Monday, April 30, 2007

Enzymatic hydrolysis of wheat flour and soybean flour within a biorefinery concept

Ruohang Wang, Mehmet Melikoglu, Yu Ji, Apostolis Koutinas, and Colin Webb. School of Chemical Engineering and Analytical Science, The University of Manchester, Sackville Street, PO Box 88, Manchester, United Kingdom

This submission summarises the integrative application of the enzyme complexes from Aspergillus awamori and Aspergillus oryzae in wheat flour hydrolysis. Temperature and pH optima of the glucoamylase from A. awamori and of the protease from A. oryzae were identified as 60C, 4.5, and 55C, 3.5, respectively. In addition to hydrolysing gelatinised starch A. awamori glucoamylase also demonstrated the capability of hydrolysing raw starch. Throughout a seven-day storage at 30C the glucoamylase maintained 86.6% of its original activity. When stored at 70C, however, over 98% of the glucoamylase lost their activity in 55 mins. An exponential decay model satisfactorily predicted the deactivation of A. awamori enzymes within a storage temperature range from 30C to 70C. The parameters generated by this model indicated that this deactivation was largely a consequence of thermal rather than proteolytic effects. When applied to hydrolyse a large volume of highly concentrated wheat flour suspension, heating to over 70C for starch gelatinisation was most problematic because of the development into extremely high viscosity. Improvement to heat transfer significantly shortened the heating process, reduced enzyme deactivation, and hence facilitated simultaneous starch gelatinisation and hydrolysis. Near completion of starch hydrolysis was achievable at any temperature between 55C to 70C with proper addition of the A. awamori enzyme complex. Protein hydrolysis, however, was much lower ranging from 13.9% at 55C to barely detectable at 70C. Proportional addition of the enzyme complexes from both fungi into the same process raised protein hydrolysis up to 30% while maintaining starch hydrolysis above 95%.