Richard W. Hartel

Food emulsifiers and their applications

Overview of Food Emulsifiers.- Synthesis and Commercial Preparation of Food Emulsifiers.- Analysis of Food Emulsifiers.- Emulsifier-Carbohydrate Interactions.- Protein/Emulsifier Interactions.- Physicochemical Aspects of an Emulsifier Functionality.- Emulsifiers in Dairy Products and Dairy Substitutes.- Emulsifiers in Infant Nutritional Products.- Applications of Emulsifiers in Baked Foods.- Emulsifiers in Confectionery.- Margarines and Spreads.- Application of Emulsifiers to Reduce Fat and Enhance Nutritional Quality.- Guidelines for Processing Emulsion-Based Foods.- Forecasting the Future of Food Emulsifiers.

Ice crystallization during the manufacture of ice cream

Control of ice crystallization during the manufacture of ice cream is important for the development of proper texture, product quality and storage stability. Improving our somewhat limited understanding of the mechanisms that control ice-crystal formation, as well as of the effects of formulation and process factors, may lead to improvements in processing techniques.

Sugar crystallization in food products

A review of the recent literature on crystallization of the commercial sugars (fructose, glucose, lactose, and sucrose) is presented. Topics include: NUCLEATION--The formation of the crystalline phase from supersaturated solutions can occur by either a spontaneous or a forced nucleation mechanism. Recent work on the mechanisms, kinetics, and impact of both heterogeneous and secondary (contact) nucleation is discussed. GROWTH--Recent studies on the mechanisms and kinetics of crystal growth will be reviewed. This discussion includes work on the growth rate dispersion exhibited by these sugars. EFFECTS OF IMPURITIES AND ADDITIVES--The presence of impurities and additives (including mixed sugar systems) affects both the nucleation and growth steps. A discussion of the recent work in this area is included. Emphasis is placed on the relationship between these crystallization phenomena and the solution structure for comparison purposes.

Principles of food processing

Introduction. Thermal Processing Principles. Pasteurization and Blanching. Commercial Sterilization. Refrigerated Storage. Freezing and Frozen-Food Storage. Liquid Concentration. Dehydration. Other Separation Processes. Food Extrusion. Index.

Arrested coalescence in Pickering emulsions

When two emulsion drops begin to coalesce, their complete fusion into a single spherical drop can sometimes be arrested in an intermediate shape if a rheological resistance offsets the Laplace pressure driving force. Arrested coalescence of droplets is important, both for its broad impact on commercial food production as well as its potential for fabricating novel anisotropic colloidal microstructures. We use a micromanipulation technique to demonstrate the dynamics of arrested coalescence between droplets with interfacially adsorbed colloids. Surface coverage of the droplets is precisely determined by a capillary aspiration technique and then their coalescence is studied in situ. Depending on their surface coverage, droplets can experience total coalescence, arrested coalescence or total stability. We use microscopic observations along with geometrical packing arguments to confirm that coalescence is arrested due to close-packed jamming of particles. The anisotropic Laplace stress within the arrested structure is balanced by the elastic modulus of the jammed interface and thus further relaxation of the arrested structure is halted. Precise mapping of the arrested coalescence regime at a microscopic scale helps us to anticipate its effects on bulk scale production of such anisotropic colloidal structures.

Recrystallization of ice in ice cream during controlled accelerated storage

Abstract Accelerated ice recrystallization in a thin film of vanilla ice cream was studied on a cold stage microscope, housed in a refrigerated glove box. Sample temperature was held constant (within ±0.01 °C) or sinusoidally oscillated for 5 days. Changes in ice crystal size distribution were monitored using an image analysis technique. Several recrystallization mechanisms were observed. Melt-refreeze recrystallization was important for oscillating-temperature conditions, while rounding was particularly apparent at a constant temperature. Accretion was evident for all conditions studied, but migratory recrystallization was observed only rarely. Mean ice crystal size increased as a function of approximately time −0.33 . Recrystallization rates increased with mean storage temperature (−20 to −5 °C) and amplitude of temperature fluctuations (0.01 to 2 °C). However, recrystallization still occurred at very low amplitudes (±0.01 °C), with a recrystallization rate about half as large as for recrystallization with temperature fluctuations of ± 1 °C. Slower temperature fluctuations (2 h cycle) resulted in an initial lag in recrystallization rate that was not observed for more rapid fluctuations (10-min cycle).

