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Rheological properties of actomyosin gels were markedly affected by protein concentration, pH and heating temperature. Gel strength increased with increasing protein concentration (30-60 mg ml(-1)) and heating temperature (55-75°C), but decreased with increasing pH (5·5-9·0). Low heating temperatures (50-55°C) favoured the formation of more cohesive actomyosin gels than the higher heating temperatures (60-75°C). Gels formed at low pH (5·5 and 6·0) were less cohesive than those formed at high pH (7·5-9·0). Addition of ATP and pyrophosphate (10 mm) prior to heating decreased gel strength and cohesiveness, whereas EDTA (1-5 mM) reduced gel strength but did not affect gel cohesiveness.

This chapter summarises the bovine milk protein system and describes methods for the commercial production of dehydrated bovine milk protein-enriched food ingredients. Selected functional properties and biological activities of these ingredients are presented. In addition, this chapter describes various applications for these milk protein-enriched ingredients in food and nutraceutical products.

In the absence of added NaCl, electrostatic repulsion prevented thermal gelation of β-lactoglobulin, pH 8.0, but added propylene glycol or urea supported weak gel structure formation. When the electrostatic barrier was reduced by added NaCl, gelation occurred and gel strength was enhanced by propylene glycol addition and reduced by added urea, N-ethylmaleimide or merceptoethanol. Cohesiveness of β-lac-toglobulin gels containing NaCl decreased on adding propylene glycol, mercaptoethanol or N-ethylmaleimide but increased on adding urea. Relative to cohesiveness, elasticity/springiness was higher following N-ethylamleimide or mercaptoethanol addition but lower following urea addition. Molecular forces involved in gel structure formation and maintenance were proposed based on observed effects.

Surface activities at the air-water interface and the emulsifying and foaming properties of sodium caseinate, conventional casein-whey protein co-precipitate prepared from milk heated at 90°C × 15 min at pH 6.6 and milk protein isolates prepared from milks heated at 90°C × 15 min at pH 7.5 or at 60°C × 3 min at pH 10.0 were determined. The surface activities of the four proteins at the air-water interface were similar, while the emulsifying capacity and emulsion stabilizing ability of casein was less than that of the milk protein isolates or the conventional co-precipitate. Fat surface areas formed on emulsification with the four proteins were similar and increased with increasing power input. Total protein adsorbed at the interface and protein load (mg protein/m2 fat) for the emulsions stabilized by sodium caseinate and the milk protein isolate prepared from the milk heated at 90°C × 15 min at pH 7.5 were similar and lower than those for emulsions stabilized by the other two proteins. Foam overruns followed the order: sodium caseinate > milk protein isolate prepared from milk heatedat90°C × 15min, pH 7.5 > milk protein isolate prepared from milk heated at 60°C × 3 min, pH 10.0 > conventional co-precipitate, while foam stabilities followed the reverse order.

As a recipient of the Robert Wood Johnson's Pipeline, Profession, and Practice: Community-Based Dental Education grant, the Extramural Education Program (EEP) at the University of Illinois at Chicago College of Dentistry was charged with developing partnerships with community-based oral health programs throughout Illinois. These programs are to be used for clinical service-learning rotations for fourth-year dental students, relying on the utilization of the dentists employed at the community site as preceptors for the students. Because the College of Dentistry had essentially no community-based service-learning experiences prior to the Robert Wood Johnson grant, procedures and protocols needed to be developed to standardize a process for site and preceptor selection. An administrative process was developed to engage, recruit, and partner with community-based oral health programs that provided direct clinical services. This article will discuss the development of criteria used to select sites and preceptors for extramural clinical rotations; the development of a set of standardized assessment instruments; and the credentialing process for community-based adjunct faculty that leads to the affiliation agreements. These community-based rotations have been integrated into the College of Dentistry curriculum as a required extramural service-learning course referred to as Extramural Clinical Experience (DADM 325).

The effects of increasing levels (0–1.0 mol/dm3) of protein-structuring (chloride, NaCl; sulfate, Na2SO4) and -destructuring anionic ions (thiocyanate, NaSCN) on rheological properties and electron microstructures of protein gels were examined. The effects of the ions varied with concentration and species. At concentrations above 100 mM they enhanced gel strength in the order SCN− > Cl− > SO42−. The hardness of gels increased with increasing concentrations up to 0.1, 0.2 and 1.0 mol/dm3 with SO42−, Cl− and SCN− respectively. Electron microstructures of the gels showed that distribution of the protein in the gel matrix became less ordered with increasing ion concentration.

