Development and Characterization of a Biodegradable PLA Food Packaging Hold Monoterpene-Cyclodextrin Complexes against Alternaria alternata

Abstract

The fungi of the genus Alternaria are among the main pathogens causing post-harvest diseases and significant economic losses. The consumption of Alternaria contaminated foods may be a major risk to human health, as many Alternaria species produce several toxic mycotoxins and secondary metabolites. To protect consumer health and extend the shelf life of food products, the development of new ways of packaging is of outmost importance. The aim of this work was to investigate the antifungal capacity of a biodegradable poly(lactic acid) (PLA) package filled with thymol or carvacrol complexed in β-cyclodextrins (β-CDs) by the solubility method. Once solid complexes were obtained by spray drying, varying proportions (0.0%, 1.5%, 2.5%, and 5.0 wt%) of β-CD-thymol or β-CD-carvacrol were mixed with PLA for packaging development by injection process. The formation of stable complexes between β-CDs and carvacrol or thymol molecules was assessed by Fourier-transform infrared spectroscopy (FTIR). Mechanical, structural, and thermal characterization of the developed packaging was also carried out. The polymer surface showed a decrease in the number of cuts and folds as the amount of encapsulation increased, thereby reducing the stiffness of the packaging. In addition, thermogravimetric analysis (TGA) revealed a slight decrease in the temperature of degradation of PLA package as the concentration of the complexes increased, with β-CD-carvacrol or β-CDs-thymol complexes acting as plasticisers that lowered the intermolecular forces of the polymer chains, thereby improving the breaking point. Packages containing 2.5% and 5% β-CD-carvacrol, or 5% β-CD-thymol showed Alternaria alternata inhibition after 10 days of incubation revealing their potential uses in agrofood industry.

Keywords: antifungal activity; carvacrol; food packaging; poly(lactic acid); thymol; β-cyclodextrin.

Figure 1

Chemical structures of carvacrol and thymol monoterpenes.

Figure 2

Boxes obtained by injection of the pellets. (a) (PLA); (b) (PLA/β-CD–thymol, 2.5%, wt%); (c) (PLA/β-CD–carvacrol, 5.0%, wt%).

Figure 3

FTIR spectra of carvacrol (blue) and thymol (green); β-CD–thymol (green) and β-CD–carvacrol (blue) complexes, and β-CD (black) in normal (a) and broad view (b).

Figure 4

SEM micrographs of fracture samples: (a) 100% PLA; (b) 98.5% PLA with 1.5% β-CD–thymol; (c) 97.5% PLA with 2.5% β-CD–thymol; (d) 95.0% PLA with 5.0% β-CD–thymol; (e) 98.5% PLA with 1.5% β-CD–carvacrol; (f) 97.5% PLA with 2.5% β-CD–carvacrol; (g) 95.0% PLA with 5.0% β-CD–carvacrol.

Figure 4

SEM micrographs of fracture samples: (a) 100% PLA; (b) 98.5% PLA with 1.5% β-CD–thymol; (c) 97.5% PLA with 2.5% β-CD–thymol; (d) 95.0% PLA with 5.0% β-CD–thymol; (e) 98.5% PLA with 1.5% β-CD–carvacrol; (f) 97.5% PLA with 2.5% β-CD–carvacrol; (g) 95.0% PLA with 5.0% β-CD–carvacrol.

Figure 5

(a) DSC curves for: (A) PLA–(β-CD–carvacrol 1.5%, wt%); (B) PLA–(β-CD–carvacrol 2.5%, wt%); (C) PLA–(β-CD–carvacrol 5%, wt%); (D) PLA. (b) DSC curves for (A) PLA–(β-CD–thymol 1.5%, wt%); (B) PLA–(β-CD–thymol 2.5%, wt%); (C) PLA–(β-CD–thymol 5%, wt%); (D) PLA.

Figure 6

(a): Thermogravimetric analysis curves for (A) PLA–(β-CD–carvacrol 1.5%, wt%); (B) PLA–(β-CD–carvacrol 2.5%, wt%); (C) PLA–(β-CD–carvacrol 5, wt%); (D) PLA. (b): Thermogravimetric analysis curves for (A) PLA–(β-CD–thymol 1.5%, wt%); (B) PLA–(β-CD–thymol 2.5%, wt%); (C) PLA–(β-CD–thymol 5%, wt%); (D) PLA.

Figure 7

Photographs of the antifungal test: (a) Control Alternaria alternata; (b) PLA–β-CD–carvacrol packaging at 2.5%, wt%; (c) PLA–β-CD–carvacrol packaging at 5%, wt% with inoculation of A. alternata after 10 days of incubation.