Depletion Flocculation of Beverage Emulsions by Gum Arabic and Modified Starch

ABSTRACT: The creaming velocity, apparent viscosity, and ultrasonic attenuation spectra (1 to 50 MHz) of 5 wt% n hexadecane oil-in-water emulsions containing different droplet radii (r = 0.15 - 0.7 μm), biopolymer types (gum arabic or modified starch), and biopolymer concentrations (0 to 2.5 wt%) were measured. Depletion flocculation was observed in the emulsions when the nonabsorbed biopolymer concentration exceeded a critical concentration (CFC). The CFC increased with decreasing droplet radius for both biopolymers because the magnitude of the depletion attraction increases with droplet size. The CFC was lower for gum arabic than modified starch because it has a higher effective volume in solution. Depletion flocculation led to an increase in creaming instability and apparent viscosity of the emulsions. Flocculation could be nondestructively monitored by measuring the decrease in ultrasonic attenuation of the emulsions. These results show that depletion flocculation by gum arabic and modified starch can have an adverse effect on the stability of beverage emulsions.     

Storage Stability of Soybean Oil-Based Salad Dressings: Effects of Antioxidants and Hydrogenation

Flavor deterioration of salad dressings was investigated to determine the effect of hydrogenation of the oil, additives and storage conditions. Flavor quality tests were developed and correlated with gas chromatographic analyses of volatile compounds in oils separated from the dressings. Hydrogenation of soybean oil with copper and nickel catalysts effectively increased the storage stability of salad dressings at 21°C but not at 32°C. The use of BHA as an antioxidant in the oil or EDTA as a metal inactivator in the starch base as well as nitrogen packaging were effective in prolonging the storage stability of salad dressings made with unhydrogenated soybean oil. Therefore, these additives or nitrogen packaging may provide economic substitutes for hydrogenation of soybean oil used in salad dressings.     

The effects of stabilised extracts of sage and oregano on the oxidation of salad dressings

The antioxidative activity of sage and oregano either dissolved in ethanol or homogenised with olive oil as a carrier was evaluated in salad dressings. These samples were stored in the dark at ambient temperature and at 40 °C, and with light exposure at ambient temperature. Sage and oregano extracts were encapsulated in liposomes by ultrasonification or microfluidisation, and their structures confirmed by microscopic examination and dye-marker carboxyfluorescein. The antioxidant effect of these preparations was evaluated in salad dressings during storage in the dark at ambient temperature, at 40 °C and at 60 °C. The oxidation process was followed by measuring the formation of conjugated diene hydroperoxides as primary and hexanal as secondary oxidation products, as well as changes in the compositions of fatty acids and tocopherols. Oregano and sage extracts homogenised with olive oil as a carrier showed higher antioxidative effects than these extracts dissolved in ethanol during storage in the dark at ambient temperature and at 40 °C. Exposure of salad dressings to light changed the antioxidative effect of plant extracts into a pro-oxidative effect. The preparation of liposomes by microfluidisation showed higher encapsulation efficiency and more homogeneous vesicles than liposomes prepared by ultrasonification. Sage liposomes prepared by micofluidisation showed high antioxidative effects similar to butylated hydroxytoluene liposomes in salad dressings during storage in the dark at ambient temperature and at 40 °C.     

RHEOLOGICAL CHARACTERIZATION OF SALAD DRESSINGS. 1. STEADY SHEAR, THIXOTROPY AND EFFECT OF TEMPERATURE

Shear stress-shear rate data of five commercial salad dressings at 2.0, 10.0, 18.3, 26.7, 32.2 and 43.3°C were obtained using a concentric cylinder viscometer. The power law and Casson equations were applicable for all products (r ≫ 0.98). The Arrhenius equation was applicable for the effect of temperature on the apparent viscosity at 100 s^−l (r ≫ 0.97). Rheological data were obtained at a constant shear rate of 275s^−l at 2.0 and 10.0° C. The results show that the Weltman equation was better than the Hahn equation in describing the thixotropic behavior of the five salad dressings.     

