At the beginning of the 1920s to 30s Sweden had a surplus of dairy milk, a marketing strategy was created to propagate a narrative with economic interests, intertwined with public health, to create a viable milk industry. Fresh pasteurized dairy milk was healthy and should be part of a daily diet. This enabled the growth and expansion of the dairy industry, but there were still some issues to be resolved. Milk, is an excellent medium for the growth of microorganisms and bacterial pathogens, in that regard milk is highly perishable in nature and spoilage can occur quite fast. Therefore it should be pasteurized and processed within 24 to 48 hours after milking, ensuring a stable milk product without compromising its nutritional and functional properties.
So other than the pasteurization process, first utilized in 1862 to remove micro-organisms allowing the milk to be preserved for months, as opposed to just 2 to 3 days while refrigerated. There was no other way to keep milk from separating and spoiling.
Maria Johanna Kronberg
Until around 1934, Maria Johanna Kronberg an inventor patented a milk powder processing method with patents number 85916 and 96765. Sadly, once pitched, the powdered milk processing method was rejected by the existing milk processing establishment. Powdered milk was just not seen as being a viable add-on. However, Maria Johanna Kronberg patented invention did not die a slow death. Around 1938, it was used by Semper formally known as Svenska Mjölkprodukter AB ( SMP). Since then Semper has become a global food manufacturing brand that started by using Maria Johanna Kronberg’s method to produce dried powdered milk and later adding infant formula and other food products to grow their business.
Due to powder research and development milk powder has become a global industry and a crucial part and additive to the many foods we consume on a daily basis. But the continued understanding of powder characteristics doesn’t stop there.
Milk powder advantages
Milk powder has many advantages and has found its way into just about anything you want to make creamier. In contrast to ordinary fresh, pasteurized or UHT milk, powdered milk made from dehydrated, pasteurized milk has several advantages. It does not require refrigeration, has a much longer shelf life, and is less bulky to transport, another benefit, milk powder does not separate. Separation does occur in liquid milk because microorganisms start processing the lactose (sugar) thereby creating lactic acid and causing the milk protein to lump together, separating the liquid from the proteins. Milk powder is much more stable in that regard.
Milk powder as a filler will add structure and consistency to an end product, making milk powder quite a functional versatile food ingredient. The powder can be used in soups, gravies, sauces, baking products, milkshakes, pudding, ice-cream, cultured milk like Kefir and Yakult, yogurts, chocolate, and confectionery but also act as a sweetener, stabilizer, or nutritional fortifier in baby formulas, etc. The few drawbacks of milk powder during processing are the potential for caking and lumping during storage or use and the Maillard reaction.
Milk safety
Even though the processing of pasteurized liquid milk to powder may be simple in essence, naturally stringent hygiene standards must be met to ensure the end product is safe for consumers. The simplest one is that milk must be pasteurized to be sold by retailers, it must also be refrigerated and handled properly to prevent foodborne illnesses. This also applies to powdered milk, including dry whole milk powder, nonfat dry milk powder, dry whey powder, and dry dairy blended powders, etc. For consumer product confidence, product safety, and Good Manufacturing Practice (GMP). Domestic and exported dairy products must conform to several stringent standards laid out in the Codex Alimentarius also known as the food code.
For example, the general standard for contaminants and toxins in food and feed (CXS 193-1995), general principles of food hygiene (CXC 1-1969), the code of hygienic practice for milk and milk products (CXC 57-2004) to name but a few. Ensuring that safe manufacturing processes are monitored and maintained for public safety and to prevent laws suits and negative company and product publicity.
Milk powder processing
Lactose milk sugar, proteins casein, and whey are three main compounds that are of interest in milk. These components have high nutritional value and are extensively utilized throughout the food processing industry. Presently spray drying, drum drying or freeze drying are the main methods used to process and transform liquid milk into powdered milk.
Milk powder production starts when a raw milk tanker arrives at the factory. The milk is tested for temperature, acidity, smell, antibiotic concentration, fat content, protein, etc. Simplifying the steps, the milk is pumped from the tanker into cooled silos. After which the milk is pasteurized and run through a centrifuge to separate the cream. The milk is preheated to reduce its viscosity and moved to a spray drying process, where the preheated milk concentrate is atomized through high-pressure nozzles into fine milk droplets that are air-dried at around 200 degrees Celsius, removing most of the moisture. The milk particles solids are cooled after which the milk powder can be dried a second or third time to remove any residual moisture, preferably with a final water activity of 0.2 to 0.6 (aw). Aw is the most important parameter of water in terms of food safety. Values at less than 0.6 will inhibit microbial growth. As for the final milk powder particle size, it is generally averaged between 30 μm-149 μm depending on product specifications.
