Frozen milk concentrate

Surplus milk is commonly stored as frozen skim milk and whole milk concentrate and used as ingredients in ice cream and other formulated food products. There has also been some interest in producing frozen milk concentrates to substitute for pasteurized and sterile fluid milk products (Webb 1970). 

The major defect, which limits exploitation of frozen milk concentrates as consumer products, is the instability of the casein micelle system (Keeney and Kroger 1974 Morr 1975). The casein micelles gradually destabilize during storage of the frozen milk concentrate. 

Several compositional and processing variables affect the physical stability of the casein micelles in frozen milk concentrates. These factors include pH, mineral composition, total solids content, forewarming treatment, homogenization and fat content, freezing rate, storage temperature, and fluctation of storage temperature (Keeney and Kroger 1974 Webb 1970). 

In frozen milk products, lactose crystallization causes instability of the casein system. On freezing, supersaturated solutions of lactose are formed e.g. in concentrated milk at -8°C, 25% of the water is unfrozen and contains 80 g lactose per 100 g, whereas the solubility of lactose at — 8°C is only about 7%. During storage at low temperatures, lactose crystallizes slowly as a monohydrate and consequently the amount of free water in the product is reduced. 

The crystallization of lactose in frozen concentrated milk has been associated with a denaluration of casein which ultimately appears as a gel structure in the thawed product. Gelation in frozen milk can be retarded by enzymic hydrolysis of pan ol the lactose before freezing or by addilion of a polyphosphate salt. 

Lonergan, D.A., Fennemma, O., and Amundson, C.H. 1982. Use of Electrodialysis to improve the protein stability of frozen skim milks and milk concentrates. J. Food Sci. 47, 1429-1434. 

Several years ago the enzyme industry looked at the cheese industry and saw lactase as a big opportunity. Besides the lactose crystallization problem in frozen and concentrated milk products, the enzyme industry saw another potentially big profit application. Over half of the cheese whey produced in making cheese is diverted to waste treatment or waste disposal systems rather than being processed for food and feed use. Upgrading cheese whey became the hot development item for the enzyme industry. 

Cows milk is more salty than milk from human mothers, and this limits its use in the preparation of infant formula. Desalting of cows milk by ED allows larger quantities of cows milk solids to be used for these purposes. Research has shown that desalting by ED to remove calcium improved the protein stability of frozen skim milk and its concentrates.7 The lumpy texture of thawed frozen milk has been attributed to clumping of micellar casein, and calcium removal led to the dissociation of micellar to serum casein. 

Cryodestabilization of casein limits the commercial feasibility of frozen milk, which may be attractive in certain circumstances. However, cryode-stabilized casein might be commercially viable, especially if applied to milks concentrated by ultrafiltration, which are less stable than normal milk. Cryodestabilized casein may be processed in the usual way. The product is dispersible in water and can be reconstituted as micelles in water at 40°C, The heat stability and rennet coagulability of these micelles are generally similar to those of normal micelles and casein produced by cryodestabilization may be suitable for the production of fast-ripening cheeses, e.g. Mozzarella or Camembert, when the supply of fresh milk is inadequate. As far as we are aware, casein is not produced commercially by cryodestabilization. 

Milk and egg products are highly desired in pet foods since they supply the highest quaHty amino acid profiles with nearly 100% digestibiHty. Most milk protein concentrates are used for human foods, but some are available to pets (see Milk and milk products). An enormous quantity of whole eggs (qv) derived from egg graders, egg breakers, and hatchery operations are handled as dehydrated, Hquid, or frozen ingredients. 

Other frozen dairy products. Although milk may become frozen inadvertently, freezing is not a common commercial practice. However, concentrated or unconcentrated milks are sometimes frozen commercially, e.g. to supply remote locations (as an alternative to dried or UHT milk), to store sheep s or goats milk, production of which is seasonal, or human milk for infant feeding in emergencies (milk banks). 

Constituent Ultrafiltrate of skim milk Ultrafiltrate of liquid portion of frozen concentrated milk... 

Tumerman, L., Fram, H. and Comely, K.W. (1954) The effect of lactose crystallization on protein stability in frozen concentrated milk. J. Dairy Sci., 37, 830-9. 

Detectable concentrations of various antibacterials in milk attained by different microbiological tests are presented in Table 27.2. Milk constitutes a matrix that, apart from heating to destroy natural inhibitory substances, does not generally necessitate further sample treatment. Some antibiotics, however, exhibit some instability to heat treatment (54-56) and, therefore, if further confirmation is required reference frozen samples should always be available. When raw milk is directly analyzed, critical evaluation is generally required because natural inhibitors such as somatic cells, immunoglobulins, and metabolites may cause zones of inhibition (56, 57). Furthermore, several factors including marked pH-devia-tions, use of paper disks that contain inhibitory substances, and work with forceps that are too hot or have not been cleaned properly can readily lead to falsepositive readings (56, 58). 

Stability. Some discussion regarding stability of milk lipases was presented in the preceding section. Egelrud and Olivecrona (1973) found that the enzyme fractions from heparin-Sepharose can be stored frozen at -20°C with less than 10% loss of activity in 2 weeks. The purified enzyme had only moderate stability at 4°C high concentrations of salt or a pH below 6.5 or above 8.5 increases the rate of inactivation. 

Lonergan, D. A. 1978. Use of electrodialysis and ultrafiltration procedures to improve protein stability of frozen concentrated milk. Ph.D. dissertation, University of Wisconsin, Madison. 

The third group of compounds are the naturally occurring benzodiazepines. Desmethyldiazepam has been isolated from human brains which were stored frozen in the 1930s, at least two decades before the benzodiazepines were developed. While there is no evidence that the benzodiazepine structure can be synthesized enzymatically in the mammalian brain, several other compounds of this type have since been isolated from cattle brain and from human breast milk. One possibility is that gastrointestinal flora can partially synthesize the benzodiazepine molecule and it is also known that plants such as wheat and potatoes are a potential source of diazepam, desmethyldiazepam and lormetazepam. If it is eventually shown that the local brain concentration of these benzodiazepines is sufficiently high to activate the benzodiazepine receptors then the possibility arises that anxiety disorders could result from a lack of these endozepines. 

When certain fruits, such as mangos and peaches, are in season, I buy them at their best taste and lowest price, let them get nice and ripe, and store them in packets in the freezer. Many stores also stock bags of frozen fruits and berries. I keep frozen orange juice and red grape juice concentrate handy as well. Egg substitute is an excellent protein source to balance the meal s nutritional profile. If your smoothie comes out thicker than you d like, just add more milk, water, or juice to thin it out to your preference. 

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