Lactic acid-forming bacteria characteristics

With that problem solved, we can now take up the case of the exploding Swiss cheese. Characteristic of this type of cheese are the large holes produced by the carbon dioxide gas that forms during the aging process. Cheese makers add a variety of bacteria to their creations as a way of ripening them. To Swiss cheese they also add a strain of Propionibacter shermanii. This bacterium uses the lactic acid secreted by other microbes as... 

Cultured buttermilk is manufactured by fermenting whole milk, reconstituted nonfat dry milk, partly skimmed milk, or skim milk with lactic acid bacteria. Most commercial cultured buttermilk is made from skim milk. Mixed strains of lactic streptococci are used to produce lactic acid and leuconostocs for development of the characteristic diacetyl flavor and aroma. Buttermilk is similar to skim milk in composition, except that it contains about 0.9% total acid expressed as lactic acid. The percentage of lactose normally found in skim milk is reduced in proportion to the percentage of lactic acid in the buttermilk. According to White (1978), the fat content of buttermilk usually varies from 1 to 1.8%, sometimes in the form of small flakes or granules to simulate churned buttermilk, the by-product of butter churning. Usually 0.1% salt is added. 

Lactic acid is a major end product from fermentation of a carbohydrate by lactic acid bacteria (Tormo and Izco, 2004). However, lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers whereas during fermentation an optically pure form of lactic acid is produced. However, this may depend on the microorganisms, fermentation substrates, and fermentation conditions. Lactic acid can be produced from renewable materials by various species of the fungus Rhizopus. This has many advantages as opposed to bacterial production because of amylolytic characteristics, low nutrient requirements, and the fungal biomass, which is a valuable fermentation by-product (Zhan, Jin, and Kelly, 2007). 

In bacteria, most fatty acids have 14 to 20 carbon atoms and are saturated or mono-unsaturated. Lactic acid bacteria also contain a characteristic cyclopropanic acid lactobacillic acid (cw-11,12-methylene-octodecanoic). Table 4.1 lists the principal fatty acids of lactic acid bacteria found in wine—notably Oenococcus oeni (Lonvaud-Funel and Desens, 1990). Malonyl CoA and acetate condense to form fatty acids with an even number of carbon atoms. For an odd number of carbon atoms, fatty acids are synthesized by the condensation of malonyl CoA and propionate. Anaerobic bacteria synthesize unsaturated acids by the action of a dehydratase on hydroxydecanoate which is formed by the addition of a malonyl unit on an octanoic acid molecule. 

Another characteristic of wines made from grapes affected by noble rot is their relatively high volatile acidity level. Its origin can be accidental, due to the presence of lactic acid bacteria in juice and especially acetic acid bacteria on grapes. Yeasts also form some volatile acidity, due to the corresponding fermentation difficulties of these juices (Section 2.3.4). 

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