The hydration related properties of sodium casemate, conventional casein-whey protein co-precipitate preparedfrom milk heatedat 90°C × 15 min at pH 6.6 and milk protein isolates prepared from milk heated at 90°C × 15 min at pH 7.5 or at 60°C × 3 min at pH 10.0 were determined. Conventional acid-precipitated casein and the acid-precipitated protein isolates preparedfrom milks heated at pH >7.0 had similar solubilities and reconstitution properties which were better than those of a conventional co-precipitate. Water sorption isotherms for all the proteins were similar. Viscosities followed the order: conventional co-precipitate > milk protein isolates > sodium caseinate.

The surface-active properties of myosin, actomyosin, F- and G-actin at the air-solvent interface, at initial bulk phase concentrations in the range of 10 − 4 % to 10 − 2 % w/v, were determined by the drop volume method. Overall myosin was the most effective surface tension depressor, followed by actomyosin, F-actin and G-actin. The surface pressures attained after 40 min at an initial bulk phase concentration of 10 − 2 % w/v were 21·02, 19·27, 17·25 and 14·91 mNm − 1 , respectively. Furthermore, myosin effected the most rapid change in surface pressure during the initial 5-min period.

Bovine milk contains ~13% solids, which include fat, lactose, protein, and organic and inorganic salts. Normal milk contains ~3.5 g total protein per 100 ml which falls into two main categories based on solubility at pH 4.6 at >~8°C. Under these conditions ~80% of the total nitrogen precipitates and this fraction is referred to as casein, while ~20% remains soluble in the serum or whey, ~15% being whey proteins with the remainder being non- protein nitrogenous components. As discussed in Chapter 1, both the casein and non-casein fractions are heterogeneous; casein includes four principal primary proteins (gene products), αs1-, αs2-, β- andκ-caseins, and several minor proteins, while the non-casein fraction includes β-lactoglobulin, α-lactalbumin, blood serum albumin, immunoglobulins. casein-derived proteose peptones, several minor proteins, including lactotransferrin, and several enzymes. The characteristics of the caseins and whey proteins differ very significantly (Table 26.1).

1 ABSTRACT A wide range of calcium-sequestering salts is available for use in cheese analogues and processed cheese manufacture. The effects of different calcium-sequestering salts, at equimolar concentrations, on the rheological behaviour of rennet casein during hydration in a simple model system were studied. The degree of protein hydration and solubilisation varied with the calcium-sequestering abilities of the salts. Hydration and solubilisation of rennet casein in the weak calcium-sequestering salt, trisodium citrate, was very limited and a dense cheese-like mass formed. In disodium orthophosphate greater hydration to form a curd-like mass of high viscosity index was observed. More effective calcium-sequestering salts such as pentasodium polyphosphate resulted in rapid solubilisation of the protein to give a solution with a low viscosity index, while disodium pyrophosphate and tetrasodium polyphosphate-based dispersions showed intermediate behaviour. The pH of the dispersions also influenced the hydration behaviour of the casein. At the low pH (6.38) of monosodium orthophosphate-based dispersions rennet casein remained as discrete particles, while at the higher pH (>9.0) of trisodium orthophosphate-based dispersions the casein was solubilised. The cation of the calcium-sequestering salt also influenced the hydration behaviour of the rennet casein. The effects of the different salts on the hydration of rennet casein in the model system are discussed in relation to their influence on functional properties such as texture and meltability of cheese analogues and processed cheeses prepared using the salts.

1 ABSTRACT Rennet casein is insoluble in water but can be hydrated in warm calcium-chelating salt solutions. Once hydrated the casein can emulsify fats or oils and when cooled the mix sets to give a matrix similar in texture to cheese and which is referred to as analogue cheese. Considerable variation has been observed in the performance of commercial rennet caseins in the manufacture of cheese analogues. Commercial caseins exhibiting a range of functional performances have been obtained and are being examined to establish possible causes of this variation in functional performance. A simplified model system of the analogue cheese making process has been devised; this involves hydrating a rennet casein in a solution of a chelating salt at 55 °C with stirring. The rheological changes that occur as the rennet casein hydrates have been followed using a controlled shear rate rheometer fitted with a purpose designed paddle stirrer. Hydration of the rennet casein particles takes place in a number of stages including swelling, aggregation, network formation and breakdown. Considerable variation was observed between casein samples in swelling times, time taken to reach maximum viscosity, maximum viscosity reached and stability of the hydrated caseins. The rheological characteristics of the rennet caseins during hydration were strongly influenced by the concentration of chelating salt in the hydrating solution.

