1. Universidad de Los Andes, Facultad de Ciencias, Departamento de Química, Laboratorio de Química Ecológica, Mérida 5101, Venezuela, Chemistry Department, The University of Waikato, Private Bag 3105, Hamilton, New Zealand, The Horticulture and Food Research Institute Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand, and New Zealand Pastoral Agricultural Research Institute Ltd., Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand