PHYSICAL CHARACTERIZATION OF ALGINATE-BASED CINNAMON ESSENTIAL OIL NANOEMULSIONS FOR THE FORMULATION OF ACTIVE COATINGS

Active coatings are formed by a biopolymer, such as alginate, and a bioactive compound. Cinnamon essential oil (CEO) is a natural preservative, which can be incorporated into active coatings to improve foods’ shelf life. This study aimed to investigate the effect of the homogenization process and the order of ingredients addition on the production of alginate-based active coatings incorporated with nanoemulsified CEO. Primary emulsions containing water, sodium alginate, Tween 80 and CEO (PEA) or water, CEO, and Tween (PE) were prepared using an Ultra-Turrax (10,000 rpm/5 min). PEA and PE were then homogenized with an ultrasound probe (150 W/3 min), generating the NEA and NE emulsions, respectively. Finally, a solution (NEAT) was prepared by homogenizing NE with an alginate solution in the Ultra-Turrax (10,000 rpm/5 min). PE and NE samples' final concentration were CEO (1% or 2%; w/w) and Tween (1% or 2%; w/w), while PEA, NEA, and NEAT were alginate (0.5% or 1%, w/w), CEO (0.5% or 1%; w/w), and Tween (0.5% or 1%; w/w). All the nanoemulsions were evaluated for mean oil droplet size (Z-average), polydispersion index (PDI), and apparent viscosity. To evaluate the stability of the emulsions, the samples were stored at room temperature. Z-Average and PDI values measured for each treatment were: PE1%: 62.74 ± 5.2 nm and 0.9 ± 0.03; PE2%: 91.32 ± 1.2 nm and 0.59 ± 0.01; PEA0.5%: 158.23 ± 2 nm and 0.68 ± 0.01; PEA1%: 214 ± 1.8 nm and 0.67 ± 0.02; NE1%: 39.57 ± 0.9 nm and 0.23 ± 0.01; NE2%: 49.21 ± 0.2 nm and 0.25 ± 0.0; NEA0.5%: 144 ± 0.8 nm and 0.59 ± 0.02; NEA1%: 205.2 ± 4.6 nm and 0.50 ± 0.11; NEAT0.5%: 80.87 ± 0.5 nm and 0.49 ± 0.03; NEAT1%: 107.81 ± 0.6 nm and 0.81 ± 0.01. Z-Average and PDI values of PE and PEA were superior to the NE and NEA solutions produced in ultrasound, indicating that this high-energy homogenization method was effective for droplet size reduction and improving emulsion homogeneity. NE, regardless of concentration of ingredients, was the only sample that did not show phase separation after 7 days of storage. Corroborating the hypothesis that nanoemulsions with sufficiently lower Z-Average and PDI may have greater kinetic stability. Nanoemulsions processed directly in the alginate solution (NEA) or later homogenized in an alginate solution (NEAT) showed different Z-average and PDI, with NEAT0.5% resulting in the best values. This result indicates that the order of alginate addition can change the nanoemulsion physical properties. PEA and NEAT1% showed a pseudoplastic behavior, while the other solutions were characterized as Newtonian fluids. PE and NE showed lower viscosity, regardless of the applied shear rate, when compared to PEA, NEA, and NEAT rates, confirming the thickening effect of alginate. Results indicate that CEO oil droplets in NEA0.5% and NEAT0.5%/1% are at the nanoscale (20 to 200 nm), confirming the viability of producing a coating based on incorporated alginate with nanoemulsified CEO. The coating evaluated in this study showed potential use for the conservation of fresh foods.