## 3 Results and Discussion
### Peroxide Value and Volatile Fatty Acid Content  
Volatile fatty acids and lipid peroxides can form due to high levels of oxidation ([PERSON] et al., 2018). When fats and oils undergo oxidation, they can form lipid peroxides, which are initial oxidation products ([PERSON] et al., 2018). Subsequently, these peroxides can break down into volatile fatty acids. Oxidation can occur due to various factors, including heat, light, air, and other oxidation-promoting agents ([PERSON] et al., 2018). In comparison, with the legal act ISO 27107:2010, which is intended for animal and vegetable fats and oils, if the amount of peroxides exceeds 10 meq/kg, it is suggested that fats are oxidized ([PERSON] et al., 2018). [PERSON] et al., in their study, found that freeze-dried methods are not suitable for mealworms because they exhibit significantly higher oxidation than the other drying methods ([PERSON] et al., 2018). So, one of the hypotheses that there is an increase in peroxides in mealworms (Table 5) is due to the selected processing method. In our research, all larvae were kept under similar conditions, but it was found that in sample 3L with brewers' spent grain, the amount of peroxide exceeded the recommended limit and the content was 100 times higher than in samples 1L, 2L, and 4L (\(p<0.01\)). However, a statistically significant difference between samples 1L, 2L, and 3L was not \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Larvae**} & \multicolumn{4}{c}{**Substrate**} \\ \hline Samples & 1L & 2L & 3L & 4 CL & 1S & 2S & 3S & 4 CS \\ Total SFA & 26.42 a & 24.15 b & 52.64 c & 17.33 d & 20.94 a & 20.79 b & 28.59 c & 20.25 d \\ Total MUFA & 45.12 a & 38.02 b & 35.89 c & 43.37 d & 24.64 a & 28.47 b & 24.13 c & 24.18 d \\ Total PUFA & 28.47 a & 36.24 b & 10.18 c & 35.11 d & 54.42a & 50.74 b & 44.63 c & 54.05 d \\ Omega-6 FA & 27.12 a & 18.65 b & 7.82 c & 29.22 d & 54.00 a & 49.54 b & 42.92 c & 53.91 d \\ Omega-3 FA & 0.32 a & 4.39 b & 1.69 c & 6.99 d & 0.03 a & 0.29 b & 2.65 c & 1.53 d \\ Omega-6/3 FA & 85.05 a & 4.25 b & 4.632 c & 4.18 d & 1838.83 a & 170.51 b & 16.20 c & 35.34 d \\ \hline \hline \end{tabular}  
* a,b,c,d—means marked with different letters in the row (in the groups larvae and substrate separately) differed significantly (\(p<0.05\), [PERSON]’s LSD criterion); SFA—saturated fatty acids; MUFA—monounsaturated fatty acids; PL—polyunsaturated fatty acids; 1L—larvae (wheat bran + brewer’s yeast + great potaces); 2L—larvae (wheat bran + brewer’s yeast + carrot); 3L—larvae (brewers’ spent grain + brewer’s yeast + carrot); 4 CL—larvae, control (wheat bran + brewer’s yeast + agar-agar gels); 1S—substrate (wheat bran = brewer’s yeast + sprouted potatoes); 2S—substrate (wheat bran = brewer’s yeast + carrot); 3S—substrate (brewers’ spent grain + brewer’s yeast + carrot); 4 CS—substrate, control (wheat bran = brewer’s yeast + agar-agar gels).  
\end{table} 
Table 4: Fatty acid ratio in lyophilized larvae and substrate, % of total FAs content, \(n\) = 3.  
detected. The higher content of peroxides and volatile acids found in larvae grown on brewers' spent grain could be explained by various factors. The possible reasons may include specific differences in chemical composition between brewers' spent grain and other growth substrates, which influence larval chemical interactions and metabolism. In our previous study, we noticed that brewers' spent grain had a significantly higher amount of fats and oils, which, if exposed to air or other oxidizing factors, could start oxidation processes leading to the formation of peroxides [67]. The volatile fatty acid content was found to be significantly higher in the sample 3L, analogously to the peroxide content. It was even tens of times higher than in samples from other cultivation conditions (\(p<0.01\)), and the reasons may also be the same. According to the previously mentioned statement by PMAP [37], the amount of volatile fatty acids in mealworms should not exceed 0.35 mL.