.beta.-glucosidase from filamentous fungi, and uses thereof

Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing compound containing saccharide radical

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435 72, 435 99, 435171, 435209, 4352541, 435244, 426590, C12P 1944, C12P 102, C12N 138, A23L 200

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060871318

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BRIEF SUMMARY
The present invention relates to a .beta.-glucosidase of fungal origin whose activity is weakly inhibited in the presence of high glucose levels, as well as to the method for producing it, and to its uses.
The .beta.-D-glucoside glucohydrolases (EC 3.2.1.21) commonly called .beta.-glucosidases catalyze the hydrolysis of alkyl- and aryl-.beta.-D-glucosides, as well as that of cellobiose. The use of these enzymes has been proposed in various fields.
It has in particular been proposed to use .beta.-glucosidases for the hydrolysis of nonodorous glycoside precursors of odorous molecules. Indeed, in a large number of fruits such as grapes [WILLIAMS et al., American Chemical Society, Washington, D.C., 35-48, (1989), GUNATA et al., J. Chromatogr., 331, 83-90, (1985)], apricot, peach, apple, passion fruit [KRAMMER et al., J. Agric. Food Chem., 39, 778-781, (1991)], a very high proportion of the molecules responsible for the flavor (terpenols, C13 norisoprenoids, phenols) are bound to sugars, in a nonodorous form.
The sugar part of these glycosides has, for example, been described in the case of grape berries [WILLIAMS et al., Phytochemistry, 21, 2013-2030, (1982)]; VOIRIN et al., J. Chromatogr. 592, 269-281 (1992)]. Present therein are .beta.-D-glucosides, rutino-sides (6-O-.alpha.-L-rhamnopyranosyl-.beta.-D-glucopyranosides), 6-O-.alpha.-L-arabinofuranosyl-.beta.-D-glucopyranosides and 6-O-.beta.-D-apiofuranosyl-.beta.-D-glucopyranosides. In grapes, as well as in other fruits, the aglycone is always bound to glucose, whether in the case of mono- or of diglycosides.
The glycosidic precursors constitute a substantial part of the flavor potential in fruits, because the proportion of sugar-bound flavor is often greater than the proportion of corresponding free flavor [GUNATA et al., J. Chromatogr. 331, 83-90, (1985); KRAMMER et al., J. Agric. Food Chem. 39, 778-781, (1991)].
Previous studies carried out by the Inventors' team at the Flavor and Natural Substances Laboratory at the Institute of Grapevine Products, INRA of Montpellier, have made it possible to elucidate the mechanism of enzymatic hydrolysis of the glycosidic precursors of grape berry flavor. The terpenic diglyco-sides are hydrolyzed in two stages: in a first stage, .alpha.-L-rhamnopyranosidase, or an .alpha.-L-arabinofuranosidase, or a .beta.-D-apiofuranosidase, cuts the glycoside bond (1.fwdarw.6) and liberates the corresponding monoglucoside. A .beta.-D-glucopyranosidase is then used to liberate the aglycone from the monoglucosides formed. In the case where the substrate contains only monoglucosides, the hydrolysis is carried out directly without requiring the first stage.
Knowledge of this mechanism and of the properties of the enzymes involved have made it possible to develop a method for producing flavors from their glycosidic precursors, which is the subject of patent application EP 9,001,545, and the production of enzymatic preparations of fungal (particularly Aspergillus niger) origin which are capable of liberating flavor molecules from glycosides [GUNATA et al., Progress in Flavour Precursor Studies, SCHREIR, P., WINTERHALTER, P., Eds, Allured: Weaton (USA),219-234, (1993); GUNATA et al., J. Inter. Sci. Vigne Vin 24, 3, 133-143, (1990)].
The use of .beta.-glucosidase may also make it possible to make other improvements to the organoleptic qualities of products derived from fruits: this is the case for citrus juices, whose bitterness is attributed in part to a glycoside (naringin=naringenin-7-rhamnosylglucoside). Hydrolysis by the successive action of an .alpha.-rhamnosidase and of a .beta.-glucosidase makes it possible to eliminate this bitterness.
However, the .beta.-glucosidase activity of fungal origin such as that of A. niger is strongly inhibited by glucose [WOODWARD and WISEMAN, Enzyme Microbio. Technol. 4, 73-79, (1982); GUNATA et al., Progress in Flavour Precursor Studies; SCHREIER, P., WINTERHALTER, P., Eds, Allured: Wheaton (USA), 219-234, (1993)].
This limits its use for the treatment of products containing glucose, such as fruit jui

REFERENCES:
Derwent Caplus ACS 1997:87700 Mallozzi et al "Effect of flavonoids on Aspergillus flavus growth and aflatoxin production" Rev. Microb. (1996, 27 (3) pp. 161-165.
Derwent Caplus ACS 1970:506534 Haluk et al Bull Soc. Chim Biol (1970) 52, (6) pp. 667-677.

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