Milk lactic acid content

Homofermentative lactic acid bacteria (such as Lactococcus lactis and Streptococcus lactis) produce (-l-)-L-lactic acid (e.g. in sour cream). Both isomers, (-l-)-L-lactic acid and (-)-D-lactic acid (8-65), are formed during milk fermentation by heterofermen-tative bacteria (lactic acid bacteria are mostly heterofermentative bacteria) and lactic acid thus also occurs as a racemate in sauerkraut, pickled cucumbers, olives and silage. For example, bacteria of the genus Leuconostoc produce d-lactic acid, while bacteria Pediococcus acidilactici and other bacteria produce racemic lactic acid. The content of lactic acid in dairy products is 0.5-1.0%. L-Lactic acid in yoghurt represents about 54% and in sour cream 96% of the total lactic acid content. The total lactic acid content in sauerkraut is 1.5 2.5%, in fermented cucumbers it ranges from 0.5 to 1.5% and fermented green olives contain 0.8 to 1.2% lactic acid. 

Yogurt is manufactured by procedures similar to buttermilk. Milk with a fat content of 1—5% and soHds-not-fat (SNF) content of 11—14% is heated to ca 82°C and held for 30 minutes. After homogenization the milk is cooled to 43—46°C and inoculated with 2% culture. The product is incubated at 43°C for three hours in a vat or in the final container. The yogurt is cooled and held at <4.4° C. The cooled product should have a titratable acidity of not less than 0.9% and a pH of 4.3—4.4. The titratable acidity is expressed in terms of percentage of lactic acid [598-82-3] which is deterrnined by the amount of 0.1 AiNaOH/100 mL required to neutralize the substance. Thus 10 mL of 0.1 AiNaOH represents 0.10% acidity. Yogurts with less than 2% fat are popular. Fmit-flavored yogurts are also common in which 30—50 g of fmit are placed in the carton before or with the yogurt. 

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. 

To increase curd elasticity and improve eye formation, the milk used to produce Swiss cheese must be clarified. Standardization of the fat content of the milk after clarification ensures uniform composition. Rennet and lactic acid from the bacteria cause casein coagulation. Swiss cheeses made in the United States are cured for three to four... 

Vitamins and Minerals. Milk is a rich source of vitamins and other organic substances that stimulate microbial growth. Niacin, biotin, and pantothenic acid are required for growth by lactic streptococci (Reiter and Oram 1962). Thus the presence of an ample quantity of B-complex vitamins makes milk an excellent growth medium for these and other lactic acid bacteria. Milk is also a good source of orotic acid, a metabolic precursor of the pyrimidines required for nucleic acid synthesis. Fermentation can either increase or decrease the vitamin content of milk products (Deeth and Tamime 1981 Reddy et al. 1976). The folic acid and vitamin Bi2 content of cultured milk depends on the species and strain of culture used and the incubation conditions (Rao et al. 1984). When mixed cultures are used, excretion of B-complex vita-... 

Kim, Y. J., and Liu, R. H. 2002. Increase of conjugated linoleic acid content in milk by fermentation with lactic acid bacteria. J. Food Sci., 67,1731-1737. 

The inhibition of the enzyme tyrosinase may very well be a key to the control of melanoma, and some of the known inhibitors include eommon substances. Thus, vitamin C, among other common and uncommon substances, has been listed as an enzyme inhibitor for tyrosinase in M.K. Jain s Handbook of Enzyme Inhibitors, 1965-1977 (1982). In addition to ascorbic acid (vitamin C), these other substances include the following halide ion (e.g., from the chloride of common salt, or from iodides and fluorides) butyric acid (from rancid butter) lactic acid (the end product of cancer cell metabolism, found naturally in sour milk products) oxalic acid (ordinarily considered toxic, although it occurs naturally in rhubarb and wood sorrel, etc.) formic acid (a component of ant stings) tyrosine itself and deadly cyanide (which is a chemically bound component of laetrile), as found in almonds (notably bitter almonds), in apricot seeds, and in certain legumes such as beans, etc., although the heat from cooking may drive off the cyanide content. 

Direct acidification with HCl or in situ production of lactic acid by a mesophilic lactic starter still dominate in the production of acid casein. A relatively recent development in the production of acid casein is the use of ion exchangers for acidification. In one such method, a portion of the milk is acidified to approximately pH 2 at 10°C by treatment with a strong acid ion exchanger and then mixed with unacidified milk in proportions so that the mixture has a pH of 4.6. The acidified milk is then processed by conventional techniques. A yield increase of about 3,5% is claimed, apparently due to the precipitation of some proteose-peptones. The resulting whey has a lower salt content than normal and is thus more suitable for further processing. The elimination of strong acid reduces the risk of corrosion by the chloride ion (Cl ) and hence cheaper equipment may be... 

Thus the hypothesis of Metchnikoff on the change testinal flora caused by fermented milk is verified by ba logical and chemical analyses. This point appears to be I all discussion. But it still remains necessary to veri mechanism of the action and to see if really, as is sup the therapeutic effect of fermented milk comes from the acid. Bulgarian ferment which has been isolated from hourt is a very active producer of acid. Inoculated into i milk, it rapidly and almost completely transforms the 1 into lactic acid. From this it is deduced that in the orj a similar phenomenon takes place. This conclusion, ho requires verification. Above all else, it would be nec to show that the ferment produces the same effect in th< intestine as it does in vitro. It would also be necessi establish the presence in this region of appreciable qua of free lactic acid after a treatment with fermented milk, proofs have not been found. Moreover, we know ths content of the large intestine has, on the contrary, an a... 

In a number of other studies, GC-MS of DMOX derivatives has been utilized to determine the CLA isomer distribution from a variety of sources. The structures of pure isomers of 9c,llt-18 2 and 10f,12c-18 2, isolated by crystallization of a CLA mixture prepared by alkali-isomerization of linoleate, were confirmed (67). The presence of 9c,llt-18 2 was established in chocolate (49). In conjunction with GC-FTIR, all possible geometrical isomers of 9,11-18 2 (c,i > t,t > c,c and t,c) were detected in human adipose tissue (10). In dehydrated castor oil, although the 9,11 isomers (c/i, c,c and t,t) appeared to be the most abundant, 7,9- and 8,10-18 2 (c/t and but not c,c) were also detected with the aid of SPA (46). The presence of It, 9c-18 2 (as well as lower levels of 7c,9c-, lt,9t- and possibly 7c,9f-18 2) was confirmed in cow s milk, cheese, beef, and human milk and adipose tissue (9). Together with silver-ion HPLC, the isomer distribution in different tissues of pigs fed commercial CLA was determined (2). The CLA content of lactic acid bacteria (44), and the nature of the CLA isomers formed as a result of add-catalyzed methylation of allylic hydroxy oleates (secondary hpid autoxidation products) (47) were also established. 

Bacteriologists found yeast, Sarcina ventriculi, in the stomach, sometimes in enormous masses. Because its optimal pH is 1.5 to 5.0, it is absent from neutral gastric contents. Clinical chemists said no more than that its fermentative processes may be inferred. Lactic acid bacilli of milk were found in gastric contents,... 

FIGURE 4.9. Correlation of I actio acid content (%) and H. pylori inhibition (mm) in soy milk fermentations (a) with six different lactic acid bacteria strains and (b) with LP2 and various concentrations of 99% cranberry + 1% COS (162). 

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