Apple pomace is one of the major agricultural residues in Aomori prefecture, Japan, and it would be useful to develop effective applications for it. As apple pomace contains easily fermentable sugars such as glucose, fructose and sucrose, it can be used as a feedstock for the fermentation of fuels and chemicals. We previously isolated a new hydrogen-producing bacterium, Clostridium beijerinckii HU-1, which could produce H-2 at a production rate of 14.5 mmol of H-2/L/h in a fed-batch culture at 37 degrees C, pH 6.0. In this work we found that the HU-1 strain produces H-2 at an approximately 20% greater rate when the fermentation medium contains the water-insoluble material from apple pomace. The water-insoluble material from apple pomace caused a metabolic shift that stimulated H-2 production. HU-1 showed a decrease of lactate production, which consumes NADH, accompanied by an increase of the intracellular pyrophosphate content, which is an inhibitor of lactate dehydrogenase. The intracellular NAD(+)/NADH ratios of HU-1 during H-2 fermentation were maintained in a more reductive state than those observed without the addition of the water insoluble material. To correct the abnormal intracellular redox balance, caused by the repression of lactate production, H-2 production with NADH oxidation must be stimulated. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.