Lactose-free dairy products: market and technologies

In a food market demanding for healthier food products, lactose intolerance represents one of the main drivers of the expansion of alternative plant-based products. However, some consumers belonging to this specific group still prefer lactose-free dairy products.

For dairy processors, lactose intolerant consumers’ expectations are an interesting marketing opportunity: epidemiological surveys on lactose intolerance highlighted that around 70% of the global population appears to be affected by lactose malabsorption; most importantly, the highest prevalence has been reported for Asian and African countries. Nowadays, their ability to meet the demand for lactose-free dairy products is supported by cutting-edge, efficient technologies.

Lactic acid fermentation is, of course, a natural way to reduce lactose in milk. Depending on the product type, fermentation by lactic acid bacteria (LAB) can be stopped at desired product features (final acidity, pH, overall sensory profile, etc.). However, end-product (thus, lactic acid) inhibition can affect cell growth rates. This means that LAB can ferment lactose up to certain quantities, then they stop growth and fermentation. Depending on the specific process, brand and recipe, dairy products made from non-delactosed milk contain certain amount of lactose, as we can see from Table 1. Moreover, cheese maturation can lower lactose content thanks to microbial activity. The longer the aging process, the lower the level of lactose residues in cheese. In 2021, Facioni and colleagues were able to enlarge the list of naturally lactose-free PDO cheeses, thus providing intolerant consumers with a useful tool for a balanced and healthy diet.

In addition to fermentation and aging, technology allows to achieve very low content of lactose, below 0.1%. Along enzymatic hydrolysis, dairy processors can rely on membrane separation.

In 2001, the Finnish Valio Group was the first, worldwide, to develop a totally lactose-free milk. The patented technology is called Zero Lactose™ and has been licensed since 2003 at a global level. In Italy, in 1968, Parmalat launched Zymil, which is a high-digestibility milk containing less than 0.1 g/100 ml of lactose.

Enzymatic hydrolysis relies on the use of lactase (β-galactosidase, EC 3.2.1.23), a hydrolytic enzyme responsible for the breakdown of lactose into glucose and galactose. Thanks to high specificity, the use of lactase has minimal side effects on the nutritional profile of milk. We can have either a batch or aseptic process. In the first case, the milk is stirred after neutral lactase addition; once lactose is completely hydrolyzed, milk is processed through thermal treatment, homogenization, and then packed. In the aseptic process, milk is first heat treated (UHT), then lactase is added before packaging. Hydrolysis will continue after packaging.

Immobilization allows operational advantages in the production of lactose free dairy foods. Stability, facilitated recovery, reusability of immobilized β-galactosidase are crucial when aiming at efficient processes; however, before reuse of enzymes, assessing their residual activity is important. Characteristics of β-galactosidase, the immobilization materials used and the specific immobilization process will affect the operation performance. Research is currently focusing on the development of immobilization materials that guarantee higher surface-volume ratios, catalytic efficiency, and surface reaction activity. An example of new material is graphene oxide, also used in membrane filtration.

Microorganisms are the best source of commercial lactase. The most used strains are Aspergillus niger, Kluyveromyces lactis, Escherichia coli, Aspergillus oryzae, Kluyveromyces fragilis. Concerning technological features, commercial lactase is required to show high lactose affinity, along with limited product inhibition. Commercial enzymes show their optima at neutral pH (7.0) and at 35-40 °C, thus showing thermostability. In batch conditions, hydrolysis occurs at low temperatures: research provided cold-adapted enzymes to achieve higher reaction rates and improved substrate solubility.

Separation of lactose through membrane technologies is another way to achieve low-lactose dairy products. Among the different processes, the industry can rely on electrodialysis, nanofiltration, ultrafiltration, reverse osmosis. The main difficulty is due to the wide size range of milk proteins that limits the efficiency of separating proteins and lactose. With ultrafiltration and nanofiltration, protein and fat are retained by membranes, while small compounds and lactose can pass through. Microfiltration is not able to ensure the same levels of protein retention as ultrafiltration and nanofiltration. It is worth noting that membrane filtration can be combined with enzymatic hydrolysis. The Valio Group went far beyond this approach: they combined chromatography, membrane technologies and the use of β-galactosidase to remove lactose from milk.

Beside technological aspects, the placing on the market of reduced-lactose or lactose free-products requires attention on what claims or statements are used on labels. Currently, there are no harmonized rules at EU level on claims concerning lactose content. Thus, the question must be considered from a national perspective. For instance, the Italian Ministry of Health states that the indication “lactose-free” can be used for milks and dairy products, but also for other products containing milky ingredients and/or additives, with a lactose residue of less than 0.1 g per 100 g or 100 ml. additional accompanying indications are required. The Food Safety Authority of Ireland (FSAI) sets the target lactose concentration to <0.01 g/100 ml to use the “lactose-free” claim; also in this case, there are further mandatory labeling statements that must be reported to protect consumers suffering from galactosemia.

Today, the main challenge for dairy processors when producing low-lactose or lactose free products is to keep nutritional, quality, and sensory features. Fortunately, research continuously develops cutting-edge and efficient technologies, which can be combined for an even more effective lactose removal treatment. Further improvement of products is possible with fortification (e.g., with vitamins and other ingredients), where the law gives room for manoeuvre. Since the market is potentially large and the demand for these products is growing, it will be important also for smaller dairy processors to consider including a specialized lactose-free line in their portfolio.

References

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