Bacterial Surface-ripened Cheeses Research Articles

A novel approach for accelerating smear development on bacterial smear-ripened cheeses reduces ripening time and inhibits the growth of Listeria and other unwanted microorganisms on the rind

Bacterial smear-ripened cheeses are commonly contaminated with fungi and the potentially dangerous pathogen Listeria monocytogenes, which compromises food safety and quality. Here, we present new approach for accelerating smear development on these cheeses, while reducing growth of unwanted microorganisms. We grew the smear microorganism Brevibacterium linens in acid whey (AW) supplemented with a by-product of whey protein hydrolysate production (FCH). B. linens grew to a high cell density (10.27 log 10 CFU/mL), and alkalized the AW-FCH medium. We found that the fermented AW-FCH, with its high pH, rapidly killed L. monocytogenes and yeasts. When culture medium was smeared on the cheese surface, the surface pH was rapidly neutralized, and in just 7 days, the cheeses developed a dense orange color and growth of spoilage fungi was inhibited. Summing up, by growing B. linens to high cell density on low-value dairy byproducts, and applying dense suspensions onto cheeses, we can reduce the time needed for establishing the smear. Added benefits are increased food safety and less spoilage, as quick smear development inhibits growth of unwanted microorganisms on the rind. Preliminary tests at a dairy show that flavor development is comparable to traditional bacterial surface-ripened cheeses with far more complex surface microflora.

Growth of Listeria monocytogenes, Salmonella spp., Escherichia coli O157:H7, and Staphylococcus aureus on Cheese during Extended Storage at 25°C

Potentially hazardous foods require time/temperature control for safety. According to the U.S. Food and Drug Administration Food Code, most cheeses are potentially hazardous foods based on pH and water activity, and a product assessment is required to evaluate safety of storage >6 h at 21°C. We tested the ability of 67 market cheeses to support growth of Listeria monocytogenes (LM), Salmonella spp. (SALM), Escherichia coli O157:H7 (EC), and Staphylococcus aureus (SA) over 15 days at 25°C. Hard (Asiago and Cheddar), semi-hard (Colby and Havarti), and soft cheeses (mozzarella and Mexican-style), and reduced-sodium or reduced-fat types were tested. Single-pathogen cocktails were prepared and individually inoculated onto cheese slices (∼10(5) CFU/g). Cocktails were 10 strains of L. monocytogenes, 6 of Salmonella spp., or 5 of E. coli O157:H7 or S. aureus. Inoculated slices were vacuum packaged and stored at 25°C for ≤ 15 days, with surviving inocula enumerated every 3 days. Percent salt-in-the-moisture phase, percent titratable acidity, pH, water activity, and levels of indigenous/starter bacteria were measured. Pathogens did not grow on 53 cheeses, while 14 cheeses supported growth of SA, 6 of SALM, 4 of LM, and 3 of EC. Of the cheeses supporting pathogen growth, all supported growth of SA, ranging from 0.57 to 3.08 log CFU/g (average 1.70 log CFU/g). Growth of SALM, LM, and EC ranged from 1.01 to 3.02 log CFU/g (average 2.05 log CFU/g), 0.60 to 2.68 log CFU/g (average 1.60 log CFU/g), and 0.41 to 2.90 log CFU/g (average 1.69 log CFU/g), respectively. Pathogen growth varied within cheese types or lots. Pathogen growth was influenced by pH and percent salt-in-the-moisture phase, and these two factors were used to establish growth/no-growth boundary conditions for safe, extended storage (≤25°C) of pasteurized milk cheeses. Pathogen growth/no-growth could not be predicted for Swiss-style cheeses, mold-ripened or bacterial surface-ripened cheeses, and cheeses made with nonbovine milk, as insufficient data were gathered. This challenge study data can support science-based decision making in a regulatory framework.

The last step in the biosynthesis of aryl carotenoids in the cheese ripening bacteria Brevibacterium linens ATCC 9175 ( Brevibacterium aurantiacum sp. nov.) involves a cytochrome P450-dependent monooxygenase

Bacterial surface-ripened cheeses such as Tilsit, Brick, Limburger, Epoisses, Livarot, Munster, Reblochon, Herve or Taleggio develop a red or orange color during ripening. Color is linked to the production of pigments by bacteria growing on the surface, and Brevibacterium linens is particularly added in milk by cheese manufacturers. Tetcyclacis, a chemical compound known to be an inhibitor of cytochrome P450 dependent monooxygenase inhibited the aerobic biosynthesis of orange hydroxylated carotenoids in the red-smear cheese ripening bacteria B. linens. Growth of the cells in the presence of tetcyclacis reduced to almost zero the level of the 3,3′-dihydroxy-isorenieratene found in stationary-phase cells. According to co-elution with carotenoid standards and LC–MS, the substrate of cytochrome P450 dependent monooxygenase was identified as isorenieratene, a carotene with Φ rings. Up to now, there are only few examples of carotenoid hydroxylases from the P450 superfamily. Moreover this is the first description of a P450 monooxygenase that catalyzes the hydroxylation of non-β-ring carotenoid in bacteria.

Purification and characterization of an extracellular proline iminopeptidase from Corynebacterium variabilis NCDO 2101.

To screen the extracellular proteolytic and lipolytic activities of Corynebacterium variabilis NCDO 2101 and to purify and characterize a proline iminopeptidase enzyme in order to investigate the role of the major component of the smear of bacterial surface-ripened cheeses. Four chromatographic steps were used to purify the enzyme and a three-factor, five-level Central Composite Design was used to study the interactive effects of cheese-related values of pH, NaCl and temperature. The proline iminopeptidase showed some biochemical properties different from the same enzyme purified from lactic acid bacteria and other smear bacteria. It tolerated NaCl concentrations up to 7.5% and was sensitive to low values of pH especially when they were combined with low temperature. The proline iminopeptidase of C. variabilis NCDO 2101 may have a role in proteolysis during ripening of smear surface-ripened cheeses. The findings of this work contribute to the knowledge of the enzymology of smear bacteria in order to improve the ripening of bacterial surface-ripened cheeses.

The bacterial flora of surface-ripened cheeses with special regard to coryneforms

Summary - Randomly-selected Austrian bacterial surface-ripened cheeses were examined for changes in the microbiological composition of the smear. The bacterial counts of the Tilsit cheeses from 14 cheese plants and of 3 types of soft cheeses selected varied fram 1()4 ta 109 cfu/cm2 smear 3 d after manufacture and fram 108 ta 109 cfu/cm2 smear after a ripening period of 3 weeks. The flora tolerated a NaCI content of at least 80 g/kg in the plate count agar. A total of 386 isolates of coryneform bacteria were identified. The bacterial flora proved ta be of mixed population. However, Brevibacterium linens accounted for a large share of the flora, comprising 30% of the total bacterial count, Besides Brevibacterium linens, the other main types found ta be present in the heterogeneous flora were creamcoloured and yellow-pigmented coryneforms, which were predominantly identified as Arthrobacter globiformis and Brevibacterium ammoniagenes. The coryneforms isolated fram the cheeses 3 d after manufacture were more prateoly1ic than those isolated at later stages of ripening.