Whey is the serum liquid portion remaining after removal of fat and casein from milk during the manufacture of cheeses and caseins. Traditionally, whey was regarded in the dairy industry as an undesirable by-product and it was either fed in limited quantities to farm animals or treated as effluent, disposed of as a pollutant into streams and rivers, or irrigated onto pastures. However, environmental awareness led to the imposition of strict controls on the disposal of waste whey which necessitated the construction and operation of costly effluent treatment plants for whey treatment prior to disposal. This, together with a recognition that whey was a potentially valuable source of nutrients, stimulated interest in the development of commercially viable processes to convert liquid whey into viable animal and human food products.

Milk was intended to supply nutrients and other important molecules to the neonatal mammal. Since there are approximately 4000 species of mammal, with different nutritional and physiological requirements, milks show very wide variations with respect to the nature and concentration of their constituents. However, the milks of only a few species have been thoroughly studied; not surprisingly, these include human milk and those of the principal species used for commercial milk production, i.e. cow, goat, sheep and buffalo.

Casein is very soluble at pH values Sorption isotherms of acidic caseins and sodium caseinate were similar up to Aw values of 0·52. Between Aw values of 0·52 and 0·87 sodium caseinate showed a greater increase in water uptake than acidic caseins, while at Aw values of 0·87–0·97 water uptake of acidic caseins increased more sharply than that of sodium caseinate, uptake being in the order acidic casein pH 2·0 > acidic casein pH 2·5 > acidic casein pH 3·0 > sodium caseinate pH 7.0.

Approximately 95% of available nitrogen can be precipitated from milk on adjustment to pH 4.6 after heating at 90°C × 15 minutes at its natural pH and pH 7.5, while 89% can be precipitated after heating at pH 10.0 at 60°C × 3 minutes. Non-recovered protein includes some serum albumin, β-lactoglobulin, α-lactalbumin and proteose peptones. Protein isolates precipitated from milk heated at pH >7.0 are more soluble in the pH range 6.0–7.0 than those precipitated from milk heated at its natural pH. Whey proteins complex onto the casein micelles after heating milk at its natural pH, while on heating at pH >7.0 whey proteins appear to interact with k-casein in the serum phase. When N-ethylmaleimide is present in milk during heating the percentage protein recovered on pH 4.6 precipitation is decreased, confirming that disulphide linkage is involved in complex formation. However, addition of β-mercaptoethanol to recovered isolates did not result in dissociation of the casein/whey protein complex, suggesting that forces other than disulphide bonding are also involved in maintaining the complex.

Skim milk and mixtures prepared by combining acid whey with skim milk at volume ratios of 2:1, 1:1, 1:2, 1:3 and 1:4 were adjusted to pH 7.5 and heated at 90°C × 15 min. Protein was isolated from these heated samples by precipitation at pH 4.6 and it was found that 65% of the whey protein was recovered in each case. Non-recovered proteins included the proteose peptones and small quantities of β-lactoglobulin, α-lactalbumin and bovine serum albumin. The solubility of these isolates, which contained from 10–25% whey protein, decreased to > 95% when the whey protein exceeded ˜16%. Further characterization of the isolate, prepared from the 1:1 volume ratio of acid whey and skim milk, showed that ˜50% of the whey protein was insoluble, bound to casein and non-functional while the other ˜50% was complexed with casein and was soluble. The addition of a reducing agent suggests that sulphydryl bonding alone is not responsible for complex formation.

