Development Of Gelatin-based Active Film And Its Application In Bread Preservation

Gelatin,a product of collagen hydrolysis,is considered a potential alternative to traditional petroleum-based plastics because of its good film-forming and degradable properties.Compared to mammalian gelatin,fish gelatin(FG)has gained widespread attention for its lack of risk of transmitting diseases such as bovine spongiform encephalopathy and avian influenza and for not causing disputes over religious beliefs.Natural fish gelatin is sensitive to moisture and is highly susceptible to swelling and even rupture when in contact with water,limiting its use in food packaging.The modification of gelatin using natural polymers is a hot topic of current research.Beeswax(BW)has good hydrophobicity and can reduce the moisture sensitivity of gelatin film after blending with gelatin.Transglutaminase(TGase)can catalyze the cross-linking between gelatin molecular chains,further improving the overall performance of the film.Most of the gelatin-based composite films documented in the literature are produced by the solution cast method,which is less efficient and cannot meet the demand of commercial market applications.In this paper,we choose the melt extrusion technology commonly used for petroleum-based plastics to prepare gelatin-based composite films and explore the effects of two modified additives,BW and TGase,on the comprehensive performance of gelatin-based composite films prepared by extrusion.Active packaging is a product of technological progress in food packaging and is an effective means of food preservation.Essential oils(EOs)have good antibacterial and antioxidant effects and are one of the most common functional additives in active packaging.In the gelatin-based reactive film formulation with the best overall performance,clove essential oil(CEO),tea tree oil(TTO),and oregano essential oil(OEO)were added to investigate the effects of the three plant essential oils on the basic film properties as well as bioactivity.The melt-extruded gelatin-based active films were applied to the preservation of toast bread,and commercially available polyethylene(PE)films were selected as blank controls to investigate the effects of different packaging methods on the shelf life of toast bread,using microorganisms,texture,moisture distribution,and sensory as the main evaluation indicators.The main research results are as follows(1)The effects of two natural modified additives,BW and TGase,on FG-based composite films prepared by the melt extrusion process were investigated.FG side chains contain a large number of hydroxyl and polar amino acids,and BW is a low-polar substance,which can combine with non-polar amino acids in gelatin side chains after mixing with FG,reducing the number of hydroxyl and polar amino acids in gelatin side chains and improving the water-sensitivity of composite films.The addition of BW will replace The covalent cross-linking between TGase and FG can compensate for the negative effect of BW on the tensile strength of the film.The composite films’ microstructure(SEM)and thermomechanical property analysis(DSC)showed good compatibility between FG and the two modified additives.Fourier transform infrared(FTIR)results confirmed the dual cross-linking effect of BW and TGase on FG.This moderate cross-linking allowed the modified gelatin particles to maintain a linear state advancing in the high-temperature spiro,facilitating film processing and production.Among all the film samples,the best packaging performance was obtained for the gelatin-based composite films that were doubly cross-linked by BW and 1% TGase,with36.63% water solubility and an 85.30° contact angle and 6.26 MPa tensile strength,which were significantly better than the unmodified FG films.All gelatin films exhibited better degradable properties,proving their potential application in mitigating the negative environmental impact of non-degradable petroleum-based packaging materials.(2)Plant essential oils(EOs)were used as functional additive components to investigate the effects of different EOs on the fundamental properties and bioactivity of gelatin-based reactive films.EOs can act as plasticizers embedded in the gelatin network and increase the elasticity and toughness of the gelatin network.In this study,the elongation at break(EAB)of all film samples containing EOs was enhanced.The addition of EOs decreased the oxygen barrier properties of the films,which was mainly due to the essential oils affecting the homogeneity of the gelatin network,increasing the pores in the film matrix,and the more accessible transport of oxygen in low-polarity materials.The gelatin films containing CEO had the highest antioxidant activity of39.38%.The films containing OEO had the highest antibacterial activity with 98.84%and 99.86% inhibition against S.aureus and E.coli,respectively.All gelatin-based active films achieved rapid degradation under specific environmental conditions,and the density of mycelium around the degraded films correlated with the antimicrobial properties of the films.(3)The effect of different packaging methods on the shelf life of bread.The effect of different packaging methods on the shelf life of toast was discussed with the commercially available PE film as the experimental control.The bread samples preserved with PE film,blank gelatin film,and active gelatin film had apparent mold growth on the 3rd,5th,and 7th days,respectively,which proved that the shelf life of the fresh-preserved bread in the three packaging forms was 2,4 and 6 days,respectively.Active gelatin film has good antibacterial properties and can effectively extend the shelf life of bread.This study is an essential guideline for the application of gelatin-based active packaging for baked food preservation.