Self-preserving Properties Research Articles

Selected Essential Oils as Natural Ingredients in Cosmetic Emulsions: Development, Stability Testing and Antimicrobial Activity

Abstract: Background: Essential oils are currently the subject of intensive scientific study, and their potential as active medicinal compounds or natural preservatives has attracted the attention of the cosmetic and pharmaceutical industries. Objectives: The objectives of the present study were: to develop a cosmetic emulsion based on different concentrations of synthetic preservative and essential oils, applied as natural preservatives; to evaluate and subsequently compare their stability and antimicrobial activity. Materials and Methods: Various samples were prepared using different concentrations of methylparaben, and essential oils as well. The fresh samples were evaluated immediately after preparation related to organoleptic and physicochemical testing. The behavior of the samples related to light tests, accelerated tests, and microbiological stability tests as well were performed for four weeks of storage. Results: During the accelerated stability test, formulations loaded with 2% essential oils were not stable as was noted a variation in the color and liquefaction in the second week of storage at 40°C; their rheological behavior showed a significant decrease in the viscosity, varying from 4890±34.7 to 3720±37.9. For all the samples, the pH levels were within the physiological skin pH range, it varied from 6.01±0.33 to 6.92±0.19. The self-preserving activity of all the cosmetic emulsions was satisfactory. Conclusion: Cosmetic emulsions loaded with essential oils, in the concentration of 1% showed promising stability, physico-chemical characteristics, and selfpreserving properties, in different storage conditions. The formulations loaded with essential oils provide a novel alternative for the preservation of “paraben-free” cosmetic products. Keywords: Cosmetic emulsion, Essential oils, Methylparaben, Formulation, Stability testing, Self-preserving activity.

Water soluble biomolecules from Nepeta nuda regulate microbial growth: A case study of apple juice preservation

The following study was designed to explore antimicrobial properties of the by-product obtained in a hydro-distillation process of essential oil from Nepeta nuda L. We strived to develop a novel drink with antimicrobial self-preserving properties based on two components, N. nuda decoct and apple juice. By using 96-well plate microdilution assay it was shown that the N. nuda decoct has antimicrobial potential towards 8 bacterial and 6 fungal species, with the range of minimal inhibitory concentrations 10-300 mg/mL. By using actual food system, such as apple juice, in combination with and without short thermal treatment, we have shown that the decoct of N. nuda can inhibit the growth of food contaminant fungus Penicillium aurantiogriseum. It was determined that 3 volumes of decoct (500 mg/mL) and 22 volumes of apple juice should be mixed in order to obtain self-preserving drink resistant to P. aurantiogriseum contamination. Likewise, when thermal treatment (80 °C for 10 s) is included, self-preserving mixture of decoct and apple juice should be made in volume ratios 3:47, respectively. The designed product maintained the pleasant taste as determined by panelists during the sensorial evaluation. Chemical investigations (UHPLC-Orbitrap MS analysis) of N. nuda decoct showed that the most abundant compound was 1,5,9-epideoxyloganic acid (0.410 mg/g of dried decoct). Since N. nuda is traditionally used as a tea, we presented the novel formulation of the drink with antimicrobial properties based on the its decoct and apple juice.

Starch-based Pickering emulsions for topical drug delivery: A QbD approach

Pickering emulsions are stabilized by solid particles instead of surfactants and have been widely investigated in pharmaceutical and cosmetic fields since they present less adverse effects than the classical emulsions. A quality by design (QbD) approach was applied to the production of w/o emulsions stabilized by starch. A screening design was conducted to identify the critical variables of the formula and the process affecting the critical quality properties of the emulsion (droplet size distribution). The optimization was made by establishing the Design Space, adjusting the concentration of starch and the quantity of the internal aqueous phase. The emulsion production process was, in turn, adjusted by varying the time and speed of stirring, to ensure quality and minimum variability. The stability was also investigated, demonstrating that an increase in starch concentration improves the stability of the emulsion. Rheological and mechanical studies indicated that the viscosity of the emulsions was enhanced by the addition of starch and, to a higher extent, by the presence of different lipids. The developed formulations was considered non-irritant, by an in vitro assay using human cells from skin (Df and HaCat) with the cell viability higher than 90% and, with self-preserving properties. Finally, the QbD approach successfully built quality in Pickering emulsions, allowing the development of hydrophilic drug-loaded emulsions stabilized by starch with desired organoleptic and structural characteristics. The results obtained suggest that these systems are a promising vehicle to be used in products for topical administration.

