Ice cream, milk, cheese, yogurt, cream, butter and all other dairy products haunt the dreams of people with lactose intolerance. Over 68% of the world鈥檚 population has some degree of lactose malabsorption which is the inability to properly digest lactose, the sugar found in dairy products. Until the introduction of lactose-free milk, these unfortunate souls had to take Lactaid pills just to be able to indulge in some of their favourite treats. Lactaid is primarily composed of lactase, the enzyme that allows for the breakdown of lactose into its components glucose and galactose that are readily absorbed. Luckily, with lactose-free milk you can ditch the pills! But how is this special milk even made?
What is lactose?
Lactose is a disaccharide found in all dairy products, the prefix 鈥渄i鈥� indicates that it is composed of two monosaccharides glucose and galactose. Saccharides are carbohydrates that can exist as monomers, dimers, or polymers. Our digestive system is only capable of absorbing monomers, which is why we require so many enzymes to do all of the breakdown work. While glucose and galactose are readily absorbed in the small intestine, lactose isn鈥檛. It is too complex to be absorbed as is and therefore must be broken down by an enzyme called lactase. Lactase catalyzes the breakdown of lactose in the body and is produced naturally in the small intestine. Enterocytes line the intestinal walls and are the cells in charge of its production. These cells form what is called the 鈥渂rush border,鈥� which is the barrier through which all food must pass to be absorbed. Food will go through the gastrointestinal tract, reach the brush border and then, if it contains lactose, will be broken down by lactase and absorbed in the small intestine. Now, if this breakdown process malfunctions, undigested lactose will pass into the colon where it is fermented by bacteria. Fermentation produces gases that can cause bloating and pain. This is categorized as lactase deficiency, where lactase is either scarcely produced or absent in the body, leading to gastrointestinal problems and embarrassing runs to the washroom.
Lactose-free milk
But what if someone still enjoys enjoying dairy but can鈥檛 produce lactase? Luckily, pills are not always necessary. Thanks to the USDA Agricultural Research Service, since 1985, lactose-free milk has been integrated in many households affected by lactose intolerance. Since then, this product has been commercialized by Lactaid and sold by multiple other companies. There are no strict rules for these products. The main restriction is that the packaging of the products must not be 鈥渕isleading鈥�. Thus, if it is claimed to be 鈥渓actose-free鈥� it should not contain lactose, and if it is 鈥渓ow-dairy鈥� it should be a significant reduction from regular dairy products. How is this achieved? Lactose hydrolysis and membrane filtration processing.
Lactose hydrolysis
This is typically a 2-step process: pre-lactose hydrolysis and aseptic post-hydrolysis. First, during pre-lactose hydrolysis, neutral lactase is added to raw milk before pasteurization. The lactase does the initial breakdown of the lactose in the milk and the heat treatment will ensure that no residual enzyme remains in the milk. To reduce the sugar in the milk at this point, additional filtration is carried out. Then, during aseptic post-hydrolysis process, sterile lactase is added to milk. Aseptic post-hydrolysis uses higher incubation times and lower quantities of lactase, and the hydrolysis occurs directly in the package. Finally, to ensure the milk is completely lactose-free, an extra filtration sequence is often applied. In some cases, filtration can extend the shelf-life of milk (microfiltration). Essentially,聽lactose-free milk is made by exploiting natural biological lactose processing with ideal levels of lactase to completely break it down the milk sugar.
The Maillard Drawback
It is common to notice that lactose-free milk tastes sweeter. Not to worry, it has the same amount of sugar as regular milk, however, there is a distinction. As discussed, lactose-free milk is made by adding lactase to raw milk in order to break down lactose into galactose and glucose. A large portion of the lactose is initially broken down in the first step of lactose hydrolysis, resulting in a close similarity to regular milk. The glucose formed when processing possesses different chemical and physical characteristics which increases the sensitivity of lactose-free milk to the Maillard Reaction (MR).
The MR can produce with multiple different products. It requires 鈥渞educing鈥� sugars such as glucose, free amino acids, and high temperatures. It is classified as a 鈥渘on-enzymatic browning reaction鈥�, that alters the flavour of food. This reaction occurs more quickly in lactose-free milk since glucose is more reactive than lactose. The MR changes the flavour profile of the milk adding a bit of a caramelized essence. Now, this doesn鈥檛 sound undesirable, but some people can really taste the difference between this modified milk and regular milk. The Maillard Reaction can be reduced using strict hygienic requirements for the lactase, pasteurizing the milk at a lower temperature and drinking it soon after purchase. By reducing the MR, the two milk varieties would become almost indistinguishable, saving people from the sometimes 鈥渆ggy鈥� flavour of lactose-free milk.
Intolerance vs Allergy
It is important to note that lactose-free milk is still a dairy product. Fundamentally, it is processed raw milk thus individuals with a dairy allergy cannot safely consume it. This leads to the important distinction between food intolerance and allergy. A food intolerance affects only the digestive system and doesn鈥檛 typically cause serious effects. A food allergy affects the immune system and can trigger a vast range of symptoms whose severity depend on the individual. An exposure to an allergen can be life-threatening even when triggered by a mere contamination. With an intolerance, people can still consume the food that upsets their body without needing treatment. Intolerances aren鈥檛 fun and can often be frustrating, however they should not be grouped in with allergies.
So, if you are lactose-intolerant, you can still thank cows for your lactose-free milk. However, the true hero is lactase, without which most of your day would be spent on the porcelain throne regretting your dietary decisions.
Angelina Lapalme is a BSc student majoring in Bio-Organic Chemistry at 平特五不中.聽
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