Abstract

The aim of this study is to partially purify and characterize xylanases from two spoilage fungiAspergillus awamori and Aspergillus phoenicis. Chromatography of xylanases from A. awamori and A. phoenicis on DEAE-Sepharose separated three (XynI, XynII and XynIII) and two (XynI and XynII) isoenzymes, respectively. Different relative activities percentage were delectated for A. awamori XynI and A. phoenicis XynI toward beachwood, oat spelts and birchwood xylans. The apparent K_m and V_max values for A. awamorii xynI and A. phoenicisxynI were 4.34 and 3.83 mg/ml, 0.28 and 0.38 µmol/ml, respectively. The acidic pH optimum has been reported for A. awamori XynI (pH 5.0) and A. phoenicis XynI (broad pH 4.5 to 5.5). The optimal temperatures of A. awamorii XynI and A. phoenicis XynI were 25 and 60°C, respectively. A. awamori XynI and A. phoenicis XynI were thermal stable up to 40 and 60°C, respectively. The effect of different metal cations on A. awamori XynI and A. phoenicis XynI showed partial inhibition and/or activation effects on the enzyme activity. p-HMB and sodium benzoate had only inhibitory effect on A. phoenicis XynI. Both benzoic and citric acids had moderate inhibitory effects on of A. awamori XynI and A. phoenicis XynI. The benzoic and citric acids were studied as antifungal compounds against A. awamori andA. phoenicis loaded on injured lemon and tomato, respectively.

Key words: Aspergillus awamori, Aspergillus phoenicis, xylanases, characterization.