|Van Hekken, Diane|
Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/3/2011
Publication Date: 7/11/2011
Citation: Tomasula, P.M., Leggett, L.N., Kwoczak, R., Van Hekken, D.L., Tunick, M.H., Renye Jr, J.A., Toht, M.J., Mukhopadhyay, S., Porto Fett, A.C., Luchansky, J.B. 2011. Use of high pressure processing to control Listeria monocytogenes in packaged Queso Fresco [abstract]. American Dairy Science Association Abstracts. 94(1):480.
Technical Abstract: Queso Fresco (QF), a fresh, Hispanic-style cheese, is manufactured using pasteurized milk; however, its high pH (>6) and moisture content (>50%) coupled with post-pasteurization labor intensive practices may lead to contamination with Listeria monocytogenes (LM). The objective of this study was to evaluate the effectiveness of high pressure processing (HPP) as an intervention strategy applied to QF after packaging to control LM. QF was manufactured from pasteurized milk using a commercial-make procedure. In preliminary experiments, about 8 kg of the dry, finely-milled and salted curd was packed into a mold and held at 4 deg C overnight before the mold was removed. QF was then cut into slices with dimensions of about 12.7 cm x 7.6 cm x 1 cm. QF slices were surface inoculated on both sides with 50 uL of a five-strain LM cocktail (ca. 5.0 log10 CFU/g), individually double vacuum-packaged and then cooled to 4 deg C. The slices were then warmed to either 22 or 40 deg C and treated using HPP at pressures of 200, 400, and 600 MPa for holding times of 0, 5, 10 or 20 min. Only HPP treatment at 600 MPa, at both temperatures and all holding times, reduced LM to below the detection level of < 0.91 log10 CFU/g. Processing at 40 deg C resulted in visible textural changes and significant “wheying-off” of the cheese and was not investigated further. In subsequent experiments, QF slices were treated at 22 deg C and 600 MPa at holding times of 0, 3, 10 and 20 min and then stored at 4 and 10 deg C for 7 d. For the 3 min holding time, LM populations increased to 2.65 + 0.92 and 4.50 + 0.50 log10 CFU/g, when QF was stored at 4 deg C and 10 deg C, respectively. For the 10 min holding time, LM populations in QF remained below the detection level when stored at 4 deg C but increased to 2.00 + 0.00 log10 CFU/g when stored at 10 deg C. For the 20 min holding time, LM populations were not evident in QF when stored at 4 deg C but approached the detection level at 10 deg C. These results show that HPP was most effective when conducted at 600 MPa for 20 min, but HPP pressures > 600 MPa, pulsed HPP, or addition of antimicrobials, may be necessary for ultimately controlling this pathogen.