The effects of pH and thermal denaturation on the surface active properties of muscle proteins at the air-solvent interface were determined by the drop volume method. The surface pressures attained after 40 min, π 40 , by myosin and actomyosin solutions heated at 45°C for 30 min were similar to those attained by the unheated protein solutions. However, the π 40 values were increased when the proteins were heated at 60°C prior to determining surface activity. The rate of surface tension decay was much faster following heating of myosin at 45°C compared with the unheated sample. Myosin heated at 60°C showed an initial induction period, which was followed by a very rapid rate of surface tension decay. The rate of surface tension decay for actomyosin heated at 45°C was similar to that of the unheated protein solution: however, heating at 60°C increased the rate compared to that of the control. The surface pressures attained after 40 min ( π 40 ) by myosin and Factin solutions were not significantly affected by the pH of the solutions. However, π 40 values for both G-actin and actomyosin were greater at pH 11·0 than at pH 5·6 or 7·0. For all the proteins studied, pH greatly affected the rates of surface tension decay, the rates being slowest at pH 5·6 and fastest at 11·0.

The effects of vaious reagents on the rheological properties of heat-induced (90°C) gels formed from plasma protein solutions (pH 9.0) were studied. Both propylene glycol (5–20%, w/v) and ethanol (5–20,%, w/v), which enhance hydrogen and electrostatic interactions, increased gel compressive strength, whereas mercaptoethanol (25–100 mM) which reduces disulfides, and the sulfhydryl-blocking agent, p-hydroxymcrcuribenzoate (25–100 mM), reduced gel strength. High levels of guanidine hydrochloride (> 1M) or urea (> 2M), which weaken both hydrogen and hydrophobic interactions, decreased gel strength. On the basis of the results, we conclude that hydrophobic interactions and hydrogen and disulfide bonding are involved in the gelation of plasma proteins.

SUMMARYThe proteins of bovine milk are the best-characterized food-protein system. Lactoproteins, which have high biological value, contribute ∼25% of dietary protein in North West Europe, North America and Oceania. However, in protein-rich western diets, milk proteins are frequently more highly valued for their functional properties than for their nutritional qualities. The remarkably high heat stability of the caseinate system permits the manufacture of a range of sterilized, concentrated and dehydrated products while its gelation on very limited proteolysis is the basis of cheese manufacture. Skim-milk powders, caseinates and whey protein concentrates are the most flexible and widely used functional proteins in food processing.This communication reviews recent studies on milk proteins with respect to molecular and colloidal properties; coagulation by Ca2+, heat and ethanol; and functional properties and their chemical and enzymic modification.

The emulsifying capacity of casein was dependent on pH, decreasing from 325 to 264 g oil/g protein as pH increased from 1·5 to 3·5 and increasing from 251 to 268 g oil/g protein between pH 5·5 and 7·0; above pH 7·0 emulsifying capacity increased sharply to ∼ 700 g oil/g protein at pH 8·5. The emulsifying capacity of sodium caseinate increased on addition of NaCl, up to 1 m , or CaCl2, up to 20 m m , while the emulsifying capacity of acidic casein (pH 2·5) increased on addition of NaCl, up to 5 m m , or CaCl2, up to 5 m m and thereafter decreased on further addition of either. The creaming stability of emulsions prepared in acidic casein increased as the pH increased from 2·0 to 3·0. Foaming capacities of caseins were in the order, acidic casein pH 2·0 > acidic casein pH 2·5 > sodium caseinate pH 7·0 > acidic casein 3·0, while foam stabilities were in the opposite order. Addition of NaCl, up to 20 m m , or CaCl2, up to 10 m m , decreased foam capacity of acidic casein (pH 2·0) but increased foam stability.

Heating β-lactoglobulin solutions at pH 8 causes an increase in viscosity, but self-supporting gels were not formed unless salts, such as sodium chloride or calcium chloride, were added. The rheological and textural properties and gel strength were markedly affected by salt concentration. Thus, gels of maximum compressive strength were obtained with sodium chloride and calcium chloride at concentrations of 200 and 10mM, respectively. Increasing the concentration of sodium chloride resulted in the formation of soft gels which released water easily. Calcium chloride strengthened β-lactoglobulin gels by forming crossbridges. However, above 10 mM it tended to enhance coagulation rather than gelation. This was confirmed by election microscopy of the gel matrix.

The rheological properties of plasma protein gels were markedly affected by protein concentration, pH, heating temperature and time and measuring temperature. Gel strength increased with increasing protein concentration (6–18%), pH (4·0–9·0), heating temperature (60–90°C) and time (15–60 min), but decreased with increasing measuring temperature (10–60°C). The ability of gels to recover following cyclic loading and unloading was low in the pH region 4·0–6·0, but increased at higher pH. Recovery increased with increasing measuring temperature, but decreased at heating temperatures above 75°C and with increased duration of heating (15–60 min).