DYNAMIC VISCOELASTIC PROPERTIES OF SOME COMMERCIAL SALAD DRESSINGS

A controlled stress rheometer (Carrimed CS) was used to carry out oscillatory viscoelastic experiments within the linear viscoelastic region for some commercial salad dressings: mayonnaise, reduced calorie mayonnaise and salad creams. All the mayonnaise samples exhibited higher values of maximum stress amplitude which guarantee linear viscoelasticity than either the reduced calorie mayonnaise samples or salad creams.
The frequency dependencies of the storage modulus and the phase angle revealed that all the standard mayonnaise samples exhibited similar viscoelastic properties, showing a higher elasticity than the reduced calorie mayonnaise samples and these, in turn had a higher elasticity than salad creams.
The absolute magnitude of the complex viscosity, |η*|, followed the power law equation with respect to frequency except for the salad creams and was compared to the steady viscosity, η. |η*|/η was related to the degree of shear destruction in the structure, which was minimum for one of the reduced calorie mayonnaise samples.
The viscoelastic properties of the salad dressings studied are related to their different structures.     

Death of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in shelf-stable, dairy-based, pourable salad dressings

The objectives of this study were to determine the death rates of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in three commercially manufactured full-fat ranch salad dressings, three reduced-fat ranch salad dressings, two full-fat blue cheese salad dressings, and two reduced-fat blue cheese salad dressings and to affirm the expectation that these dressings do not support the growth of these pathogens. The respective initial pH values of the four types of shelf-stable, dairy-based, pourable dressings were 2.87 to 3.72, 2.82 to 3.19, 3.08 to 3.87, and 2.83 to 3.49, respectively. Dressings were inoculated with low (2.4 to 2.5 log CFU/g) and high (5.3 to 5.9 log CFU/g) populations of separate five-strain mixtures of each pathogen and stored at 25 degrees C for up to 15 days. Regardless of the initial inoculum population, all test pathogens rapidly died in all salad dressings. Salmonella was undetectable by enrichment (<1 CFU/25-ml sample in three replicate trials) in all salad dressings within 1 day, and E. coli O157:H7 and L. monocytogenes were reduced to undetectable levels by enrichment between 1 and 8 days and 2 and 8 days, respectively. E. coli O157:H7 was not detected in 4 of the 10 salad dressings stored for 2 or more days and 9 of the 10 dressings stored for 6 or more days after inoculation. L. monocytogenes was detected in 9 of the 10 salad dressings stored for 3 days but in only one dressing, by enrichment, at 6 days, indicating that it had the highest tolerance among the three pathogens to the acidic environment imposed by the dressings. Overall, the type of dressing (i.e., ranch versus blue cheese) and level of fat in the dressings did not have a marked effect on the rate of inactivation of pathogens. Total counts and populations of lactic acid bacteria and yeasts and molds remained low or undetectable (<1.0 log CFU/ml) throughout the 15-day storage period. Based on these observations, shelf-stable, dairy-based, pourable ranch and blue cheese salad dressings manufactured by three companies and stored at 25 degrees C do not support the growth of Salmonella, E. coli O157:H7, and L. monocytogenes and should not be considered as potentially hazardous foods (time-temperature control for safety foods) as defined by the U.S. Food and Drug Administration Food Code.     

Use of Magnetic Resonance Procedures for Measurement of Oil in French-style Dressings

Magnetic resonance imaging and spectroscopy techniques have been developed for measuring percentage of edible oil in French-style salad dressings. In imaging, one takes advantage of the variations in signal intensities related to differences in relaxation times of the oil and aqueous phases, and of the proportionality of projected frequencies to spatial distribution of sample constituents. In spectroscopy, percentage of oil is determined from standard curves where the integrals of oil/ total spectra are correlated to known amounts of oil in standard preparations. Both procedures permit rapid, nondestructive analysis of commercially packaged dressings in unopened bottles with nonmagnetic closures. Results obtained in imaging or by NMR spectroscopy were within ± 2% of the expected values.     

