The authors are grateful to Dr. Frank G.F. Qin and Dr. Sally Alkhafaji
at the University of Auckland, New Zealand, for their helpful
comments. Research support was provided by International Research
Center of Sugar Green Processing of Guangdong Province and S&T
project of Guangdong Province (2007B080401010), as well as the
National Key Technology R&D Program of China (No. 2006BAD27B04).