Conversion of Lactose

Figu re 3.4 Comparison of the performance of the immobilized enzyme microreactors during continuous conversion of lOOmM of lactose (80°C and pH 5.5) [21,22]. GPMR (full circles) PDMS microreactor (full squares). 

Reactions were performed using a volumetric enzyme activity of82U/ml (GPMR, two stacked plates, and total volume of 49pl) and 6U/ml (PDMS microreactor and total volume of167pl). 

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FIGURE 28-6 Lactose metabolism in /. coli. Uptake and metabolism of lactose require the activities of galactoside permease and /3-galactosidase. Conversion of lactose to allolactose by transglycosyla-tion is a minor reaction also catalyzed by /3-galactosidase. 

When lactose is used as a substrate for fermentation processes, a wide variety of end products are produced. Some processes are in commercial operation, for example, the Carbery, Ireland, process for the production of alcohol from whey permeate. This plant produces about 22,000 liters of alcohol from 600,000 liters of whey permeate per day. The conversion of lactose to alcohol is about 86%. Single-cell protein has been produced from whey by a Wisconsin plant for many years this plant also produces potable alcohol. 

The most important fermentative reaction used in dairy processing is the homofermentative conversion of lactose to lactic acid. The efficient manufacture of high-quality cultured products, including most cheese varieties, yogurt, and cultured buttermilk, requires a rapid and consistent rate of lactic acid production. Lactic acid helps to preserve, contributes to the flavor, and modifies the texture of these products. Nearly all starter cultures used to produce acidified dairy products contain one or more strains of lactic streptococci, because these organisms can produce the desired acidity without causing detrimental changes in flavor or texture. Strains of lactic streptococci can be classified as... 

Conversion of lactose into edible protein for animal or human consumption has appeal because of trends in nutrition which emphasize the importance of protein in diets. The high content of purines and pyrimidines in yeast cells is a limitation in consumption of yeasts by humans. These materials in the diet can lead to high levels of uric acid in blood, which may then lead to gout. Principles underlying microbiological conversion of sugars to protein have been available for many years. 

Conversion of lactose to allolactose, the natural inducer of the lac operon. Ultimately, lactose is broken down to its constituent monosaccharides, galactose and glucose. 

Whey is the liquid obtained by separating the coagulum from milk, cream, and/or skim milk in cheese making. Whey obtained from the process in which a significant amount of lactose is converted to lactic acid or obtained from the curd formed by direct acidification of milk is known as acid-type Whey. Whey obtained from the process in which there is insignificant conversion of lactose to lactic acid is known as sweet-type Whey. The acidity of Whey may be adjusted by the addition of safe and suitable pH-adjusting ingredients. The final product is pasteurized and is available as a liquid or dry product. 

Conversion of lactose to galactose and glucose Stabilization of milk proteins in frozen milk by removal of lactose... 

Figure 3.4 summarizes the results of microreactor experiments in which the effect of a varied flow rate on the enzymatic conversion of lactose was analyzed. The... 

It may be noted that simple alkaline-catalyzed isomerization of glucose to fructose is possible, but gives rise to serious lactic acid and coloured by-product formation. Alkaline catalysis, however, is still applied for the conversion of lactose to lactulose, used in treatment of constipation and PSE. The reason is that no enzyme has been found that is able to isomerize the glucose unit of lactose into a fructose moiety. As a consequence, a low conversion is applied or borate is used as a protecting group. In the latter case extra separation and recycle steps are required. 

Milk Substrates Cheese is perhaps the oldest of the fermented foods. (Fig. 1) The basic underlying microbial transformation in all cheese manufacture is the conversion of lactose of milk into lactic acid. The microorganisms in the starter culture contribute significantly to the flavor of the cheese. The secondary microbial flora of the cheese also elaborate taste and odor active substances. These organisms may be present as chance contaminants or introduced intentionally(8), and result in distinctive types of cheeses such as Cheddar, blue veined and Swiss. 

The primary glycolytic event, the conversion of lactose to lactate, is normally mediated by the starter culture during curd preparation or the early stages of cheese ripening. In cases where glycolysis has not been completed by the starter, nonstarter lactic bacteria may contribute. The metabolism of lactose was discussed in Section IIIA5. 

Fluid milk contains about 5 % of lactose. Lactose has low solubility and low sweetness, and a significant part of the world s population does not tolerate lactose in the diet. For these reasons the conversion of lactose to the component sugars, glucose and galactose would be worthwhile. Commercial lactases have been developed from lactose-fermenting yeasts and shown to have utility in the hydrolysis of lactose in a variety... 

The Amadori rearrangement of glycosylamines has long been employed as a eonvenient access method to ketose derivatives. For example, Kuhn et demonstrated a facile conversion of lactose into lactulose in 3 steps via diazotization of lactulosamine (Scheme 42). 

A third, more complex possibility arises from the anaerobic conversion of lactose to lactic acid in a first process step using lactobacilli capable of producing lactic acid with high yields (more than 0.9 g of lactic acid per gram of carbon source). In a subsequent aerobic cultivation, lactic acid is metabolized to acetyl-CoA and further to PHAs by numerous strains, e.g. most common PHA producers such as C. necator, A. latus and A. vinelandii. Alternatively, lactic can be converted to PLA, if wanted. Hence, for PHA production from whey, the decision whether to apply whey lactose, hydrolysed whey lactose or a first-step fermentation towards lactic acid mainly depends on the production strain (Fig. 6). 

Champluvier B, Francart B, Rouxhet PG. (1989b). Co-immobilization by adhesion of (1-galactosidase in nonviable cells of Kluyveromyces lactis with Klebsiella oxytoca-. Conversion of lactose into 2,3-butanediol. Biotechnol Bioeng, 34, 844—853. 

Active immobilized enzyme continuous conversion of lactose... 

The conditions for the maximum conversion of lactose to hexose sugars have been studied by Ramsdell and Webb 75). Using 0.007 M HCl as the hydrolyzing agent and a temperature of 147°, 30 % solutions of lactose are converted to hexose sugars to the extent of 93 % of the theory in less than 65 minutes. A mixture of equal parts of D-glucose and D-galactose is soluble in water to the extent of 42 % at 25°. 

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