黄原胶对色拉调味料的流变性质与稳定性的影响

本文研制了一种含有稳定剂、乳化剂与增稠剂的国产黄原胶色拉调味料。用Hanke RV12旋转粘度计测定了含黄原胶的色拉调味料的流变性质和触变结构破裂的程度,它的表观粘度,结构破裂的时间以及结构破裂所需的力与功均随黄原胶浓度的增加而增加,它的流动指数远小于1,是一个高度假塑性的触变体系。光学显微镜证实了在色拉调味料中添加一定量的黄原胶后,可以阻止油滴长大,这是由于黄原胶的乳化性、假塑性与触变性阻止了油滴的长大,从而增加了色拉调味料的稳定性。     

Oxidative stability of salad dressing with Spanish plum leaf extract

The objectives of this study were to determine the oxidative stability of salad dressing with added Spanish plum (Elaeocarpus hygrophilus Kurz.) leaf extract. Spanish plum leaves were aqueously extracted (ratio leaves:water of 1:10 weight/volume) at room temperature. The major phenolic compounds of the extract were gallic acid, epigallocatechin, catechin and gallocatechin. Various concentrations of extract (0, 200, 400, 800, 1600 ppm) were added to a salad dressing. All of the tested salad dressings displayed no change in emulsion stability index after 4 weeks of storage at 4 °C. Total oxidation of the salad dressing decreased with increased leaf extract concentration.     

Potential for β-Cyclodextrin as Partial Fat Replacer in Low-fat Foods

ABSTRACT: Headspace gas chromatography analysis of a series of flavored milks and yogurts indicated that addition of β-cyclodextrin to nonfat products results in flavor-release profiles similar to those of corresponding higher-fat-content products, suggesting the potential for this material as a partial fat replacer. A follow-up sensory evaluation study was carried out with a number of yogurts and salad dressings. Although addition of β-cyclodextrin to nonfat yogurt did not result in a product more like a low-fat product (based on flavor and texture), flavor profiles of nonfat Italian-style and ranch-style dressings were indeed more similar to the corresponding full-fat products. Therefore, the use of β-cyclodextrin as a partial fat replacer in salad dressings appears worthy of further study.     

The rheological behaviour of low fat soy‐based salad dressing

Low fat soy‐based salad dressings were formulated with different oil levels (3%, 13% and 23%) and emulsifiers (whey protein concentrate, soy‐lecithin and sodium caseinate) using either blender or ultra‐turrax (UT) homogeniser. Results showed that the rheological behaviour of these samples were highly dependent on the oil content, emulsifiers and blending methods. The UT method produced samples with better viscosity and have droplet size of 2–100 μm. Samples containing higher oil level have higher viscosity, smaller droplet size, larger G′ and G″ values. All samples show a shear‐thinning effect and larger G′ than G″, indicating the elastic nature of the samples. A quantity Q(t)% was applied to estimate the elasticity and the values were found to be in the range 22.8–85.2%. G′ and G″ were found to decrease with increased temperature. However, tan δ increased slightly with temperature; the values ranged from 0.2 to 0.4 at 5 °C to 0.3–0.5 at 25 °C. Current results demonstrated that the formulated samples have good stability compared with commercial products.     

Rheological properties and stability of model salad dressing emulsions prepared with a dry-heated soybean protein isolate–dextran mixture

The rheological characteristics of model salad dressing emulsions, incorporating a dry-heated soybean protein isolate (SPI)–dextran mixture as emulsifier, were investigated by applying dynamic rheometry tests in an attempt to probe the emulsion structure and to elucidate the mechanism of their stability against creaming. Both the viscoelastic properties and the creaming behaviour of the dressings were greatly influenced by the extent of protein–dextran conjugation and also by xanthan gum addition. The results are discussed in terms of emulsion droplet interactions which, depending on the extent of glyco-conjugation, may be dominated by depletion or ‘bridging’ flocculation effects and, thereby, influence the droplet network structure collapse during ageing.     

