Effect of Microfluidization Condition on Physicochemical Properties and Inhibitory Activity of Nanoemulsion Loaded with Natural Antibacterial Mixture

Effects of Microfluidization on the Physical and Storage Stability of Walnut Protein Emulsion and Beverages

Walnut meal is a by-product produced during the production of walnut oil and is often treated as a waste. However, the nutrients in walnut meal mean it has significant potential for development as a plant-based milk. This study investigated the effect of microfluidization on the stability of walnut protein emulsion (WPE) and walnut protein beverage (WPB) produced from walnut meal, compared with conventional homogenization. The particle size, zeta potential, rheological properties, and stability of WPE all significantly improved after microfluidization. The mean particle size and zeta potential of the microfluidized WPE significantly decreased (p < 0.05). The rheological properties demonstrated that the viscosity of the microfluidized WPE decreased by 80%, and that the shear force increased 4.5 times as the shear rate increased. This gave the resulting product the characteristics of non-Newtonian fluid. LUMisizer stability demonstrated that microfluidization improves stability through protein absorption on the oil-water interface. Microfluidization increased the denaturation temperature (Tm) of WPE from 135.65 to 154.87℃. Moreover, microfluidization improved the color, centrifugal precipitation rate, and viscosity in WPB compared to the control at all studied temperatures. The Arrhenius approach was used to establish a shelf-life model, which predicted that microfluidized WPB could be stored for 175 d at 4℃. This study provided a new reference for the widespread application of microfluidization in the production of food-based emulsion and beverage products.

Onion Essential Oil-in-Water Emulsion as a Food Flavoring Agent: Effect of Environmental Stress on Physical Properties and Antibacterial Activity

Plant essential oils (EOs), which are acknowledged as generally recognized as safe (GRAS) by the Food and Drug Administration (FDA), have the potential to be used as a flavoring agent. However, there are limitations to some EOs, such as low water solubility and high volatility, which limit their application in food technology. This study was conducted to develop onion (Allium cepa) EO as a flavoring agent and determine its stability against environmental stress via an emulsification technique, with different concentrations of sodium caseinate, as a delivery system. Emulsions containing onion EO were prepared using different concentrations of sodium caseinate (3, 5, and 7% w/w) via the solvent-displacement technique. The physical properties (average droplet size, color, turbidity, and stability measurement) and antibacterial activity (agar disk diffusion method) of emulsions were then determined. Results show that emulsion with 7% (w/w) sodium caseinate was the most desirable sample in terms of physical properties and antibacterial activity. Hence, it was selected for environmental stress studies (i.e., thermal processing, freeze-thaw cycles, and ultraviolet (UV) exposure). Results revealed that all types of environmental stresses had significant (p < 0.05) effects on droplet size, color, turbidity, and stability. Generally, the environmental stresses increased the droplet size except in the freeze-thaw cycle case, while all stresses decreased the stability and lightness. All types of environmental stress treatment did not show a significant (p < 0.05) effect on antibacterial activity enhancement against Salmonella Typhimurium and Listeria monocytogenes except in the case of UV treatment against L. monocytogenes. Therefore, the present work has demonstrated the potential use of emulsion as an encapsulation and delivery system of EO flavors for food applications.

Linalool Nanoemulsion Preparation, Characterization and Antimicrobial Activity against Aeromonas hydrophila

Aeromonas hydrophila is one of the most important aquatic pathogens causing huge economic losses to aquaculture. Linalool, a vital ingredient of a variety of essential oils, was proved as a good antimicrobial agent in our previous studies. However, the low solubility and volatility of Linalool obstruct its application in the field of aquatic drugs. Thus, in this study, Linalool nano-emulsion (LN) was prepared to solve these obstructions. We investigated the physicochemical properties, antibacterial activity, and mode of action of LN against A. hydrophila. LN with different medium chain triglycerides (MCT) concentrations were prepared by ultrasonic method. The results showed that the emulsion droplet size of LN was the smallest when MCT was not added to the formulation. Nano-emulsions are usually less than 500 nm in diameter. In our study, LN in this formulation were spherical droplet with a diameter of 126.57 ± 0.85 nm and showed good stability. LN showed strong antibacterial activity, the MIC and MBC values were 0.3125% v/v and 0.625% v/v, respectively. The bacterial population decreased substantially at 1 × MIC of LN. LN exhibited disruptive effect on cell membranes by scanning electron microscope (SEM) and transmission electron microscope (TEM). The present study provided a formulation of Linalool nano-emulsion preparation. Moreover, the good antibacterial activity of LN showed in our study will promote the application of Linalool for the control and prevention of A. hydrophila in aquaculture.