Preserving nutrients in milk via UHT

Preserving nutrients in milk via UHT

Made Astawan, Jakarta, astawan@indo.net.id

Milk is the best food for land mammals because it contains an almost perfect composition of nutrients, such as water, protein, carbohydrates, minerals, fat, along with sufficient amounts of vitamins A, C and D.

Today, unlike decades ago, it is seldom that milk is consumed fresh, straight from a cow. Generally, in liquid form, it is processed either via UHT or pasteurization treatment or is made into a powder form.

Pasteurization basically means heating milk to between 63 and 720 C for about 15 seconds to kill the pathogen bacteria. Pasteurized milk has to be refrigerated at around 50 to 70 C and this milk is good for only about 14 days.

Powdered milk, meanwhile, is derived from fresh milk combined with or without other ingredients, such as fat or protein, which is dried using the spray or roller dryer method.

This type of long-life milk can be kept for a maximum of two years if stored correctly. There are three categories of powdered milk: Full cream milk powder, composite skim milk powder and skim milk powder.

Finally, there is Ultra High Temperature (UHT) milk. UHT heats milk at between 1350 and 1450 C for about two to five seconds to kill all of the microorganisms while at the same time not disrupting the nutritional ingredients of the milk, including the color, aroma and taste.

Factors that contribute to the quality of UHT milk include the cow feed, the composition of the raw milk, and the milking and packaging process that must be hygienic.

At the factory, processing is conducted using highly sophisticated sterile tools to minimize milk's contact with bacteria. Multi-layer packaging is used in the milk cartons to prevent any bacteria and damaging ultra violet rays from entering the package.

These safeguards ensure the freshness and quality of UHT milk as required by international hygienic standards. Besides being free from bacteria, the UHT process makes it possible for the milk to be stored for a long time without preservatives and with no refrigeration, for up to 10 months after production, which is much longer than pasteurized milk. Once the pack is opened however, the milk must be stored in a refrigerator for further use.

Some tips on checking UHT Milk

UHT Milk in cartons can go bad if there is a leak in the package. An easy way to check this is to see if the pack is bloated or 'puffed'. This is the result of microbes entering the damaged pack, fermenting the milk, causing CO2 to be released, thus causing the pack to bloat.

Avoid consuming UHT milk which appears thick of lumpy - bacteria which has infected the milk causes coagulation leading to a break-up of proteins and a decrease of organic acid.

Damage to the product can of course be easily detected by its smell and taste. One precaution to be borne in mind is storing UHT milk in very high temperature - above 50 degree centigrade - as this causes the milk to go sour quickly.

--- the writer is a senior lecturer on Food and Nutrition at the Bogor Farming Institute (IPB)