Effect of urea on the heat coagulation of the caseinate complex in skim-milk

Muir, D. D.; Sweetsur, A. W. M.

doi:10.1017/s0022029900020173

Cited by 54 publications

(35 citation statements)

References 21 publications

(2 reference statements)

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“…2 (a) show the effect of added urea (5-20 HIM) on the HCT-pH curve of skim-milk at 140 °C; the results are basically similar to those of Muir & Sweetsur (1977) and are included for comparative purposes. Biuret, triuret, methyl urea and ethyl urea had essentially the same effect on the HCT-pH curve as urea and were about equally effective at equimolar concentrations.…”

Section: Resultsmentioning

confidence: 71%

“…A significant positive correlation between the heat stability at 120 °C of bulk milk at its natural pH and the level of non-protein nitrogen (NPN) was shown by Robertson & Dixon (1969) and addition of small amounts of urea, the predominant component of the NPN fraction, to milk was shown to increase its heat stability. Subsequent work (Muir & Sweetsur, 1976, 1977Muir, Abbot & Sweetsur, 1978;Holt, Muir & Sweetsur, 19786) confirmed the stabilizing influence of urea on unconcentrated milks particularly at pH values around the heat coagulation time (HCT)-pH maximum and has shown that natural variations in urea concentration are responsible for most of the variation in the heat stability of bulk milks. However, the heat stability of concentrated milk was not influenced by addition of small amounts of urea .…”

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confidence: 95%

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Effect of selected amides on heat-induced changes in milk

Fox

Nash

Horan

et al. 1980

Journal of Dairy Research

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The effect of 15 amides and related compounds on the heat stability of milk was investigated; of these urea, biuret, triuret, methyl urea and ethyl urea had a similar stabilizing effect. These 5 compounds reacted with lysine to form a ninhydrin-positive compound, possibly homocitrulline, and with lactose produced Maillard-type browning, but some of the other compounds studied were also capable of participating in one or both of these reactions. The only effect which the 5 stabilizing amides had in common and which the other compounds did not share was a significant pH-buffering capacity in synthetic systems and in milk. It is suggested that urea exercises its stabilizing influence in milk principally through its ability to buffer the pH of the system during heating.Addition of 002 % (3-6 mM) or 0-05 % (8-4 mM) urea to milk before heating increased its coagulation time from 35 to 62 and 104 min respectively (Pyne, 1958). A significant positive correlation between the heat stability at 120 °C of bulk milk at its natural pH and the level of non-protein nitrogen (NPN)

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Section: Resultsmentioning

confidence: 71%

mentioning

confidence: 95%

Effect of selected amides on heat-induced changes in milk

Fox

Nash

Horan

et al. 1980

Journal of Dairy Research

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“…Among the numerous characteristics of milk that may influence matured chee se properties, urea content, which depends mainly on nitrogen balance of the diet (Journet et al, 1975;Oltner et al, 1985;Vérité et al, 1995) seems to play an important role (Gravert et al, 1990;Martin and Coulon, 1995). An increase in milk urea content leads to partial dissociation of ail casein components, calcium and phosphate, into the soluble phase (Muir and Sweetsur, 1977;Ali et al, 1980;Dalgleish et al, 1987) and decreased milk clotting ability (Mariani et al, 1992). Sorne authors show that urea inhibits activity of starter culture (Podhorsky and Cvak, 1989) and modifies fresh cheese's chemical composition (Guinot-Thomas, 1992).…”

Section: Introductionmentioning

confidence: 99%

Effect of milk urea content on characteristics of matured Reblochon cheeses

Martin¹,

Coulon

Chamba

et al. 1997

Lait

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Summary -According to a crossed experimental design, two groups of 14 Montbéliarde dairy cows received in the winter two hay-based diets, with a normal or a high nitrogen level, obtained by substituting in the diet 2.5 kg of soybean meal to 2.5 kg of cereal concentrate. During the last week of the two experimental periods of 3 weeks, four batches of Reblochon cheese were manufactured with three different milks: control milk, milk from soya-fed cows and control milk with 0.25 gIL of added urea. Twenty-four batches were manufactured under identical conditions with full fat raw milk. A high nitrogen level diet increased milk urea content, which rose from 0.24 to 0.49 g/L, and decreased the protein content slightly. Rennet clotting time and curd firming time were slightly higher in the high nitrogen level. Milk fat, casein, total and soluble Ca and P were not modified by the diet. A high milk urea content, whether it cornes from addition to milk or from feeding, leads to a lower acidification rate in mould and at demoulding to moister ripened cheeses. Nitrogen fractions, pH, and Ca content of cheeses were not modified by milk urea content. While eating, compared with control cheeses, cheeses from soya-fed cows were significantly less firm, less pasty, less chalky. Their taste was creamier, less acid and sweeter. Cheeses from added urea milk were close to cheeses from soya-fed cows in their chemical composition and texture, and to control cheeses in their tas te. This suggests that milk urea, whether it cornes from addition to milk or from feeding, influences directly acidification kinetics, chemical composition and texture characteristics of matured cheeses, however, urea is not directly involved in taste differences. diet nitrogen levell milk urea 1 cheese 1 Reblochon 1 sensory characteristic Résumé -Effet de la teneur du lait en urée sur les caractéristiques des reblochons affinés. Deux lots de 14 vaches laitières de type Montbéliardes ont reçu au cours de l'hiver, selon un dispositif expérimental croisé, deux régimes à base de foin avec un niveau d'apports azotés normal (C) ou élevé (S) obtenu en substituant 2,5 kg de tourteau de soja à 2,5 kg de céréales dans la ration. A huit reprises, des reblochons ont été réalisés dans des conditions technologiques contrôlées et identiques * Correspondence and reprints 506 B Martin et al d'une fabrication à l'autre, à partir de trois laits différents: lait des animaux recevant le régime C, lait des animaux recevant le régime S et lait C dans lequel 0,25 g/L d'urée a été ajouté (lait AU). Le régime S a provoqué une augmentation de la teneur du lait en urée, qui est passée de 0,24 g/L (régime C) à 0,49 glL et une légère détérioration du taux protéique et de l'aptitude à la coagulation. Comparativement aux fromages C, les fromages S ont été significativement moins fermes, moins pâteux, moins plâtreux, plus crémeux, moins acides et plus doux. Les fromages AU se rapprochent des fromages S en ce qui concerne leur composition chimique et leur texture et des fromages C en ce qui con...

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“…There is a seasonal variation in the ratio, P-1actoglobulin:casein (e.g. Muir et al 1978) but this appears to be related to lactational rather than dietary factors. The manipulation of milk protein content and composition is reviewed by Thomas (1983).…”

Section: I '0mentioning

confidence: 99%