Microemulsions for Nasal Drug Delivery Systems: An Overview

Most drugs cannot be given orally because of significant degradation in the GIT or first pass metabolism in the liver. Nasal route for the delivery of some drugs offers an alternative in the pharmaceutical industry. The present review deals with the utility of the nasal route for the delivery of drugs to the brain as a microemulsion system in the treatment of a number of ailments like migraine, epilepsy, and hypertension. The nasal route could be important for drugs that are used in crisis treatments, such as for pain, and for centrally acting drugs where the pathway from nose to brain might provide a faster and more specific therapeutic effect. The purpose of the article is to provide an overview of the concept of microemulsion, selection of surfactant, co-surfactant, oils, formulation of microemulsion, phase diagram study, and evaluation of microemulsion. The review also focuses on the excipients available for formulation of microemulsions for nasal delivery and describes the investigations reported for the various classes of therapeutic agents. The interesting features of microemulsion such as spontaneity of formation, ease of manufacturing, high solubilization capacity and self-preserving properties make them the vehicle of choice for nasal delivery.

Self-Preserving Mixing Properties of Steady Round Buoyant Turbulent Plumes in Uniform Crossflows

The self-preserving mixing properties of steady round buoyant turbulent plumes in uniform crossflows were investigated experimentally. The experiments involved salt water sources injected into fresh water crossflows within the windowed test section of a water channel. Mean and fluctuating concentrations of source fluid were measured over cross sections of the flow using planar-laser-induced fluorescence which involved seeding the source fluid with Rhodamine 6G dye and adding small concentrations of ethanol to the crossflowing fluid in order to match the refractive indices of the source flow and the crossflow. The self-preserving penetration properties of the flow were correlated successfully based on the scaling analysis of Diez, Bernal, and Faeth (2003, ASME J. Heat Transfer, 125, pp. 1046–1057) whereas the self-preserving structure properties of the flow were correlated successfully based on the scaling analysis of Fischer et al. (1979, Mixing in Inland and Coastal Waters, Academic Press, New York, pp. 315–389); both approaches involved assumptions of no-slip convection in the cross stream (horizontal) direction (parallel to the crossflow) and a self-preserving line thermal having a conserved source specific buoyancy flux per unit length that moves in the streamwise (vertical) direction (parallel to the direction of both the initial source flow and the gravity vector). The resulting self-preserving structure consisted of two counter-rotating vortices having their axes nearly aligned with the crossflow direction that move away from the source in the streamwise (vertical) direction due to the action of buoyancy. Present measurements extended up to 202 and 620 source diameters from the source in the streamwise and cross stream directions, respectively. The onset of self-preserving behavior required that the axes of the counter-rotating vortex system be nearly aligned with the crossflow direction. This alignment, in turn, was a strong function of the source/crossflow velocity ratio, uo∕v∞. The net result was that the onset of self-preserving behavior was observed at streamwise distances of 10–20 source diameters from the source for uo∕v∞=4 (the smallest value of uo∕v∞ considered), increasing to streamwise distances of 160–170 source diameters from the source for uo∕v∞=100 (the largest value of uo∕v∞ considered). Finally, the counter-rotating vortex system was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to axisymmetric round buoyant turbulent plumes in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex system were 2–3 times larger than the transverse dimensions of self-preserving axisymmetric plumes at similar streamwise distances from the source.

Round Turbulent Thermals, Puffs, Starting Plumes and Starting Jets in Uniform Crossflow

