Effects of interactions between the constituents of chitosan-edible films on their physical properties

The main objective of this work was to evaluate the effect of chitosan and plasticizer concentrations and oil presence on the physical and mechanical properties of edible films. The effect of the film constituents and their in-between interactions were studied through the evaluation of permeability, opacity and mechanical properties. The effects of the studied variables (concentrations of chitosan, plasticizer and oil) were analysed according to a 2 3 factorial design. Pareto charts were used to identify the most significant factors in the studied properties (water vapour, oxygen and carbon dioxide permeability; opacity; tensile strength; elongation at break and Young's modulus). When addressing the influence of the interactions between the films' constituents on the properties above, results show that chitosan and plasticizer concentrations are the most significant factors affecting most of the studied properties, while oil incorporation has shown to be of a great importance in the particular case of transport properties (gas permeability), essentially due to its hydrophobicity. Water vapour permeability values (ranging from 1. 62 × 10 -11 to 4. 24 × 10 -11 g m -1 s -1 Pa -1) were half of those reported for cellophane films. Also the mechanical properties (tensile strength values from 0. 43 to 13. 72 MPa and elongation-at-break values from 58. 62% to 166. 70%) were in the range of those reported for LDPE and HDPE. Based on these results, we recommend the use of 1. 5% (w/w) chitosan concentration to produce films, where the oil and plasticizer proportions will have to be adjusted in a case-by-case basis according to the use intended for the material. This work provides a useful guide to the formulation of chitosan-based film-forming solutions for food packaging applications.The author MA Cerqueira is a recipient of a fellowship from Fundacao para a Ciencia e Tecnologia (FCT, SFRH/BD/23897/2005) and BWS Souza is a recipient of a fellowship from the Coordenacao Aperfeicoamento de Pessoal de Nivel Superior, Brazil (Capes, Brazil)

Cooling and Freezing of Fruits and Fruit Products

The use of low temperatures is an important factor for maintaining postharvest quality of fruits and greatly influences the rate of deterioration. The objective of cooling is to prolong the commercial life of perishable products, by decreasing metabolic activity without causing chilling or freezing injuries, reduction of microbial growth and water loss of the product, between others. On the other side, freezing results in improved effects with respect to shelf life of fruits and availability throughout the year, however various undesirable changes occur due to ice formation.In the present chapter pre-cooling treatments and refrigerated storage of fruits are analyzed. The use of controlled and modified atmosphere storage, novel technologies (thermal treatments, UV-C irradiation, etc.), minimally processed fruits and the use of edible coatings are analyzed.With reference to fruit freezing the formation of ice in tissues (nucleation and crystal growth, intra and extracellular ice), initial freezing point, state diagrams, glass transition temperature, freezing rates and the different equipment used for freezing are described.The effect of freezing rate on fruit quality, physical and chemical modifications, nutritional properties and microbial stability of frozen fruit are discussed. Preparatory operations for freezing such as pre-treatments of fruits using sugar syrups, and dehydrofreezing are explained. Recommended packaging and industrial freezing methods, shelf-life of frozen fruits and new trends in freezing technology are also analyzedFil: Chaves, Alicia Raquel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Zaritzky, Noemi Elisabet. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentin