Instant, sensitive, and distinct colorimetric response of electrospun poly(vinyl alcohol)/tannic acid nanofibrous membrane coated with anthocyanins and carboxymethyl cellulose for intelligent food packaging.

Abstract

Colorimetric indicator systems for highly perishable foods during distribution are limited by poor water resistance of hydrophilic matrices and weak anthocyanin immobilization. In this study, composite nanofibrous membranes (NFMs) based on poly(vinyl alcohol) (PVA) and tannic acid (TA) were fabricated by electrospinning, and water resistance was imparted to them solely through heat treatment, without using chemical crosslinking agents, thereby enhancing their applicability in food-related applications. Anthocyanins (ANTs), natural pigments derived from purple sweet potato that easily degrade during heat treatment, were introduced onto the electrospun PVA/TA NFMs as pH sensors using a dip-coating method under the mediation of carboxymethyl cellulose (CMC). CMC was used as a coating agent to induce electrostatic interactions and hydrogen bonding between the ANTs and CMC on the NFM surface, thereby improving the immobilization stability of ANTs. Scanning electron microscopy analysis confirmed that the nanofibrous structure was preserved after dip-coating, and the synergistic effect of TA and ANTs enhanced the UV-shielding, antioxidant, and antibacterial activities of the NFM. The NFMs responded sensitively to pH changes, exhibiting a noticeable color change (△E > 5) within 1 min; they exhibited a distinct color change in response to pH variations during five repeated exposures to ammonia and acetic acid vapors. Finally, when applied to real food packaging, a distinct color change was observed after 36 h of storage as the spoilage of packaged food progressed, indicating the potential of the developed NFMs as intelligent indicators for monitoring food freshness in real time.