•Pickering emulsions based on starch granules and egg granules have high stability.•Partial in situ gelatinization of starch granules enhances barrier properties.•Starch and egg granule stabilized ...emulsions had superior freeze–thaw stability.•Pickering emulsions have many useful formulation applications.
Pickering emulsions are emulsions that are stabilized by fine particles. They have been the focus of considerable research in the past decade due to their properties such as high stability with respect to coalescence and Ostwald ripening, as well as due to advances in nanotechnology that allows us to create and characterize nano-scale structures in new ways. This work reviews some of the recent work in the area of biomass-based particles for Pickering emulsions in the context of foods and topical creams, and discusses some of the theory and particularities of Pickering type emulsions. Formulation examples are given with a focus on two types of biomass-based particles isolated with their natural structure intact: starch granules from quinoa and egg yolk granules. In contrast to particles commonly used for Pickering emulsions such as latex, silica, and clay particles, starch (including hydrophobically modified starch) and egg-fractions are accepted food ingredients, as well as pharmaceutical and cosmetic excipients.
The particle stabilization of emulsion drops is possible due to partial dual wettability of particles at the oil–water interface. Native starch is not intrinsically hydrophobic; however hydrophobicity can be increased by chemical modification with octenyl succinic anhydride. Egg-granules on the other hand are quite hydrophobic and at low ionic strength (<0.3M NaCl) are insoluble with a compact structure. Quinoa starch granules and egg-granules can be used to generate Pickering type emulsions in the 10–100μm range with high levels of stability. Size decreased with increasing concentration and could be controlled by the granule to oil ratio. In the case of starch granule stabilized oil drops, heat can be applied to induce a partial gelatinization of the starch granules forming a cohesive layer at the oil–water interface increasing barrier properties. Although the droplet size of granule stabilized emulsions was relatively large, their excellent stability, encapsulation properties, and freeze–thaw stability can prove suitable for applications such as encapsulation of sensitive, bioactive ingredients in food and topical formulations.
A computer vision system (CVS) was implemented to quantify standard color of fruit and vegetables in
sRGB,
HSV and
L
*
a
*
b
* color spaces, and image capture conditions affecting the results were ...evaluated. These three color spaces are compared in terms of their suitability for color quantification in curved surfaces. The results show that
sRGB standard (linear signals) was efficient to define the mapping between
R′
G′
B′ (no-linear signals) from the CCD camera and a device-independent system such as CIE
XYZ. The CVS showed to be robust to changes in sample orientation, resolution, and zoom. However, the measured average color was shown to be significantly affected by the properties of the background and by the surface curvature and gloss. Thus all average color results should be interpreted with caution.
L
*
a
*
b
* system is suggested as the best color space for quantification in foods with curved surfaces.
Starch granules are an interesting stabilizer candidate for food‐grade Pickering emulsions. The stabilizing capacity of seven different intact starch granules for making oil‐in‐water emulsions has ...been the topic of this screening study. The starches were from quinoa; rice; maize; waxy varieties of rice, maize, and barley; and high‐amylose maize. The starches were studied in their native state, heat treated, and modified by octenyl succinic anhydride (OSA). The effect of varying the continuous phase, both with and without salt in a phosphate buffer, was also studied. Quinoa, which had the smallest granule size, had the best capacity to stabilize oil drops, especially when the granules had been hydrophobically modified by heat treatment or by OSA. The average drop diameter (d32) in these emulsions varied from 270 to 50 μm, where decreasing drop size and less aggregation was promoted by high starch concentration and absence of salt in the system. Of all the starch varieties studied, quinoa had the best overall emulsifying capacity, and OSA modified quinoa starch in particular. Although the size of the drops was relatively large, the drops themselves were in many instances extremely stable. In the cases where the system could stabilize droplets, even when they were so large that they were visible to the naked eye, they remained stable and the measured droplet sizes after 2 years of storage were essentially unchanged from the initial droplet size. This somewhat surprising result has been attributed to the thickness of the adsorbed starch layer providing steric stabilization. The starch particle‐stabilized Pickering emulsion systems studied in this work has potential practical application such as being suitable for encapsulation of ingredients in food and pharmaceutical products.
Intact starch granules are an interesting stabilizer candidate for food grade Pickering emulsions. The stabilizing capacity of seven different intact starch granules for making oil‐in‐water emulsions has been the topic of this screening study. Among all types of starch studied quinoa had the predominantly best emulsifying properties and surprising long term stability over 2 years of storage.
Extractability of red pigment from red beetroot was investigated using pulsed electric field (PEF) treated tissue in a solid–liquid extraction process. Thin disks of the tissue were subjected to PEF ...at different intensities and, 3–4 min after the treatment, the release of red pigment and ionic species into an isotonic solution was measured in situ using a spectrophotometer and a conductivity meter. The highest degree of extraction achieved with PEF was compared with that of freezing and mechanical pressing.
