Publisher Summary Hydration can be considered a process of adding water incrementally to dry protein, until a level of hydration is reached beyond which further addition of water produces no change and only dilutes the protein. The hydration process has several stages and an end point, reflected similarly in different types of measurements. Time-average measurements appear to have a common pattern and most closely fit a single picture of the process. Dynamic measurements sometimes show a dependence on hydration level that lies outside the common pattern of the time-average results. The chapter summarizes the literature that bears on the protein hydration process and the hydration shell, categorized by type of measurement, and provides picture of the hydration process and the hydration shell and an assessment of the ways in which the hydration shell may modulate enzyme and other protein functions. The percolation model is discussed that focuses on the long-range connectivity established at a threshold coverage of a surface or volume with conducting or otherwise functional elements.

Protein hydration and function.

There is abundant information concerning the functional behavior of whey proteins in model systems. The data on functional properties reported by different researchers, however, reveal wide discrepancies in values. For example, in the case of comparable whey preparations, apparent solubilities may range from 10 to 100%; strength of gels from 0.3 to greater than 10 N, foam overruns from 250 to 1500%, and foam stabilities from 0.5 to 30 min. Many of the data are of limited value in assessing the true functional characteristics of different preparations, treatments, or processing effects. Reports to date are useful in indicating the relative behavior of different proteins; however, the data do not always predict the performance of such proteins in actual food systems. This reflects the fact that in foods, extensive interactions with other components may occur, resulting in modified behavior of the proteins. Harper, (1984) has advocated the testing of these various preparations in simulated food systems which should validly relate the behavior to performance in commercial systems. Emphasis on standardization of specific protocols, with regard to order of addition in ingredients, temperature, pH control, and amount of energy input during mixing, homogenization, emulsification, etc. deserves serious consideration. While this approach is justifiable in terms of providing valuable data to commercial users, it does not minimize the importance of examining these proteins in model systems where the physicochemical basis of each functional attribute can be described in molecular terms (Kinsella, 1987). Such information is necessary to expedite appropriate methods of processing in order to control compositional variability, extent of denatauration, and possible protein modification. In addition, rapid, reliable tests for routine quality assurance that can provide practical information concerning functional applications would be of great value. Whey protein preparations vary immensely in functional behavior and are presently relegated to limited use as functional ingredients in the food industry. This need not be the case since conventional and new technologies permit rigorous control of production protocols, e.g., careful control of heat treatments can result in the production of whey protein preparations with consistent, reliable functional properties (deWit, 1981, 1984; Harper, 1984; Morr, 1985). As the market for functional proteins continues to expand, the whey industry must seek the means to refine whey protein products; determine useful functional properties; develop standardized manufacturing protocols; demonstrate the effectiveness of whey as a functional ingredient; promote, and then market, whey on the basis of performance at competitive cost.

Proteins in whey: chemical, physical, and functional properties

Because of the growing trend toward widespread use of protein ingredients in food formulation and fabrication, an understanding of the relationships between the physical properties of proteins and their behavior in food systems is desirable. A range of milk-derived protein preparations, i.e., dry milk, milk proteins, caseins, whey proteins, and lactalbumin, are used in a range of food products for their specific functional attributes. In this paper some of the apparent relationships between the properties of the protein components and specific functional properties are discussed. Thus, the roles of milk proteins in determining some important physical characteristics (i.e. color, bulk density, sinkability, dispersibility) of milk powders and their involvement in a range of functional properties (water holding, solubility, rheological behavior, gelation, film formation, emulsification, and foaming) are reviewed. Because of the various methods and conditions used in determining functional properties and the variability in composition of preparations it is difficult to compare data and/or reconcile differences in published information. The desirability of developing standard methods is emphasized.

Milk proteins: physicochemical and functional properties

Substantial progress has been made in understanding the basic chemical and structural properties of the principal whey proteins, that is, beta-lactoglobulin (beta-Lg), alpha-lactalbumin (alpha-La), bovine serum albumin (BSA), and immunoglobulin (Ig) This knowledge has been acquired in terms of: (1) procedures for isolation, purification, and characterization of the individual whey proteins in buffer solutions; and (2) whey fractionation technologies for manufacturing whey protein concentrates (WPC) with improved chemical and functional properties in food systems This article is a critical review of selected publications related to (1) whey fractionation technology for manufacturing WPC and WPI; (2) fundamental properties of whey proteins; and (3) factors that affect protein functionality, that is, composition, protein structure, and processing

Whey protein concentrates and isolates: Processing and functional properties

Rheological Properties of Foods, H. Dogan and J. L. Kokini Reaction Kinetics in Food Systems, R. Villota and J. G. Hawkes Phase Transitions and Transformations in Food Systems, Y. H. Roos Transport and Storage of Food Products, M.A. Rao Heating and Cooling Processes for Foods, R. P. Singh Food Freezing, D. R. Heldman Mass Transfer in Foods, B. Hallstroem, V. Gekas, I. Sjoeholm, and A. M. Romulus Evaporation and Freeze, K. R. Morison and R. W. Hartel Membrane Concentration of Liquid Foods, M. Cheryan Food Dehydration, M. R. Okos, O. Campanella, G. Narsimhan, R. K. Singh, and A. C. Weitnauer Thermal Processing of Canned Foods, A. Teixeira Extrusion Processes, L. Levine and R. C. Miller Food Packaging, J. M. Krochta Cleaning and Sanitation, E. A. Plett and A. Grasshoff Appendix Index

Handbook of food engineering

Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-lactoglobulin, α-lactalbumin, serum albumin, γ-globulin, apo- and Fe-lactoferrin, lysozyme, ribonuclease, α-chymotrypsin and xanthine oxidase. Denaturation enthalpies (ΔHD), denaturation temperatures (TD) and the half width of the denaturation peaks in DSC thermograms (ΔT½D) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (α-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturation.

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A calorimetric study of the thermal denaturation of whey proteins in simulated milk ultrafiltrate

Hydration and thermal denaturation of β-lactoglobulin. A calorimetric study

Hydration of Ca and Na caseinates which were prepared from whole casein at different pH levels (range 4·7–8·0) was determined by means of water vapour sorption measurements in the water activity (aw) range 0·58–0·95. Water uptake of Ca caseinates was systematically lower than that of Na caseinates prepared at equal pH, the differences increasing with increasing pH and aw. Plots of the water content ν. the amount of added hydroxide at constant aw revealed a linear relationship between water uptake and cation content, suggesting that the increase in water uptake is mainly determined by the amount and type of cations associated with the caseins. In the aw range tested, Ca2+ adsorbed about 2–7 and Na+ 3–18 mol water/mol of cation. This implies that replacement of one mol of casein-bound Na+ by Ca2+ is accompanied by a displacement of 1–11 mol water at aw 0·58–0·95. The loss of water is a consequence of conformational changes induced by the chelating and cross-linking effects of Ca2+, which also lead to micelle formation.

Effect of calcium on the hydration of casein. I. Water vapour sorption and fine structure of calcium caseinates compared with sodium caseinates in the pH range 4·6–8·0

U. Moor

Papers

A calorimetric study of the thermal denaturation of whey proteins in simulated milk ultrafiltrate

Hydration and thermal denaturation of β-lactoglobulin. A calorimetric study

Effect of calcium on the hydration of casein. I. Water vapour sorption and fine structure of calcium caseinates compared with sodium caseinates in the pH range 4·6–8·0

Fine structure changes of Gruyere cheese during ripening. A study with scanning electron microscope.

2.1. Hydration and Thermal Stability of a-Lactalbumin. A Calorimetrie Study