pH and amylase dual stimuli-responsive electrospinning membrane for smart releasing thymol to control melon Rhizopus stolonifer

Antimicrobial active packaging was limited by the inability to release the antimicrobial agents at the required location, required time, and required quantity. Hence, it is necessary to develop smart release active packaging material that can on-demand release antimicrobial agents according to the storage microenvironment. In this work, a pH and amylase dual responsive release membrane (THY@PLA-COS-DAS) was designed by grafting dialdehyde starch (DAS) onto positively charged chitosan oligosaccharide-modified electrospinning porous poly (lactic acid) (PLA) nanofiber via Schiff base bond. The dialdehyde starch as the smart gatekeeper for on-demand releasing thymol had not only glycosidic bonds that could be hydrolyzed by amylase but also Schiff base bonds that formed with PLA-COS and were sensitive to acidic pH. And the cumulative release rate confirmed that the THY@PLA-COS-DAS could respectively release 78.1% and 98.6% of thymol after 120 h at pH 5.0 or 2 mg/mL glucoamylase conditions. More importantly, the secretion assay demonstrated that Rhizopus stolonifer (R. stolonifer) could secrete acid and amylase, which respectively facilitate the breaking of Schiff base bond and glycosidic bond, thus allowing smart release thymol in response to changes in the storage microenvironment. Meanwhile, THY@PLA-COS-DAS showed a 94.5% inhibition rate against R. stolonifer. More importantly, the biocompatible THY@PLA-COS-DAS could considerably maintain the melon's appearance and hardness compared with the control group. Thus, this pH and amylase dual responsive release nanofiber membrane achieved the sustainable on-demand release of antimicrobial agents to cost-effectively inhibit spoilage microorganisms and had significant potential in innovative antimicrobial active packaging materials.