A flexible release-tuning platform based on spray-coated soy protein isolate/pectin multilayer films for potential food packaging

The susceptibility of fresh produce to microbial contamination poses a challenge to maintaining freshness and safety throughout the supply chain. To address the issue in a sustainable way, multilayer films were fabricated on a polylactic acid (PLA) substrate by alternatively depositing soy protein isolate (SPI) and high methoxyl pectin (HMP) on a soy-based primary layer enriched with an active compound (carvacrol), using spray coating. Carvacrol is one of the main components in essential oils from certain herbs. The layer-by-layer structure was captured by a scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (SEM-EDS). Atomic force microscopy (AFM) and surface wettability revealed that the structure of the multilayer film became increasingly homogeneous upon depositing additional layers. The permeability coefficient for carvacrol was determined as a function of the number of layers. Adding three or more layers resulted in a significant decrease of the permeability of the film for carvacrol, thus enabling a sustained release of carvacrol. The delayed release did not compromise the antimicrobial activity of the multilayer films in strawberry preservation. The perishable rate was decreased by more than two times using antimicrobial films. These films can act as active pads, enabling a sustained release of essential oils in confined packaging and thereby protecting fresh produce from microbial damage in an environmentally friendly way.