Nonstarter Lactic Acid Bacteria NSLABLactobacillus paracasei

There are almost always bacteria that are not added as a culture during cheese production that grow to high numbers in the cheese during ripening. Facultative heterofermentative Lactobacillus (FHL) and most commonly Lb. paracasei are found dominating in high-quality Scandinavian semihard cheeses, and their importance increases with ripening time (12-14). They are present at low numbers at the beginning of ripening, and no significant influence on the primary production of medium-sized peptides from casein in cheese has been shown or indicated. They may have caseinolytic enzymes, but they do probably not need them in ripening cheese with its large supply of small peptides and amino acids produced by the starter bacteria. They are extremely good survivors in a nutritional restricted environment that is changing slowly all through ripening, and one could expect them to have strict regulation mechanisms that allow production of enzyme systems only when they are needed. Their role in ripening of the semihard cheese varieties is under investigation. It is obvious that their importance is largest in long-time-ripened cheeses and they may interact with the starter in characteistic ways. The FHL occupy a niche in the cheese and prevent detrimental bacteria from growing and metabolizing. This may result from plain competition for nutrients, but also direct antimicrobial activities could be used. Defined strains of these bacteria, mainly Lactobacillus paracasei, may also be added as adjuncts during cheese production. Flavor production in the Swedish cheeses Hushallsost, Svecia, Prast and Herrgaird and the Norwegian cheese Norviega depends completely on DL-starter bacteria and the nonstarter FHL.

B. Smear Surface Microflora

The smear surface-ripened Danish cheeses may be sprayed by Brevibacterium linens or just treated in a way that stimulates the growth on the cheese surfaces if the right bacteria already are present at significantly large numbers in the salting or ripening room. Usually, yeasts establish first on the surfaces and effect an increase in pH to more suitable levels for Br. linens. The smear surface microflora contain several kinds of bacteria that contribute to lipolysis, to a strong proteolysis at the surface, and to production of sulfuric aroma compounds by catabolism of sulfuric amino acids (15). The microflora growing on the surface of cheese may contribute with some alternative biochemical activities because it grows aerobically. Oxidative deamination can be used in amino acid catabolism, and this activity produces ammonia that will easily migrate into the cheese body, increase pH, and stimulate the activity of proteolytic enzymes such as plasmin and the lactococcal cell-envelope protease lactocepin. Esrom is a smear surface-ripened cheese as are most brands of Danbo and Havarti cheeses (Table 1).

C. Propionic Acid Bacteria (PAB)

Cultures of propionic acid bacteria (PAB) are added to Jarlsberg, Greve, Magre, and Svenbo (Table 1), giving these cheeses their characteristic flavor and texture. To stimulate the growth and activities of PAB, the pH of the cheeses is somewhat increased, the salt content is decreased, and the cheeses are ripened fo a period of a couple of weeks at a higher temperature (14-18°C). PAB contribute to CO2 production, and those cheeses typically have very large eyes, as a result of gas production from both DL starter and PAB. CO2 is produced together with propionic and acetic acid from lactic acid, and PAB also contribute to producing flavor compounds. Their proteolytic enzyme system is mainly intracellular and contains specific peptidases releasing phenylalanine and proline (16). Proline contributes to the sweet note of PAB cheeses.

D. Adjuncts and Heat-Treated Cells of Lactobacillus helveticus

Low-fat, semihard cheese varieties, Kadett (20% FDM), Vastan (20% or 10% FDM) (Table 1), and some types of Samso (30% FDM) are produced with adjuncts of Lb. helveticus. A spray-dried powder of heat-treated cells is used in Kadett and Vastan to accelerate the peptide breakdown in those cheeses (17). The heat-treated cells contain a large amount of highly active intracellular peptidases with broad specificity, and the activity of the cell-bound protease is reduced and the acidification ability is inactivated by the heat treatment. The peptidases are kept within their own cell membranes in the cheese vat and will be incorporated into the curd. The intracellular peptidases are released early in cheese and influence the ripening process. The amount of amino acids produced within some weeks is far larger than in any normal-fat cheese and both flavor and consistency are improved.

Compared to a control cheese without heat-treated Lb. helveticus, the consistency is shorter, more ripened and the flavor is mild, clean, nutty, and aromatic, with a sweet note.

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