Lactose Free Milk ; It's A Wonderful Thing.

Have you ever had a cup of regular milk, and ended up feeling gassy, bloated, having abdominal cramps, or rumbling stomach that discomforts you? If these symptoms occur every time you have milk or other certain dairy product, you probably have lactose intolerance. Being a lactose intolerant means that your body does not produce sufficient amount of lactase to hydrolyse lactose into it’s monomer of glucose and galactose. It is an emulsion of tiny droplets of fat globules and suspension of casein micelles, all of which are suspended in an aqueous phase. Lactose is a natural carbohydrate in milk and in every 100 grams of cow's milk contains approximately 4.8 g of lactose. Being a primary sugar in cow’s milk, lactose is the second most dominant component of gross cow’s milk composition of about 4.9 % , right after water at 87.7 %. Other components that makes up milk is fat, protein and minerals. Milk composition will vary depending on the species, breed, animal’s feed and the stage of lactation. However, the raw milk is collected in bulk storage tanks and will provide a relatively constant composition of milk all year round. Milk contains 3.4 % of total fat that is composed of approximately 65% saturated, 30% monounsaturated, and 5% polyunsaturated fatty acids .  Approximately 82 % of milk protein is composed of casein and the remaining is whey protein. Milk contains  water soluble vitamin B and C. Fat soluble vitamins A, D, E and K are dependent on the fat content of the final milk product.

So, if lactose is the major sugar in regular milk, does this mean lactose intolerant will have to stop consuming milk ? Worry not ! This is because recent technologies has made consumption of milk for people having difficulties to breakdown lactose possible. Dairy manufacturers such as Lactaid, Valio and Liddels has innovated the production of lactose free milk. Do the lactose inside the milk is taken out, or something is added into the milk to breakdown the lactose?. The latter is however technologically feasible and is opted by most manufacturers. The whole manufacturing process is the same as that of regular milk, with an extra step of adding external enzyme either free or immobilised lactase enzyme to hydrolyse the lactose molecule into glucose and galactose inside the milk.

Example of processing line of lactose free milk production

According to the United States patent number US4007283A, the enzyme beta-D-galactoside-galactohydrolase with the numerical designation of E.C. 3.2.1.2.3 is also known as lactase. Once the raw milk enters the system, it will pass through a storing unit where it is held at a low temperature of lower than 4.4 °C. Next it will be warmed up to 37 °C if desired prior to centrifugation for separation, clarification and standardization. During this step, fat may be added or removed and non-fat milk solids may be added or removed to achieve the desired milk fat content required for the end product (1%, 2%, or 3.25%). Subsequently, the lactase enzyme is added to catalyse the hydrolysis of the lactose in the milk. For example, in amount equal to about 0.03 percent of the weight of raw milk. Then it will be stored at a storing unit and held at a temperature lower than 4.4 °C. The milk with added enzyme will flow through a heat exchanger unit for pre-heating the milk to 60 °C before it is passed to a holding unit where commercial thermal treatment of high temperature short time (HTST) of milk is employed. The temperature is about 63 °C and holding time is about 15 s to accomplish pasteurisation. The preheating step is carried out prior to HTST treatment to slowly raise the temperature to ensure the stability of the lactase enzyme thus optimally functioning to hydrolyse lactose in the milk. For milk, the pasteurized milk will move to packaging operation. This method is one of the two methods to produce lactose free milk. Another method is by treating milk for ultra high temperature treatment, at a temperature of not less than 135 °C for at least 2 s to render it commercially sterile. It is then cooled to ambient temperature at which sterile filtered lactase is added and the product is sterile packed. The lactase is allowed to react with lactose in the milk until the enzymatic reaction stops when the substrate has depleted. The end product of lactose free milk will taste sweeter than regular milk because the enzymatic hydrolysis breaks down lactose into galactose and glucose, which the latter is about five times sweeter than lactose. Finnish regulation requires lactose free milk to contain maximum of 0.01 % lactose while according to Malaysian Food Regulations 1985, regulation 96, lactose hydrolysed milk shall not contain more than 1.25 percent of lactose.

Lactase is commercially synthesised from bacteria and various strains of lactose-fermenting yeasts including Kluyveromyces fragilis, with a pH optimum of 6.5-7.0, suitable for the treatment of milk. Method of producing lactase by K. fragilis is commonly used and the isolated and purified lactase readily hydrolyse lactose in milk and milk products. However, lactase from yeast has a relatively lower stability towards thermal treatment. Another source of lactase that is used in the dairy industry to decrease lactose content in milk is from limited strains of bacteria from genera Lactobacillus and Bifidobacterium. Lactobacilli isolated from fermented milk product produces lactase in a significant amount but is thermostable thus giving better yields at higher temperature. Novozymes A/S produced lactase enzyme by submerged fermentation of a Bacillus licheniformis and commercially marketed as Saphera. It is used as a processing aid during manufacture of lactose free UHT milk.

In a nutshell, commercial lactose free milk is no different than regular milk except that it has very low percentage of lactose content due to the addition of lactase enzyme during the processing. Lactase will aid the break down of lactose into glucose and galactose, making it safe to be consumed by all especially those that are intolerance to lactose without feeling discomforted.