Solubility of fatty acids in supercritical carbon dioxide

The solubilities of lauric, linoleic, myristic, oleic, palmitic and stearic acid in supercritical carbon dioxide (SC-CO2) at different pressures and temperatures were measured. The solubility values obtained in this work were compared with previously published data, and possible causes for observed discrepancies were discussed. The solubilities of the six fatty acids were modeled by Chrastil’s equation, and estimated model parameters were used to plot the solubility isotherms of fatty acids at 313, 323 and 333°K (40, 50 and 60°C) as a function of SC-CO2 density. The comparison of solubility isotherms of fatty acids and vegetable oil suggests that separation of fatty acids from triglycerides might be possible by using SC-CO2 at densities less than 700 kg/m3. From the effect of temperature on fatty-acid and vegetable-oil solubility, it seems that the extraction yield could be increased without sacrificing the selectivity of SC-CO2 for fatty acids by choosing a higher operating temperature. The data also suggest that fractionation of certain fatty acids might be possible by manipulating the processing conditions. Given the values of the constants, Chrastil’s equation could serve as a guideline for choosing appropriate processing conditions and predicting the effect of pressure and temperature of SC-CO2 on solute solubility.

Kinetics of butterfat crystallization

Fractionation of butterfat by melt crystallization is a commercial process in many countries for making butter fractions with varying melting, textural and flavor properties for use as food ingredients. However, the crystallization phenomena in this complex system are poorly understood and difficult to optimize and control. In this study, the crystallization kinetics of anhydrous butterfat were determined by cooling a melted sample to the final crystallization temperature in either a lab-scale (2 L) batch crystallizer or a pilot-scale (20 L) crystallization vessel. The butterfat was cooled sequentially from an initial temperature of 60°C to final temperatures of 30, 20 and 15°C at a constant cooling rate. Crystals formed at each temperature were separated by vacuum filtration, with the liquid cooled to the next crystallization temperature. Nucleation rates were determined by counting the number of crystals in a given volume of suspension during the course of crystallization. Crystal growth rates were obtained from image analysis of optical photomicrographs. Changes in viscosity, turbidity and mass of crystals also were determined. Effects of impeller velocity (75, 100 or 125 rpm) on the crystallization kinetics were determined. Nucleation and mass deposition rates increased while crystallization lag times decreased with increasing agitator velocities. Growth rates increased with agitator rpm at 20 and 15°C, but decreased with agitator rpm at 30°C, indicating different growth mechanisms. At 20 and 30°C, aggregation was the primary mechanism of crystal growth, whereas little aggregation was observed at 15°C. Crystallization at the larger scale, 20 L, showed only minor differences.

A kinetic analysis of crystallization of a milk fat model system

Abstract Crystallization behavior of milk fat, pure triacylglycerol (TAG) fraction of milk fat and three blends of 30, 40 and 50% of high-melting fraction (MDP=47.5°C) in low-melting fraction (MDP=16.5°C) of milk fat were studied by turbidimetry and nuclear magnetic resonance (NMR). Nucleation behavior was similar for these systems. In all cases, curves of log of induction time vs. temperature were continuous, which means that when samples were crystallized from the melt, only one polymorphic form was obtained at all temperatures. X-ray patterns verified formation of the β′ form. The calculated activation free energies of nucleation were quite low, but close to the ones published for other fats systems, such as hydrogenated sunflower oil. Only a low supercooling was needed to start crystallization. When isothermal crystallization was studied by NMR, the same behavior was also found for all samples. For low supercooling (crystallization temperatures above 25°C), curves had sigmoidal shapes with a period of induction of crystallization at the beginning. For high supercooling (temperature below 25°C), no induction times were observed as crystallization occurred rapidly. An intermediate plateau in SFC was clearly visible in all curves. The step in this plateau decreased steadily both in rate and height as Tc was increased. The curves were interpreted with the Avrami kinetic model, and parameters Kn and n were calculated. In all cases, the best fit was obtained by setting n to 3. Kn was, on average, 10 times lower above 25°C.

Scraped Surface Heat Exchangers

Scraped surface heat exchangers (SSHEs) are commonly used in the food, chemical, and pharmaceutical industries for heat transfer, crystallization, and other continuous processes. They are ideally suited for products that are viscous, sticky, that contain particulate matter, or that need some degree of crystallization. Since these characteristics describe a vast majority of processed foods, SSHEs are especially suited for pumpable food products. During operation, the product is brought in contact with a heat transfer surface that is rapidly and continuously scraped, thereby exposing the surface to the passage of untreated product. In addition to maintaining high and uniform heat exchange, the scraper blades also provide simultaneous mixing and agitation. Heat exchange for sticky and viscous foods such as heavy salad dressings, margarine, chocolate, peanut butter, fondant, ice cream, and shortenings is possible only by using SSHEs. High heat transfer coefficients are achieved because the boundary layer is continuously replaced by fresh material. Moreover, the product is in contact with the heating surface for only a few seconds and high temperature gradients can be used without the danger of causing undesirable reactions. SSHEs are versatile in the use of heat transfer medium and the various unit operations that can be carried out simultaneously. This article critically reviews the current understanding of the operations and applications of SSHEs.