The aim of the study was to assess the content of biogenic amines and physical properties of fruiting bodies of white and brown button mushrooms subjected to the process of controlled lactic acid fermentation. Lactiplantibacillus plantarum 299v with documented probiotic properties and L. plantarum EK3, i.e., an isolate obtained from spontaneously fermented button mushrooms, were used as starter strains. Fresh, blanched, fermented, and refrigerated fruiting bodies were analysed. The mushroom samples were found to contain three amines: spermidine, putrescine, and tyramine in amounts that do not pose a threat to consumer health. The highest content of spermidine was found in the fruiting bodies of unprocessed brown and white mushrooms (367.22 ± 14.19 and 266.47 ± 13.38 mg/kg, respectively). Putrescine and tyramine were found only in the fermented mushrooms. Putrescine ranged from 0.58 ± 0.25 to 10.11 ± 0.5 mg/kg, while tyramine ranged from 1.44 ± 0.25 to 69.04 ± 1.39 mg/kg. Histamine, which is the most toxic biogenic amine, was not detected in any of the samples. The technological process caused substantial changes in all colour parameters. The blanching process resulted in a decrease in the value of parameter L* and an increase in the value of parameters a* and b*. The process of lactic acid fermentation increased the brightness parameter. It also caused a substantial increase in the yellowness parameter and reduced the redness of the fermented mushrooms. Blanching exerted a significant effect on the texture of the mushroom fruiting bodies, contributing to an increase in the puncture force value from 2.78 ± 0.22 to 4.90 ± 0.43 N and from 3.21 ± 0.23 to 5.59 ± 0.3 N in the case of the white and brown mushrooms, respectively. During the refrigerated storage, the firmness of the fermented mushrooms did not change.