John N. Coupland

Lipid Oxidation in Food Emulsions

Lipid oxidation is a major cause of quality deterioration in food emulsions. The design of foods with improved quality depends on a better understanding of the physicochemical mechanisms of lipid oxidation in these systems. The oxidation of emulsified lipids differs from that of bulk lipids, because of the presence of the droplet membrane, the interactions between the ingredients, and the partitioning of ingredients between the oil, aqueous and interfacial regions.

Crystallization in emulsions

The more widespread application of ultrasonic and X-ray techniques have stimulated further examination of the phase transitions in the lipid phase of oil-in-water emulsions. The improved experimental data have supported the development of theories to describe the processes.

Modeling the effect of glycerol on the moisture sorption behavior of whey protein edible films

Abstract Moisture sorption isotherms (aw=0.115–0.94) were measured for a series of whey protein isolate (WPI) edible films prepared with different amounts of glycerol as a plasticizer (glycerol:total non-volatile material G=0–0.5) and for native WPI. The moisture sorption characteristics of the native protein were similar to those of the G=0 films and the equilibrium moisture content of the films increased linearly with G at all humidities. The Guggenheim-Anderson-de Boer was superior to either the Peleg or BET model as a model for the measured isotherms. The equilibrium moisture content of the films, M, was modeled using a four-parameter empirical model, M=k 1 exp (k 2 a w )+k 3 exp (k 4 a w )G , where k1–4 are 0.0016, 2.72, 0.0046, and 6.24, respectively (r=0.98).

Ultrasonic determination of fish composition

Abstract Our objective was to ascertain the relationship between the ultrasonic properties of fish and their composition. Fish analogs with varying protein (15–25 wt%), lipid (0–25 wt%) and moisture (55–80 wt%) contents were prepared by mixing dried cod powder, sunflower oil and distilled water. The temperature dependence of the ultrasonic velocity of fish analogs was measured from 5 to 35 °C. The ultrasonic velocity increased with solids-non-fat at all temperatures, but had a more complex dependence on fat content. Around 15 °C the ultrasonic velocity was independent of fat, at lower temperatures it increased with fat, and at higher temperatures it decreased. Empirical equations were developed to relate the ultrasonic velocity to composition. By measuring the ultrasonic properties of fatty tissue at at least two temperatures it should be possible to determine both the fat and solids-non-fat content. For non-fatty fish, the solids-non-fat content can be determined from a single measurement. Our results highlight the potential of ultrasonic velocity measurements to rapidly and nondestructively determine fish composition.

Droplet size determination in food emulsions : comparison of ultrasonic and light scattering methods

Abstract Ultrasonic velocity and attenuation spectra (1–5 MHz) were measured for a series of corn-oil-in-water emulsions (20 wt% oil in 2 wt% polyoxyethylene sorbitan monolaurate) with a range of different mean droplet diameters (0.5–1.5 μm). Multiple scattering theory was used to calculate mean diameters for each emulsion from both spectra. Droplet size was also determined using two commercial light scattering instruments. All techniques showed the same general trend of decreased size with increased degree of homogenization but there was only limited quantitative agreement between the various measurement techniques.

Influence of molecular structure of hydrocarbon emulsion droplets on their solubilization in nonionic surfactant micelles

Light scattering was used to study the mass transport of hydrocarbon molecules from emulsion droplets to nonionic surfactant micelles. The hydrocarbons used as the dispersed phase of the emulsions were: 1-tetradecene, n-tetradecane, 1-hexadecene, n-hexadecane, 1-octadecene and n-octadecane. Oil-in-water emulsions were prepared which had the same initial droplet diameter (0.3 μm), but different droplet concentrations (0 to 0.05 wt.%). The emulsion droplets were then suspended in either pure water or an aqueous micellar nonionic surfactant solution (2 wt.% polyoxyethylene sorbitan monolaurate) and the time-dependence of the droplet concentration and size distribution monitored at 30°C using static light scattering. In the absence of surfactant micelles the size and concentration of the hydrocarbon droplets remained constant, but in their presence the droplet concentration decreased with time, and the mean droplet diameter increased, indicating that solubilization occurred. The growth in droplet size with time is attributed to enhanced Ostwald ripening in the presence of surfactant micelles. The mass-transport rate of oil molecules from droplets to micelles, the growth in droplet size with time and the maximum amount of oil solubilized per unit amount of surfactant, increased in the following order: n-octadecane<1-octadecene

