Acidified milks

Experiments on interactions of polysaccharides with casein micelles show similar trends to those with casein-coated droplets. For example, Maroziene and de Kruif (2000) demonstrated the pH-reversible adsorption of pectin molecules onto casein micelles at pH = 5.3, with bridging flocculation of casein micelles observed at low polysaccharide concentrations. In turn, Tromp et al. (2004) have found that complexes of casein micelles with adsorbed high-methoxy pectin (DE = 72.2%) form a self-supporting network which can provide colloidal stability in acidified milk drinks. It was inferred that non-adsorbed pectin in the serum was linked to this network owing to the absence of mobility of all the pectin in the micellar casein dispersion. Hence it seems that the presence of non-adsorbed pectin is not needed to maintain stability of an acid milk drink system. It was stated by Tromp et al. (2004) that the adsorption of pectin was irreversible in practical terms, i.e., the polysaccharide did not desorb under the influence of thermal motion. 

Sejersen, M.T., Salomonsen, T., Ipsen, R., Clark, R., Rolin, C., Engelsen, S.B. (2007). Zeta potential of pectin-stabilized casein aggregates in acidified milk drinks. International Dairy Journal, 17, 302-307. 

The so-called Ling oxalate titration indicates that CCP consists of 80% Ca3(P04)2 and 20% CaHP04, with an overall Ca P ratio of 1.4 1 (Pyne, 1962). However, the oxalate titration procedure has been criticized because many of the assumptions made are not reliable. Pyne and McGann (1960) developed a new technique to study the composition of CCP. Milk was acidified to about pH 4.9 at 2°C, followed by exhaustive dialysis of the acidified milk against a large excess of bulk milk this procedure restored the acidified milk to normality in all respects except that CCP was not reformed. Analysis of milk and CCP-free milk (assumed to differ from milk only in respect of CCP) showed that the ratio of Ca P in CCP was 1.7 1. The difference between this value and that obtained by the oxalate titration (i.e. 1.4 1) was attributed to the presence of citrate in the CCP complex, which is not measured by the oxalate method. Pyne and McGann (1960) suggested that CCP has an apatite structure with the formula ... 

U.S. federal standards have recently been established for several acidified fluid milk products that simulate such cultured products as acidified milk, acidified lowfat milk, and acidified skim milk (FDA 1981A). 

Acidified milks are made by souring the product with one or more acidifying ingredients, with or without the addition of characterizing... 

Bifidobacterium Fermentation. A unique form of lactic fermentation has been observed in members of the genus Bifidobacterium. These anaerobic bacteria are commonly found in the intestinal tract and feces of human infants and adults, as well as many animal species. Most Bifidobacterium spp. can acidify milk, and they produce acetic and lactic acids in an approximate 3 2 molar ratio when growing on glucose (Buchanan and Gibbons 1974). The Bifidobacterium fermentation (Fig-... 

Home, D.S. (1999). Formation and straeture of acidified milk gels vocabulary development and the relations between sensory properties. Ini. Dairy J. 9, 261-268. 

Sedlmeyer, F., Brack, M., Rademacher, B., and Kulozik, U. (2004). Effect of protein composition and homogenization on the stability of acidified milk drinks. Int. Dairy J. 14, 331 336. 

The pH value of the milk is critical in the occurrence of internal micellar fouling. There is in cation of membrane pore blockage when the milk pH is above 5.6. At a pH below 5.6, no internal micellar fouling is evident. This transition is also reflected in the permeate flux. For example, the permeate fluxes at a pH of 4.4 (acidified milk) and 6.62 (milk), under otherwise identical conditions, are 130 and 35 L/hr-m, respectively, for an 0.8 pm alumina membrane. 

FIGURE 21.19 Elemental configuration of EDBM cell used for skim milk solution, principles of CEM fouling formation, basified and acidified milk side microscopic photographs (magnitude x45) of EDBM CMX membrane. (Adapted from Bazinet, L., Montpetit, D., Ippersiel, D., Amiot, J., and Lamarche, F., J. Interface Colloid Sci., 237(1), 62, 2001.)... 

Attia, H., Bennasar, M., and Trodo de la Fuente, B., Study of the Fouling of Inorganic Membranes by Acidified Milks Using Scanning Electron Microscopy and Electrophoresis, J. of Dairy Research, 58 39-50 (1991)... 

Direct acidification with HCl or in situ production of lactic acid by a mesophilic lactic starter still dominate in the production of acid casein. A relatively recent development in the production of acid casein is the use of ion exchangers for acidification. In one such method, a portion of the milk is acidified to approximately pH 2 at 10°C by treatment with a strong acid ion exchanger and then mixed with unacidified milk in proportions so that the mixture has a pH of 4.6. The acidified milk is then processed by conventional techniques. A yield increase of about 3,5% is claimed, apparently due to the precipitation of some proteose-peptones. The resulting whey has a lower salt content than normal and is thus more suitable for further processing. The elimination of strong acid reduces the risk of corrosion by the chloride ion (Cl ) and hence cheaper equipment may be... 

Native casein. An exciting new development is the production of native casein. Few details on the process are available at present but it involves electrodialysis of skim milk at 10°C against acidified whey to reduce the pH to about 5 the acidified milk is centrifuged and the sedimented casein dispersed in water, concentrated by UF and dried. The product disperses readily in water and is claimed to have properties approaching those of native casein micelles. 

Strains for nse in dairy applications are examined for their ability to acidify milk at varions temperatnres in microtiter plates. The change in the pH of the milk is followed by the inclnsion of pH indicators (bromocresol pnrple and bromocresol green) in the milk and scanning on a flatbed scanner typically at 6-min intervals. The data are exported to a snitable spreadsheet such as Microsoft Excel (Microsoft Corporation, Redmond, WA, USA) for ease of calculation. Acidification curves are obtained, and descriptors like total pH drop, maximum acidification rate, and specific time intervals snch as time to acidify from pH 6.0 to pH 5.5 are easily derived in the spreadsheet. The formation of volatile organic compounds in the acidified milk is measured by head space gas chromatography, allowing quantitative assessment of the production of relevant metabolites such as acetaldehyde, acetoin, and 3-methyl-butanal. Tolerance to NaCl is also tested in milk by following the acidification in the presence and absence of 4% (w/v) NaCl. 

Kildegaard, H., Lpkke, M. M. and Thybo, A. K. (2011a) Effect of increased fruit and fat content in an acidified milk product on preference, hking and wanting in children, Journal of Sensory Studies, 26, 226-236. 

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