The influence of different pretreatment methods on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H(2)) producing mixed culture using glucose as the substrate. The efficiency of H(2) yield and the glucose fermentation pathway were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. The H(2) yield could be increased by appropriate pretreatment methods including the use of heat, alkaline or acidic conditions. Heat pretreatment of the inoculum for 30 min at 80 degrees C increased the H(2) yield to 53.20% more than the control. When the inoculum was heat-pretreated at 80 degrees C and 90 degrees C, the glucose degraded via ethanol (HEt) and butric acid (HBu) fermentation pathways. The degradation pathways shifted to HEt and propionate (HPr) types as the heat pretreatment temperature increased to 100 degrees C. When the inoculum was alkali- or acid-pretreated, the fermentation pathway shifted from glucose to a combination of the HPr and HBu types. This trend became obvious as the acidity increased. As the fermentation pathway shift from the HEt type to the HPr and HBu types, the H(2) yield decreased. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.