Abstract
Low density polyethylene (LDPE) films were prepared with the incorporation of natural agents (carvacrol and trans-cinnamaldehyde) by the melting process. The co-precipitation method was used successfully to complex the carvacrol or trans-cinnamaldehyde with β-cyclodextrin (β-CD). The active compounds encapsulated in β-CD achieved ca. 90% encapsulation efficiency (E.E.). The inclusion complex studied by scanning electron microscopy (SEM) found particles of different sizes, ca. 4 μm. The active compounds were added directly (1 and 5 wt %) into the polymer matrix, yielding LDPE + carvacrol and LDPE + cinnamaldehyde films. The active compounds encapsulated in β-cyclodextrin (β-CD) were added to LDPE, yielding LDPE + β-CD-carvacrol and LDPE + β-CD-cinnamaldehyde films. The incorporation of carvacrol and trans-cinnamaldehyde, and their corresponding inclusion complexes with β-cyclodextrin, did not affect the thermal properties of LDPE. The microcapsules distributed in all polymer matrices had sizes of 5–20 μm as shown by scanning electron microscopy (SEM). In terms of mechanical properties, the polymers showed a slight decrease of Young’s modulus (12%) and yield stress compared (14%) to neat LDPE. This could be due to the essential oil acting as a plasticizer in the polymer matrix. The LDPE + carvacrol and LDPE + cinnamaldehyde films had the capacity to inhibit fungi by 99% compared to neat LDPE. The effectiveness against fungi of LDPE+β-CD + active agent was slower than by the direct incorporation of the essential oil in the LDPE in the same amount of active agent. The biocidal properties were related to the gradual release of active compound from the polymer. The results confirm the applicability of carvacrol, trans-cinnamaldehyde, and their corresponding inclusion complexes in active packaging, as well as their use in the food delivery industry.
Highlights
The deterioration of fruits caused by the action of pathogenic microorganisms like Botrytis cinerea can cause gray rot in grapes
The inclusion of carvacrol (β-CD-carvacrol) presented encapsulation particles of smaller size than the inclusion complexes with cinnamaldehyde (β-CD-cinnamaldehyde) that obtained different sizes of microencapsulated particles having an average of ca. 5 μm
The nature of the agglomeration was more homogeneous for the carvacrol complexes and more heterogeneous for cinnamaldehyde, which could affect its size distribution
Summary
The deterioration of fruits caused by the action of pathogenic microorganisms like Botrytis cinerea can cause gray rot in grapes. They can be extracted from various aromatic plants that synthesize them [18] These essential oils, in particular cinnamon and oregano, possess various biological activities, mainly antibacterial, antifungal, and antioxidant properties, with potential applications in packaging [19,20,21]. Wen et al [28] studied the incorporation of an inclusion complex of cinnamon essential oil (CEO). Chen et al [29] studied the antimicrobial activity of films using sulfated cellulose as polymer matrix and mustard essential oil (MEO) complexed previously with β-CD (β-CD-active agent). There are no reports related to the effect of the incorporation of active compounds (carvacrol and trans-cinnamaldehyde) in low density polyethylene (LDPE) against B. cinerea. The agent’s active release over time and the fungicidal activity of the films against B. cinerea were studied These composites could be attractive to be used as food packaging in special Chilean table grapes
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