1. Chemistry Dept., College of Science; King Saud Univ.; P.O. Box 2455 Riyadh 11451 Saudi Arabia
2. UR Physico-Chimie des Matériaux Solides, Chemistry Dept., Science College; Tunis El Manar Univ.; 2092 Tunis Tunisia
3. Dept. of Food Technology, Faculty of Food Science and Technology; Univ. Putra Malaysia; 43400 Serdang Selangor Malaysia
4. Inst. of Advanced Technology; Univ. Putra Malaysia; 43400 UPM Serdang Selangor Malaysia