Lactic spoilage

Mannitol is derived from reduction of the Ci on mannose. In wine, it is produced by the reduction of the C2 on fructose by lactic bacteria. Mannitol is usually present in very small quantities. Higher concentrations are due to lactic bacteria or possibly Botrytis cinerea. Abnormally high concentrations indicate severe lactic spoilage. 

The same lactic bacteria, however, are likely to break down sugars. The consequences may be serious, especially if the wine has a high sugar concentration. The most common situation occurs when alcoholic fermentation stops, leaving the sweet medium open to lactic bacteria. For this reason, winemakers take great care to avoid stuck fermentations, although the bacteria may also take over just before the end of fermentation if it has slowed down. The initial result of this bacterial contamination is malolactic fermentation, but lactic spoilage may follow. This situation must be avoided, especially as the development of these bacteria may prevent the completion of alcoholic fermentation. 

Besides acetic acid, lactic spoilage produces lactic acid and various secondary compounds that contribute to various olfactory defects. Some bacteria convert fructose into mannitol, explaining why this phenomenon used to be known as man-nitic fermentation. 

Sulfiting is the most common technique (Section 8.7.4) for controlling unwanted bacterial development. A 200-300 mg/1 dose of lysozyme provides a useful complementary treatment, especially in white wines, where lysozyme is more stable than in red wines. Lysozyme not only prevents lactic spoilage, but is also effective just after spoilage starts the addition of 25 g/hl reduces the bacterial population very rapidly from several million bacteria to fewer than 100. 

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

Sucrose is often used as a decorative agent to impart a pleasing appearance to baked goods and confections (36). In jams and jeUies, sugar raises osmotic pressure and lowers water activity to prevent spoilage (18). Sucrose is a fermentation substrate for lactic acid in cultured buttermilk (40) and lowers the freezing point of ice cream and other frozen desserts to improve product mouthfeel and texture. 

Lactic acid is generally present in spoiled canned, nonfermented vegetables, and it has been suggested that this can serve as a good indicator of microbial spoilage in this type of foods (Ackland and Reeder 1984). 

Ackland MR and Reeder JE. 1984. A rapid chemical spot test for the detection of lactic acid as an indicator of microbial spoilage in preserved foods. J Appl Bacteriol 56 415—419. 

Rouse S, Harnett D, Vaughan A and Van Sinderen D. 2008. Lactic acid bacteria with potential to eliminate fungal spoilage in foods. J Appl Microbiol 104(3) 915-923. 

Schillinger U and Holzapfel WH. 2006. Lactic acid bacteria. In De W. Blackburn C, editor. Food Spoilage Microorganisms. Cambridge Woodhead, pp. 541-578. 

Modern methods of livestock production are intensive and the environmental conditions stress the animals. The use of antibiotics promotes growth and protects the animals from otherwise certain infection under these conditions. Antibiotic-like compounds formed in lactic acid fermentations prevent proliferation of spoilage and pathogenic microorganisms and increase the shelf life of the products. Nisin is a antimicrobial produced by a lactic acid bacterium and is used in some countries as a food preservative. Some lactic acid bacteria are capable of favorably influencing the fecal flora in man and animals. 

The key feature which draws attention to these peptides in respect to food applications is their ability to inhibit undesirable organisms, either spoilage or pathogenic organisms. Although the peptides from eukaryotic sources appear far-removed from immediate application in foods, it is important to study their mechanism(s) of action in relation to those of lactic acid bacteria to better understand commonalities in structure-function Such commonalities may serve as a base from which to initiate molecular... 

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