Bioactive-Infused Multifunctional Smart Bilayer Films Based on Buckwheat Starch/Chitosan and Zein/Gelatin for Active Grape Packaging Applications

Abstract

Multifunctional smart bilayer films were developed by solvent casting for active packaging of green grapes. The inner layer consisted of buckwheat starch/chitosan (BS/CH) incorporated with mulberry anthocyanin extract (MAE) as a pH-sensitive freshness indicator, while the upper zein/gelatin (ZN/GEL) layer contained β-cyclodextrin-encapsulated curry leaf essential oil (β-CD@CLEO; 2–12%, w/w) as an antimicrobial component. The idea of the study is to form a bilayer film in which the inner layer acts as an indicator layer and the upper layer possesses antioxidant, antimicrobial, and water-resistance capabilities. The effects of MAE and β-CD@CLEO on the physicochemical, mechanical, morphological, thermal, UV-barrier, antioxidant, and antibacterial properties of the films were investigated. The film containing 1% MAE and 8% β-CD@CLEO (F5 film) was chosen as the selected film formulation, as it exhibited the highest hydrophobicity and superior overall functional performance. F5 refers to the bilayer film containing 1% (w/w) mulberry anthocyanin extract (MAE) in the inner BS/CH layer and 8% (w/w) β-CD-encapsulated curry leaf essential oil (β-CD@CLEO) in the upper ZN/GEL layer. The F5 film exhibited a water contact angle of 82.50 ± 3.50° and a tensile strength of 40.2 ± 2.75 MPa, and the lowest water vapor permeability ((3.19 ± 0.48) × 10–11 g m–1 s–1 Pa–1). It was found that incorporation of MAE and β-CD@CLEO enhanced tensile properties, water resistance, and thermal stability. The films also exhibited excellent UV-barrier performance and sustained release behavior, where approximately 75.90% of CLEO was gradually released from F5 over 160 h. The bilayer films also showed robust antioxidant activity (75.73% DPPH and 35.01% ABTS) and antibacterial activity against E. coli and S. aureus, with inhibition zones of 15.92 ± 1.73 and 16.27 ± 0.78 mm, respectively. Packaging trials demonstrated that the selected F5 film significantly preserved grape quality, outperforming conventional polyethylene packaging.