Effect of homogenization and pasteurization on the structure and stability of whey protein in milk

Abstract

The effect of homogenization alone or in combination with high-temperature, short-time (HTST) pasteurization or UHT processing on the whey fraction of milk was investigated using highly sensitive spectroscopic techniques. In pilot plant trials, 1-L quantities of whole milk were homogenized in a 2-stage homogenizer at 35°C (6.9 MPa/10.3 MPa) and, along with skim milk, were subjected to HTST pasteurization (72°C for 15 s) or UHT processing (135°C for 2 s). Other whole milk samples were processed using homogenization followed by either HTST pasteurization or UHT processing. The processed skim and whole milk samples were centrifuged further to remove fat and then acidified to pH 4.6 to isolate the corresponding whey fractions, and centrifuged again. The whey fractions were then purified using dialysis and investigated using the circular dichroism, Fourier transform infrared, and Trp intrinsic fluorescence spectroscopic techniques. Results demonstrated that homogenization combined with UHT processing of milk caused not only changes in protein composition but also significant secondary structural loss, particularly in the amounts of apparent antiparallel β-sheet and α-helix, as well as diminished tertiary structural contact. In both cases of homogenization alone and followed by HTST treatments, neither caused appreciable chemical changes, nor remarkable secondary structural reduction. But disruption was evident in the tertiary structural environment of the whey proteins due to homogenization of whole milk as shown by both the near-UV circular dichroism and Trp intrinsic fluorescence. In-depth structural stability analyses revealed that even though processing of milk imposed little impairment on the secondary structural stability, the tertiary structural stability of whey protein was altered significantly. The following order was derived based on these studies: raw whole>HTST, homogenized, homogenized and pasteurized>skimmed and pasteurized, and skimmed UHT>homogenized UHT. The methodology demonstrated in this study can be used to gain insight into the behavior of milk proteins when processed and provides a new empirical and comparative approach for analyzing and assessing the effect of processing schemes on the nutrition and quality of milk and dairy product without the need for extended separation and purification, which can be both time-consuming and disruptive to protein structures.

Application of non-invasive technologies in dry-cured ham: An overview

“…There was a study focused on purine and pyrimidine content, which are compounds declared as indicators of microbial spoilage, in which no differences were observed between untreated samples and samples treated at 600 and 900 MPa, maybe due to the water and salt contents, since a low a w preserves the cells from pressure effects (Clariana et al, 2011). Moreover, diverse studies showed that the HP application at 100 MPa causes lysosomal membranes destruction and reversible protein denaturation, and the protein denaturation at pressures beyond 200 MPa becomes irreversible (dos Santos et al, 2018;Qi et al, 2015) facilitating proteolytic reactions. These structural protein modifications also cause higher water losses.…”

New Trends in the Bioactive Compounds of Milk: A Review of the Functional Activities and Processing Effects

“…Moreover, some studies have shown that the germination of aerobic spores can be started by the pasteurization process (Hansonet al 2005). However, pasteurization causes the disruption of the tertiary structural environment of whey proteins and the degradation of vitamin C (Michalski and Januel, 2006;Qi et al, 2015).…”

Effect of High Pressure Homogenization on Improving the Quality of Milk and Sensory Properties of Yogurt: A Review

“…The structural changes in milk proteins strongly relate to the pressure treatment. The denaturation of proteins at 100 MPa is reversible whereas the irreversible denaturation of proteins occurs above 200 MPa [31]. The homogenization pressure could induce some conformational changes in whey proteins and caseins, which could increase their susceptibility to proteolysis, and therefore the availability of free amino acids, which are used by probiotic bacteria directly; and so, their viability increased [7].…”

“…The following order shows their stability level [15], [31]: HTST 1 , Homogenized > homogenized and pasteurized > HPH…”