Lactose, conversion

Prior to the first hydrogenation batches, the supported ruthenium catalysts were reduced in the autoclave under hydrogen flow at 200°C for 2 hours (10 bar H2, heating/cooling rate 5°C/min). As the catalyst had been reduced, a lactose solution saturated with hydrogen was fed into the reactor rapidly and the hydrogen pressure and reactor temperature were immediately adjusted to the experimental conditions. Simultaneously, the impeller was switched on. This moment was considered as the initial starting point of the experiment. No notable lactose conversion was observed before the impeller was switched on. 

Where k =Ek j. The concentration ratio expressed with the aid of lactose conversion (X) is Cqa/ca=1-X. A series of first-order test plots were prepared and they revealed that lactose obeys pseudo-first order kinetics very well. 

The concentration versus lactose conversion (X) plots have maxima for B and C, while the concentrations of D, E, F and G increase monotonously with conversion E, F and G showing a steep decrease at high lactose conversions. 

Figure 12.4. Galactitol (left) and sorbitol (right) concentrations versus lactose conversion comparison of consecutive model (1-3, 4b upper figures) and parallel model (1-3, 4a, lower figmes). Reaction conditions 120°C, 50 bar (left) and 60 bar (right), Ru/C catalyst.

Using the previous information provided by the voltammetric measurements, the oxidation of 10 mM lactose was carried out in carbonate buffer and in the presence of lead adatoms ([Pb2+] = 5 x 10 6 M). Electrolysis was carried out in a two-compartment cell (270 cm3) for 3 h by applying the suitable triple pulse potential program repeatedly. The oxidation potential was set to 0.6 V versus RHE on platinum, which had an active surface area of 18 cm2. After 3 h, the recorded quantity of electricity, Qexp = 15.1 C, showed that the lactose conversion yield was 87% and 90% of selectivity in lactobionate was obtained75,76 ... 

The lactose conversion into various derivatives has been achieved using (3-galactosidase immobilized in an ionic liquid-cellulose film [127]. Enzyme was immobilized via GA approach involving the pre-activation of the supported film. This biocomposite architecture allowed to preserve around 60% of the initial -galactosidase activity. The lactose derivatiza-tion was performed in a batch system, where the biocatalyst was repeatedly used for 16 reaction cycles without any drastic decrease of the enzyme activity [127]. 

For FOS produced by microbial FTases, the maximum theoretical yield that can be obtained is 55—60% based on the initial sucrose concentration.This yield caimot be further increased due to the high amounts of glucose that are coproduced during the fermentation, which inhibits the transfructosylating reactions. Yields of GOS (based on the initial lactose concentration) between 15% and 77% (w/w) are achieved when lactose conversion is between 45% and 95%. However, the most common optimized yield values are between 30% and 40% (w/w). ... 

Except the LBL deposition for the enzyme immobilization, lactose has been hydrolyzed using covalently immobilized P-galactosidase on thermally stable carrageenan coated with chitosan. The immobilized enzyme showed lactose conversion of 70 % at 7 h compared to 87 % for the free enzyme. However, the... 

Saccharic acid. Use the filtrate A) from the above oxidation of lactose or, alternatively, employ the product obtained by evaporating 10 g. of glucose with 100 ml. of nitric acid, sp. gr. 1 15, until a syrupy residue remains and then dissolving in 30 ml. of water. Exactly neutralise at the boiling point with a concentrated solution of potassium carbonate, acidify with acetic acid, and concentrate again to a thick syrup. Upon the addition of 50 per cent, acetic acid, acid potassium saccharate sepa rates out. Filter at the pump and recrystaUise from a small quantity of hot water to remove the attendant oxahc acid. It is necessary to isolate the saccharic acid as the acid potassium salt since the acid is very soluble in water. The purity may be confirmed by conversion into the silver salt (Section 111,103) and determination of the silver content by ignition. 

More than 30 years ago Jacob and Monod introduced the Escherichia coli lac operon as a model for gene regulation. The lac repressor molecule functions as a switch, regulated by inducer molecules, which controls the synthesis of enzymes necessary for E. coli to use lactose as an energy source. In the absence of lactose the repressor binds tightly to the operator DNA preventing the synthesis of these enzymes. Conversely when lactose is present, the repressor dissociates from the operator, allowing transcription of the operon. 

Figure 20-6. Pathway of conversion of (A) galactose to glucose in the liver and (B) glucose to lactose in the lactating mammary gland.

Hydrogenation of lactose to lactitol on sponge itickel and mtheitium catalysts was studied experimentally in a laboratory-scale slurry reactor to reveal the true reaction paths. Parameter estimation was carried out with rival and the final results suggest that sorbitol and galactitol are primarily formed from lactitol. The conversion of the reactant (lactose), as well as the yields of the main (lactitol) and by-products were described very well by the kinetic model developed. The model includes the effects of concentrations, hydrogen pressure and temperature on reaction rates and product distribution. The model can be used for optinuzation of the process conditions to obtain highest possible yields of lactitol and suppressing the amounts of by-products. 

At a given temperature the parameters k, KM, and Kx are constants. KM is known as a Mi-chaelis constant and K1 as an inhibition constant. S and Px are the concentrations of reactant S and product Pl9 respectively. What effective space time for a tubular reactor will be required to obtain 80% conversion of the lactose at 40 °C where KM = 0.0528M, Kx = 0.0054M and k = 5.53 moles/(liter-min). The initial lactose concentration may be taken as 0.149M. 

An interesting approach to unususal glycosides (with relatively large carbocyclic aglycon) from lactose was proposed by Thiem s group.85 They postulated a conversion of the glucose part into the cyclooctanone skeleton (Fig. 64). Similar approach to the glucose derivative provided non-substituted cyclooctane.86... 

Orotic acid in the diet (usually at a concentration of 1 per cent) can induce a deficiency of adenine and pyridine nucleotides in rat liver (but not in mouse or chick liver). The consequence is to inhibit secretion of lipoprotein into the blood, followed by the depression of plasma lipids, then in the accumulation of triglycerides and cholesterol in the liver (fatty liver) [141 — 161], This effect is not prevented by folic acid, vitamin B12, choline, methionine or inositol [141, 144], but can be prevented or rapidly reversed by the addition of a small amount of adenine to the diets [146, 147, 149, 152, 162]. The action of orotic acid can also be inhibited by calcium lactate in combination with lactose [163]. It was originally believed that the adenine deficiency produced by orotic acid was caused by an inhibition of the reaction of PRPP with glutamine in the de novo purine synthesis, since large amounts of PRPP are utilized for the conversion of orotic acid to uridine-5 -phosphate. However, incorporation studies of glycine-1- C in livers of orotic acid-fed rats revealed that the inhibition is caused rather by a depletion of the PRPP available for reaction with glutamine than by an effect on the condensation itself [160]. 

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. 

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