In Situ Ultrasonic Characterization of Cocoa Butter Using a Chirp

Differences between tempered and untempered cocoa butter were investigated by an ultrasonic signal “chirp” generated by contact transducers. Polarized light microscopy and powder X-ray diffraction were used to characterize the morphology and polymorphism of tempered and untempered cocoa butter, whereas pulsed nuclear magnetic resonance was used to determine the amount of crystalline solids present. Ultrasonic wave velocity and attenuation data were collected simultaneously throughout the 5-h crystallization process for cocoa butter. Ultrasonic velocity and attenuation changed at the different solid fat contents (SFC): 4, 8, and 11 %. Untempered cocoa butter showed an attenuation of 3 dB/cm at 1.7 MHz and 4 % SFC, whereas tempered cocoa butter showed an attenuation of 4.5 dB/cm at 1.7 MHz and 4 % SFC. At 3 MHz, the attenuation was 2 dB/cm for untempered and 6 dB/cm for tempered cocoa butter. Under these conditions (4 % SFC, 3 MHz), the chirp wave of tempered sample showed a phase angle change of 0.5 rad, whereas the untempered sample showed ?0.5 rad relative to the canola oil that was taken as 0. The study suggests that an ultrasonic chirp can be effectively used to detect differences between tempered and untempered cocoa butter when measuring attenuation and ultrasonic wave phase angle changes as a function of frequency. The in-line characterization of chocolate “temper” using such nondestructive ultrasonic measurements could be applied to industrial chocolate manufacturing.     

Dielectric analysis of hen egg white with denaturation and in cool storage

Dielectric relaxation spectra (DRS) of fresh hen raw egg white solutions and thermally denatured gels were measured at frequencies between 1 MHz and 3 GHz by using the coaxial line reflection method with a network analyser and an open-ended coaxial probe. The values of the dielectric constant ε of the denatured gels were higher than those of the raw solutions at frequencies lower than 100 MHz and then became close to each other with the increase in the frequency. No significant change in effective conductivity σ was found on denaturation, implying that this process does not affect the binding of water. The gels were stored at 5°C for 13 days to be subjected to a dehydration process that led to a corresponding decrease in dielectric constant and conductivity. When the dielectric data had been measured, the molecular motions and water status in the egg whites were analysed.     

SALAD DRESSINGS—PRELIMINARY RHEOLOGICAL CHARACTERIZATION1

The Weissenberg rheogoniometer was used to characterize a number of commercial mayonnaises and salad dressings. Steady shear measurements were used to determine flow properties and to estimate the degree of structure breakdown with shear. Dynamic measurements, at strain amplitudes greater than the linear uiscoelastic limit, were made to establish the properties of the essentially undisturbed samples. The results were analyzed in terms of the parameters of a modified Bingham body. Ranges for the various rheological properties of commercial salad dressings were established.     

The effect of choice and psychographics on the acceptability of novel flavors

This study investigated the effect of consumer test format (choice versus no choice) and food neophobia and acceptability of novel flavors of salad dressing. Half of the subjects chose the salad dressings from a list (choice test) while the other half were randomly assigned dressings (no choice test). Having respondents choose a product(s) was associated with higher hedonic ratings, and neophilics tended to score products higher. Neophobics scored products similarly to neophilics under a no choice test format, whereas neophilics responded higher with choice. These results demonstrate the enhancing effect of providing choice to consumers in food evaluations. Prior research showed that choice was associated with higher ratings; the present results demonstrate that psychological factors such as neophobia play an important interactive role in these responses and might function in a broader manner than simply affecting responses to novelty.     

