Influence of emulsion droplet size on antimicrobial activity of interesterified Amazonian oils

Carvacrol-loaded nanoemulsions produced with a natural emulsifier for lettuce sanitization

Carvacrol is an antimicrobial agent that shows potential for eliminating microorganisms in vegetables, increasing food safety. However, intense odor and low water solubility of carvacrol are limiting factors for its application for fresh vegetables sanitization, which can be overcome by nanotechnology. Two different nanoemulsions containing carvacrol (11 mg/mL) were developed by probe sonication: carvacrol-saponin nanoemulsion (CNS) and carvacrol-polysorbate 80 nanoemulsion (CNP). Formulations presented appropriate droplet sizes (from 74.7 nm to 168.2 nm) and high carvacrol encapsulation efficiency (EE) (from 89.5 % to 91.5 %). CNS showed adequate droplet size distribution (PDI < 0.22) and high zeta potential values (around -30 mV) compared to CNP, with saponin chosen for the following experiments. Carvacrol nanoemulsions presented Bacterial Inactivation Concentration (BIC) against the Salmonella cocktail from 5.51 to 0.69 mg/mL and for the E. coli cocktail from 1.84 to 0.69 mg/mL. Among all tested nanoemulsions, CNS1 presented the lowest BIC (0.69 mg/mL) against both bacterial cocktails. Damage to bacterial cells in lettuce treated with nanoemulsion was confirmed by scanning electron microscopy. For lettuce sanitization, CNS1 showed a similar effect to unencapsulated carvacrol, with a high bacterial reduction (>3 log CFU/g) after lettuce immersion for 15 min at 2 × BIC. Using the same immersion time, the CNS1 (2 × BIC) demonstrated equal or better efficacy in reducing both tested bacterial cocktails (>3 log CFU/g) when compared to acetic acid (6.25 mg/mL), citric acid (25 mg/mL), and sodium hypochlorite solution (150 ppm). Lettuce immersed in CNS1 at both concentrations (BIC and 2 × BIC) did not change the color and texture of leaves, while the unencapsulated carvacrol at 2 × BIC darkened them and reduced their firmness. Consequently, carvacrol-saponin nanoemulsion (CNS1) proved to be a potential sanitizer for lettuce.

Cassava-Starch-Based Films Incorporated with Buriti (Mauritia flexuosa L.) Oil: A New Active and Bioactive Material for Food Packaging Applications

The objective of this study was to develop and characterize cassava-starch-based films incorporated with buriti (Mauritia flexuosa L.) oil and emulsifier (Tween 20). An experimental factorial design 22 with three central points was used to develop the films, by varying the concentrations of buriti oil (0.15 to 0.45% w/v) and emulsifier (0.02 to 0.04% w/v). Film thickness and weight increased with increasing buriti oil concentration. The water vapor permeability of the films ranged from 0.22 to 0.366 g mm h−1 m−2 kPa−1. The tensile strength values varied from 4.21 to 6.95 MPa, the elasticity modulus varied from 538.53 to 722.78 MPa, and elongation to rupture varied from 1.13 to 1.66%. The film color was characterized as yellowish, dark, and intense (higher oil content); and clear and a low-intensity color (lower oil content). The films presented a total carotenoid content ranging from 3.63 to 29.73 μg β-carotene/g, which may have resulted in their antioxidant potential against DPPH• (1,1-diphenyl-2-picryl-hydrazyl) radical (from 74.28 to 87.74%). The central formulation of the experimental design (buriti oil 0.30% and emulsifier 0.03%) presented a good performance and can be applied as packaging for foods with a lower water content and that demand protection against oxidation.

