Extracts from oyster mushrooms (Pleurotus ostreatus) protected frozen beef burgers for up to 90 days, performing as well as or better than sodium erythorbate, a common synthetic antioxidant. Stipe extracts best preserved red color and reduced lipid oxidation, while cap extracts better stabilized brightness and myoglobin, showing different parts protect meat in different ways. Both extracts increased free amino acids, improving flavor without changing texture or cooking loss.