Reactive Extrusion of Nonmigratory Active and Intelligent Packaging

Abstract

The environmental and economic burden of food waste demands new preservation technologies to reduce the degradative actions of spoilage such as moisture, oxygen, and microorganisms. Direct food additives can help maintain product quality; however, the limited life span of these additives combined with consumer desire for “clean label” products has motivated research into new food manufacturing technologies like active and intelligent packaging that can prevent and detect food spoilage. In this work, curcumin was grafted to polypropylene (PP-g-Cur) via reactive extrusion to produce nonmigratory active and intelligent packaging through a solvent-free, efficient, and continuous method. Immobilization of curcumin was confirmed by a standard migration assay exhibiting a maximum of 0.011 mg/cm2 migration, significantly below the EU migratory limit for food contact materials (0.1 mg/cm2). Compared to native PP films, PP-g-Cur films blocked 93% of UV light while retaining 64% transparency in the visible region, allowing for desirable product visibility while inhibiting UV degradation of packaged goods. While the ability of PP-g-Cur to inhibit growth of E. coli and L. monocytogenes was insignificant compared to control PP, free curcumin exhibited poor bacterial inhibition as well, suggesting that without hydrophilic modification, native curcumin has limited antimicrobial efficacy. PP-g-Cur films displayed significant radical scavenging in both organic (11.71 ± 3.02 TroloxEq (nmol/cm2)) and aqueous (3.18 ± 1.04 TroloxEq (nmol/cm2)) matrices, exhibiting potential for antioxidant behavior in both lipophilic and hydrophilic applications. Finally, when PP-g-Cur films were exposed to ammonia, an indicator of microbial growth, the color visually and quantitatively changed from yellow to red, demonstrating potential to indicate spoilage. These findings demonstrate the potential of a scalable technology to produce active and intelligent packaging to limit food waste and advance the capabilities of functional materials in a variety of applications.

Reactive Extrusion of Poly(lactic acid)-graft-Curcumin Antioxidant and Intelligent Packaging

“…Our previous work involving polypropylene- graft -curcumin (PP- g -Cur) demonstrated significant DPPH radical scavenging capacity, up to 11.67 Trolox Eq (nmol/cm 2 ) for the 2% w/w curcumin sample (PP- g -Cur2) . In contrast, the PLA- g -Cur2 films analyzed in this DPPH assay demonstrated only 2.52 Trolox Eq (nmol/cm 2 ).…”

“…Thus, curcumin can react with DCP to form a phenoxy radical, benzyl radical, or enolic alkoxy radical that can react with the polymer macroradical to generate the grafted product. While only one product is proposed here (Scheme ), alternative reaction pathways are noted in our previous work, demonstrating PLA grafted to the phenol, keto-enol, and aromatic ring of curcumin.…”

“…gPLA, DCP, and curcumin were used to create active and intelligent PLA- g -Cur via radical grafting (Scheme , made with ChemDraw 20.1 by PerkinElmer, USA) by reactive extrusion based on similar methods to those described previously . A mortar and pestle was used to grind DCP flakes into a fine, homogeneous powder, which was stored at 4 °C until further use.…”

“…An Attention theta optical tensiometer (Biolin Scientific, Stockholm, Sweden) was used to analyze the wettability of treated and control films by the dynamic water contact angle based on methods previously reported . In brief, ∼4 μL of distilled water was deposited on the surface of each sample, with contact angle values recorded during droplet deposition and withdrawal.…”

“…Colorimetric 2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS • +) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH • ) assays were used to quantify the antioxidant properties of PLA- g -Cur films, based on methods from previous work . In brief, a 7 mM solution of ABTS and a 2.45 mM solution of potassium persulfate were each made in 4 mM phosphate buffered saline (PBS, pH 7.4).…”