Kornacki Jeffrey L, Marth Elmer H
Department of Food Science and The Food Research Institute, University of Wisconsin, Madison. Wisconsin 53706.
J Food Prot. 1989 Sep;52(9):631-637. doi: 10.4315/0362-028X-52.9.631.
Cells of Staphylococcus aureus strains 196E, 481, and 425 were thermally stressed at 56°C for 10 min in milk and enumerated on Plate Count Agar (PCA), Mannitol Salt Agar (MSA), and PCA with an overlay of MSA. PCA recovered more S. aureus 196E and 481 than did PCA/MSA, which recovered more than MSA. PCA/MSA recovered slightly more S. aureus 425 than did PCA, which recovered more than MSA. At 58°C, in order of decreasing heat resistance, the four strains of S. aureus originally isolated from food were 425 > 100 and 481 > 196E. Their D-values were 26,14,13, and 3.0 min, respectively. S. aureus 425 was more heat resistant in the stationary than in the log phase when heated at 58°C in whole milk. Heat resistance at 58°C increased overall during the stationary growth phase, but was fairly stable when the culture was from 17 to 25 h or from 41 to 49 h old. S. aureus 425 exhibited no consistent differences in heat resistance in concentrated (4X by volume) and unconcentrated skim or whole milk. Adjustments of protein (3.5-4.0% to 12.6-16%), milkfat (0.28-1.12% to 10%), and lactose (ca. 4.5-5.0% to ca. 14.5-15%) contents of milk and 4X (volume concentration) UF milk retentates afforded no significant thermal protection to S. aureus 425. Diafiltration of 4X skim milk reduced thermal protection of S. aureus 425 in the retentate over that of unconcentrated skim milk of the same lot when tested at 63 and 74°C. S. aureus 425 had greatest D-values (min) in skim milk (0.36 ± 0.05) and permeate (0.30 ± 0.14) followed by permeate from diafiltration (0.28 ± 0.06) when tested at 63°C.
将金黄色葡萄球菌196E、481和425菌株的细胞在牛奶中于56°C热应激10分钟，然后在平板计数琼脂（PCA）、甘露醇盐琼脂（MSA）以及覆盖有MSA的PCA上进行计数。PCA回收的金黄色葡萄球菌196E和481比PCA/MSA更多，而PCA/MSA回收的比MSA更多。PCA/MSA回收的金黄色葡萄球菌425比PCA略多，PCA回收的比MSA更多。在58°C时，按耐热性从高到低排序，最初从食品中分离出的四株金黄色葡萄球菌为425 > 100和481 > 196E。它们的D值分别为26、14、13和3.0分钟。当在全脂牛奶中于58°C加热时，金黄色葡萄球菌425在稳定期比对数期更耐热。在稳定生长期，58°C时的耐热性总体上有所增加，但当培养物为17至25小时或41至49小时龄时相当稳定。金黄色葡萄球菌425在浓缩（体积比4倍）和未浓缩的脱脂或全脂牛奶中的耐热性没有一致的差异。将牛奶和4倍（体积浓缩）超滤牛奶截留物的蛋白质（3.5 - 4.0%至12.6 - 16%）、乳脂肪（0.28 - 1.12%至10%）和乳糖（约4.5 - 5.0%至约14.5 - 15%）含量进行调整，对金黄色葡萄球菌425没有显著的热保护作用。当在63°C和74°C测试时，4倍脱脂牛奶的渗滤降低了截留物中金黄色葡萄球菌425相对于同批次未浓缩脱脂牛奶的热保护作用。当在63°C测试时，金黄色葡萄球菌425在脱脂牛奶（0.36±0.05）和渗透物（0.30±0.14）中的D值最大，其次是渗滤后的渗透物（0.28±0.06）。
