Matsutake mushroom (Tricholoma matsutake) preserved with ultrasound-assisted slightly acidic electrolyzed water freezing kept microbial counts low while reducing browning enzymes. The method also maintained antioxidant activity by limiting oxidative membrane damage during freezing. The payoff is better texture, aroma, color, and shelf life for one of the world’s most expensive edible mushrooms, which normally loses over 40% postharvest under conventional storage.