该研究以聚乙二醇为引发剂,ε-己内酯开环制备聚乙二醇-聚己内酯嵌段共聚物,通过溶剂挥发法将茜素包埋于聚乙二醇-聚己内酯胶束中,冻干后压片制备具有pH响应性的比色指示片,以监测猪肉的新鲜度。通过氢核磁共振、傅里叶变换红外光谱、差示扫描量热、表征共聚物的结构与热学性能,透射电镜观察胶束的形态。紫外吸收光谱表明,pH增加,茜素溶液最大吸收峰发生红移,且在pH 2~12从黄色变为紫色,同时比色片对不同浓度氨气均具有响应能力。应用于猪肉新鲜度监测上,当猪肉挥发性盐基氮为23.1 mg/100g超过国家标准时,比色片变为紫色,ΔE与pH、菌落总数、挥发性盐基氮和硫代巴比妥酸反应物值呈显著相关(P<0.01)。结果表明比色片可用于猪肉新鲜度的监测。
In this study, poly (ethylene glycol)-poly(caprolactone)(MPEG-PCL) diblock copolymers were synthesized by ring-opening polymerization of ε-caprolactone using monomethoxy PEG as initiator. Alizarin-loaded MPEG-PCL micelles were fabricated using a solvent evaporation method. After freeze-drying, pH-responsive colorimetric tablets were fabricated by compression to monitor the freshness of pork. The composition, molecular weight, structure and thermal properties of the polymer were studied by proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR). Morphology and size of the micelles were observed by transmission electron microscope (TEM). Ultraviolet visible spectroscopy (UV-vis) showed that the light absorption peak of alizarin solution shifted to a longer wavelength as the pH increased and the colorimetric tablet showed a distinct color change of alizarin solution from yellow to purple when pH value in the range of 2-12. The colorimetric tablet was found to be sensitive to different concentrations of volatile ammonia. The colorimetric tablet was applied to explore the freshness of pork and the brown tablet changed to purple as total volatile basic nitrogen (TVB-N) of the pork reached 23.1 mg/100g, which exceeds the threshold value of freshness in the Chinese standard. The results showed a high correlation between the ΔE of the color change and the TVB-N, pH, total viable count (TVC), thiobarbituric acid reactive substances (TBARS) change of the sample. Therefore, the colorimetric tablet could effectively be used to monitor pork freshness.
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