Fizikalno-kemijska obdelava, kot je postopek mikrofiltracije (MF) in ultrafiltracije (UF) sirotke, povzroča reverzibilno in ireverzibilno mašenje por keramičnih membran kot tudi spremembe v strukturi in interakciji proteinov s številnimi komponentami sirotke ter površino membran. Slednje vodi do denaturacije in agregacije proteinov in ravno tako prispeva k mašenju membrane. Vrste in obseg proteinskih interakcij so odvisni od pogojev obdelave, sestave in ionske moči sirotke ter vrednosti pH. Obdelave, ki destabilizirajo strukturo sirotkinih proteinov in spodbujajo razvijanje proteinov, pospešijo interakcije med sirotkinimi proteini v raztopini in vodijo do različnih intramolekularnih ali intermolekularnih reakcij.
Sirotka vsebuje različne komponente, kot so mikroorganizmi, encimi in proteini, zaradi katerih se njihove lastnosti s časom in z različnimi pogoji shranjevanja spreminjajo in vplivajo na medsebojne interakcije. Pomembno je bilo opredeliti fizikalno-kemijsko in mikrobiološko stabilnost sirotke, ki se je spremljala po preteku enega tedna, da se določi vpliv temperature in način shranjevanja sirotke pred pričetkom postopkov MF in UF.
Namen testiranj MF in UF membran je bila je optimizacija procesov, s ciljem doseganja visoke prepustnosti za sirotkine proteine (predvsem laktoferina - LF) in zadrževanje mikroorganizmov ter drugih komponent sirotke, ki bi omejevale uporabo sirotke v nadaljnjih postopkih predelave. V eksperimentih smo opredelili najbolj učinkovit režim delovanja MF keramične membrane ter režim čiščenja le-teh, ki omogoča čim daljše delovanje filtracije brez zamašitve membran ter povrnitev polnega pretoka po zamašitvi.
Ugotovili smo, da aktivnost encima laktoperoksidaze (LPO) hitro pada ne glede na shranjevanje sirotke. Protein LF je stabilen 8 dni v hladilniku, medtem ko na sobni temperaturi postopoma razpade. Z MF keramično membrano s premerom por 0,5 μm smo dosegli 51 % prepustnost LF v permeat pri tlaku 1 bar. Opazili smo, da je membrana učinkovito očiščena v treh korakih, in sicer s 0,4 % raztopino natrijevega hidroksida (NaOH), 0,3 % raztopino dušikove kisline (HNO3) in 0,5 % raztopino natrijeviega hipoklorida (NaOCl) pri temperaturi 60 °C in pri večji hitrosti črpalke kot je delovna ter pri tlaku povratnega toka 0,5 bar. UF keramična membrana s premerom por 0,05 μm je 100 % zadržala protein LF v retentatu.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
