1. Instituto de Química Orgánica General (CSIC), C/ Juan de la Cierva 3, 28006 Madrid, Spain, Instituto de Fermentaciones Industriales (CSIC), C/ Juan de la Cierva 3, 28006 Madrid, Spain, and Department of Food Biosciences, University of Reading, Whiteknights, P.O. Box 226, Reading RG6 6AP, Berkshire, U.K.