SummaryPorcine and bovine pepsins were very stable in 5·0 M-urea at pH 2·0 or 2·5 at 30 °C while chymosin and Mucor miehei and M. pusillus proteases were rapidly denatured under these conditions. These differences may provide the basis of a quantitative assay of the complement of individual milk clotting enzymes in a coagulant and a possible scheme is suggested.

The interfacial properties of proteins extracted from muscle using salt solutions of different concentration and for different extraction times were determined by the drop volume method. At a bulk phase concentration of 10 −2 wt%, it appears that the sarcoplasmic-rich fraction of muscle is more surface active than the salt-soluble fraction. The average equilibrium surface pressure at the air-liquid interface was 21·5 mN m −1 for an aqueous extract and 20·1 mN m −1 for a 1 m KCl-extract. The equilibrium surface pressure decreased from 21·7 mN m −1 to 19·50mN m −1 as the extraction time with Weber-Edsall solution increased from 15 min to 48 h.

Added salts influenced the rheological properties of heat-induced plasma protein gels. Gel strength increased in the presence of 0·01 m added CaCl 2 and 0·02 m added MgCl 2 . However, gel strength was reduced at higher concentrations of these salts. The ability of plasma protein gels to recover following deformation was lower than for the control (no added salt) in the presence of 0·02–0·1 m added CaCl 2 and MgCl 2 , but gel cohesiveness was markedly higher. The strength of plasma protein gels formed in the presence of added potassium salts was in the order F − >SO 2− 4 >Cl − >I − >SCN − . These salts had similar effects on gel cohesiveness and gumminess. KF and K 2 SO 4 decreased gel recoverability following deformation; KI and KSCN increased recoverability, while KCl had little effect. The study suggests that hydrophobic interactions and electrostatic forces play an important role in the formation and stabilisation of plasma protein gels.

Summaryβ-Casein, was enzymically modified by incubation with plasmin to yield γ-caseins and proteose peptones. Whole γ-, γ1-, γ2/γ3-caseins and whole proteose peptone (pp) were isolated from the hydrolysate mixture. The time dependence of surface tension at the air-water interface of solutions of β-casein and its plasmin derived fragments, at concentrations of 10−1 to 10−4% (w/v) protein, pH 7.0, was determined, at 25 °C, using a drop volume apparatus. The ranking of the proteins with respect to rate of reduction of surface tension, during the first rate determining step, at 10-2% (w/v) protein, was γ2/γ3 ≫ pp > whole γ- > γ1- > β-casein. The ranking of the proteins with respect to surface pressures attained after 40 min (π40) was concentration dependent. γ2/γ3-Caseins were found to be very surface active, decreasing surface tension rapidly and giving a high π40. γ1 Casein decreased surface activity somewhat faster than β-casein, but generally reached a lower π40. Whole γ-casein reflected the properties of both γ1 and γ2/γ3-caseins. Proteose peptone was found to decrease surface tension rapidly during the initial rate determining step; it gave a relatively high π40 at a bulk phase concentration of 10−3% (w/v) protein, but, it was the least surface active protein at 10−1 and 10−2% (w/v) protein.

Piglet gastric proteinase was weakly proteolytic on bovine α s1 -casein. Preliminary experiments indicate that this enzyme might be satisfactory for the manufacture of cheese in which the milk-coagulating enzyme is not actively proteolytic against the major caseins, but further confirmatory work is needed.

The surface active properties of myosin and its proteolytic fragments, light meromyosin (LMM), heavy meromyosin (HMM), subfragment-1 (S-1) and myosin rod, at initial bulk phase concentrations in the range of 10−4% to 10−2% w/v were determined by the drop volume method. Overall, S-1 was the most effective surface tension depressor, whereas the tail portions of myosin, i.e. LMM and myosin rod were less surface active than the parent myosin molecule. The surface pressures attained after 40 min, at an initial bulk phase concentration of 10−2% (w/v), were 22·00, 21·77, 21·02, 16·77 and 16·77 mNm−1 for S-1, HMM, myosin, LMM and myosin rod, respectively. Furthermore, S-1 effected the most rapid change in surface pressure during the initial 5 min period.