Three popular cultivated mushroom species (Agaricus bisporus, Lentinula edodes, and Pleu- rotus ostreatus) were biopreserved through a directed lactic acid fermentation process. Lactiplantibacillus plantarum strain EK11 obtained from A. bisporus fruiting bodies subjected to spontaneous lactic acid fermentation was used as a starter culture. Regardless of the mushroom species, the pH value on experimental day 7 was ≤3.75, which guarantees the shelf life of fermented products; however, it decreased to 3.51–3.6 during refrigerated storage. The number of lactic acid bacteria in the final products exceeded 7 log colony forming units per mL. The fermentation process significantly reduced the caloric value and the digestible carbohydrate content, regardless of the mushroom species. It also reduced the protein content in the P. ostreatus and L. edodes. The protein in all the analyzed samples was composed of all essential amino acids, with the dominance of glutamic and aspartic acids responsible for the umami flavor. The fermentation process significantly improved the fatty acid profile, increasing the proportion of polyunsaturated fatty acids in the P. ostreatus and L. edodes. The fermented mushrooms contained significantly lower amounts of thiamine and riboflavin than the fresh ones, except for L. edodes, where the vitamin B1 content was unchanged. The starter used did not have the ability to synthesize biogenic amines. The fermented mushrooms achieved organoleptic scores ranging from 6.83 to 8.04 on a 9-point scale. L. plantarum strain EK11 can be regarded as a suitable starter culture for lactic acid fermentation of mushrooms