A novel pH-responsive intelligent indicator was developed using electrospun grass pea protein isolate (GPPI)/ polyvinyl alcohol (PVA) nanofibers incorporating sumac anthocyanins and cross-linking via vapor-phase glutaraldehyde. Cross-linking significantly enhanced the nanofibers’ water resistance, mechanical strength, and thermal stability. The incorporated anthocyanins exhibited distinct and reversible color changes in response to pH variation and volatile basic compounds, enabling effective real-time monitoring of trout freshness during refrigerated storage. A strong correlation was observed between color variation (ΔE) and total volatile basic nitrogen (TVB-N) values, confirming the reliability of the indicator system. In summary, the results indicated that the cross-linked nanofiber exhibited remarkable physicochemical characteristics and good pH sensitivity, making it an attractive option for the development of smart packaging materials.

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