Proteins for foods, in addition to providing nutrition, should also possess specific functional properties that facilitate processing and serve as the basis of product performance. Functional properties of proteins for foods connote the physicochemical properties which govern the behavior of protein in foods. This general article collates the published information concerning the major functional properties of food proteins, e.g., solubility, binding properties, surfactant properties, viscogenic texturizing characteristics, etc. The effects of extraction and processing on functional properties and possible correlations between structure and function are discussed, in relation to practical performance in food systems. Modification of proteins to improve functional characteristics is briefly mentioned.

Functional properties of proteins in foods: A survey

Nomenclature of the Proteins of Cows’ Milk—Sixth Revision

Rennet-coagulated cheeses are ripened for periods ranging from about two weeks to two or more years depending on variety. During ripening, microbiological and biochemical changes occur that result in the development of the flavour and texture characteristic of the variety. Biochemical changes in cheese during ripening may be grouped into primary (lipolysis, proteolysis and metabolism of residual lactose and of lactate and citrate) or secondary (metabolism of fatty acids and of amino acids) events. Residual lactose is metabolized rapidly to lactate during the early stages of ripening. Lactate is an important precursor for a series of reactions including racemization, oxidation or microbial metabolism. Citrate metabolism is of great importance in certain varieties. Lipolysis in cheese is catalysed by lipases from various source, particularly the milk and cheese microflora, and, in varieties where this coagulant is used, by enzymes from rennet paste. Proteolysis is the most complex biochemical event that occurs during ripening and is catalysed by enzymes from residual coagulant, the milk (particularly plasmin) and proteinases and peptidases from lactic acid bacteria and, in certain varieties, other microorganisms that are encouraged to grow in or on the cheese. Secondary reactions lead to the production of volatile flavour compounds and pathways for the production of flavour compounds from fatty acids and amino acids are also reviewed.

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Biochemistry of Cheese Ripening

Nomenclature of Proteins of Cow's Milk: Fifth Revision

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

Reduced-fat cheese (17% fat, 44% moisture) was considerably firmer and more elastic than full-fat cheese (35% fat, 35% moisture), even though the moisture levels in the nonfat matter (MNFM) of the cheese were the same, at 54%. Electron microscopy and compositional analysis revealed about 30% more protein matrix in the reduced-fat cheese. Apparently more of this matrix must be cut or deformed in sensorial and texture assessments. A practical implication is that MNFM should be slightly higher in the reduced-fat cheese than in full-fat cheese to achieve more similar texture.



Homogenization of milk tended to increase the moisture content and decrease firmness and elasticity, but not markedly. The smaller fat globules, per se, did not apparently affect texture as measured in these experiments. Curd granule junctions were prominent in nonhomogenized-milk cheese, because large fat globules were lost at the granule surfaces leaving protein-dense junctions; those in homogenized-milk cheese were less apparent because the protein-dense areas, which resulted from the loss of small fat globules, were narrower.



Sensory and textural parameters for firmness and elasticity were inter-correlated. The Bite Test was more useful than Instron measurements of deformation (20%), apparently because the latter was markedly affected by a slight openness in the cheese.

Milk gel structure. x. texture and microstructure in cheddar cheese made from whole milk and from homogenized low-fat milk

Influence of Volatile and Nonvolatile Fractions on Intensity of Cheddar Cheese Flavor

Physical and Sensory Properties of Yogurt Stabilized with Milk Proteins

The effects of 3 different thickening agents on the microstructure of yoghurt were examined by scanning and transmission electron microscopy. Unsupplemented yoghurt consisted of casein micelles fused together and linked in long chains; they seldom appeared in clusters. The addition of 0·5% gelatin caused no observable change in the yoghurt structure. Carrageenan (0·4%) formed a markedly fibrillar microstructure which connected large clusters of casein micelles. The fibres were thin and long and no free terminations were observed. Pregelatinized waxy maize starch (2%) appeared under scanning electron microscopy in the form of short fibres and sheets. The fibres frequently had free terminations and only some of them were connected with small clusters of casein micelles. Transmission-electron microscopy did not distinguish between pregelatinized starch and carrageenan additives.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022029900015491

D.B. Emmons

Papers

Milk gel structure. x. texture and microstructure in cheddar cheese made from whole milk and from homogenized low-fat milk

Influence of Volatile and Nonvolatile Fractions on Intensity of Cheddar Cheese Flavor

Physical and Sensory Properties of Yogurt Stabilized with Milk Proteins

Milk-gel structure. IV. Microstructure of yoghurts in relation to the presence of thickening agents

Properties of whey protein concentrate prepared by heating under acidic conditions