Graduate Thesis Or Dissertation
 

The influence of preadsorbed milk proteins on adhesion of Listeria monocytogenes to silica surfaces

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  • β-lactoglobulin (β-Lg), bovine serum albumin (BSA), α-lactalbumin (α-Lac), and β-casein were adsorbed onto silanized silica surfaces of low and high hydrophobicity for 8 h, and β-Lg and BSA for 1 h. The surfaces were incubated in buffer for 0, 5, 10, or 15 h and then contacted with Listeria monocytogenes for 3 h. Cell adhesion was quantified using image analysis. Following 8 h of protein contact, adhesion to both surfaces was greatest when β-Lg was present and lowest when BSA was present. Preadsorption of α-Lac and β-casein showed an intermediate effect on cell adhesion. Adsorption of β-Lg for 1 h resulted in lower numbers of cells adhered as compared to the 8 h adsorption time, while the opposite was observed with BSA, but adhesion to BSA was observed to decrease slowly with film age to values comparable to the 8 h tests. The adsorption of BSA and β-Lg to both surfaces was also carried out where each protein was allowed to contact the surface in sequence and simultaneously. In sequential tests performed with an 8 h contact/protein, cell numbers on each surface were near that expected for the bare hydrophobic surface when β-Lg contact preceded introduction of BSA, whereas adhesion was reduced to values below that expected for the bare hydrophilic surface when BSA preceded β-Lg contact. In short-term sequential tests (1 h contact/protein), adhesion was lower than that recorded on bare hydrophilic surfaces in each case. Adhesion to each surface following contact with an equimolar mixture of β-Lg and BSA was lower than that measured on the bare hydrophilic surface in each case, with adhesion following 1 h contact being greater than that following 8 h contact. Adhesion following competitive adsorption was greater to hydrophobic than to hydrophilic surfaces. These results were explained with reference to the surface passivating character of BSA, and its ability to rapidly attain a nonexchangeable state upon adsorption, relative to β-Lg.
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