Importancia do xilitol no metabolismo e sua obtenção a partir de residuos agricolas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1973

RESUMO

Xylitol is a polyol derived from xylan; it is a caloric sweeting agent which may substitute sucrose in common diet. Hovever as long as its price is not competitive, its use will he restricted to the treatment of meta¬bolic disorders, such as diabetes mellitus, as its utilization does not seen to depend on insulin. Several methods have been tried for the obtention of xylitol. The most widespread nowadays is a chemical one. By treating crushed sugar cane with 1,9% sulfuric acid at 121ºC, 95,4% of xylose is produced by hydrolvsis of xylan within 50 minutes, the solid/liquid ratio being 36:100. When a tem¬perature of 100ºC is used, the efficiency decreases and solid/liquid ratio is disadvantageous - 6:100. By catalytic reduction of xylose in the presence of metallic nickel in autoclave at a temperature of 150ºC for 5 hours, 85% of this compound is converted to xylitol and a variety of by-products are pro¬duced. In a study aiming the production of 15,00 t of xylitol in one year, it was estimated that the price of one ton would be Cr$ 1,300.00; at the same time, 4,000 t of furfural, 1,800 t of dextrose, 5,00 t of industrial yeast and 25,00 t of lignin were produced. Furthermore two microbiological methods for obtention of xylitol have gained acceptance: one uses xylan as starting material, upon its enzimatic hydrolvsis xylose is formed. The enzyime is xylanase produced by seve¬ral microorganisms, such as sobressaem Chaetomium trilaterale, Tri choderma viride, Aypergillus oryzae, Aspergillus batatae and chiefly Streptomyces xylophagus, capable of hydrolysing all xylan with the production of 7,32 mg of xylose within 15 minutes at a pH ranging from 7 to 8,6. Conversion of xylose to xylitol is also due to enzymatic activity of a number of microorganisms, such Pichia miso, Mirothecium verrucaria, Penicillim chrisogenum and Candida utilis The second microbiological method uses glucose as starting material, which may be obtained by hydrolysis of cellulose, starch, etc. First, through the action of Debaryomyeps hansenii, glucose is converted to D-arabitol. This polyol is then oxidized by Acetobacter suboxidans, producing D-xylulose which on reduction by Candida guilliermondii var. soya, forms xylitol as end-product.

ASSUNTO(S)

adoçantes artificiais - metabolismo

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