- Influence of reaction conditions on the selectivity of the synthesis of lactulose with microbial β-galactosidases
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Commercial β-galactosidase preparations from Bacillus circulans, Kluyveromyces lactis and Aspergillus oryzae were evaluated as catalysts for the synthesis of lactulose. Among them, the enzyme from A. oryzae was selected for further studies. The effect of reaction conditions was then studied on product composition during the kinetically controlled synthesis of lactulose by transgalactosylation with A. oryzae β-galactosidase. Product composition was not affected by pH, temperature, total initial concentration of sugar (lactose plus fructose) and enzyme to substrate ratio within the ranges studied. However, lactose to fructose ratio strongly influenced product composition being then possible to control the lactulose to galacto-oligosaccharide ratio within ample margins. Maximum lactulose yield (0.282 g of lactulose per g initial lactose) was obtained using 1/8 lactose to fructose molar ratio, 50% (w/w) total initial sugars, 40 °C, pH 4.5 and enzyme to initial lactose ratio equivalent to 200 IU/g.
- Guerrero, Cecilia,Vera, Carlos,Plou, Francisco,Illanes, Andres
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- Tuning Ca-Al-based catalysts' composition to isomerize or epimerize glucose and other sugars
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One of the key reactions to achieve good productivity in the transformations of cellulose derived from biomass feedstocks is the isomerization of glucose to fructose, the latest being the platform molecule for obtaining other important derivatives. In this work, Ca-Al containing catalysts based on hydrotalcite-type derived materials were used to perform the selective isomerization of glucose to fructose, and the selective epimerization of glucose to mannose, using water as the solvent under mild reaction conditions. The catalysts showed high activity (conversion = 51-87%), and excellent selectivity (63-88%) towards fructose, compared with the current industrial process based on the glucose transformation via biocatalysis. It was also possible to modulate the selectivity towards fructose or mannose by tuning the amount of basic sites of the catalysts and their composition. The combination of basic and acid sites present in the Ca-Al-based catalysts plays a key role in the reaction, a fact that is discussed in the text together with other important operational parameters. The stability and recyclability of the catalysts were tested, detecting only a small activity loss after 5 consecutive runs. The synthesis of the catalysts and their characterization are also discussed since they are one of the few cases found in the literature of this kind of hydrotalcite-type material with such a high level of Ca incorporation. Some green metrics, such as E-factor, have been calculated to evaluate our system as an environmentally friendly process.
- Ventura, Maria,Cecilia, Juan A.,Rodríguez-Castellón, Enrique,Domine, Marcelo E.
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p. 1393 - 1405
(2020/03/11)
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- Optimization of lactulose synthesis from whey lactose by immobilized β-galactosidase and glucose isomerase
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In the present study, commercially available whey was used as a lactose source, and immobilized β-galactosidase and glucose isomerase were used to synthesize lactulose from whey lactose in the absence of fructose. Optimal reaction conditions, such as lactose concentration, temperature, ionic strength of the buffer, and ratio of immobilized enzymes, were determined to improve lactulose synthesis using immobilized enzymes. Lactulose synthesis using immobilized enzymes improved markedly after optimizing the reaction conditions. When the lactulose synthesis was carried out at 53.5 °C using 20% (w/v) whey lactose, 12 U/ml of immobilized β-galactosidase and 60 U/ml of immobilized glucose isomerase in 100 mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 7.68 g/l and 0.32 mg/U h, respectively. Additionally, when the immobilized enzymes were reused for lactulose synthesis, their catalytic activity was 57.1% after 7 repeated uses.
- Song, Yoon-Seok,Lee, Hee-Uk,Park, Chulhwan,Kim, Seung-Wook
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- ISOMERIZATION AND HYDROLYSIS REACTIONS OF IMPORTANT DISACCHARIDES OVER INORGANIC HETEROGENEOUS CATALYSTS
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Isomerisation and hydrolysis reactions of cellobiose, maltose, and lactose were investigated over various minerals and synthetic zeolite catalysts.Zeolites of type A, X, and Y are the most active for such reactions.Product distributions were determined from batch experiments and are compared with those obtained under homogeneous alkaline conditions.Product distributions indicate that reaction routes consist of parallel hydrolysis and isomerisation of the disaccharides to their corresponding ketoses, followed by hydrolysis of the ketoses.Approximately 10-13percent of the disaccharide reacted is not accounted for in the product distribution, indicating that degradation reactions occur, probably in the alkaline broth of the mixtures.
- Shukla, Rajesh,Verykios, Xenophon E.,Mutharasan, Rajakkannu
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