| In order to solve the pollution of plastic films to the ecological environment,ASKG was used as the film-forming substrate to prepare edible films in this paper.The effects of three different plasticizers on film-forming properties were investigated and the film-forming mechanism was also analyzed.Purple onion peel anthocyanins(POPA)and red cabbage anthocyanins(RCA)were used as natural indicators,carboxymethyl cellulose(CMC)and anionic nanocellulose fibril(ACNF)were used as anchoring agents and anchoring/hydrophobic agents to prepare an edible ASKG-based intelligent film that can anchor anthocyanins.The microstructure and physical properties of the prepared intelligent films were characterized and tested for analyzing the interactions among each component and the film-forming mechanism of the intelligent films.The response characteristics of the intelligent films to pH were also constructed.In order to construc the relationship between the freshness of meat and the chroma of intelligent films,the prepared intelligent films were applied to monitor the freshness of freshwater shrimp and pork.This paper provides some theoretical basis for the further development of ASKG,it also provides strong technical supports for the popularization of food safety monitoring in the future.Rheological results of film-forming solutions with different contents of glycerol,sorbitol and triethyl citrate(TEC)showed that all the film-forming solutions were non-Newtonian fluids,and new hydrogen bonds formed between plasticizers molecules and ASKG molecules.The formation of new hydrogen bonds destroyed the partial interactions among ASKG molecular chains.The plasticizing effect of glycerol and sorbitol was better than that of TEC.FTIR results were well consistent with rheological results.TG results showed that the addition of glycerol and sorbitol did not change the thermal stability of the films,while the addition of TEC reduced it.SEM observations indicated that the surfaces and cross-sections of the ASKG films with glycerol and sorbitol were smooth and compact,while those with TEC showed many pores.The tensile strength and light transmittance of the ASKG film decreased with the increase of glyceol and sorbitol,but the elongation at break,oxygen permeability and moisture permeability increased.The mechanical properties of the ASKG film with TEC showed no obvious rules.According to these results,the tensile strength and elongation at break of the ASKG film with 40%of glycerol could reach 32.15 MPa and 52.80%.For adding intelligence to ASKG film,an edible ASKG/POPA intelligent film was prepared.Rheological results showed that the addition of POPA destroyed the entangled structures among the partial ASKG molecular chains and formed new hydrogen bonds with ASKG and glycerol.Moreover,the film-forming solutions were still non-Newtonian fluids.FTIR results were consistent with rheological results.SEM observations indicated that the surfaces and cross-sections of the intelligent films were still smooth and compact.TG results showed that the addition of POPA reduced the thermal stability of the intelligent films.The addition of POPA reduced the mechanical properties and light transmittance of the intelligent films,however,the barrier properties improved.The intelligent films also showed UV shielding effect.POPA solution exhibited different colors at different pH values.The intelligent films showed good response to different buffer solutions and ammonia.The increase of relative humidity could promote the response effect of the intelligent film to ammonia.CMC was used as anchording agent and RCA was used as natural indicator to prepare an in-situ edible ASKG/CMC/RCA intelligent film.Zeta potentials of film-forming solutions and release test results of the intelligent films showed that RCA was anchored in the film-forming system through electrostatic attraction.Rheological results showed that the addition of RCA destroyed and reconstructed the hydrogen bonds among ASKG,CMC and glycerol.Moreover,the film-forming solutions were still non-Newtonian fluids.FTIR and XRD results were well consistent with rheological results.TG results showed that the addition of RCA did not reduce the thermal stability of the intelligent films.SEM observations indicated that the morphology of the intelligent films was very compact.The mechanical properties and light transmittance of the intelligent films decreased with the increase of RCA,but the barrier properties increased.The intelligent films also showed UV shielding effect.RCA solution showed different colors at different pH values,and the maximum visible light absorption peak of it shifted to longer wavelength with the increase of pH.The intelligent films showed good response to different buffer solutions and ammonia.However,the high water sensitivity of the intelligent films affected their practical applications.In order to reduce the water sensitivity of the intelligent films,CMC was replaced by ACNF to prepare intelligent films.Zeta potentials of film-forming solutions and release test results of the intelligent films showed that RCA was anchored in the film-forming system through electrostatic attraction.The addition of RCA destroyed and reconstructed the hydrogen bonds among ASKG,ACNF and glycerol,but the film-forming solutions were still non-Newtonian fluids.FTIR and XRD results were well consistent with rheological results.TG results showed that the addition of RCA had little effects on the thermal stability of the intelligent films.TEM results showed that ACNF is a long fibrillar with diameter of nanoscale and length of microscale.SEM observations indicated that the layer structure in the cross-section of the intelligent films decreased,and the cross-section was more compact with the increase of RCA.The tensile strength and light transmittance of the intelligent films decreased with the increase of RCA,but the elongation at break and barrier properties increased.The intelligent films also showed UV shielding effect.The intelligent films showed good response to different buffer solutions and ammonia,and the color change was obvious.The pH-responsing properties of the intelligent films with RCA were better than that of those with anthocyanin standard.The water contact angle of the intellifent film with 15%of RCA could reach 93.25°,indicating that the water sensitivity of the intelligent films was low.In order to evaluate the practical application of the intelligent film,it was applied to monitor the freshness of freshwater shrimp and pork in real-time,and the relationship of response characteristics between the color change of the intelligent film and the freshness of reshwater shrimp and pork were also constructed.The results showed that the pH value and TVB-N value of freshwater prawn and pork increased as storage time increases.Moreover,0.01 g of the intelligent film could precisely monitor the freshness of 25 g of freshwater shrimp and 50 g of pork. |
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