Subjected to 270 rectangular pulses of 10 μs at 1 kV/cm field strength, with an energy consumption of 7 kJ/kg, the samples released about 90% of total red colouring and ionic content following 1 h aqueous extraction. The increase in tissue electric conductivity after PEF treatment correlated approximately linearly with the extraction yield of red pigment and ionic species only up to an extraction level of 60–80%. No differential permeabilization of the intracellular components was found. Higher degree of variation of the extractability of pigment and ionic species at intermediate PEF treatments was interpreted as related to non-homogenous permeabilization of the tissue due to cell size.
Reversible electropermeabilization of plant tissues with heterogeneous structure represents a technological challenge as the response of the different structures within the same specimen to the ...application of electric field may differ due to different cell sizes, extracellular space configurations, and electrical properties. The influence of five different pulsed electric field protocols with different pulse polarity, number of pulses (25, 50, 75, 100, 250, and 500), and intervals between pulses (no intervals and 1- and 2-ms intervals) on the reversible permeabilization of rucola (Eruca sativa) leaves was investigated. The electric field intensity was 600 V/cm. Electrical resistance of the bulk tissue was measured before and after electroporation, and propidium iodide was used to analyze the electroporation at the surface of the leaf. Leaf viability was assessed from survival in storage, and cell viability was investigated with fluorescein diacetate. Results indicate that the viability of the leaves could not be predicted by measurements of electrical resistance or permeabilization levels of the leaf surface. Higher survival rate was demonstrated when applying bipolar pulses compared with monopolar pulses, but the latter proved to be more effective than bipolar pulses for permeabilizing the surface of the leaves. Longer intervals between bipolar pulses resulted in increased viability preservation, while the number of electroporated cells on the leaf surface was comparable for all tested protocols.
Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might be an alternative approach to the frying of food products. In this study, convective heat transfer coefficient ...during atmospheric and high pressure frying was compared. For this purpose, a pressure cooker was modified to allow the immersion of a sample into frying oil under pressure and temperature measurement of sample and oil. Heat transfer coefficient versus frying time was determined on potato slabs using changes of total mass of the experimental set-up. At the pressure of 2
bar, the results showed an almost doubled heat transfer coefficient compared to the atmospheric pressure frying. The knowledge of heat transfer coefficient during pressure frying is expected to allow accurate determination of temperature distribution and hence the kinetic calculations to lead to development of an alternative frying process.
This study explores metabolic responses of germinating barley seeds upon the application of pulsed electric fields (PEF). Malting barley seeds were steeped in aerated water for 24 h and PEF-treated ...at varying voltages (0 (control), 110, 160, 240, 320, 400 and 480 V). The seeds were then allowed to finish germination in saturated air. It is shown that exposure of germinating barley to PEF affects radicle emergence without significantly affecting the seeds’ gross metabolic activity, as quantified by isothermal calorimetry. An exploration of protein 2-DE profiles of both the embryo and the starchy endosperm showed that, at the studied time scale, no significant changes were found in proteins present at concentrations higher than the detection limit. However, western blotting demonstrated that α-amylase concentration decreases in the PEF-treated seeds.
► We treated germinating barley seeds with pulsed electric fields. ► Exposure to pulsed electric fields affected radical emergence without affecting the seed’s gross metabolic activity. ► α-Amylase concentration decreases in the treated seeds.
A model was developed to describe the droplet formation mechanism in membrane emulsification from the point of view of Gibbs free energy with the help of the Surface Evolver, which is an interactive ...finite element program for the study of interfaces shaped by surface tension. A program to test the model was written and run which allows the user to track the droplet shape as it grows, to identify the point of instability due to free energy, and thus predict droplet size. The inputs of the program are pore geometry, oil–aqueous phase interfacial tension, and contact angle. The model reasonably predicted droplet sizes for oblong-shaped pores under quiescent conditions where the force balance approach is not applicable. The model was validated against experimental conditions from the literature where the average error of the predictions compared to the mean droplet sizes was 8%.
Compression stress relaxation of potato tissue exposed to pulsed electric field (PEF) treatment, with or without osmotic pretreatment, was measured and modelled with five parameter generalised ...Maxwell model. The changes in viscoelastic model coefficients were quantified as a response to applied field strength, pulse length, and pulse number and were correlated with conductivity changes. Using the same approach, additional effects of different osmotic treatments along with constant PEF treatment were also studied.
As measured by the post-PEF conductivity, the residual elasticity was the parameter most affected at lower levels of PEF treatment. At high PEF levels, the longer of the relaxation times dropped from 10 to 2–3 s range. Maximal PEF treatment had a similar effect to 0.7 M hyper-osmotic treatment, implying that the effect of PEF on relaxation behaviour was dominated by loss of turgor. Neither hypo-osmotic nor hyper-osmotic pretreatment appeared to interact with the PEF treatment.
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