Maillard reaction
Even though milk powder is essentially simple to produce, the complex composition of milk is still a major challenge because there is still a large percentage of milk spoilage during production. Roughly 1 in every 3 gallons of milk is wasted and that already starts at the farm. This is due to Gram-negative bacteria, Alcaligenes, Flavobacterium, and the majority roughly 70%. being Pseudomonas. This accounts for a milk wastage of 33%. Milk spoilage is something that goes back centuries. Pasteurization and powder processing does help but they do not solve all the issues. Higher pasteurization temperatures do inhibit more microorganisms but the milk according to consumer reviews gets a strange taste, so higher temperatures are not a solution at this time.
Another more complex problem to be solved is the Maillard reaction that can occur during milk powder processing and storage. It is a chemical reaction between milk proteins, amino acids, and carbonyl groups of the reducing sugars which form a brownish discoloration. However, it is not all bad. The Maillard reaction is very common and is used in some food industries and unknowingly at home because the reaction produces more flavor and aromas during the heating process of our foods.
That being said, Maillard is not wanted in milk processing or storage. Milk powder may form crystallization of lactose due to humidity or increases in temperature, resulting in the formation of brown spots. To name a few other effects, Maillard reaction can also decrease milk emulsification and foaming properties. It causes milk powder protein aggregations, which inevitably lessens milk powder solubility and can cause clumping.
Conveying
Like with all industries conveying in some form or another is required to move product to and from different product processing stages. Heat and humidity during milk powder pneumatic conveying can cause stickiness due to the presence of fat and the high lactose content making milk powder in general more hygroscopic. The sticky powder is a concern and the big reason why powder deposits agglomerate inside pneumatic pipe equipment, causing caking and lumping which reduces flow-ability and can lead to downtime and powder loss. This can also be caused by amorphous lactose smearing the pipeline’s inner walls and eventually also clogging up the system. Requiring shutdown and unclogging of the pipeline. The impact of milk powder particles during pneumatic conveying and mechanical stresses can also cause proteins to unfold, which destabilizes them and can also affect future solubility.
Storage
For milk powder, like with many other food products storage is an integral part of a production facility. Milk storage and prolonged higher temperatures can cause milk powder to undergo a variety of chemical reactions that can accelerate the browning process. That Maillard reaction can be triggered by reducing sugars, increase in moisture, stickiness due to fats, and not to forget copper, iron, and zinc ions.
There are myriad factors to take into account while processing milk. It does not end there the Maillard reaction can be found at multiple stages of milk processing and can also affect milk powder while in storage causing a decrease in the milk powder pH levels. This pH decrease is a result of amino acids bonding with lactose. Even though this does not pose a significant product quality issue and is not noticed by consumers, it is still an undesired effect caused by processing.
For reference, there is a distinct difference between browning due to heat causing caramelization, and browning due to the Maillard reaction which involves amino acid reactions, whereas caramelization involves pyrolysis reactions of sugar particles.
In summary
Finally to truly understand the chemical reactions, nutritional effects, and bio-availability of the milk proteins and minerals in regards to the Maillard reactions in milk powder processing. More testing is required to find the problem areas during production and storage.
However, in some instances, the Maillard reaction also increases food nutrition. It might be a good idea to collaborate with a particle research laboratory, testing samples and looking at collected data from other industries that can give a perspective in finding a solution or mitigating existing processes. Since the Maillard reaction is prevalent also in proteins, as previously states. Ultra-high temperature heating not only affects milk processing but is also prevalent in other industries. Some negative and some positive. Acrylamides are mentioned in the media as having probable carcinogenic properties. For example, the Maillard reaction is the main cause of forming acrylamides in fried starchy foods.
Every industry is dealing with powder technology at multiple stages of their product production, including storage facilities. To stop unwanted chemical reactions from occurring or to better control them, to find or solve specific processing requirements, continued innovation is needed. Such as following courses, training, and having samples tested by dedicated powder technology laboratories committed to improving existing processes and finding the causes and fix unwanted issue powder issues.
