A simple method for purifying glycosidases: α-l-rhamnopyranosidase from Aspergillus niger to increase the aroma of Moscato wine

α-l-rhamnopyranosidase (Rha, EC 3.2.1.40) is an enzyme of considerable importance in food technology for increasing the aroma of wines, musts, fruit juices and other alcoholic beverages. The aim of this research is to study the purification of Rha contained in a commercial preparation already used in the winemaking industry. With the procedure adopted, Rha recovery values were excellent (ca 85%), comparable with those we found in a previous paper on the purification of other glycosidases such β-d-glucopyranosidase (βG) and α-l-arabinofuranosidase (Ara) . The Rha purification value (4.3) and drastic reduction in brown compounds (ΔAbs 95%) represent other strengths of the proposed method that has proved inexpensive and simple to apply. In addition, purified Rha has shown itself to be more stable than other glycosidases. This had optimum effect at pH 4, while optimum temperature was 70°C, greater than that found for other glycosidases. The purified enzyme was characterized in terms of the kinetic parameters Km (1.40 mM) and Vmax (1.30 U mg−1 of protein) and subsequently used to increase aroma a model wine solution containing aromatic precursors extracted from the skins of Moscato grapes, with an increase in the content of total terpenols of ca 2.3 times.