## 1 Introduction  
Hemicelluloses are a complex group of polysaccharides found in plant cell walls in close association with lignin and cellulose. Mannan, one of the major constituent groups of hemicellulose in softwood, is composed of linear or branched polymers derived from sugars such as d-mannose, d-galactose, and d-glucose [1; 2; 3]. The linear mannan structure is composed of linear main chains of 1,4-linked \(\beta\)-d-mannopyranosyl residues [4]. It also contains galactoglucomanan with mannose/glucose/galactose residues in a ratio of 3:1:1 and glucomanan with mannose/glucose residues in the ratio of 3:1 [5]. The mannan structure may be substituted with branches containing acetyl and galactosyl residues. The enzyme systems that catalyze hydrolysis of mannan include \(\beta\)-mannanase, \(\beta\)-glucosidase, and \(\beta\)-mannosidase. Additional enzymes such as acetylmannan esterase and \(\alpha\)-galactosidase are important for the removal of side chain groups of mannan [6]. Based on the primary structures of their catalytic domains, \(\beta\)-mannanases are found in the glycoside hydrolase families 5, 26, and 113 [4; 7; 8]. These enzyme families present a double-displacement mechanism with retention of anomeric configuration. \(\beta\)-mannanases can be produced by microorganisms, such as bacteria and filamentous fungi [9]. According to [PERSON] and [PERSON] [10], the filamentous fungi strains are the most interesting producers by right of higher yields of extracellular enzymes and association with cellulases production. Thermostable \(\beta\)-mannanases have great advantages, such as reducing the risk of contamination, increasing the substrate solubility, and improving the mass transfer rate [8; 10].  
Mannan-degrading enzymes are not only of interest in plant physiology, but also have potential applications in a wide range of industrial enzyme markets such as in the food and feed industries [3]. \(\beta\)-Mannanases can be applied to preparation of mannooligosaccharides improving digestion and absorption of nutrition in feedstuff, reducing viscosity of the coffee extracts and extraction of vegetable oils from leguminous seeds [10; 11]. As example of \(\beta\)-mannanase application, [PERSON] _et al._[12] reported that the supplementation of \(\beta\)-mannanase in feeds containing guar meal reduced intestinal viscosity and feed conversion ratio, increased body weight and alleviated the deleterious effects associated with guar meal feeding. Agro-industrial residues, including soybean husk, represent an alternative source available for microbial growth and enzyme production [13]. The residual plant biomass is a valuable source of lignocellulosic components, which can be converted into various value-added products [14]. The treatment of spent coffee ground (a residue generated in the production of instant coffee) with endo-mannanase is reported as an alternative for the release of mannooligosaccharides, which have potential application as prebiotic products in human and animal feed [11]. [PERSON] _et al._[10] reported an enzyme solution from _Penicillium chrysogenum_ QML-2 (containing xylanase and mannanase activities) that was applied to saccharification of aqueous ammonia solution pretreated corn cob powder. In this case, maximum yields of xylose (236.63 mg/g) and reducing sugar (553.94 mg/g) were obtained.  
The focus of the present work was to characterize the properties of a \(\beta\)-mannanase preparation (Man 58) from _Aspergillus foetidus_ (_A. foetidus_) when grown on soybean husk as substrate. To our knowledge, this is the very first report describing partial purification and characterization of a \(\beta\)-mannanase from _A. foetidus_.