An Endo-β-D1,4-Galactanase Secreted by Aspergillus niger During Solid State Fermentation on Soybean Pulp

Abstract

Production ofprotein soybean curd tofu is one ofthe important food industries in Indonesia. However, huge materials as soybean pulp (SP) wastes wrc produced without any economic value. We examined, this material consist of around 60% total sugars, 30% of crud; proteins and 10% lipids. Through GC analysis, SP mainly composted by galactose (40.3%), arabinose (21.1%), X>'.lose (II .7 Vo) and rnannose ( I 0.9%). Solid state fermentation of soybean pulp by introducing Aspergillus niger revealed that lh1s fungus could grew well, indicated by the bulky block spores emerged after four days solid state fermentation. An extracellular galact.an was hested by water extraction containing l % NaCl and 0.1% toluene (v/v). For the purification, the crude enzyme was precipitated using 70"/o saturated and further chromatographcd on a DEAE Butyl Toyopearl 650M, Q·Scpharosc and Mono-Q column chromatography. 111is purification steps, resulted io 3.1% yield and 3.330 fold purification ofenzyme. Estimated by SDS· PAGE, galactanase has molecular weight 44 KDa approximately. The enzyme exhibited maximum activity at pH 3.6 and S5°C, and retained nearly 100%activity in a pH range of3-6 and below ss•c after 30 minutes exposure to respective temperatures. By TLC analysis, it was detected to be capable ofreleasini; galactose and galactosyl oligomcrs (dimer, trimer, tctramer, pcntamer, etc) from soybean pulp nlkali extract substrate, in similar manner as from citrus pectin galactan which is known to have backbone chain of P·D-(1,4) linked. The results, confirmed that this galactanase is an Endo-p.1).1,4-0alactanase (E·PGAL) which specifically hydrolyzed internal fl-D·(l.·1}-galactopyranosc linkage al random.