Lactose fermenters

Cheese whey soHds contain 70—75% lactose, which can serve as the carbon source for lactose fermenting yeasts such as Klujveromjcesfragilis. The total volume produced is considerably smaller than for the other yeasts described. 

Lactase (P-galactosidase) is produced commercially from the lactose fermenting Klujveromjcesfragilis. The enzyme has a pH optimum of 6—7 and is used ia the hydrolysis of lactose ia milk or skim milk. 

Shigella are nonmotile, gram-negative, non-lactose-fermenting rods and are members of the family Enterobacteriaceae. There... 

Salmonella are motile, non-lactose-fermenting, gram-negative bacilli. In salmonellosis, the organisms penetrate the epithelial lining to the lamina propia with production of diffuse inflammation. The distal ileum and colon are sites of infection. 

The production of fermented milks no longer depends on acid production by the indigenous microflora. Instead, the milk is inoculated with a carefully selected culture of LAB and for some products with LAB plus lactose-fermenting yeasts (Table 10.12). The principal function of LAB is to produce acid at an appropriate rate via the pathways summarized in Figure 10.12. The yoghurt fermentation is essentially homofermentative but the characteristic flavour of cultured buttermilk is due mainly to diacetyl which is produced from citrate by Lactococccus lactis ssp. lactis biovar diacetylactis, which is included in the culture for this product (Figure 10.31). 

Kefir and Koumiss contain about 1 and 6% ethanol, respectively, which is produced by lactose-fermenting yeasts, usually Kluyveromyces marxianus. The ethanol modifies the flavour of the products and the C02 produced in the fermentation affects both their flavour and texture. Koumiss, which is produced traditionally from mares milk, mainly in Russia and surrounding areas of Asia, is not in fact coagulated. 

Excessive or insufficient acid development during manufacture can produce variability in the moisture content of cheese and defects in flavor, body, texture, color, and finish (Van Slyke and Price 1952). The rate of lactose fermentation varies with the type of cheese, but the conversion to lactic acid is virtually complete during the first weeks of aging (Van Slyke and Price 1952 Turner and Thomas 1980). Very small amounts of lactose and galactose may be found in cheese months after manufacture. (Huffman and Kristoffersen 1984 Turner and Thomas 1980 Harvey et al. 1981 Thomas and Pearce 1981). Turner and Thomas (1980) showed that the fermentation of residual lactose in Cheddar cheese is affected by the storage temperature, the salt level in the cheese and the salt tolerance of the starter used. 

In Russia, a popular milk drink traditionally made from unpasteurized mare s milk is known as kumiss. The fermentation is caused principally by L. bulgaricus, lactose-fermenting Torula yeasts, and Lactobacillus leichmannii. 

Lactose-fermenting yeasts have been known for some time, but their use to produce ethyl alcohol and yeast from whey received serious attention only much later. Certain Torula species yield more alcohol than might have been expected from statements in the literature. Four kefir yeasts, two Torula species, one of Torulopsis and one additional yeast species, produced alcohol yielding 68 to 80% of the theoretical quantity. A maximal yield, 80.3%, based on a theoretical yield of 4 moles of alcohol per mole of lactose fermented, was obtained with a strain of Torula cremoris in a 21.7-hr fermentation at 30 to 32°C (Marth 1974). 

Lactose-fermenting yeasts contain the following vitamins in milligrams percent on a dry basis vitamin A, traces Bi, 12.8 B2, 4.4 nicotinic acid, 8.3 ascorbic acid, 7.8 and provitamin A, 40.5 (Springer... 

Cords, B. R. and McKay, L. L. 1974. Characterization of lactose-fermenting revertants from lactose-negative Streptococcus lactis C2 mutants. J. Bacteriol. 119, 830-839. 

Thomas, T. D. 1976B. Regulation of lactose fermentation in Group N streptococci. Appl. Environ. Microbiol. 32, 474-478. 

Thomas. T.D., Pearce, K.N. 1981. Influence of salt on lactose fermentation and proteolysis in Cheddar cheese. N.Z. J. Dairy Sci. Technol. 16, 253-259. 

Continuous lactic acid production from whey permeate is carried out in a process that consists of three separate operations in (1) a bioreactor, (2) an ultrafiltered (UF) model, and (3) an ED cell. With the UF process, recycling of all or part of the biomass is achieved. It is also possible to separate low molecular weight metabolites, such as sodium lactate, resulting from lactose fermentation. This product can then be extracted and concentrated continuously by ED. A disadvantage of continuous lactic acid production is, however, that it tends to clog the ultrafiltration membranes, which restricts permeate flow (Bazinet, 2004). 

De Raucourt, A., Girard, D., Prigent, Y., and Boyaval, P. 1989. Lactose fermentation with cells recycled by ultra-filtration and lactate separation by electrodialysis Modeling and simulation. Applied Microbiology and Biotechnology 30 521-527. 

In the membrane fdtration method (Standard Method 9211B), the test sample is passed through a membrane filter and the filter is placed on the surface of a plate containing M-7 FC agar medium. After incubating for 7 h at 41.5 °C, the presence of yellow fecal cohform colonies (from lactose fermentation within the FC agar) serves as a positive test. 

Yersinia spp. are non-lactose-fermenting gram-negative coccobacilli that are widely distribnted in natnre. The genns Yersinia includes six species known to cause disease in humans. The best known species is Y pestis, the causative agent of plague, which is usually spread by bites from infected animals, such as fleas, rodents, or cats. Y. enterocolitica and, to lesser extent, Y. pseudotuberculosis are most likely associated with intestinal infection, but overall, both are a relatively infrequent cause of diarrhea and abdominal pain. More than 50 serotypes of Y. enterocolitica exist of these, serotypes 0 3, 0 8, and 0 9 are associated most frequently with enterocolitis. Infections are reported commonly from northern Europe, and the peak incidence occurs during the winter months. 

Whey wine is an experimental product being test marketed. After deprotein-izing with UF, the lactose is fermented for about a week by special lactose-fermenting yeast. The finished product is a pale-yellow, tart, dry wine with a subdued aroma and bouquet. 

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