Effect Of Extraction Conditions And Procyanidins On Film Formation Of Tilapia Skin Gelatin

In order to alleviate the environmental pollution caused by plastic packaging,people began to look for environmentallyfriendly and degradable materials to be applied in the field of food packaging.As a natural macromolecule,gelatin mainly exists in the skin,bone,and tendon of animals,and shows excellent degradability,compatibility and film-forming properties.In recent years,the frequent occurrence of zoonotic diseases such as foot-and-mouth and mad cow disease and religious barriers have severely limited the application of terrestrial mammalian gelatin.In this context,aquatic gelatin had been paid attention to.Tilapia is one of the main farmed fish species in China,and China is the largest export of tilapia in the world.During the processing of tilapia,a large number of by-products(fish skin,scales,bones,etc.)were produced,which are rich in gelatin.According to the film-forming property,gelatin film was prepared,which not only was helpful for achievenet of safe and environmentally-friendly packaging,but also increased the added-value of aquatic products processing and promotes the development of aquaculture and processing industries.In industry,extraction of gelatin mainly included pretreatment and water extraction.The pretreatment means that the raw materials were pretreated by Ca(OH)₂solution,which would take long time and produce a large amount of lye polluting the environment.In this study,KOH solution was used to pretreat fish skin not only shortening the treatment time,but also the produced lye being processed into potash fertilizer for reuse.Considering this,tilapia skin was pretreated by KOH solution to extract gelatin,and then gelatin film was prepare.The effects of extraction conditions on gelatin film-forming property of gelatin were explored.Furthermore,the effects of procyanidin on the properties of gelatin film were analyzed,and the multifunction was discussed.Meanwhile,procyanidin–gelatin film was applied to the preservation of bread,which would provid the basis and reference for the development and application of gelatin in the field of food packaging film.The results are as follows:1.The influence of the pretreatment conditions on the film-forming property of gelatin was studied with the concentration of KOH solution and pretreatment time as the influencing factors.Furthermore,the melanin in fish skin affected the sensory quality of gelatin film,so the properties of gelatin film were discussed after the pigments were removed thoroughly by KOH solution.The results showed that the pretreatment conditions had a significant effect on the properties of gelatin film.When the concentration of KOH solution was 0.7 mol/L and the pretreatment time was 8 h,the film showed good chromaticity and mechanical properties,and water vapor permeability,water content and water solubility were lower.Besides,the effects of KOH solution concentration and pretreatment time on gelatin film properties showed synergistic and cross effects.2.The influence of water extraction conditions on the film-forming property of tilapia skin gelatin was explored by the water extraction temperature and time as the influencing factors..The results showed that the conditions of water extraction had no significant effect on the chromaticity,thickness,light transmittance and microstructure of the gelatin film.When the temperature was 70? and time was 4 h,the gelatin film showed lower water content and solubility,which were 15.09%and19.44%,respectively.Meanwhile,the gelatin film had a regular structure,and the tensile strength and elongation at break reached 43.07 MPa and 28.95%,respectively,showing good mechanical properties.3.The effects of procyanidins on the film-forming property of tilapia skin gelatin were explored.The results showed that with the increase of procyanidins content,the structure of the composite film was more compact and smooth due to the hydrogen bonding between it and gelatin,and the mechanical properties of the composite film were improved.At the same time,the composite film showed the enhanced antioxidant and antibacterial properties.The hydrophobic group of procyanidins endowed the improved hydrophobicity of the composite film,which reduced the water vapor permeability,water content and water solubility.However,procyanidinswith higher content caused the physical and chemical properties of film to be declined.When the content of procyanidin was 10%,the water vapor permeability,water content and solubility of the composite film were lower;and the tensile strength and elongation at break of the composite film increased by 63.41%and 77.85%,respectively,compared with the single gelatin film.Bread was treated with procyanidin-gelatin film,and with the prolongation of storage time,the moisture content was higher than unpackaged bread,and the weight loss rate was significantly reduced,indicating that the composite film showed good packaging effect.