Essential oils microemulsions prepared with high-frequency ultrasound: physical properties and antimicrobial activity

Essential oils (EOs) have demonstrated antimicrobial activity against bacteria due to the effects of their major components. The direct application of EOs may present a rapid volatilization of its components and can decrease their effectiveness. Encapsulation by means of emulsification can provide protection to lipid compounds on a microscale. The aim of this study was to characterize microemulsions of cinnamon essential oil (CEO), oregano essential oil (OEO), and rosemary essential oil (REO) prepared by high-frequency ultrasound and evaluate their antimicrobial activities against Escherichia coli and Listeria monocytogenes. The microemulsions (oil-in-water, O/W) of EOs were prepared using high-frequency ultrasound, applying a wave amplitude of 84 µm for 15 min (REO and CEO) or 30 min (OEO). The antimicrobial activity was determined by inoculating 10⁸ CFU/mL of bacteria. Nonsurvival of the bacteria was confirmed by plate count in tryptic soy agar, determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The microemulsions exhibited droplet size diameters of 1.98 to 5.46 µm, showing high encapsulation efficiencies (79.91-81.97%) and low separation rates (2.50-6.67%). The MIC and MBC for the microemulsions for both bacteria were 20-75% less than values obtained for the non-encapsulated EOs. This study demonstrates that high-frequency ultrasound is a suitable technique for obtaining stable microemulsions to deliver natural antimicrobials that can be applied to control bacteria of high relevance in food safety.

Physicochemical characterization and antimicrobial activity in novel systems containing buriti oil and structured lipids nanoemulsions

Buriti oil nanoemulsions were prepared using non-interesterified buriti oil or buriti oil interesterified for 6 or 24 h (NBO, NBO6h, and NBO24 h), respectively. The aim was to investigate the effects of interesterified oils on the physicochemical and biological properties of nanoemulsions. Samples were stored at 4 and 25 °C for 30 days, and their physicochemical properties and biological activities were evaluated. The mean droplet diameter of nanoemulsions ranged from 196 to 270 nm. NBO24 h had the smallest droplet size and was the most stable during the storage period. Furthermore, NBO24 h demonstrating the good oxidative stability, had a high antioxidant capacity, and was less susceptible to droplet aggregation. NBO and NBO24 h had similar biological activity against Gram-negative bacteria (Escherichia coli O157: H7); bacterial growth was inhibited by at least 60% at 3.12 mg mL-1. The nanoemulsions have interesting properties for the production of pharmaceutical, cosmetic, and food formulations with antimicrobial activity.

Stability and antimicrobial activity of eucalyptus essential oil emulsions

We evaluated various formulations of oil-in-water emulsions prepared from eucalyptus essential oil, for their stability and antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. These formulations were developed using a response surface experimental design and analyzed with Design-Expert® 10 software. The emulsions were prepared in a colloid mill, and emulsion characterization was performed using the zeta ( ζ)-potential, droplet size distribution, and phase separation. The antimicrobial effects were assessed by death kinetics. The droplet size and ζ-potential of the 16 emulsions ranged from 1.071 to 1.865 µm (based on Feret's diameter) and -34.8 to -24 mV, respectively. Three formulations (14, 15, and 16) demonstrated the highest stability parameters (no phase separation) during the 28 days of evaluation. Eucalyptus essential oil emulsions exhibited antimicrobial activity against E. coli, S. aureus, and P. aeruginosa in less than 1 min.

Lipase catalyzed interesterification of Amazonian patauá oil and palm stearin for preparation of specific-structured oils

This study showed that enzymatic interesterification of Amazonian oils could be an important tool in order to produce new oils with physicochemical properties that improve the applications of these raw materials. Structured oils of Amazonian patauá oil and palm stearin using two lipases were produced in three different enzymatic systems: first, a crude lipase from the fungus Rhizopus sp (a microorganism isolated in our laboratory); second, a commercial lipase; and third, to check any synergistic effect, a mixture of both lipases (Rhizopus sp and commercial). The lipase from Rhizopus sp was specific in the incorporation of oleic acid at the sn-1,3 positions of the triacylglycerol, resulting in an oil richer in saturated fatty acid in the sn-2 position. This enzyme, produced by solid-state fermentation, even though crude, was fatty acid and positional specific and able to operate at low concentration (2.5 %, w/w). In the second enzyme system, the commercial lipase from Thermomyces lanuginosus was not specific in the tested conditions; there was no change in the distribution of saturated and unsaturated fatty acids in the three positions of the triacylglycerol profile, there was only a replacement by the type of fatty acid at the same position. In the third enzyme system, the mixture of both lipases shows no synergic effect. The structured oils retained the concentration of bioactive α- and γ- tocopherol in the three enzyme systems. Triacylglycerol classes and Thermal behavior tests indicated the formation of more homogeneous triacylglycerols, especially the mono and di-unsaturated.