Challenges associated in stability of food grade nanoemulsions

Investigating the biomolecular interactions between model proteins and glycine betaine surfactant with reference to the stabilization of emulsions and antimicrobial properties

Binding effect and interaction of 2-pentadecanoyloxymethyl)trimethylammonium bromide (DMGM-14) with bovine serum albumin (BSA) and hen egg white lysozyme (HEWL) were systematically investigated by the fluorescence spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), surface tension analysis, and molecular docking studies. The emulsion properties and particle size distribution of surfactant/protein complexes containing sunflower oil were studied using static light scattering and confocal laser scanning microscopy (CLSM). The fluorescence spectroscopy and ITC analysis confirmed the complexes formation of DMGM-14 with BSA and HEWL which was also verified by surface tension measurements. CD results explained the conformational changes in BSA and HEWL upon DMGM-14 complexation. Molecular docking study provides insight into the binding of DMGM-14 into the specific sites of BSA and HEWL. Besides, the studies drew a detailed picture on the emulsification properties of DMGM-14 with BSA and HEWL. In addition, the in vitro experiment revealed a broad antibacterial spectrum of DMGM-14 and DMGM-14/HEWL complex including activity against Gram-positive and Gram-negative bacteria. In conclusion, the present study revealed that the interaction between DMGM-14 with BSA and HEWL is important for the pharmaceutical, biological, and food products.

Improving emulsion stability based on ovalbumin-carboxymethyl cellulose complexes with thermal treatment near ovalbumin isoelectric point

Ovalbumin (OVA) is an important protein emulsifier. However, it is unstable near the isoelectric point pH, which limits its applications in the food industry. Polysaccharides may be explored to tackle this challenge by improving its pH-dependent instability. In this work, carboxymethyl cellulose (CMC) was used as a model polysaccharide to mix with OVA near its isoelectric point (pH 4.7) with subsequent mild heating at 60 °C for 30 min. The molecular interactions between OVA and CMC were comprehensively studied via a series of characterizations, including turbidity, zeta potential, intrinsic fluorescence, surface hydrophobicity, circular dichroism (CD) spectra and Fourier transform infrared spectroscopy (FTIR). The droplet sizes of the emulsions prepared by OVA-CMC were measured to analyze emulsifying property and stability. The results indicated that free OVA was easily aggregated due to loss of surface charges, while complexing with CMC significantly inhibited OVA aggregation before and after heating owing to the strong electrostatic repulsion. In addition, OVA exposed more hydrophobic clusters after heating, which resulted in the growth of surface hydrophobicity. Altogether, the heated OVA-CMC complexes presented the best emulsifying property and stability. Our study demonstrated that complexing OVA with CMC not only greatly improved its physicochemical properties but also significantly enhanced its functionality as a food-grade emulsifying agent, expanding its applications in the food industry, as development of emulsion-based acidic food products.

Facile methodology of nanoemulsion preparation using oily polymer for the delivery of poorly soluble drugs

Aqueous solubility of an active pharmaceutical ingredient (API) is a determining factor that has a direct impact on formulation strategies and overall bioavailability. Fabrication of nanoemulsions of poorly soluble drugs is one of the widely utilized approaches to overcome this problem. However, thermodynamic instability and tedious manufacturing processes of nanoemulsions limit their clinical translation. Therefore, this study was focused on circumventing the abovementioned hurdles by utilizing the polymer as an oil phase, instead of conventional oils. The nanoemulsion was prepared via a facile low-energy nanoprecipitation method using renewable poly(δ-decalactone) (PDL), as an oil phase and Pluronic F-68 as surfactant. The prepared nanoemulsions were characterized in terms of size, drug encapsulation efficiency, stability, and toxicity. Five different hydrophobic drugs were utilized to evaluate the drug delivery capability of the PDL nanoemulsion. The prepared nanoemulsions with sizes less than 200 nm were capable to enhance the aqueous solubility of the drugs by 3 to 10 times compared with the well-established Pluronic F-68 micelles. No phase separation or significant changes in size and drug content was observed with PDL nanoemulsions after high-speed centrifugation and 3 months of storage at two different temperatures (20 °C and 50 °C). PDL nanoemulsions were found to be non-heamolytic up to concentrations of 1 mg/mL, and the cell cytotoxicity studies on MDA-MB-231 and MEF cells suggest a concentration and time-dependent toxicity, where the PDL polymer itself induced no cytotoxicity. The results from this study clearly indicate that the PDL polymer has a tremendous potential to be utilized as an oil phase to prepare stable nanoemulsions via a facile methodology, ultimately favouring clinical translations.

