Imitation cheeses containing 3% native maize, waxy-maize, wheat, potato or rice starch were manufactured and the microstructure, meltability, texture and dynamic rheology of these products were compared to a control (0% starch). Fat globules in starch-containing products (except potato) were smaller than in the control as evidenced by electron microscopy. All starches reduced meltability and cohesiveness of the imitation cheeses. Hardness was increased by wheat, potato or maize starch but reduced by waxy-maize or rice starch. Starches significantly reduced tan ␦ peaks compared to the control with potato starch having the greatest effect. Rice starch appears to have the most potential as a partial casein substitute in imitation cheese.

Imitation cheese was manufactured with various levels of pre-gelatinized maize starch. Melt characteristics were assessed by an empirical melt test, based on the Olson and Price method. Using dynamic rheology, the storage modulus (G9), the loss modulus (G0) and the loss angle (tan d) were measured as a function of temperature (22-100°C). Meltability decreased with increasing levels of starch. Maximum tan d values and the temperature at which they occurred decreased with increasing starch levels. A high correlation (r 2 = +0.96) was found between the maximum tan d values and meltability as assessed by the empirical method. Tan d may be a useful indicator of imitation cheese meltability.

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The ability of alphas1/beta-casein and micellar casein to protect whey proteins from heat-induced aggregation/precipitation reactions and therefore control their functional behavior was examined. Complete suppression (>99%) of heat-induced aggregation of 0.5% (w/w) whey protein isolate (pH 6.0, 85 degrees C, 10 min) was achieved at a ratio of 1:0.1 (w/w) of whey protein isolate (WPI) to alphas1/beta-casein, giving an effective molar ratio of 1:0.15, at 50% whey protein denaturation. However, in the presence of 100 mM NaCl, heating of the WPI/alphas1/beta-casein dispersions to 85 degrees C for 10 min resulted in precipitation between pH 6 and 5.35. WPI heated with micellar casein in simulated milk ultrafiltrate was stable to precipitation at pH>5.4. Protein particle size and turbidity significantly (P

-This work investigated the effect of transglutaminase on (1) micellar casein (phosphocasein) suspensions at pH 6.7; (2) gel formation at pH 4.6; and (3) viscosity of the subsequently produced sodium caseinates. Micellar casein (25 g protein·kg -1 in simulated milk ultrafiltrate, pH 6.7) was incubated with and without 1% microbial transglutaminase (Tgase) at 40°C for 5-60 min, prior to thermal inactivation (78°C × 30 min). The particle size of micellar casein incubated with Tgase (mean between treatments of 213 nm) was not markedly different from the control micellar casein (195 nm), indicating very little inter-micellar cross-linking. Heat stability was markedly improved at pH > 6.8 following incubation with Tgase. When Tgase was not inactivated prior to acidification gels were markedly stronger. The maximum in casein hydration (pH 5.2-5.5) and tan δ (pH 5.0) were eliminated by the action of Tgase indicating a loss of casein mobility. In the absence of Tgase, a sodium caseinate suspension had a low apparent viscosity of 7.6 mPa·s (100 s -1 ) with Newtonian behaviour, low turbidity (A 600nm = 0.28 and an ethanol stability of 530 mL·L -1 ). Sodium caseinate could not be produced where the Tgase was active during the acidification step. Sodium caseinate made from micellar casein treated with Tgase (5 min) showed increased viscosity (64.6 mPa·s at 100 s -1 ), turbidity (A 600nm = 1.37) and ethanol stability (621 mL·L -1 ). With the exertion of proper control, Tgase can improve some of the functional properties of micellar casein or its sodium caseinate derivative.high viscosity / sodium caseinate / transglutaminase / milk protein Résumé -Influence de la transglutaminase sur les propriétés de la caséine micellaire et de ses produits dérivés. L'effet de la transglutaminase sur (1) des suspensions de caséine micellaire (phosphocaséine) à pH 6,7; (2) la formation de gel à pH 4,6; et (3) la viscosité du caséinate de sodium obtenu par la suite, était étudié. La caséine micellaire (25 g protéine·kg -1 dans un ultrafiltrat de lait simulé, pH 6,7) était incubée en présence ou non de 1 % de transglutaminase (Tgase) d'origine microbienne à 40 °C pendant 5-60 min, avant inactivation thermique (78 °C × 30 min). La taille des particules de caséine micellaire incubée avec la Tgase (moyenne de 213 nm entre traitements) n'était pas considérablement différente de celle du contrôle de caséine micellaire (195 nm), indiquant de très faibles liaisons inter-micellaires. La stabilité thermique était considérablement améliorée à pH > 6,8 après incubation avec la Tgase. Quand la Tgase n'était pas inactivée avant acidification, les gels étaient considérablement plus forts. Les maxima d'hydratation de la caséine (pH 5,2-5,5) et tan δ (pH 5,0) étaient éliminés par l'action de la Tgase indiquant une perte de mobilité de la caséine. En absence de Tgase, une suspension de sodium de caséinate avait une faible viscosité apparente de 7,6 mPa·s (100 s -1 ) avec un comportement Newtonien, une faible turbité (A 600nm = 0,28) et une stabilité à...

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