Mucilage of Opuntia ficus-indica (OFI) was extracted and characterized by its composition and molecular weight distribution. Mucilage film-forming dispersions were prepared under different pHs (3, 4, 5.6, 7, and 8) and calcium concentration (0% and 30% of CaCl(2), with respect to mucilage's weight), and their particle size determined. Mucilage films with and without calcium (MFCa and MF, respectively) were prepared. The effect of calcium and pH on mucilage films was evaluated determining thickness, color, water vapor permeability (WVP), tensile strength (TS), and percentage of elongation (%E). The average molecular weight of the different fractions of mucilage was: 3.4 x 10(6) (0.73%), 1 x 10(5) (1.46%), 1.1 x 10(3) (45.79%), and 2.4 x 10(2) Da (52.03%). Aqueous mucilage dispersions with no calcium presented particles with an average size d(0.5) of 15.4 microm, greater than the dispersions with calcium, 13.2 microm. MFCa films showed more thickness (0.13 mm) than the MF films (0.10 mm). The addition of calcium increased the WVP of the films from 109.94 to 130.45 gmm/m(2)dkPa. Calcium and pH affected the mechanical properties of the films; the largest TS was observed on MF films, whereas the highest %E was observed on MFCa films. The highest differences among MF and MFCa films were observed at pHs 5.6 and 7 for TS and at pHs 4 and 8 for %E. No effect of pH and calcium was observed on luminosity and hue angle. Chroma values were higher for MF when compared with MFCa, and increased as pH of the films increased. Practical Application: In this study mucilage from nopal was extracted and characterized by its ability to form edible films under different pHs, and with or without the addition of calcium. Opuntia ficus-indica mucilage had the ability to form edible films. In general, it can be considered that mucilage films without modification of pH and without the addition of calcium have the best water vapor barrier properties and tensile strength. Mucilage from nopal could represent a good option for the development of edible films in countries where nopal is highly produced at low cost, constituting a processing alternative for nopal.
Chitosan films (CF) with carvacrol (CAR) [0.5%, 1.0% and 1.5% v/v] were prepared by the emulsion method. The retained CAR, water solubility, water vapor permeability (WVP), optical, mechanical properties, antibacterial and antioxidant capacity of films were analyzed. The results indicate that the retention of CAR in the CF was ≈50%. The incorporation of CAR to CF decreased the water solubility, the WVP, the yellowing and transparency and the tensile strength, but increased the stiffness. Microcapsules with diameters of 2 to 7 µm were found on the surface CF-CAR. The CF-CAR with highest CAR concentrations showed antibacterial activity against S. typhimurium and E. coli O157:H7. The CF-CAR had higher antioxidant capacity and an increased protective effect against oxidation of erythrocytes in different grades. These results suggest potential applications of CF-CAR as active packaging to preserve food products.
Films were prepared using oxidized banana starch and glycerol. Oxidized banana starch was synthesized at three oxidation levels (0.5, 1.0 and 1.5% of active chlorine). Thermal gelatinization and casting were used for film preparation. Tensile strength, elongation, X‐ray diffraction pattern and water vapor permeability were tested. The tensile strength of the films was higher when the oxidation level of the banana starch was higher. When films were stored for 30 and 60 days, there were no statistical differences in tensile strength. However, differences occurred when those films were compared with the films stored for 90 days. The film with added sunflower oil presented the lowest value of elongation at 30 and 60 days of storage. When elongation values were assessed at 90 days of storage no statistical differences (α=0.05) were found among the films prepared from native starch with added sunflower oil, oxidized banana starch with 1.0% and oxidized banana starch with 1.5% oxidation level. All films had a B‐type X‐ray pattern. When the oxidation level in the starch increased, the peaks of crystallinity of the films increased as well. An additive effect was shown due to the higher interactions among polymer chains and among polymer and glycerol molecules as determined by the mechanical properties of the films analyzed. The corrected water vapor permeability (WVPc) of the films stored for 30 and 60 days did not show statistical differences (α=0.05). The films prepared with oxidized banana starch had the highest WVPc and those values increased when the oxidation level in the starch was higher. Oxidized banana starch can be used for preparation of films with adequate physicochemical characteristics.
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