Theory of droplet size distribution measurements in emulsions using ultrasonic spectroscopy

Ultrasonic spectroscopy is a rapid nondestructive method of measuring droplet size distributions in concentrated emulsions in situ. The ultrasonic velocity and attenuation coefficient of an emulsion are measured over a range of frequencies, and then multiple scattering theory is used to convert these measurements to a droplet size distribution. In this article we discuss the physical basis of ultrasonic spectroscopy, present mathematical equations for converting ultrasonic measurements to droplet size distributions, and discuss the advantages and limitations of the ultrasonic technique compared to other techniques.

Ultrasonic monitoring of food freezing

The time of flight of an ultrasonic pulse moving parallel to the direction of heat flux was measured in blocks of food (gelatin, chicken, beef) during freezing. Echoes were recorded from the food surfaces and from the moving ice front within the food. The changing return times of these echoes were used to calculate the percentage of the food frozen as a function of time either from the measured position of the ice front or by assuming the overall time of flight of the acoustic pulse was the sum of times spent traveling through a frozen and unfrozen phase. Both methods are predicated on the observation that for foods the change in speed of sound on freezing is much greater than the changes with respect to temperature in the absence of a phase change. Both methods gave reasonable prediction of the time for complete freezing as measured by thermocouples but the latter was more practical as the ice front was difficult to measure as the muscle foods became increasingly frozen.

Droplet composition affects the rate of oxidation of emulsified ethyl linoleate

Our objective was to study the influence of droplet composition on the rate of lipid oxidation in emulsions. A series of oil-in-water emulsions stabilized by a nonionic surfactant (Tween 20) was studied. These emulsions had the same total oil concentration (5 wt%) and initial droplet diameter (0.3 μm), but contained droplets with different ratios of ethyl linoleate (substrate) andn-tetradecane (inert diluent). Lipid oxidation was measured as a function of time by three different methods: gas-chromatographic determination of residual substrate; ultraviolet-visible spectrophotometric determination of conjugated dienes; and measurement of aqueous thiobarbituric acid-reactive substances. All three methods showed similar trends for emulsions of similar composition. The progress of lipid oxidation in the emulsions was dependent on the concentration of ethyl linoleate in the emulsion droplets. At low concentrations (1% oil as substrate), oxidation proceeded at a relatively slow and constant rate. At intermediate concentrations (20%), the oxidation rate was rapid initially and then slowed down with time. At high concentrations (100%), the oxidation rate was slow at first, and then increased with time. An explanation of our results is proposed in terms of the distribution of substrate molecules between the droplet interior and interface, and the ingress of aqueous radicals into the emulsion droplets.

Physical Approaches to Masking Bitter Taste: Lessons from Food and Pharmaceuticals

Many drugs and desirable phytochemicals are bitter, and bitter tastes are aversive. Food and pharmaceutical manufacturers share a common need for bitterness-masking strategies that allow them to deliver useful quantities of the active compounds in an acceptable form and in this review we compare and contrast the challenges and approaches by researchers in both fields. We focus on physical approaches, i.e., micro- or nano-structures to bind bitter compounds in the mouth, yet break down to allow release after they are swallowed. In all of these methods, the assumption is the degree of bitterness suppression depends on the concentration of bitterant in the saliva and hence the proportion that is bound. Surprisingly, this hypothesis has only rarely been fully tested using a combination of adequate human sensory trials and measurements of binding. This is especially true in pharmaceutical systems, perhaps due to the greater experimental challenges in sensory analysis of drugs.