Publicação
Characterisation of new hydrocolloids to be used as food coatings and integration of their application with ohmic heating
| Resumo: | The interest in the development of edible films and coatings for foods has grown considerably due to consumers demand for high quality foods and environmental concerns over the disposal of nonrenewable food packaging materials. The potential of edible films to control water transfer, and to improve food quality and shelf life, has received increasing attention from researchers and industry. Currently, technologies utilizing electrical fields directly into food processing raised a significant interest in the food industry. Several of those are now being used on a commercial scale for processing of an extensive range of food products. The application of electric fields has also been addressed by researchers in the area of edible films and coatings. In this context, the leitmotiv of this Thesis is to provide added-value to natural materials from renewable sources (algae from sea-farms and by-products from the fishing industry) with the more “at-large” objective of bringing development to underdeveloped regions of the World. In particular, the research undertaken was directed to the chemical characterization and evaluation of the antioxidant activity of sulfated polysaccharides from the red seaweed Gracilaria birdiae (Gb), farmed in the north-eastern coast of Brazil. The work performed allowed to conclude that the sulfated polysaccharide from Gb is composed of galactose (65.4 %) and methyl derivatives 6-O-methyl-galactose (9.2 %) and in smaller quantities 3-O- and 4-O-methyl-galactose (0.33 %). This polysaccharide also presents a high content of 3,6-anhydrogalactose (25.6 %) and has a sulfate content of 8.4 %. The sulfated polysaccharide of Gb characterized by FTIR exhibits the characteristic bands of agarocolloids (at 1375 and 770 cm-1). It has also been shown that the Gb sulfated polysaccharide is a promising agent to be evaluated for the application in the food industry, and that it presents a significant antioxidant activity. A study of the applications of this sulfated polysaccharide was performed and the possibility of using it as coating material on semi-hard cheese was found. The choice of the best coating was made taking into consideration its wettability, permeability and opacity properties. A second objective was related with determining the effect of field strength on transport properties of chitosan coatings (obtained from lobster from the Cuban coasts). Four different field strengths were tested (50, 100, 150, 200 V·cm-1) and, for each electric field treatment, the water vapor, oxygen and carbon dioxide permeabilities of the films formed were determined, together with their color, opacity and solubility in water. Results showed that electric field had statistically significant effects on film’s physical properties and structure. In general, the most pronounced effect of the field strength was observed for treatments made at 100 Vcm-1 or higher, a positive correlation being found between the water vapor, oxygen and carbon dioxide permeability coefficients and field strength. In the same perspective the effect of electric fields applied at different field strength values on mechanical and thermal properties of chitosan films/coatings was evaluated. XRD analyses indicated that electrically treated chitosan films exhibited a more ordered structure and a clearly higher crystallinity when compared with non-treated films, thus displaying significant effects on the value of the crystallinity index (CI). SEM micrographs evidenced that the surface morphology of chitosan films was influenced by the electric field. In fact, the electric field treatment led to a structure with more regular layers. The application of the electric field to chitosan film-forming solutions resulted in an increase of the tensile strength (ca. 9 %) and elongation-at-break (ca. 18 %) of the corresponding chitosan films. The reported results demonstrate that the application of an electric field to film-forming solutions of chitosan is an interesting instrument to taylor relevant properties of the films or coatings produced from them. Finally, the effects of the application of chitosan coating with or without electric field treatment in sliced salmon stored in ice at 0 °C were analyzed. In a first stage, the surface properties of salmon fillets and the wetting capacity of the coatings on fish were evaluated. The best wettability results were obtained with 1 % chitosan solutions with a spreading coefficient (Ws) of -4.73 mN·m-1. For shelf-life analyses the fillets were coated and stored at 0 °C for 18 days. The control and the coated fish samples were analyzed periodically for total mesophilic count (TPC), pH, total volatile base nitrogen (TVB-N), trimethylamine (TMA), thiobarbituric acid (TBA) and ATP breakdown products (K-value). A significant reduction (p < 0.05) in pH and K-value starting from the sixth day until the end of analysis (day 18) and in TVB, TMA and TBA from the ninth until the last day, was observed for fish samples coated with chitosan, when compared to control samples. In terms of microbial growth, a slower increase in TPC was observed for the coated fish, indicating that chitosan-based coatings were effective in extending for 3 more days the shelf-life of salmon. These results demonstrate that chitosan-based coatings may be an alternative for extending the shelf-life of salmon fillets during storage at 0 °C. However, no significant differences (p < 0.05) were observed between chitosan coatings with or without electric field treatment. In short, the sulfated polysaccharide of Gb is a promising coating-forming and antioxidant agent for applications in the food industry. The application of electric fields during chitosan coating solutions preparation may provide a novel method for production of coatings with taylored properties. However, further research is needed for a clearer understanding of the importance of these changes on real food systems. Important data have also been generated on the use of chitosan edible coatings on fish. |
