Gregory R. Ziegler

The gelation of proteins

Publisher Summary This chapter describes the process of the gelation of proteins. Gelation is a phenomenon; therefore, its definition and that of its product, a gel, is dependent on the perspective of the observer and the technique(s) used to observe it. For example, gels may be defined by their ability to immobilize a liquid, their macromolecular structure, or their textural or rheological properties. The chapter reviews a variety of protein gel systems with a broad perspective stressing similarities between them, yet not without mentioning the important differences that make each unique. It describes the multicomponent protein gels. The rheological and optical properties of thermally irreversible gels are the outcome of two events. First, a change in protein structure is needed that permits protein–protein interactions. The subsequent aggregation process, which is highly influenced by the solvent environment, may produce the gel microstructure, which is responsible for the optical and rheological properties. The physical integrity of a gel is maintained by counterbalancing forces of attraction and repulsion among polymer molecules and between the polymer network and the surrounding solvent

Protein functionality in food systems

Structure-Function Relationship of Food Proteins Solubility of Proteins - Protein-Salt-Water Interactions Protein Separation and Analysis of Certain Skeletal Muscle Proteins - Principles and Techniques Computer-Aided Techniques for Quantitative Structure Activity Relationships Study of Food Proteins Protein Interactions in Emulsions: Protein-Lipid Interactions Protein Interactions in Foams - Protein-Gas Phase Interactions Protein Interactions in Gels - Protein-Protein Interactions Protein-Polysaccharide Interactions Chemical and Enzymatic Modification of Proteins for Improved Functionality Functionality of Soy Proteins Whey Protein Functionality Color as a Functional Property of Proteins Protein Gel Ultrastructure and Functionality Proteins as Fat Substitutes Edible Films and Coatings from Proteins.

Fat, Moisture, and Ethanol Migration through Chocolates and Confectionary Coatings

The migration of fat, moisture, and ethanol is a common problem with chocolate-coated confectionery products. Migration of one of these components into the coating leads to visual and sensory defects such as sugar or fat bloom, making the product unacceptable to the consumer. The migration rate depends on the structure and composition of the coating. The migration of each of these species can be slowed to a certain extent by proper tempering of the coating, because proper tempering will give a structure that resists migration. In the continuous lipid phase, these chemical species migrate mainly through the liquid portion. Thus, the migration rate depends on the amount of liquid oil present in the product. Migration can be delayed either by reducing the liquid fat content or by immobilizing the liquid phase. The actual mechanisms for the migration processes are speculative, and a more thorough understanding is necessary to better abate quality deterioration. Armed with this understanding, a manufacturer would know a priori the effect of changing the ingredient or process. A few methods for control have been suggested, but have found limited application. Mathematical models have been proposed to predict the migration behavior, but their application is hindered because of the simplified assumptions employed. There is a need for developing better models that combine mass transfer with the phase behavior to be able to accurately predict the migration process. This review discusses the current understanding of fat, moisture, and ethanol migration through chocolate coatings and also includes a brief description of the theoretical aspects governing migration.

Role of Molecular Entanglements in Starch Fiber Formation by Electrospinning

We have demonstrated a method of fabricating pure starch fibers with an average diameter in the order of micrometers. In the present study, correlation between the rheological properties of starch dispersions and the electrospinnability was attempted via the extrapolation of the critical entanglement concentration, which is the boundary between the semidilute unentangled regime and the semidilute entangled regime. Dispersions of high amylose starch containing nominally 80% amylose (Gelose 80) required 1.2-2.7 times the entanglement concentration for effective electrospinning. Besides starch concentration, molecular conformation, and shear viscosity were also of importance in determining the electrospinnability. The rheological properties and electrospinnability of different starches were studied. Hylon VII and Hylon V starches, containing nominally 70 and 50% amylose, respectively, required concentrations of 1.9 and 3.7 times their entanglement concentrations for electrospinning. Only poor fibers were obtained from mung bean starch, which contains about 35% amylose, while starches with even lower amylose contents could not be electrospun.

