To prepare an indicator that can stably and sensitively indicate the freshness of fresh-cut fruits and vegetables, indicator hydrogels were prepared using sodium alginate (SA) and polyvinyl alcohol (PVA) as the hydrogel-forming materials, and methyl red & bromothymol blue mixture was used as the indication agent in this study.Firstly, the preparation parameters such as the indication agent addition amount, crosslinking agent concentration, and crosslinking time were optimized by using the color-changing sensitivity and mechanical properties as the optimization indexes.Then the structures and properties of the hydrogels prepared by the optimal technology were characterized.Finally, it was used to monitor the freshness of fresh-cut cantaloupe.Results showed that the hydrogel prepared with 5% of indication agent, 7 g/L of crosslinking agent concentration, and 18 h of crosslinking time had complete structures and porous interior, good hardness and elasticity, and an active color response in the range of pH 3-11.Furthermore, when it was applied to monitor fresh-cut cantaloupe freshness under refrigeration (4 ℃), the fresh-cut cantaloupe changed from fresh to sub-fresh on the third day, and the color of the indicator hydrogel from yellow-green to orange.Therefore, the hydrogel prepared in this study has good application prospects as a freshness indicator for fresh-cut fruits and vegetables and helps to improve the safety of fresh-cut fruits and vegetables and the consumer experiences.
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