Lactic acid substrates conversion

In a series of controlled experiments, Dosi et al. used the conversion of glucose to lactic acid as a model for the potential of controlling (automatically by computer) the concentrations of the constituents.45 Nice schematics for the reactor setup and connections to the computer/NIR spectrometer/microhltration unit, etc., are shown. Six cases are described, each using a conventional batch process. Transition from batch mode to automatic was triggered by predefined criteria such as degree of substrate conversion or biomass concentration. Control charts and comparisons of NIR data with conventional assays are given for all six cases. 

Reactions were studied under the pseudo first-order condition of [substrate] much greater than [initial dihydroflavin]. Under these conditions, the reactions are characterized by a burst in the production of Flox followed by a much slower rate of Flox formation until completion of reaction. The initial burst is provided by the competition between parallel pseudo first-order Reactions a and b of Scheme 3. These convert dihydroflavin and carbonyl compound to an equilibrium mixture of carbinolamine and imine (Reaction a), and to Flox and alcohol (Reaction b), respectively. The slower production of Flox, following the initial burst, occurs by the conversion of carbinolamine back to reduced flavin and substrate and, more importantly, by the disproportionation of product Flox with carbinolamine (Reaction c followed by d). Reactions c and d constitute an autocatalysis by oxidized flavin of the conversion of carbinolamine back to starting dihydroflavin and substrate. In the course of these studies, the contribution of acid-base catalysis to the reactions of Scheme 3 were determined. The significant feature to be pointed out here is that carbinolamine does not undergo an elimination reaction to yield Flox and lactic acid (Equation 25). The carbinolamine (N(5)-covalent adduct) is formed in a... 

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. 

Cellulose powder and milled newspaper were used by Abe and Takagi [23] as the substrate for lactic acid production by L. delbruckii in the presence of cellulase derived from Trichoderma reesei. The highest conversion rate was at pH... 

Under anaerobic conditions, normal excised rat skin and skin extracts in the absence of added substrate produce lactic acid at a low rate. After treatment with sulphur mustard in vivo, residual glycolysis, i.e. no added substrate, of excised but otherwise intact skin remains unaltered. However, if glucose is added to the system, its conversion to lactic acid is almost completely inhibited (Dixon, 1943). 

In liver, most of the phosphoenolpyruvate is formed by the continued action of pyruvate carboxykinase and pyruvate carboxylase. In fact, the carboxykinase reaction determines whether the original substrate, oxaloacetate, is converted to glucose or oxidized in the Krebs cycle. The conversion of pyruvic acid to phosphoenolpyruvate is a rate-limiting step in the conversion of 3-carbon compounds (alanine and lactic acid, for example) to glucose. When glucogenesis is increased e.g./ n diabetes and after the administration of glucocorticoids), carboxylase and carboxykinase activities are also increased. 

Various substrates have been proposed for the synthesis of lactic acid. Many polyols have been reported to be precursors for lactic acid via alkaline hydrothermal conversion. For example, mannitol and xylitol showed a high conversion rate, a maximum LA yield of 25.6% was obtained with sorbitol at 300 °C with 1.75 M NaOH (Zhou et al., 2010). However, studies proved that there is a selectivity of substrates for lactic acid production. This is mainly due to the large number of competitive reactions with the highly functionalized hexitol (Ramirez-Lopez et al., 2010). 

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