Research On The Preparation And Performance Of Bio-based Food Freshness Indicator Detection

It is of great significance to determine food quality and safety to reduce food safety risk.Traditional chemical methods,such as the determination of total volatile base nitrogen,played a crucial role in food spoilage evaluation due to their relatively precise results,but they need to be conducted in specialized laboratories with time-consuming processes.As food spoilage is highly time-dependent,it is important to determine real-time food spoilage.Recently,intelligent food packaging has attracted more and more attention,because of its potential to‘on-package’monitor real-time food quality.Among these systems,which could provide qualitative or semi-quantitative information by means of color changes have been widely studied,since they are easy to read by the naked eye.In this paper,three freshness indicator labels were prepared,including gel freshness indicator,film freshness indicator and porous sheet freshness indicator.This paper studied the mechanical properties of the carrier materials by adjusting the structure of the carrier,and explored the color sensitivity of the freshness indicator and its application in food freshness detection using different freshness detection principles.However,there is still a great demand to explore more distinctive and effective indicators.The specific research contents are as follows:1.Nano silver hybrid dialdehyde starch-chitosan-polyvinyl alcohol-glycerol gel was prepared based on the principle of high sensitivity of nano silver to hydrogen sulfide（H₂S）.The reductive dialdehyde starch was obtained from cassava starch by oxidation reaction.Chitosan and polyvinyl alcohol were used as cross-linking agents of dialdehyde starch,and glycerol was used as solvent.Through cross-linking reaction and in situ reduction reaction,nano-Ag hybrid dialdehyde starch-chitosan-polyvinyl alcohol-glycerol gels were prepared.The experimental results indicated that the nanosilver hybrid glycerol gels prepared with glycerol instead of water as the solvent had higher mechanical strength and shape stability.The strength of gel increased from 137.85 g/cm²to 303.10 g/cm².In addition,the Ag nanoparticles hybrid dialdehyde starch-chitosan-polyvinyl alcohol-glycerol gels showed obvious color change after encountering H₂S.The value of G for the color change is linear in the ambient H₂S concentration:y=-37.797x+142.62,with a correlation coefficient R²=0.9209.It could be used as a intelligent packaging material to monitor the freshness of chicken breast and pork tenderloin.2.A novel polysaccharide biomolecular film was developed by solution mixing and liquid phase separation.Using hydroxypropyl starch（HPS）as the base material,carboxymethyl cellulose（CMC）as the cross-linking agent,glycerol（Gly）as the plasticizer,and Lycium ruthenicum anthocyanin（LRA）as the color indicator,the biopolymer film with high pH sensitivity was prepared.The experimental results indicated that LRA and CMC are incompatible with HPS,resulting in a"sea-island"microstructure of the film cross section,but without reducing the uniformity of the film.The HPS/CMC/Gly/LRA film has a swelling rate of 2369%,an initial thermal decomposition temperature of 228℃,and a tensile strength of 26.9 MPa.Anthocyanins from Lycium ruthenicum had high pH sensitivity.This polysaccharide biomolecular film was used to monitor the freshness of pork,shrimp and milk.The results showed that the color change of HPS/CMC/Gly/LRA film was consistent with the spoilage degree of pork,shrimp and milk.Therefore,this film has great application potential in the field of smart food packaging materials as indicator labels to detect the freshness of packaged foods..3.Lycium ruthenicum anthocyanins and shikonin mixed pigments are used as pH-sensitive indicators.Polyvinyl alcohol（PVA）and acrylic acid（AA）monomer were used as matrix materials.Glutaraldehyde was used as cross-linking agent and polyvinyl alcohol/polyacrylic acid（PVA/PAA）prepolymer was generated by polymerization of acrylic acid monomer.Then,the semi-interpenetrating network system（SIPN）was constructed by the cross-linking reaction of glutaraldehyde and polyvinyl alcohol in the prepolymer,and the porous sheet was prepared by freeze-drying method.Finally,the mixed pigments are loaded on the porous sheet to prepare the indicator with a porous structure.It was shown that the semi-interpenetrating network structure was able to effectively improve the mechanical properties and thermal stability of the material.The tensile strength of the prepared SIPN PAA/PVA film is 106 MPa,and the initial thermal decomposition temperature is 330℃,which are higher than those of the physical blend film of PVA and PAA.Due to the peculiar porous structure,the gas sensitivity of the material is significantly enhanced,with a minimum detection concentration of acid/alkaline gas about 0.035 mmol.The SIPN PAA/PVA porous sheet attached with mixed pigments can effectively monitor the spoilage process of pork and shrimp.This chapter aims to provide a reference for the structure design of freshness indicator label carriers.