Whey is a liquid that remains after curdling the milk using a rennet or after acidifying the milk by fermentation or another method of reducing the pH value. Sweet whey is a by-product of cheese production, while acid whey is a by-product of fermentation and acid coagulation of milk, for example, the production of cottage cheese and recently popular Greek yoghurt. While sweet whey has several commercial uses, sour whey is often treated as waste and is discharged to wastewater treatment where it represents a high organic load. Despite the content of a significant amount of valuable nutrients, treatment of acid whey is much more demanding than the treatment of sweet whey.
Acid whey has a lower pH, contains lower concentrations of proteins and lactose, and higher concentrations of calcium, phosphorus and lactic acid. Spray drying, to produce mixed whey protein powders is, therefore, demanding as proteins are sticking together. An additional problem is a difference in the composition and properties of whey from various methods of technological processing of milk, which take place at different temperatures, pH and other factors. All of this requires diverse approaches to the treatment of acid whey. According to estimates from various sources, only about 40% of all whey is treated in the EU.
Acid whey contains between 11 and 14% proteins, 60-70% lactose, 0.5-1.5% fats, and 9-12% mineral content, measured in dry matter. Among the proteins, functionally and nutritionally relevant fractions are represented, such as -lactalbumin (-La), β-lactoglobulin (β-Lg), bovine serum albumin BSA, lactoferrin (LF), lactoperoxidase (LP) and immunoglobulins (Ig). Sweet whey also contains glycomacropeptide (GMP).
Important whey functional proteins represent LF, LPO and Ig. These proteins conserve biological activity after ingestion and are not degraded and absorbed as amino acids in the small intestine. For example, LF is a glycoprotein with the ability to bind iron. It exhibits antimicrobial and anti-inflammatory activity and therefore plays a major role in strengthening the immune system. It is used in dietary supplements, baby milk blends and oral hygiene products, which makes it marketable. LPO is an antimicrobial glycoprotein. It causes damage to membranes of streptococci with oxidation reactions and thus their lysis. It is used in food products and products for personal hygiene (oral water, skin creams, shampoos). Immunoglobulins are a sophisticated group of monomeric and polymeric glycoproteins (IgG, IgA, IgM). Because of their properties of strengthening immune resistance, they are used in nutritional formulas.
The goal of pilot testing and demonstration of further technological processing of acid whey is to present to dairies new business opportunities offered by acid whey. We will use several whey processing approaches in the LIFE for Acid Whey project instead of the usual treatment of acid whey together with wastewater in aerobic processes. We will show the possibilities such as isolating individual whey components that have market value, its use as a medium for cultivating probiotics and the final anaerobic processing stage, which enables the exploitation of its energy for the production of biogas as renewable energy source.
In addition to dried whey powder and whey protein concentrates with a different proportion of proteins, individual isolated whey proteins have been increasingly sought-after recently. Different proteins, such as lactoferrin, lactoperoxidase and immunoglobulins, represent not only the source of amino acids but are important regulatory factors with a broad biological role or so-called functional proteins. They can be isolated from liquid whey using membrane filtration, affinity and cation exchange chromatography. In the LIFE for Acid Whey project, we will use the innovative technology of short monolithic chromatographic columns, which allow a much higher separation rate of proteins compared to the particulate columns since they allow convection flow through columns, where diffusion does not limit transport of proteins to ligands.
Due to the complex composition of whey, it can be an excellent medium for the cultivation of dairy starter cultures, which are used in the food and feed industry. In the LIFE for Acid Whey project we will test the potential of using pre-processed whey for their cultivation, with emphasis on cultivating probiotic bacteria. All previous processing of whey will, therefore, be guided in the direction of minimising whey denaturation.
In the LIFE for Acid Whey project, we will also test the possibility of further drying of the previously processed whey to obtain whey powder with the remaining water, which will no longer represent an environmental burden. We will define the most optimal combination of concentrating, crystallisation, centrifuging and drying systems.
Given that 2.5m3 of whey corresponds to the organic load of water caused by 1000 inhabitants, treatment of whey in a conventional aerobic wastewater treatment system with dispersed biomass would require a lot of energy consumption and at the same time a high loss of chemically stored energy in the whey itself. For this purpose, instead of an aerobic biological wastewater treatment, anaerobic treatment with the formation of biogas is the preferable choice, enabling coverage of a part of the energy needs of the dairy.