Development of pH-responsive absorbent pad based on polyvinyl alcohol/agarose/anthocyanins for meat packaging and freshness indication

Absorbent pads with antioxidant and pH-responsive color changing functions have been developed based on polyvinyl alcohol (PVA), agarose (AG), and purple sweet potato anthocyanins (PSPA), aiming for fresh keeping and freshness indication of meat. The effects of PSPA content on the structure, physical properties, and colorimetric response towards pH changing of pads were evaluated. The results showed that PSPA interacted with PVA and AG and influenced the crystallinity, thermal stability and micro-morphology of pads. The increase of the PSPA content from 3% to 12% improved the strength and DPPH radical scavenging activity of the pads, but reduced the swelling ratio. Significant color change of the pads was observed when pH increased from 3 to 10, and the pad containing 9% PSPA presented the most distinguishable color change with the change of pH. When applied as an absorbent pad for minced meat packaging, the pad indicated the real-time spoilage of the meat through obvious color change, and also extended the shelf life by at least 24 h. Therefore, the dual-functional pad shows great potential to be applied as a smart and active packaging for fresh meat, which would play an important role in ensuring food safety and improving food storage quality.