Ultrahigh- temperature (UHT) processing fresh whole- and semi-skimmend milk from Europe
 
       
               
                   
 
- UHT Milk Products. Brand: "Baba" -

 

HDPE is known for its large strength-to-density ratio. The density of HDPE can range from 0.93 to 0.97 g/cm3 or 970 kg/m3. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously). High-density polyethylene, unlike polypropylene, cannot withstand normally required autoclaving conditions.

- Fresh UHT whole milk and UHT semi skimmed milk -
1000 ml, 500 ml and 250 ml / Tetra Pak and PET bottles

UHT processing It is inevitable that heating a product such as milk at temperatures up to ~140°C will have some effect on its constituents, in addition to the intended bactericidal effects. Furthermore, storage at room temperature for long periods of time (up to 12 months) causes additional effects.

To consumers used to drinking pasteurised milk which differs little in flavour from raw milk, UHT milk often appears to have a cooked or heated flavour. Modern UHT technology minimises the production of this flavour but most consumers can still detect it and it is one reason why many consumers prefer pasteurised milk. The typical flavour of UHT milk is due a combination of flavours, the chief of which are sulphurous flavours caused by volatile sulphur compounds released from the whey protein, and the proteins in membrane surrounding the milk fat globule. Other contributors are the aliphatic carbonyl compounds formed during heating and compounds formed in the Maillard reaction. Immediately after manufacture, UHT milk has a strong sulphurous smell and taste due to hydrogen sulphide and other volatile sulphur compounds such as methane thiol. These compounds are markedly reduced in the first week, presumably through oxidation.

OEM - UHT flavoured milk drinks made from semi skimmed fresh milk

The whey proteins , particularly β-lactoglobulin which forms about 50 per cent of these soluble proteins in milk, are denatured by heating over about 70°C so that in UHT milk, a large percentage of the whey proteins are in the denatured state and exist largely as complexes with caseins. The instability of the whey proteins to heat has another consequence during UHT processing. Some whey protein denatures and attaches to the surfaces of the heat exchangers in proteinaceous deposits which obstruct the flow of milk and can eventually cause the plant to be closed down for cleaning. However, this is not the only type of deposit formed during UHT processing. At high temperatures, above about 110°C, calcium phosphate also precipitates on the walls, adding to the ‘fouling' caused by the whey proteins

Surprisingly, the UHT process has only a minimal effect on the nutrient value of milk. There is a small decrease in the water-soluble vitamins but virtually no change in the fatsoluble vitamins. The proteins, in fact, have been shown to be more digestible in UHT milk as a result of the heat treatment11. UHT treatment may also reduce the allergenicity of the milk proteins. Milk is a highly perishable food so to enable it to be stored and distributed for consumption without spoilage, and without being a health risk through growth of pathogenic bacteria, it is heat treated. The most common type of heat treatment in many parts of the world is pasteurisation, which is performed at a minimum of 72°C for 15 seconds. This is the least heat treatment needed to destroy most pathogenic microorganisms and it also destroys most spoilage organisms. However, a small number of bacteria remain after pasteurisation and packaging, and can grow during storage. Such growth is slow at low temperature and consequently pasteurised milk is always kept refrigerated. Even under refrigeration, pasteurised milk only keeps for about two weeks1.

One way of extending the shelf-life of milk is to heat it at temperatures high enough to destroy almost all microorganisms, and then store it in sealed containers without contamination by bacteria. There are two ways in which this can be carried out: in-container sterilisation and ultrahigh- temperature (UHT) processing. Both produce a ‘commercially sterile' product which means the milk does not contain microorganisms which can grow under the normal conditions of storage which, in this case, is room temperature. In-container sterilisation, which uses canning technology, is a batch operation which involves heating the final containers of milk in an autoclave at 110-120°C for 10-20 minutes. By contrast, UHT processing involves heating the milk in a continuous flow system at about 140°C for a very short time – around five seconds. While the two procedures have the same microbiological effect they have very different chemical effects on the milk constituents. In-container sterilised milk typically has a marked cooked flavour and a slight brownish colour. On the other hand, UHT milk has much less cooked flavour and very little, if any, brown discolouration.

 

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