Tesis Doctorado
Development of edible coatings and films based on hydrocolloid blends with polyphenol-rich extract: rheology and functiónality
Autor
Silva-Weiss, Andrea Cristina
Institución
Resumen
The development of edible films and coatings has been considered for their capability to improve quality and safety in fresh food. Natural abundant biodegradable polymeric materials such as cellulose derivatives (including methyl cellulose (MC) and carboxymethylcellulose (CMC)) chitosan, gums, starches or proteins are convenient for films and coatings production, due to lower environmental consequences compared with common synthetic plastic materials. Theproperties of edible films and coatings can be improved by combining the characteristics of hydrocolloids. Furthermore, incorporation of natural polyphenolic extract with bio-active properties in these blend solutions and composite films can enhance their active properties such as antioxidant and UV-barrier properties. However, the physical and chemical properties of edible films and coatings could also be modified when polyphenol-rich extracts are added.In these work, the ultrasound assisted-extraction was optimized and compared with conventional extraction of phenolic compounds from murtilla (Ugni molinae Turcz) leaves (Chapter 3). Then, the influence of polyphenol-rich extract from murtilla leaves on rheological properties of sixblends of hydrocolloids based solutions were analyzed (Chapter 4). In addition, resulting films were analyzed in terms of FT-IR spectra, mechanical properties of the films, and film morphology (Chapter 5).The natural source of polyphenols that should be used in edible coatings based on hydrocolloid blends was selected in previous studies. We analyzed inhibition of the copper-catalyzed oxidation of ascorbic acid, as well as scavenging capacity of DPPH. and ABTS.+ free radical of six naturalaqueous extracts. The best antioxidant capacity was for murtilla leaves, which showed the lowest concentration of aqueous extract required for 50% reduction of DPPH. and ABTS.+ free radicals, and the greatest total phenolic compound concentration (P < 0.05). Murta or murtilla is an endemic shrub found in central- southern Chile. Phenolic acids as gallic acid as well as flavonoids aglycones and glycosides of quercetin, myricetin and kaempferol are among the maincompounds found in murtilla leaf extract.Ultrasound-assisted extraction allows a higher recovery of phenolic compounds from murtilla leaves than conventional maceration. In addition, the operating cost of ultrasound process in the determined optimal conditions is more efficient and has higher performance than extraction by maceration. The efficiency of the phenolic compounds recovery by ultrasound-assisted extraction depends on the effect of parameter interaction, exposure time/amplitude, as well as of independent variables, duty cycle and time.In this investigation, a viscosity between 3 and 11 Pa s at 25 °C proved to be adequate for spreading the film-forming solutions and form the film, which also is reflected in a thickness homogeneous film. The polyphenol-rich extract from murtilla leaf reduced viscosity of filmforming solutions based on CMC and CMC-starch, being their viscosity ranges, with and without extract, suitable for coatings and films production. Solutions based on gelatines of high and lowmolecular weight leave both an unstable rheological behavior when blended with polyphenolic compounds, due to pH reduction and consequently polyphenol/protein interaction form aggregates. When incorporating murtilla extract in chitosan and chitosan-starch solutions, theformation and detachment of 0.5 1.5 cm long brown aggregates were observed. These brownaggregates could be produced by strong hydrophobic interaction of chitosan chains as well as chitosan polyphenols interaction. In addition, sol gel transition occurred when extract from murtilla leaves was added to chitosan and chitosan-starch solutions, increasing strongly their viscosity and elasticity. However, viscosity of chitosan solution with murtilla leaf extract at 100s-1 shear rate (7.11 Pa×s) and chitosan-starch solution with murtilla leaf extract at 50 s-1 shear rate (5.86 Pa×s) is suitable for casting process.Chitosan-starch solution with murtilla leaf extract form a more continuous and homogeneous film structure than the solution based on chitosan with murtilla leaf extract, due to corn starch stabilized the interaction between chitosan and murtilla leaf extract. Moreover, the extract increased thickness and yellow color of these films and reduced considerably the polymer chain mobility and, consequently, the flexibility and force of the films. The interaction mechanism of polyphenol-rich extract from murtilla leaves with chitosan chains inside the films is due to electrostatic interactions (ionic complexations under acidic conditions, pH: 4.5), ester linkages and hydrogen bonds, whereas interaction of polyphenols from extract with starch chains is due tohydrogel bonds and ester linkages.All these results indicate that the incorporation of murtilla leaf extract modifies the physical and chemical properties of edible coatings and film-forming solutions. Depending of the product onwhich this film-forming solution will be applied, these modifications increase the shelf life of the product. PFCHA-Becas Doctorado en Ciencias de Recursos Naturales 217p. PFCHA-Becas TERMINADA