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| Autores principais: | Souza, B. W. S. |
| Ano: | 2010 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The interest in the development of edible films and coatings for foods has grown considerably due to consumers demand for high quality foods and environmental concerns over the disposal of nonrenewable food packaging materials. The potential of edible films to control water transfer, and to improve food quality and shelf life, has received increasing attention from researchers and industry. Currently, technologies utilizing electrical fields directly into food processing raised a significant interest in the food industry. Several of those are now being used on a commercial scale for processing of an extensive range of food products. The application of electric fields has also been addressed by researchers in the area of edible films and coatings. In this context, the leitmotiv of this Thesis is to provide added-value to natural materials from renewable sources (algae from sea-farms and by-products from the fishing industry) with the more “at-large” objective of bringing development to underdeveloped regions of the World. In particular, the research undertaken was directed to the chemical characterization and evaluation of the antioxidant activity of sulfated polysaccharides from the red seaweed Gracilaria birdiae (Gb), farmed in the north-eastern coast of Brazil. The work performed allowed to conclude that the sulfated polysaccharide from Gb is composed of galactose (65.4 %) and methyl derivatives 6-O-methyl-galactose (9.2 %) and in smaller quantities 3-O- and 4-O-methyl-galactose (0.33 %). This polysaccharide also presents a high content of 3,6-anhydrogalactose (25.6 %) and has a sulfate content of 8.4 %. The sulfated polysaccharide of Gb characterized by FTIR exhibits the characteristic bands of agarocolloids (at 1375 and 770 cm-1). It has also been shown that the Gb sulfated polysaccharide is a promising agent to be evaluated for the application in the food industry, and that it presents a significant antioxidant activity. A study of the applications of this sulfated polysaccharide was performed and the possibility of using it as coating material on semi-hard cheese was found. The choice of the best coating was made taking into consideration its wettability, permeability and opacity properties. A second objective was related with determining the effect of field strength on transport properties of chitosan coatings (obtained from lobster from the Cuban coasts). Four different field strengths were tested (50, 100, 150, 200 V·cm-1) and, for each electric field treatment, the water vapor, oxygen and carbon dioxide permeabilities of the films formed were determined, together with their color, opacity and solubility in water. Results showed that electric field had statistically significant effects on film’s physical properties and structure. In general, the most pronounced effect of the field strength was observed for treatments made at 100 Vcm-1 or higher, a positive correlation being found between the water vapor, oxygen and carbon dioxide permeability coefficients and field strength. In the same perspective the effect of electric fields applied at different field strength values on mechanical and thermal properties of chitosan films/coatings was evaluated. XRD analyses indicated that electrically treated chitosan films exhibited a more ordered structure and a clearly higher crystallinity when compared with non-treated films, thus displaying significant effects on the value of the crystallinity index (CI). SEM micrographs evidenced that the surface morphology of chitosan films was influenced by the electric field. In fact, the electric field treatment led to a structure with more regular layers. The application of the electric field to chitosan film-forming solutions resulted in an increase of the tensile strength (ca. 9 %) and elongation-at-break (ca. 18 %) of the corresponding chitosan films. The reported results demonstrate that the application of an electric field to film-forming solutions of chitosan is an interesting instrument to taylor relevant properties of the films or coatings produced from them. Finally, the effects of the application of chitosan coating with or without electric field treatment in sliced salmon stored in ice at 0 °C were analyzed. In a first stage, the surface properties of salmon fillets and the wetting capacity of the coatings on fish were evaluated. The best wettability results were obtained with 1 % chitosan solutions with a spreading coefficient (Ws) of -4.73 mN·m-1. For shelf-life analyses the fillets were coated and stored at 0 °C for 18 days. The control and the coated fish samples were analyzed periodically for total mesophilic count (TPC), pH, total volatile base nitrogen (TVB-N), trimethylamine (TMA), thiobarbituric acid (TBA) and ATP breakdown products (K-value). A significant reduction (p < 0.05) in pH and K-value starting from the sixth day until the end of analysis (day 18) and in TVB, TMA and TBA from the ninth until the last day, was observed for fish samples coated with chitosan, when compared to control samples. In terms of microbial growth, a slower increase in TPC was observed for the coated fish, indicating that chitosan-based coatings were effective in extending for 3 more days the shelf-life of salmon. These results demonstrate that chitosan-based coatings may be an alternative for extending the shelf-life of salmon fillets during storage at 0 °C. However, no significant differences (p < 0.05) were observed between chitosan coatings with or without electric field treatment. In short, the sulfated polysaccharide of Gb is a promising coating-forming and antioxidant agent for applications in the food industry. The application of electric fields during chitosan coating solutions preparation may provide a novel method for production of coatings with taylored properties. However, further research is needed for a clearer understanding of the importance of these changes on real food systems. Important data have also been generated on the use of chitosan edible coatings on fish. |
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