Abstract The self-preserving properties of round turbulent thermals, puffs, starting plumes and starting jets, in unstratified and uniform crossflow, were investigated experimentally. The experiments involved dye-containing fresh water (for nonbuoyant flows) and salt water (for buoyant flows) sources injected vertically downward into crossflowing fresh water within a water channel. Time-resolved video images of the flows were obtained using CCD cameras. Experimental conditions were as follows: source exit diameters of 3.2 and 6.4 mm, source Reynolds numbers of 2,500–16,000, source/ambient velocity ratios of 4–35, source/ambient density ratios (for buoyant flows) of 1.073 and 1.150, volumes of injected source fluid (for thermals and puffs) comprising 16–318 source diameters, streamwise (vertical) penetration distances of 0–200 source diameters and 0–13 Morton length scales (for buoyant flows) and crosstream (horizontal) penetration distances of 0–620 source diameters. Near-source behavior varied significantly with source properties and distance from the source but the flows generally became turbulent for streamwise distances within 5 source diameters from the source and became self-preserving for streamwise distances from the source greater than 40–50 source diameters. Crosstream motion satisfied the no-slip convection approximation. Streamwise motion for self-preserving conditions satisfied the behavior of corresponding self-preserving flows in still fluids: round thermals and puffs in still fluids for round thermals and puffs in crossflow and two-dimensional line thermals and puffs in still fluids for round starting plumes and jets in crossflow. The no-slip convection approximation for crossflow motion combined with self-preserving approximations for streamwise motion were also effective for predicting flow trajectories at self-preserving conditions for steady round turbulent plumes and jets in crossflow.

Self-Preserving Properties of Unsteady Round Buoyant Turbulent Plumes and Thermals in Still Fluids

The self-preserving properties of round buoyant turbulent starting plumes and starting jets in unstratified environments. The experiments involved dye-containing salt water sources injected vertically downward into still fresh water within a windowed tank. Time-resolved images of the flows were obtained using a CCD camera. Experimental conditions were as follows: source diameters of 3.2 and 6.4 mm, source/ambient density ratios of 1.070 and 1.150, source Reynolds numbers of 4,000–11,000, source Froude numbers of 10–82, volume of source fluid for thermals comprising cylinders having the same cross-sectional areas as the source exit and lengths of 50–382 source diameters, and streamwise flow penetration lengths up to 110 source diameters and 5.05 Morton length scales from the source. Near-source flow properties varied significantly with source properties but the flows generally became turbulent and then became self-preserving within 5 and 20–30 source diameters from the source, respectively. Within the self-preserving region, both normalized streamwise penetration distances and normalized maximum radial penetration distances as functions of time were in agreement with the scaling relationships for the behavior of self-preserving round buoyant turbulent flows to the following powers: time to the 3/4 power for starting plumes and to the 1/2 power for thermals. Finally, the virtual origins of thermals were independent of source fluid volume for the present test conditions.

Erratum: “Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids” [ASME J. Heat Transfer, 124, pp. 460–469 (2002)

Erratum: “Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids” [ASME J. Heat Transfer, 124, pp. 460–469 (2002)

Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids

Abstract The self-preserving properties of round nonbuoyant turbulent starting jets, puffs, and interrupted jets were investigated both experimentally and theoretically for flows in still and unstratified environments. The experiments involved dye-containing fresh water sources injected into still fresh water within a large windowed tank. Time-resolved video images of the flows were obtained using a CCD camera. Experimental conditions were as follows: jet exit diameters of 3.2 and 6.4 mm, jet exit Reynolds numbers of 3000–12,000, jet passage lengths in excess of 50 injector passage diameters, volume of injected fluid for puffs and interrupted jets up to 191 source diameters, and streamwise penetration lengths up to 140 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent within 5 source diameters from the source and self-preserving behavior was generally observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, both the normalized streamwise penetration distance and the normalized maximum flow radius varied as functions of time in agreement with estimates for self-preserving turbulent flows to the following powers: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs and interrupted jets. Effects of injected fluid quantity for self-preserving puffs and interrupted jets could be handled by correlating the location of the virtual origin as a function of the volume of the injected fluid represented by the number of passage lengths of injected fluid. In particular, the virtual origin for puffs was independent of injected fluid volume for injected passage lengths less than 120 but became proportional to the injected fluid volume thereafter, defining a boundary between puff and interrupted-jet behavior.

The development and structure of turbulent plane jets

The structure and development of turbulent plane jets in still air and moving streams are described. The nature of the small-scale turbulence cannot be accurately ascertained because of the difficulties inherent in the measurement of dissipation in highly turbulent flows. Although correlation measurements in a jet in still air indicate a large-scale structure which can best be described as ‘local flapping’, measurements in a jet in a moving stream do not reveal a similar structure. The development of the turbulence structure in a jet in a moving parallel stream is described and the properties of turbulent jets and wakes are shown to be reasonably well predicted by the use of a variable-eddy-viscosity formula together with the formal self-preserving properties of the equations of motion.