| Summary: | 碩士 === 國立嘉義大學 === 食品科學系研究所 === 106 === Sodium caseinate (NaCas), a water-soluble polymer, is a material for edible packaging films due to high nutritional quality, excellent sensory properties and film-forming properties. However, NaCas film have poor water vapor barrier and mechanical properties because of the relatively higher hydrophilicity compared to general synthetic plastic films. Cross-linking to form covalent bonds in protein molecules is a possible solution to obstruct migration of water molecules within the protein-based materials. In this study natural cross-linking agent, genipin (GP) was used as the cross-linking agent. NaCas-GP films were prepared by adding GP at the levels of 0.2, 0.4, 0.6, 0.8, 1.0, and 1.5 mg/g NaCas. In the first part of this study, the effect of cross-linking reaction on the physicochemical properties of NaCas films and the selection of optimal ratio of GP addition were investigated. In the second part of this study, gallic acid (GA) was added into GP cross-linked NaCas films to development antioxidant active packaging films.
The results indicated that film thickness and moisture content were not affected by the concentration of GP. The addition of GP resulted in films with light blue appearance. L* and white index (WI) decreased as the amount of GP increased. Both a* and b* turned from positive to negative values. The water vapor barrier properties of NaCas films gradually increased with the increase of GP, and the lowest water vapor permeability (0.759±0.026 g‧mm/m2‧h‧kPa) was detected at NaCas-1.5 GP film. However, the NaCas film cross-linked with GP did not improve the water solubility of NaCas films. In addition, the increase of GP concentration caused significantly increased the tensile strength and Young’s modulus, and decreased the break elongation of the films. FTIR spectra show that enhanced peak intensity in the main characteristic bands after addition of GP, which further demonstrate the cross-linking reaction between NaCas and GP. Since NaCas film with 1.0 mg/g NaCas GP was better than other films, NaCas-1.0 GP was chosen in the second part of the study.
In the second part of this study, the results showed that the addition of GA further darkened the appearance of the cross-linked film, but didn’t affect the thickness and moisture content. The addition of low concentrations of GA increased water vapor permeability. However, the highest water vapor barrier property was detected in NaCas film with 15 mg GA and the lowest water vapor barrier properties was detected in NaCas film with 5 mg GA. The addition of GA improved the mechanical properties of the film. FTIR spectra revealed interactions between GA and protein. During the storage at room temperature up to 90 days, NaCas-GP-GA films still exhibited good antioxidant activity. GA was almost completely released from the film into food simulants (95% ethanol as fatty food simulants) at 25 and 40°C.
In conclusion, the modification of NaCas film by GP could effectively improve the mechanical properties and moisture barrier ability. Moreover, incorporation of GA could not only provide antioxidant activity but also enhance mechanical properties and water vapor barrier capabilities. In the future, this type of film may be applied to the inner packaging of prepared foods or instant noodles with additional potential as antioxidant active packaging materials.
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