## 3 Results
### Biogenic Amine Profile of the Mushroom Samples  
The total biogenic amine contents formed from the free amino acids of the pretreated mushroom samples are presented in Figure 10. The oyster mushroom samples contained seven biogenic amines. In the pretreated sample group, the total biogenic amine content ranged from 0.17 to 0.34 mg/g, with an average of 0.27 mg/g. The limit for the total biogenic amine content is 0.75-0.9 mg/g food (EU Commission 2017, EFSA, 2011 [15; 16]). The lowest biogenic amine content was observed in the fresh samples (0.17 mg/g), while the highest was in the UV-light-pretreated (0.34 mg/g) samples. Compared to the fresh samples, all the pretreated samples showed increased biogenic amine levels: the UV-light-pretreated samples by 95.7%, the oven-pretreated samples by 77.7%, the HHP-pretreated samples by 70.6%, the steamed samples by 50.2%, the microwave-pretreated samples by 45.6%, and the blanched samples by 39.6%. However, the increase was not significant for the blanched and microwaved samples (\(p>0.05\)). In the pretreated fermented sample group (Figure 11), the biogenic amine content ranged from 0.14 to 5.05 mg/g. The biogenic amine content in most cases exceeded the limit value for the total biogenic amine content (0.75-0.9 mg/g food) [15; 16]. The UV-light-pretreated fermented oyster mushrooms exhibited the highest biogenic amine content (5.05 mg/g), while the lowest was observed in the blanched fermented samples (0.14 mg/g). The fermented samples generally displayed higher biogenic amine levels (5.72 times higher than their pretreated counterparts overall) except for the blanched fermented samples. This result is not surprising, as the microbes involved in fermentation produce biogenic amines from free amino acids through decarboxylase activity. However, the disproportionately high contribution of the UV-light-pretreated fermented samples to this overall increase should not be neglected. Among the fermented samples, only the UV-light-pretreated samples had a higher biogenic amine concentration (2.7 times) compared to the fresh fermented samples. In all other cases, a reduction in biogenic amine content was observed within the fermented group: the blanched samples decreased by 92.8%, the microwave-pretreated samples by 76.0%, the steamed samples by 57.3%, the oven-treated samples by 52.1%, and the HHP-pretreated samples by 17.6%. These reductions highlight the effectiveness of the pretreatments in mitigating biogenic amine production during fermentation. In the fresh oyster mushrooms, small amounts of spermidine (0.15 mg/g) and cadaverire (0.02 mg/g) were detected. In the pretreated samples, three biogenic amines were identified: spermidine, cadaverire, and tyramine. Spermidine (0.24-0.31 mg/g) was the dominant biogenic amine in the pretreated samples, accounting for 94% of the total biogenic amine content. Spermidine and putrescine are reported as typical fungal polyamines, often occurring in higher concentrations compared to other biogenic amines in mushrooms [46]. Additionally, cadaverire was present in small amounts (0.01-0.04 mg/g) in the fresh, steamed, and HHP-pretreated samples, contributing to 4% of the total biogenic  
Figure 11: Total biogenic amine content of the pretreated oyster mushroom samples after fermentation (mean \(\pm\) SE, n = 4). Values with different letters (a–e) differ significantly among total BA values after fermentation (\(p\) < 0.05) (overall biogenic amine content limit: 0.75–0.9 mg/g food [15; 16]). Figure 10: Total biogenic amine content of the oyster mushroom samples after pretreatments (mean \(\pm\) SE, n = 4). Values with different letters (a–c) differ significantly among total BA values after pretreatments (\(p\) < 0.05). amine content. Tyramine was detected only in the UV-light-pretreated oyster mushrooms (0.04 mg/g), making up 2% of the total biogenic amine content (Appendix E). In the fermented samples, seven biogenic amines were identified: histamine, tyramine, putrescine, cadaverine, spermidine, agmatine, and spermine.