THE ROLE OF PARTICLE SIZE DISTRIBUTION OF SUSPENDED SOLIDS IN DEFINING THE SENSORY PROPERTIES OF MILK CHOCOLATE

The melting of chocolate in the mouth is a dynamic process. The time evolution of the perceived flavor and texture of chocolate during fat melting and sugar dissolution has been observed and quantified using time-intensity sensory methodology. Five milk chocolates varying in particle size distribution and rheology were prepared. Additionally, two chocolates varying in particle size were standardized to the same viscosity. Particle size and rheology significantly influenced effort, thickness, chocolate and sweetness attributes, although in some unanticipated ways. Averaging time-intensity responses to produce consensus curves generally yielded the same conclusions as averaging parameters extracted from individual curves. However, the later were amenable to statistical analysis using ANOVA and partial least squares regression. Multivariate analysis was a useful technique for identifying those physical properties most correlated with sensory perception.

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.

Antioxidant property of edible mushrooms collected from Ethiopia.

Two cultivated (P. ostreatus and L. edodes) and five wild (L. sulphureus, A. campestris, T. clypeatus, T. microcarpus and T. letestui) edible mushrooms were analyzed for their antioxidant activities, total phenolics, total flavonoids, phenolic profile and ergothioneine content. Results showed that A. campestris had the greatest antioxidant activity in all assays with lower EC50 (mg/ml) values of 1.4, 3.6 and 0.035 for scavenging, reducing and chelating activities, respectively. To correlate well with activities, A. campestris also exhibited greater total phenolics and total flavonoids content of 14.6 mg GAE/g and 1.97 mg CE/g, respectively. The maximum concentration (μg/g) of the individual phenolic compounds were 7.80 (P. ostreatus) for caffeic acid, 4.55 (T. letestui) for chlorogenic acid, 15.8 (T. microcarpus) for p-coumaric acid, 20.3 (A. campestris) for ferulic acid, 561.9 (A. campestris) for gallic acid, 38.7 (A. campestris) for p-hydroxybenzoic acid and 7.08 (A. campestris) for myricetin. All samples tested contained different amounts of ergothioneine ranging from 0.08 (L. sulphureus) to 3.78 (P. ostreatus) mg/g in dry weight.

Quantitative relationship between electrospinning parameters and starch fiber diameter.

The diameter of the starch fibers produced by electrospinning is a key parameter for most potential applications. In this study, a quantitative relationship between fiber diameter and certain electrospinning parameters, i.e. starch concentration, applied voltage, spinning distance and feed rate, was established by empirical modeling using a fractional factorial experimental design in a constrained region. Response surface methodology was employed to analyze the interactions of the electrospinning parameters and predict the direction to minimize and maximize the fiber diameters.

Residence time distribution in a co-rotating, twin-screw continuous mixer by the step change method

Residence time distributions were determined for the continuous processing of chocolate in a twin-screw, co-rotating mixer, and modeled using as a series combination of piston flow and ideal mixing elements or as equal size tanks in series. Color (L-value) was measured after a step change from milk chocolate to white chocolate. Both models fit the data well, although the series combination of piston flow and ideal mixing fit better for short mean residence times, accurately predicting the observed deadtime. The series of tanks model appeared to fit data better under conditions where longer mean residence times were observed. The mean residence time was significantly influenced by feed rate, screw speed and gate opening. A high shear, low conveyance screw configuration was used that led to a high fill fraction (>0.85). Therefore, feed rate had the greatest effect on the mean residence time. The time of first appearance was affected only by the gate opening, and ranged from 0.44 to 0.68 times the mean residence time.

Chemical and thermal characteristics of milk-fat fractions isolated by a melt crystallization

Anhydrous milk fat (AMF) was fractionated by a two-stage dry fractionation process to produce three fractions: high melting (HMF), middle melting (MMF), and low melting (LMF). The HMF (m.p. 42°C) exhibited a broad melting range similar to a plastic fat. The MMF (m.p. 33°C) resembled the original AMF (m.p. 31°C), but with slightly higher solid fat content. The LMF (m.p. 16°C) was liquid at ambient temperature. Differences in the thermal properties of these fractions were attributed to the triacylglycerols (TAG) and their fatty acid composition. Saturated TAG with carbon numbers of 36–54 were concentrated in the HMF; whereas unsaturated TAG of carbon number 36–54 predominated in the LMF. Likewise, the long-chain saturated fatty acids were significantly higher and the long-chain unsaturated fatty acids were significantly lower in the HMF fraction. Binary blends of milk-fat fractions with a range of melting profiles were produced by mixing HMF with AMF, MMF, or LMF. Laboratory-prepared fractions were similar to commercially available fractions.