Food spoilage is a significant problem and constitutes a major economic loss. The formation of coloured spoilage in food products is largely due to the activity of two classes of redox enzymes: copper-containing phenol oxidases and heme-containing peroxidases. This effect was studied with an inhibitor of phenol oxidases and peroxidases that was isolated from leaves of the tea plant and applied in two model systems, namely cultures of the unicellular alga, Chlorella vulgaris and excised roots of wheat seedlings. The data demonstrated that the tealeaf inhibitor can affect algal and plant cells through changes in their energy status as exemplified by the rates of oxygen consumption, oxygen evolution and heat production. It is hypothesized that the effects can be caused not only by the modulation of the activity of phenol oxidases but also alterations in membrane ATPase systems. (C) 2004 Elsevier B.V. All rights reserved.