|Abstract:||Physicochemical treatment, such as the process of microfiltration (MF) and whey ultrafiltration (UF), causes reversible and irreversible fouling of ceramic membrane pores, as well as changes in protein structure and interaction of proteins with many whey components and membrane surface. The latter leads to protein denaturation and aggregation and also contributes to membrane fouling. The types and extent of protein interactions depend on the processing conditions, the composition and ionic strength of the whey, and the pH value. Processes that destabilize the structure of whey proteins and promote the development of proteins, accelerate interactions between whey proteins in solution and lead to various intramolecular or intermolecular reactions.
Whey consists of various components, such as microorganisms, enzymes and proteins, due to which, also taking into account different storage conditions, its characteristics change over time and can affect the interactions between them. It was important to determine the physicochemical and microbiological stability of whey monitored in a one-week period, to establish the effect of temperature, and how the whey was stored prior to the initiation of MF and UF procedures.
The purpose of MF and UF membrane testing was to optimize processes, with the aim of achieving high permeability for whey proteins (especially lactoferrin - LF) and retention of microorganisms and other whey components, that would limit the use of whey in further processing operations. In the experiments, we determined the most efficient mode of operation of the MF ceramic membrane and the regime of cleaning them, which allows the filtration to last as long as possible without membrane fouling and restoring the full flow after fouling.
We observed that the activity of the lactoperoxidaze (LPO) enzyme declines rapidly regardless of whey storage conditions. The LF protein is stable 8 days in the refrigerator, while gradually decomposing at room temperature. A MF ceramic membrane with a pore diameter of 0,5 μm achieved a 51 % permeability in permeate of LF at a pressure of 1 bar. We detected, that the membrane was effectively cleaned in three steps, with 0,4 % sodium hydroxide solution (NaOH), 0,3% nitric acid solution (HNO3) and 0,5 % sodium hypochlorite solution (NaOCl) at 60 °C and at a higher pump speed than the operating speed and at the pressure of reverse flow at 0,5 bars. An UF ceramic membrane with a pore diameter of 0,05 μm held the LF protein in retention.|