Stabilization of olive oil – lemon juice emulsion with polysaccharides

An olive oil – lemon juice Greek salad dressing was developed employing xanthan gum as stabilizer and gum arabic or propylene glycol alginate as emulsifier in various combinations. In general, samples containing xanthan gum arabic were more stable against oil droplet coalescence and less stable against creaming. The use of propylene glycol alginate in the place of gum arabic, on the other hand, resulted in emulsions of higher creaming stability. Application of steady shear rheology and determination of rheological parameter values from the shearing stress-rate of shear curves, indicated that the rheological properties of the dressings were decreased with storage. Dressing texture assessment preference tests indicated that potential consumers of the product may opt for a medium viscosity product and this has to be taken into consideration when designing polysaccharide – stabilized dressings exhibiting a decrease in their textural characteristics with storage time.     

SMALL DEFORMATION PROPERTIES OF MODEL SALAD DRESSINGS PREPARED WITH REDUCED CHOLESTEROL EGG YOLK

Low-fat, low-cholesterol materials were extracted from spray-dried egg yolk using as solvents petroleum ether, petroleum ether/ethanol, ethanol/water, and supercritical CO₂. The four extracts and their source (spray-dried yolk) were incorporated into traditional recipes for oil in water salad dressings. The linear viscoelasticity of these systems was characterised by dynamic oscillation and creep/relaxation curves on a stress-controlled Carri-Med rheometer. The high protein content of the extracts generates stronger and more elastic structures than those of commercial salad dressings but they are comparable to the viscoelastic properties of commercial mayonnaises which contain high cholesterol egg yolk. Measurements of the size of oil droplets over a period of eleven days demonstrate that these emulsions maintain acceptable consistency. The methodology adopted and the conclusions derived might assist in the purposeful formulation of low-cholesterol salad dressings.     

Detection of Mustard, Egg, Milk, and Gluten in Salad Dressing Using Enzyme-Linked Immunosorbent Assays (ELISAs)

ABSTRACT:  Enzyme-linked immunosorbent assay (ELISA) is a commonly used method for the detection of trace amounts of potentially allergenic protein residues in foods. However, food matrices and processing conditions can affect the detection of protein residues. The effects of acidity on the detectability of several allergenic proteins commonly found in salad dressing using ELISAs was investigated. First, recovery experiments were performed on salad dressing formulated with 0 to 1000 ppm mustard flour (mustard). The mean percent recovery for mustard from the salad dressing was only 7.7%± 1.6%. When the pH of the salad dressing was adjusted to pH 7 prior to spiking with mustard, recovery improved to 94.1%± 7.6%. However, if the pH was adjusted to pH 7 after spiking and extraction, the recovery was only 11.1%± 1.7%. When vinegar was spiked with mustard flour at pH 3, 3.5, and 4, detectability of mustard was lowest at pH 3. Basic extraction of mustard proteins from salad dressing did not improve the mustard detection. Acidic salad dressing matrices reduced the detectability of mustard by the mustard ELISA probably because of acid precipitation of mustard proteins that renders them insoluble and nonextractable. Commercial salad dressings containing 100 ppm (mg/kg) of egg, milk, or gluten were analyzed every 2 to 4 d for 90 d using 3 commercially available ELISAs. A decrease in the detection of the egg, milk, and gluten in the salad dressing upon storage was observed. Our study highlighted the importance of evaluating the utility of various ELISAs for specific food matrices and the recovery as a function of product storage.     

α-Relaxation in honey study versus moisture content: High frequency ultrasonic investigation around room temperature

Ultrasonic longitudinal attenuation and velocity have been measured for various frequencies between 0.5 and 13.5 MHz versus temperature, in honeys with moisture contents between 15% and 19%. With the help of attenuation measurements, the temperature of the alpha transition T_α (associated with the glass transition) has been deduced versus moisture content and ultrasonic frequency. Regarding the high sensitivity of T_α towards moisture content, one can distinguish two honeys with moisture contents difference less than 0.1%. Considering the fact that the experiments are not difficult to perform and are carried out at around room temperature, this technique could be useful for honey quality control or more generally for aqueous polymers study.