Behavior of Listeria monocytogenes During Manufacture and Ripening of Brick Cheese

Publisher Website
Google Scholar
Abstract
Brick cheese was made by the washed-curd procedure from pasteurized whole milk inoculated to contain ca. 1 .times. 102 to 1 .times. 103 Listeria monocytogenes [strain Scott A, Ohio, V7, or California]/ml. Cheeses were ripened (15.degree.C/95% relative humidity) with a surface smear for 2, 3, or 4 wk to simulate production of mild, aged, or "Limburger-like" brick cheese, respectively, and then stored an additional 20 to 22 wk at 10.degree.C. Populations of strains Scott A, Ohio, V7, and California increased 1.89, 1.72, .83, and .86 orders of magnitude, respectively, following completion of brining ca. 32 h after the start of cheese making. All four L. monocytogenes strains leached from cheese into brine during 24 h and survived in brine at 10.degree.C at least 5 d after removal of cheese. Strains Scott A and Ohio grew rapidly during the initial 2 wk of smear development and attained maximum populations of ca. 6.6 and 6.2, 7.0 and 6.9, and 5.6 and 5.1 log1O/g in 4-wk-old slice (pH 6.0 to 6.5), surface (pH 6.5 to 6.9), and interior (pH 5.6 to 6.2) samples of cheese, respectively. Numbers of strains Scott A and Ohio generally decreased 1- to 7-fold during 20 to 22 wk at 10.degree.C. Strains V7 and California failed to grow appreciably in any cheese during or after smear development, despite pH of 6.8 to 7.4 in fully ripened cheese; the strains were never isolated from 2- and 3-wk-old cheese and with direct plating were detected sporadically at levels generally .ltoreq.4.0 log10/g in cheese aged .gtoreq.4 wk. Cold enrichment of slice, surface, and interior samples of cheeses aged .gtoreq.4 wk generally yielded positive results for L. monocytogenes; strains V7 and California were detected in all cheeses after 20 to 22 wk at 10.degree.C. At 10 ppm, methyl sulfide, dimethyl disulfide, or methyl trisulfide (compounds commonly produced during ripening of brick and Limburger cheese) failed to inhibit appreciably growth of L. monocytogenes.