or as a coating on food. In order to commercialize casein films as food packaging and coatings, the stability of the films over the widest range of environmental conditions that include low-to-high humidities combined with low-to-high temperatures, to simulate a wide variety of processing and end-user conditions, must be known. It was found that the functional and protective (barrier) properties of the casein films must be improved for high temperature and high humidity conditions. To improve the films, various edible additives were tested. It was found that pectin (extracted from citrus peels) fortified the casein structure under the high humidity conditions. The new casein-pectin film formulations allow tailoring of the mechanical properties and barrier properties of the films so that they can be used to protect foods under a variety of storage conditions.
Technical Abstract: Thin casein films for food packaging applications reportedly possess good strength and low oxygen permeability, but low water-resistance and elasticity. Modifying and customizing the mechanical properties of the films to target specific behaviors depending on environmental conditions would enable a variety of commercial applications for casein-based films. The static and dynamic mechanical properties of solvent-cast (15% solids) calcium-caseinate/glycerol films (CaCas:Gly ratio 3:1) were measured as a function of processing and testing conditions, including film thickness, formulation, temperature (T) and relative humidity (from 22 to 70% RH through the year). While elongation at break (EAB) decreased strongly with reduced thickness, tensile strength (S) and modulus (E) decreased approximately linearly with increased RH, while EAB improved. Small amounts (0.05 to 1%) of Citric Pectin (CP) were then incorporated in the films using 7 different formulations (mixing sequences) to study CP effects on tensile properties and structure of CaCas/Gly/CP films and enhance mechanical properties and T- and RH-resistance. At constant thickness and ~60% RH, microscopy showed large formulation- and composition-dependent structural changes. Humidity-controlled dynamic mechanical analyses using a DMA-RH attachment configured to Humidity Sweep (20 to 80% RH at 20 deg C) or Temperature Sweep (5 to 90 deg C at 50% RH) modes demonstrated subtle or strong effects of RH, T, composition, and formulation on the dynamic mechanical properties of the films, suggesting changing network configurations, and revealing several T- or RH-induced secondary transitions. DMA-RH information can help understand complex CaCas/Gly/CP binding interactions to optimize casein films.