Enzymatic acylation of flavonoid glycosides by a carbohydrate esterase of family 16.

The acetyl esterase of Trichoderma reesei belonging to carbohydrate esterase (CE) family 16 catalyzes transacylations to carbohydrate moieties of flavonoid glycosides, esculin and rutin. The enzyme recognizes as acyl donors vinyl esters of short carboxylic acids. Esculin was acylated at position 3 of the glucosyl residue in aqueous solutions saturated with vinyl acetate and vinyl propionate. The yields of esculin monoacetate and monopropionate of esculin in aqueous medium (esculin 40 mM, enzyme 40 µg/ml, 40 °C, 3 days) were 67 and 55 %, respectively. Replacement of water by 2-propanol was required for a similar acylation of rutin at 4 mM concentration. The yields of rutin monoacetate and propionate were 60 and 30 %, respectively. The results indicate that the enzyme could be used for an easy modification of solubility and hydrophobicity of glycosylated compounds, including drugs and functional food additives.

Citronella as an insect repellent in food packaging.

Of five commercial plant extracts (citronella, garlic oil, neem extract, pine oil, and pyrethrum), citronella was found to be effective in deterring the infestation of cartons containing muesli and wheat germ by red flour beetles. The chemical components were applied as part of a coating on the carton board. In an experimental set up that accelerates infestation over a 2 week period, citronella-treated cartons (0.2 g/m2 of carton board) reduced beetle infestation to approximately 50% of the level observed in control cartons. Evidence was provided to indicate that an insect repellent effect persists for at least 16 weeks. Additional work on the controlled release of the insect repellent would be required to prolong the effect.

High-humidity performance of paperboard after treatment with xylanase, endoglucanse, and their combination.

For paperboard used to produce packaging, treatment of its fiber constituents with commercial enzymes can improve its compressive strength under cycling and high-humidity conditions. Xylanase that selectively removes pulp xylan (ca. 2% of the pulp by mass) yielded most of the observed beneficial effects, which did not appear related to the packing of the fiber network in the sheet or to the uptake of moisture at high humidity. There was also a marginal increase in the drainability of the pulp slurry, which may increase the rate of papermaking. Although endoglucanase activity also enhances certain pulp properties, there was little benefit in adding it to the xylanase treatment.

Transacetylations to carbohydrates catalyzed by acetylxylan esterase in the presence of organic solvent.

Various conditions were applied to test the ability of acetylxylan esterase (AcXE) from Schizophyllum commune to catalyze acetyl group transfer to methyl beta-D-xylopyranoside (Me-beta-Xylp) and other carbohydrates. The best performance of the enzyme was observed in an n-hexane-vinyl acetate-sodium dioctylsulfosuccinate (DOSS)-water microemulsion at a molar water-detergent ratio (w(0)) of about 4-5. Although the enzyme was found to have a half-life of about 1 h in the system, more than 60% conversion of Me-beta-Xylp to acetylated derivatives was achieved. Under identical reaction conditions, the enzyme acetylated other carbohydrates such as methyl beta-D-cellobioside (Me-beta-Cel), cellotetraose, methyl beta-D-glucopyranoside (Me-beta-Glcp), 2-deoxy-D-glucose, D-mannose, beta-1,4-mannobiose, -mannopentaose, -mannohexaose, beta-1,4-xylobiose and -xylopentaose. This work is the first example of reverse reactions by an acetylxylan esterase and a carbohydrate esterase belonging to family 1.