{Reference Type}: Journal Article {Title}: Effect of steam cooking and particle size on the nutritional composition, phytochemicals and antioxidant activities of oyster mushroom (Pleurotus ostreatus) powder. {Author}: Fomekong GC;Nguimbou RM;Tsague MV;Djantou EB;Yanou NN; {Journal}: Food Sci Biotechnol {Volume}: 33 {Issue}: 10 {Year}: 2024 Jul {Factor}: 3.231 {DOI}: 10.1007/s10068-024-01586-0 {Abstract}: In this study raw and steamed Pleurotus ostreatus were dried and ground and fractionated by sieving into four granulometric classes (< 200 µm, 200-250 µm, 250-355 µm and > 355 µm) and unsieved powders. The combined steam cooking and sieving improved the content of total polyphenols (+ 59.45%), flavonoids (+ 76.47%), condensed tannins (+ 68.75%) and trace elements (+ 45.51% Fe, + 63.63% Cu, + 62.42% Mn, + 121.11% Zn, and + 53.52% Se) as well as in-vitro and in-vivo antioxidant activities in the finest fraction < 200 µm compared to the raw powder. It was found that the intake at a dose of 250 mg/kg body weight of the finest fractions of raw and steamed powders by the stressed rats had more of a hepatoprotective effect marked by a reduction in the level of transaminases ALAT and ASAT. This work opens a new approach for valuing edible mushrooms in the development of new food products with high antioxidant value.