Purification and characterization of an alpha-L-rhamnosidase from Aspergillus niger

Homologous Expression and Characterization of α-L-rhamnosidase from Aspergillus niger for the Transformation of Flavonoids

Aspergillus niger has been used for homologous and heterologous expressions of many protein products. In this study, the α-L-rhamnosidase from A. niger (Rha-N1, GenBank XP_001389086.1) was homologously expressed in A. niger 3.350 by Agrobacterium tumefaciens-mediated transformation. The enzyme activity of Rha-N1 was 0.658 U/mL, which was obtained by cultivation of engineered A. niger in a 5-L bioreactor. Rha-N1 was purified by affinity chromatography and characterized. The optimum temperature and optimum pH for Rha-N1 were 60 °C and 4.5, respectively. Enzyme activity was promoted by Al³⁺, Li⁺, Mg²⁺, and Ba²⁺ and was inhibited by Mn²⁺, Fe³⁺, Ca²⁺, Cu²⁺, and organic solvents. The result indicated that rutin was the most suitable substrate for Rha-N1 by comparison with the other two flavonoid substrates hesperidin and naringin. The transformed products of isoquercitrin, hesperetin-7-O-glucoside, and prunin were identified by LC-MS and ¹H-NMR.

Glycosidically bound aroma precursors in fruits: A comprehensive review

Fruit aroma is mainly contributed by free and glycosidically bound aroma compounds, in which glycosidically bound form can be converted into free form during storage and processing, thereby enhancing the overall aroma property. In recent years, the bound aroma precursors have been widely used as flavor additives in the food industry to enhance, balance and recover the flavor of products. This review summarizes the fruit-derived aroma glycosides in different aspects including chemical structures, enzymatic hydrolysis, biosynthesis and occurrence. Aroma glycosides structurally involve an aroma compound (aglycone) and a sugar moiety (glycone). They can be hydrolyzed to release free volatiles by endo- and/or exo-glucosidase, while their biosynthesis refers to glycosylation process using glycosyltransferases (GTs). So far, aroma glycosides have been found and studied in multiple fruits such as grapes, mangoes, lychees and so on. Additionally, their importance in flavor perception, their utilization in food flavor enhancement and other industrial applications are also discussed. Aroma glycosides can enhance flavor perception via hydrolyzation by β-glucosidase in human saliva. Moreover, they are able to impart product flavor by controlling the liberation of active volatiles in industrial applications. This review provides fundamental information for the future investigation on the fruit-derived aroma glycosides.

Extracellular phytase from Aspergillus niger CFR 335: purification and characterization

Phytase, that is extensively used as a feed additive is capable of hydrolyzing phytic acid, an antinutrient found in about 60-80 % of all the plant commodities. This enzyme improves the bioavailability of essential minerals such as Ca(2+), Mg(2+), P, Zn(2+), Fe(3+), that are bound to phytic acid. An extracellular phytase from a local fungal isolate, Aspergillus niger CFR 335 was purified to homogeneity through a three-step column chromatography using DEAE-Sephadex anion exchanger. An active fraction of the enzyme was obtained with NaCl gradient of 2.5 M in DEAE Sephadex column. The enzyme was purified up to 16 fold with a yield of 28.5 %. Substrate specificity studies revealed a highest specific activity of 32.6 ± 3.1 U/mg for sodium phytate with the Km value of 0.08 ± 0.1 mM. The molecular weight of the enzyme was 66 kDa with an optimum temperature of 30 °C and pH 4.5. Up to 80 % of the activity was retained even after storing the enzyme for 6 months at 4 °C.

Aspergillus niger DLFCC-90 rhamnoside hydrolase, a new type of flavonoid glycoside hydrolase

A novel rutin-α-L-rhamnosidase hydrolyzing α-L-rhamnoside of rutin, naringin, and hesperidin was purified and characterized from Aspergillus niger DLFCC-90, and the gene encoding this enzyme, which is highly homologous to the α-amylase gene, was cloned and expressed in Pichia pastoris GS115. The novel enzyme was classified in glycoside-hydrolase (GH) family 13.

Construction of a genetically modified wine yeast strain expressing the Aspergillus aculeatus rhaA gene, encoding an alpha-L-rhamnosidase of enological interest

The Aspergillus aculeatus rhaA gene encoding an alpha-L-rhamnosidase has been expressed in both laboratory and industrial wine yeast strains. Wines produced in microvinifications, conducted using a combination of the genetically modified industrial strain expressing rhaA and another strain expressing a beta-glucosidase, show increased content mainly of the aromatic compound linalool.

Purification and characterization of two different alpha-L-rhamnosidases, RhaA and RhaB, from Aspergillus aculeatus

Two proteins exhibiting alpha-L-rhamnosidase activity, RhaA and RhaB, were identified upon fractionation and purification of a culture filtrate from Aspergillus aculeatus grown on hesperidin. Both proteins were shown to be N glycosylated and had molecular masses of 92 and 85 kDa, of which approximately 24 and 15%, respectively, were contributed by carbohydrate. RhaA and RhaB, optimally active at pH 4.5 to 5, showed K(m) and V(max) values of 2.8 mM and 24 U/mg (RhaA) and 0.30 mM and 14 U/mg (RhaB) when tested for p-nitrophenyl-alpha-L-rhamnopyranoside. Both enzymes were able to hydrolyze alpha-1,2 and alpha-1,6 linkages to beta-D-glucosides. Using polyclonal antibodies, the corresponding cDNA of both alpha-L-rhamnosidases, rhaA and rhaB, was cloned. On the basis of the amino acid sequences derived from the cDNA clones, both proteins are highly homologous (60% identity).