Graphical abstract

Citral and linalool nanoemulsions: impact of synergism and ripening inhibitors on the stability and antibacterial activity against Listeria monocytogenes

The present work explored the influence of individual and combinations of citral and linalool along with different Ostwald ripening inhibitors on the nanoemulsion stability and their antibacterial activity against Listeria monocytogenes. Nine different nanoemulsions (N1-N9) containing individual or combinations of citral, linalool with or without ripening inhibitors (medium chain triglycerides, coconut oil, sesame oil and castor oil) were formulated with 5% Tween-80 using ultrasonic emulsification. N1 formulation containing 5% citral without ripening inhibitors showed the least mean droplet diameter of 20.44 nm. Addition of linalool with the citral nanoemulsions was found to have deleterious effect on the thermodynamic and kinetic stabilities. Incorporation of ripening inhibitors controlled the increase of droplet size and polydispersity index in N6-N9 during the 90 days storage period, but decreased their antibacterial activity. N8 formulation containing sesame oil as ripening inhibitor was found to be the best in controlling Ostwald ripening. N1 formulation which showed the best antibacterial activity (MIC 0.312%) was found to disrupt the bacterial membrane integrity. N1 formulation also showed a promising biofilm inhibition of 83.51%. Therefore, N1 formulation containing 5% citral could be recommended as an efficient disinfectant against food-borne pathogen Listeria monoctyogenes in food industry. Moreover, addition of sesame oil in the nanoemulsion formulation of citral or linalool could increase their stability.

Oral behaviour of emulsions stabilized by mixed monolayer

Controlled flavour release is highly important for the formulation of food emulsions. However, manipulating oral behavior and maintaining the stability of the flavoured emulsion is quite challenging. Hence, this study aims to investigate the effect of emulsion stability and oral behaviour using mixed emulsifier monolayers of different nature for their controlled flavour release. Orange oil flavoured (0.1% orange oil +10% sunflower oil) oil-in-water emulsions were prepared by microfluidization through modified starch (MS) and whey protein isolate (WPI) with different mass ratios (0.5:0.5, 0.5:1, 1:0.5, 1:1, 1:0 and 0:1) of emulsifiers. The fabricated emulsions were <0.13 μm in size (d₃₂) with stable oil droplets having strong negative charges. The 0.5:0.5 and 0:1 emulsion were depicted an increase in size d₃₂ (1.17 and 0.93 μm) and unstable during storage at 28 ± 1 °C than the emulsions stored at 4 ± 0.1 °C. All the emulsions were exhibited Newtonian flow; however once mixed with artificial saliva, the 1:0 emulsion showed shear thinning behaviour. During oral processing, in-vitro and in-vivo exhibited flocculation and coalescence; subsequently, structural deformation was observed with an increase in size (d₃₂) and weak negative charge in 1:0.5 and 1:0 emulsions. Backscattering profile revealed more destabilization for 1:0 and less for 1:0.5 emulsions. Contrarily, other emulsions did not show any changes. Therefore, oral processing of emulsions results suggested that 1:0 had quick destabilization and 1:0.5 changed gradually. Thus, mixed emulsifier monolayer contributed significantly to the behavior of emulsions when interacting with saliva and it can be useful for controlled flavour release.

Techniques for Formulation of Nanoemulsion Drug Delivery System: A Review

Nanoemulsion drug delivery systems are advanced modes for delivering and improving the bioavailability of hydrophobic drugs and the drug which have high first pass metabolism. The nanoemulsion can be prepared by both high energy and low energy methods. High energy method includes high-pressure homogenization, microfluidization, and ultrasonication whereas low energy methods include the phase inversion emulsification method and the self-nanoemulsification method. Low energy methods should be preferred over high energy methods as these methods require less energy, so are more efficient and do not require any sophisticated instruments. However high energy methods are more favorable for food grade emulsion as they require lower quantities of surfactant than low energy methods. Techniques for formulation of nanoemulsion drug delivery system are overlapping in nature, especially in the case of low energy methods. In this review, we have classified different methods for formulation of nanoemulsion systems based on energy requirements, nature of phase inversion, and self-emulsification.

