Orientador: Prof. Dr. Elton Gutendorfer Bonafé

Data da Defesa: 22/02/2021


INTRODUCTION. Conventional oil-based packaging is becoming a huge problem due their high degradation time, resulting in environmental pollution. Therefore, natural packaging, based on proteins and polysaccharides, with a short degradation time has been studied. The starch is one of the most used polysaccharides in biodegradable biofilms due to its capacity to form a continuous matrix, plenty, low cost, renewability and eco-friendly. Starch granules are gelatinized with a plasticizer (such as glycerol) excess water and temperature between 60º C and 100º C producing the thermoplastic starch (TPS). Despite nontoxic and biodegradable, the TPS films do not have good mechanical and barrier properties. Thus, TPS and different polymers blends (including synthetic polymers, such as polyvinyl alcohol; PVA) can produce films with improved features, suitable for use in food. Few studies have reported the starch and κ- carrageenan (linearly sulfated polysaccharide extracted from red algae) blends. The κ- carrageenan as a gelling agent, used in the production of the biodegradable films, for example, GENUGEL®. The GENUGEL® is a commercial product based on κ-carrageenan developed by CP Kelco and used as a thickener, stabilizer, gelling and texturizing agent in food applications. However, GENUGEL® was not used in biodegradable films or any mixture with starch, by the solvent evaporation method. The κ-carrageenan application is approved by Food and Drug Administration (FDA), and both (κ-carrageenan and GENUGEL®) can be used as food ingredients and in food packaging.
AIMS. Evaluate the effect of the incorporation of a commercial κ-carrageenan on the physicochemical properties of starch-based films for the first time. PVA and glycerol were used as plasticizers. MATERIALS AND METHODS. Films were created from the casting method. Glycerol and PVA were dissolved in distilled water under magnetic stirring. Then, desirable κ-carrageenan and cassava starch contents were slowly added to the aqueous glycerol and PVA solution with magnetic stirring for 20 min. The mixture was heated to 90 °C for 30 min under magnetic stirring to prepare polymer blends and support starch gelatinization. After, the mixtures were added to the ultrasonic bath to remove air bubbles and then, transferred to Petri dishes to solvent evaporation. After the solvent evaporation, each film was peeled off the Petri dish and stored in an appropriate package at room temperature for further analysis. It was produced five different films at κ- carrageenan: starch weight ratios of 100:0 (100κ-c), 75:25 (75κ-c), 50:50 (50κ-c), 25:75 (25κ-c) and 0:100 (0κ-c). The thickness of films was analyzed by an electronic digital micrometer, while the mechanical properties were verified by a texturometer, where was evaluated the tensile strength (σ - MPa), elongation at break (ε - %), and Young's modulus (MPa) (Modulus of elasticity related to the stiffness). The Fourier transform infrared spectroscopy (FTIR) spectra of films and their precursors were also considered. In terms of thermal analysis, we realized the thermogravimetric (TGA/DTG) and differential scanning calorimetry (DSC). The physicalchemical films characteristics were also studied across moisture and water solubility, swelling degree (SD) and swelling kinetic, water and oil vapor permeability. The color and apparent opacity were studied by spectrophotometer.
RESULTS AND DISCUSSIONS. Overall, κ-carrageenan: starch films showed excellent processability, handleability, and homogeneity. The films' thickness ranged from 150 to 190 μm. This finding can support packages for food applications. Small bubbles remained in the 100κ-c solution even after the treatment. It happens because the aqueous κ-carrageenan solution should support a high viscosity due to the linear polymer structure and high molar mass, so, the bubbles do not escape from the blend. The moisture (MC) for κ-carrageenan: starch films was low and ranged from 2.52 to 3.74%. The MC increases as the starch concentration rise due to the higher density of hydroxyl groups on the starch molecules. The water solubility (WS) ranged from 39.22 to 62.86%. The 100κ-c, 75κ-c, and 50κ-c presented higher WS than the 25κ-c and 0κ-c. This was because the κ-carrageenan presents ionized sulfate sites stabilized by metallic ions. The SD results varied from 391.6 (0κ-c) to 2002% (100κ-c). The SD increases as the κ-carrageenan concentration raise because the κ-carrageenan solutions provide physical hydrogels at the presence of metallic ions. Therefore, they can absorb more water than the starch-based film (0κ- c). The film structures remained stable even after the maximum water gain in the kinetic curve profile. This result suggests that the films present stable networks due to the active association between the film precursors. The 100κ-c and 75κ-c were more permeable to water vapor than the 25κ-c and 0κ-c. The 50κ-c supported a WVP significantly lower than the WVP for 75κ-c (p > 0.05). Stiff structures (with low SDs) should promote low WVPs. The films displayed excellent visual appearance. The high values for L and WI, and low measures for E, suggest colorless films. The film opacity ranged from 0.67 to 0.88. The films with a higher amount of starch have greater opacity. The oil permeability was between 0.0033 and 0.0043 mm m2 d−1 for the κ- carrageenan: starch films, low oil permeability indicates that the oil molecules have difficulty in transposing the film, this is due to the hydrophobic groups of the precursors. As for mechanical, as the κ-carrageenan content increased, the tensile strength was higher. The films with the highest amount of κ-carrageenan had a higher Young's modulus, that is, they were more rigid, however, they had less elongation at break. The FTIR spectrum bands indicate films composed by PVA, glycerol, starch and κ-carrageenan. Thermogravimetric analyzes indicate that starch is more thermally stable compared to κ-carrageenan, so films with a higher amount of starch will be more stable at high temperatures. Films with the highest amount of starch (0κ-c and 25κ-c) show endothermic peaks on DSC analysis, while in the other films only exothermic peaks occurred. Endothermic peaks indicate the melting of the material and exothermic peaks to the degradation of the material; therefore, this result also indicates that films with higher amounts of starch are more thermally stable.
CONCLUSION. According to results obtained is possible conclude that the casting method was efficient for producing films from selected parameters. The κ-carrageenan: starch ratio was essential on mechanical, physical and chemical properties obtained. The addition of starch to the κ-carrageenan produced flexible films with high thermal stability. The presence of κ-carrageenan provided stiff films. Depending on the desired application, the film's traits can be modulated by tuning the κ-carrageenan: starch weight ratio in the polymer blend.
Keywords: Polysaccharides; food packaging; Biopolymers.


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