Properties and Applications of Antioxidant Bilayer Films Based onFish Skin Gelatin Containing Epigallocatechin Gallate

Abstract

Bilayer films prepared by the lamination of fish gelatin film (GF) and its corresponding emulsified film (EF) with different layer thickness ratios (7:3, 5:5 and 3:7) were characterized. Bilayer films had the similar tensile strength (TS) to EF (P > 0.05) but showed lower clongation at break (EAB) (P < 0.05). All bilayer films showed the lower water vapor permeability (WVP) but higher oxygen permeability (OP) than GF. The highest total color different (AE*) value was observed in bilayer film laminated with higher thickness ratio of EF (P < 0.05). Lower light transmission and higher transparency value were obtained for bilayer films, compared to GF (P < 0.05). All bilayer films consisted of two layers. Pifferential scanning calorimetric (DSC) analysis revealed that the bilayer films had the higher glass transition temperature (T.) than GF but lower than EF. All bilayer films were heat sealable, however their seal strength and seal efficiency were lower than those of GF (P < 0.05). PLAF/GF bilayer films with different layer thickness ratios (1:9, 2:8, 3:7, 4:6 and 5:5) were prepared by casting and characterized. Bilayer films exhibited lower TS but higher EAB than PLAF (P < 0.05). All bilayer films showed lower WVP and transparency, compared to GF. Bilayer films had less barrier property toward UV light transmission, especially with increasing PLAF layer thickness ratio. All bilayer films exhibited better oxygen barrier property than PLAF and GF layer thickness had no impact on oxygen permeability of resulting bilayer films. All films showed smooth surface and the two layers of cross-section were observed for all bilayer films. Bilayer films were heat scalable. The lowest seal strength and seal efliciency were attained for film with PLAF/GF layer thickness ratio of 5:5 (P < 0.05). DSC analysis revealed that the PLAF/GF (4:6) bilayer film exhibited two distinet endothermic peaks, corresponding to the melting transition of gelatin and PLA. Epigallocatechin gallate (EGCG) possessing antioxidant activities was incorporated to GF at various concentrations (0-5.71 wt%, based on protein content) and the properties of fish gelatin-based films was also investigated. Films containing 4.29 and 5.71 wt % EGCG exhibited higher TS and WVP but lower EAB and light transmission, compared with the control film (without EGCG) (P < 0.05). All films incorporated with EGG showed higher a -, b"- and AE" than that without EGG (P < 0.05). All films had smooth surface. The incorporation of 5.71 wt% EGCG increased glass transition temperature (Tg) of gelatin film. FTIR analysis revealed the interaction between protein and EGG. Higher seal strength and seal efficieney were observed for film incorporated with 5.71 wt % EGG in comparison with control film (without EGCG) (P < 0.05). Highest release of EGG was found for film containing 5.71 wt % EGCG after 18 days of storage. Bilayer films showed higher TS, water vapor, light barrier properties, opaqueness and yellowness than monolayer films. No differences in EAB and oxygen barrier property between monolayer and bilayer films were observed. Those films were used to produce pouches, in which chicken skin oil (CSO) was packaged. CSO packaged in the pouches prepared with the films containing EGG showed lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and volatile compounds after 30 days of storage in comparison with that packaged in linear low-density polyethylene (LLDPE) pouch. Additionally, at the end of the storage, linoleic acid (C18:2 n-6) and linolenic acid (C18:3 n-9) were more retained in CSO packaged in the pouches made from the films containing EGG. When active films based on fish gelatin and EGG fabricated by thermo-compression molding were prepared, EGG, used as a natural antioxidant, promoted the interaction with gelatin, as shown by Fourier transform infrared spectroscopy, total soluble matter, X-ray diffraction and thermogravimetrie analyses. This interaction led to the formation of homogeneous structures. Films with EGCG at 5.71 wt% showed good mechanical properties, both TS and EAB. In addition, EGCG provided films with lower gloss and mass loss as well as slow release profile of EGCG as indicated by DPPH radical scavenging activity. An altemative approach fabricated by thermo-compression molding was also investigated. Thermo-compression molded bilayer films showed good handling. transparency and low WVP. The incorporation of EGG promoted interactions with gelatin, as shown by Fourier transform infrared spectroscopy. These interactions contributed to homogeneous structures, as observed by SEM. Bilayer films with 12 wt % EGG showed good mechanical properties, high water and UV-visible light barrier properties as well as a high DPPH radical scavenging activity. These bilayer films were used to produce bags, in which striped catfish slices (SCS) were packaged. After 7 days of storage at 4 °C, SCS packaged in bags prepared with 12 wt% EGG had lower psychrophilic bacteria count, weight loss, PV and TBARS values along with higher docosahexacnoic acid (C22:6 n-3) content than those packaged in bags prepared without EGG or in LLDPE bags. However, no difference in overall likeness score was found among all the samples packaged in different bags after 7 days of storage. Active bilayer films (PLAF/E-GF or EF/E-GF) based on fish gelatin incorporated with EGCG (E-GF) laminated with poly(lactic) acid film (PLAF) or emulsified gelatin film (EF) fabricated by thermo-compression molding were also prepared. Thermo-compression molded bilayer films showed good handling. low water vapor and oxygen permeabilities. The incorporation of 12 wt% EGG promoted interactions with gelatin, as indicated by good mechanical and UV-visible light barrier properties. Additionally, the developed bilayer films were sealed to produce bags, in which fried salmon skin (FSS) were packaged. After 30 days of storage, FSS packaged in bilayer bags prepared from gelatin containing EGG laminatied with EF (EF/E-GF) had lower yellowish, hardness, PV, TBARS and volatile compounds along with higher overall likeness score as well as linoleic acid (C18:2 n-6) and linolenic acid (C18:3 n- 3) contents than those packaged in the bags from gelatin films laminated with PLAF (PLAF/E-GF). Nevertheless, moisture content of FFS was higher. Therefore, EF/E-GF bilayer film possessed satisfactory properties, which could be used as alternative packaging for high lipid foods.