Ultrasonication-Enhanced Physicochemical Stability and Antimicrobial Efficacy of Zein-Based Nanomaterials Loaded with Cinnamaldehyde and D-Limonene.

The objective of this work was to evaluate the effect of processing via ultrasonication on the physiochemical and antimicrobial properties of zein nanoemulsions (NE) loaded with essential oils (cinnamaldehyde [CA], D-limonene [Lim], and their combination [CO]). NE consisting of 2% zein and 1% EO were prepared using probe sonication. Nanofilms (NF) were prepared from the subsequent NE using the solvent casting technique. Zeta potential, particle size, and polydispersity index (PDI) were monitored for 30 days at 4 and 22°C. Minimum inhibitory concentrations (MICs), minimal bactericidal concentrations (MBCs), and microbial reductions were also determined. Ultrasonication effectively reduced particle size, increased storage stability, and enhanced antimicrobial efficacy. SEM imaging revealed that the nanomaterial droplets ranged from 93.98 nm to 227.95 nm in diameter and remained stable after 1 month of storage at 4 or 22°C. In-vitro results showed that NEs with CA and CO inhibited the growth of both Escherichia coli O157:H7 (EC) and Listeria monocytogenes (LM) at concentrations < 2000 ppm, whereas NEs with Lim had the least antimicrobial effect, with much higher MICs and MBCs than CA. NEs with CA exhibited bactericidal activity against EC and LM after 24 h of treatment. SEM imaging also showed that CA induced noticeable morphological changes in EC cells, indicating cell damage. Results confirm that essential oils, specifically cinnamaldehyde, can be loaded into zein-based films and may be used as antimicrobial preservatives to enhance food safety. PRACTICAL APPLICATIONS: In recent years there has been an increase in foodborne disease outbreaks associated with ready-to-eat produce. Two major bacterial pathogens responsible for these outbreaks are Listeria monocytogenes and Escherichia coli O157:H7. Several studies have shown that encapsulation of natural antimicrobials into edible nanoemulsion coatings and films can enhance their antimicrobial activity in food systems. The results of this study demonstrate that films and coatings made from zein-based polymer loaded with cinnamaldehyde, limonene, and a combination of both essential oils effectively reduced populations of these pathogens. Our results also demonstrate that these nanoemulsions may be a promising tool to enhance the safety and quality of fresh produce.