title: Zein films with unoxidized or oxidized tannic acid.
abstract: BACKGROUND
  Corn zein is a predominatly hydrophobic protein, forming films with relatively good water resistance. Tannic acid, especially in its oxidized form, is supposed to cross-link proteins including zein, which may be explored to further enhance the water resistance of zein films. The effects of different contents (0-8 wt%) of unoxidized and oxidized tannic acid (uTA and oTA, respectively) on the properties of zein films at different pH values (4-9) were studied, according to central composite designs.
  
  
  RESULTS
  Increasing tannic acid contents and pH values resulted in decreased water solubility and increased tensile strength and modulus of films. The presence of tannic acid provided the films with a yellowish color and increased opacity. Paired t-tests indicated that oTA films presented higher tensile strength, lower water vapor permeability and lower water solubility than uTA films.
  
  
  CONCLUSIONS
  Higher tannic acid contents and pH values resulted in films with better overall physical properties, which might be ascribed to cross-linking, although the films were still not water resistant. The resulting films have potential to be used for food packaging and coating applications. © 2017 Society of Chemical Industry.
authors.affiliation: Chemical Engineering Department, Federal University of Ceara, Fortaleza, CE, Brazil.
authors.forename: Talita M
authors.initials: TM
authors.lastname: Santos
authors.affiliation: Embrapa Tropical Agroindustry, Fortaleza, CE, Brazil.
authors.forename: Men de Sá M
authors.initials: MSM
authors.lastname: Souza Filho
authors.affiliation: Embrapa Tropical Agroindustry, Fortaleza, CE, Brazil.
authors.forename: Celli R
authors.initials: CR
authors.lastname: Muniz
authors.affiliation: Embrapa Cotton, Campina Grande, PB, Brazil.
authors.forename: João Paulo S
authors.initials: JPS
authors.lastname: Morais
authors.affiliation: Department of Chemistry, Federal University of Ceara, Fortaleza, CE, Brazil.
authors.forename: Lloyd Ryan Viana
authors.initials: LRV
authors.lastname: Kotzebue
authors.affiliation: Department of Chemistry, Federal University of Ceara, Fortaleza, CE, Brazil.
authors.forename: André Luís Sousa
authors.initials: ALS
authors.lastname: Pereira
authors.affiliation: Embrapa Tropical Agroindustry, Fortaleza, CE, Brazil.
authors.forename: Henriette Mc
authors.initials: HM
authors.lastname: Azeredo
mesh_terms: D003116:Color; D018857:Food Packaging / Q000295:instrumentation*; D010084:Oxidation-Reduction; D010539:Permeability; D012995:Solubility; D013634:Tannins / Q000737:chemistry*; D013718:Tensile Strength; D003313:Zea mays / Q000737:chemistry; D015028:Zein / Q000737:chemistry*
chemical_list: D013634:Tannins; D015028:Zein
keywords: biodegradable films; cross-linking; phenolic acids; protein