N: Nanoscale Food Science JFS N: Nanoscale Food Science, Engineering, and Technology Preparation and Characterization of Whey Protein Film Incorporated with TiO 2 Nanoparticles J.J. ZHOU, S.Y. WANG, AND S. GUNASEKARAN ABSTRACT: Biodegradable titanium dioxide (TiO 2 )/whey protein isolate (WPI) blend films were made by casting denatured WPI film solutions incorporated with TiO 2 nanoparticles. X-ray diffraction, UV-vis spectra, and fluo- rescence spectra of the films showed the successful incorporation of TiO 2 nanoparticles into the WPI matrix and indicated the interactions between TiO 2 and WPI. Mechanical tests revealed the antiplasticizing effect of TiO 2 nanoparticles on the WPI/TiO 2 film. Small amounts (<1 wt%) of added TiO 2 nanoparticles significantly increase the tensile properties of WPI film, but also decrease the moisture barrier properties. The addition of higher amounts (>1 wt%) of TiO 2 improves moisture barrier properties but lowers the tensile properties of the film. Microstructural evaluation confirmed the aggregation and distribution of TiO 2 nanoparticles within the WPI matrix and validated the results of functional properties of the WPI/TiO 2 film. Keywords: mechanical properties, microstructure, TiO 2 nanoparticles, water vapor permeability, whey protein isolate films Introduction P lasticized, self-supporting films made of globular proteins are potentially useful as edible coatings and wrappings (Lefevre and others 2005). Whey proteins are widely used in food products because of their high nutritional value and their ability to form gels, emulsions, or foams (Foegeding and others 2002). The native whey proteins are globular protein complexes but become random coils upon denaturation and form 3-dimensional network when certain conditions are met. This functionality enables whey proteins to be good candidates for biodegradable films. However, films made us- ing whey proteins without any modification have poor moisture barrier properties and relatively low mechanical properties com- pared with synthetic or other commercial food packaging materials and therefore have limited applications (Alcantara and others 1998; Perez-Gago and others 1999; Fugh-Berman 2000; Ouattara and oth- ers 2002; Shaw and others 2002; Yoshida and others 2002; Cisneros- Zevallos and Krochta 2003; Mei and Zhao 2003; Yoshida and others 2003). High-performance composite materials are actively sought in the quest to add novel properties to polymer-based systems used in the food industry. Recently, the application of the nanocompos- ite concept is becoming a promising option to improve mechani- cal and barrier properties of biodegradable biopolymer based films (Avella and others 2005). Titanium dioxide (TiO 2 ) is an inert, nontoxic, and inexpensive material with potential activity against a wide variety of microbes due to its photocatalytic activity. When TiO 2 is incorporated into a polymer matrix such as packaging material, it will provide protec- tion against foodborne microorganisms as well as odor, staining, MS 20081021 Submitted 12/16/2008, Accepted 6/5/2009. Authors Zhou and Gunasekaran are with Dept. of Biological Systems Engineering and author Wang is with Dept. of Food Science, Univ. of Wisconsin-Madison, Madi- son, WI 53706, U.S.A. Direct inquiries to author Gunasekaran (E-mail: guna@wisc.edu). deterioration, and allergens on the presence of radiation of rela- tively low wavelength near the ultraviolet region. Thin TiO2 films exhibit excellent mechanical and chemical durability in the visi- ble and near-infrared region (Tazawa and others 2004; Okada and others 2006). Incorporation of TiO 2 into synthetic plastic matrix to increase the biodegradability has been investigated (Kubacka and others 2007). However, there has been no attempt to investigate the incorporation of TiO 2 nanoparticles into biopolymer matrix. As a part of the project to develop a new biodegradable and an- timicrobial nanocomposite food packaging materials using TiO 2 , the purpose of this study was to fabricate TiO 2 nanoparticles incor- porated WPI film and to characterize its physical, mechanical, and functional properties. The results of this study together with ongo- ing antimicrobial study in our lab are expected to gather the suffi- cient knowledge to develop a new biodegradable and antimicrobial nanocomposite food packaging materials by incorporating nanos- tructure TiO 2 into biopolymer polymeric hosts matrices as the al- ternative to synthetic plastics. Materials and Methods Materials TiO 2 nanoparticle (anatase, particle size <20 nm) was purchased from Sigma-Aldrich (St. Louis, Mo., U.S.A.). Whey protein isolate (WPI, 98 wt% protein) was obtained from Davisco Foods Intl., Inc. (Eden Prairie, Minn., U.S.A.). All other reagents were of analytical grade. Deionized water was used for all sample preparations. Preparation of TiO 2 /WPI blend films WPI (5%, wt/vol) was dissolved in deionized water, and glycerol (5%, wt/vol) was added to the WPI solution before degassing un- der vacuum. The solution was heated in a water bath at 90 ◦ C for 30 min and rapidly cooled on ice, followed by vacuum degassing again to remove trapped air bubbles in the solution. Various amounts of TiO 2 nanoparticles (0.5% to 4%, w/w) were added to the N50 JOURNAL OF FOOD SCIENCE—Vol. 74, Nr. 7, 2009 C  2009 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2009.01270.x Further reproduction without permission is prohibited