Microfluidization trends in the development of nanodelivery systems and applications in chronic disease treatments

Plant bioactive compounds are known for their extensive health benefits and therefore have been used for generations in traditional and modern medicine to improve the health of humans. Processing and storage instabilities of the plant bioactive compounds, however, limit their bioavailability and bioaccessibility and thus lead researchers in search of novel encapsulation systems with enhanced stability, bioavailability, and bioaccessibility of encapsulated plant bioactive compounds. Recently many varieties of encapsulation methods have been used; among them, microfluidization has emerged as a novel method used for the development of delivery systems including solid lipid nanocarriers, nanoemulsions, liposomes, and so on with enhanced stability and bioavailability of encapsulated plant bioactive compounds. Therefore, the nanodelivery systems developed using microfluidization techniques have received much attention from the medical industry for their ability to facilitate controlled delivery with enhanced health benefits in the treatment of various chronic diseases. Many researchers have focused on plant bioactive compound-based delivery systems using microfluidization to enhance the bioavailability and bioaccessibility of encapsulated bioactive compounds in the treatment of various chronic diseases. This review focuses on various nanodelivery systems developed using microfluidization techniques and applications in various chronic disease treatments.

Essential oil based nanoemulsions to improve the microbial quality of minimally processed fruits and vegetables: A review

Due to the convenience and nutritional value, minimally processed fruits and vegetables (MPFV) are one of the rapid growing sectors in the food industry. However, their microbiological safety is a cause of great concern. Essential oils (EOs), known for potent antimicrobial efficacy have been shown to reduce microbial load in MPFV, but their low water solubility, high volatility and strong organoleptic properties limit their wide use. Encapsulating EOs to nanoemulsion offers a viable remedy for such limitations. Due to the unique properties of the EOs nanoemulsion, there has been an increasing interest in their fabrication and use in food system. The present review article encompasses the overview of the prominent microflora present in MPFV, the recent developments on the fabrication and stability of EOs based nanoemulsion, their in vitro antimicrobial activity and their application in MPFV. This review also discusses the EOs based nanoemulsions antimicrobial mechanism of action and their regulatory issues related to their use. Application of EOs based nanoemulsion either as washing disinfectant or with incorporation into edible coatings have been shown to considerably improve the microbial quality and safety of MPFV. This efficacy has been further shown to increase when combined with other hurdles. However, further studies are required on the toxicity of EOs based nanoemulsion to assure its commercial exploitation.

Optimization of cinnamon oil nanoemulsions using phase inversion temperature method: Impact of oil phase composition and surfactant concentration

Essential oils, such as those isolated from cinnamon, are effective natural antimicrobial agents, but their utilization is limited by their low water-solubility. In this study, phase inversion temperature (PIT) was used to prepare cinnamon oil nanoemulsions. To this aim, it was hypothesized that cinnamon oil nanoemulsions could be fabricated by optimizing the oil phase composition and surfactant concentration of the system and their stability could be enhanced using a cooling-dilution method during the PIT. A mixture of cinnamon oil, non-ionic surfactant, and water was heated above the PIT of the system, and then rapidly cooled with continuous stirring, which led to the spontaneous generation of small oil droplets. The impact of oil phase composition and surfactant concentration on the formation and stability of the nanoemulsions was determined. Cinnamon oil nanoemulsions with the smallest mean droplet diameter (101 nm) were formed using 40:60 wt% of cinnamon oil and medium chain triglyceride (MCT) in the total lipid phase. Increasing surfactant concentration significantly decreased the mean droplet diameter of the nanoemulsions but did not alter their particle morphology. In addition, using the cooling-dilution method, the nanoemulsions were stable for at least 31 days when stored at 4 °C or 25 °C.

Solid lipid nanoparticle enhances bioavailability of hydroxycitric acid compared to a microparticle delivery system

Solid lipid nanoparticles (SLN) are the most promising delivery system that improves the stability, bioavailability and controlled release of food bioactive compounds.

The influence of droplet size on the stability, in vivo digestion, and oral bioavailability of vitamin E emulsions

Vitamin E (α-tocopherol) is a nutraceutical compound, which has been shown to possess potent antioxidant and anticancer activity.

Fabrication of a nutrient delivery system of docosahexaenoic acid nanoemulsions via high energy techniques

A high energy nanoemulsification technique has been developed to encapsulate docosahexaenoic acid (DHA), with the major objective of enhancing its chemical and kinetic stability for a substantial storage period.