## 3 Results and Discussion
### FTIR of Insect Powders  
FTIR allows us to predict molecular structure and identify functional groups in the tested materials [73]. FTIR spectra have shown similar patterns for tested insect powders but with diverse absorbance levels (Figure 4).  
The spectral region between 3300 and 3200 cm\({}^{-1}\) exhibits a weak, broad stretching vibration that corresponds to hydroxyl (-OH) groups in water molecules and amino acids, together with N-H bonds in the amide A group [74; 75]. Two distinct C-H stretching peaks appear in the spectrum: a strong absorption at 2920 cm\({}^{-1}\) corresponding to asymmetric stretching of methyl (-CH\({}_{3}\)) groups, generally observed in alkanes and alkene aromatics, alongside a medium-intensity peak at 2850 cm\({}^{-1}\), representing symmetric stretching of methyl (-CH\({}_{3}\)) groups, typically found in alkanes and aldehydes [74]. These peaks are related to lipids rich in alkanes, alkenes [39], and chitin [74]. The peak at 2920 cm\({}^{-1}\) also reflects the stretching vibration of the C-H bond in the amide B group [75]. The stretching vibration of the C\(\equiv\)N bond in nitrile compounds reflects a weak peak at 2360 cm\({}^{-1}\)[76].  
A medium peak at 1744 cm\({}^{-1}\) for CD insect powder and 1736 cm\({}^{-1}\) for IR-CD insect powder is connected to the stretching vibration of the C=O bonds in lipids [73; 74]. A  
Figure 4: The FTIR spectra of black soldier fly powders processed by convective (CD) and infrared convective (IR-CD) drying methods.  
medium peak at 1625 cm\({}^{-1}\) corresponds to the stretching vibration of the C=O bonds in the amide I group [75]. The powder produced by convective drying (CD) exhibited reduced absorption levels, generally linked to disruptions in protein secondary structures. This occurs because the C=O bond, critical for maintaining these structures, is particularly sensitive to CD processing conditions [29]. The spectral profile of three major peaks between 1744 and 1500 cm\({}^{-1}\) is in parallel with literature indicating an \(\alpha\)-chitin structure [75]. A medium peak at 1524 cm\({}^{-1}\) and 1235 cm\({}^{-1}\) corresponds to the bending vibrations of the N-H bond and the stretching vibrations of the C-N bond in the amid group. These peaks indicate, respectively, amide II and amide III [73,75]. Considering the amide III region (1350-1200 cm\({}^{-1}\)), the highest absorption was observed at 1235 cm\({}^{-1}\). This indicates that the secondary structure of the protein molecules is dominated by \(\beta\)-sheets, related to the exoskeleton of the insect, and gives information on how chitin interacts with the protein molecules [77]. A moderate-intensity peak observed near 1457 cm\({}^{-1}\) corresponds to C-H bond bending vibrations arising from lipids, proteins [73], and polysaccharides that contain -CH\({}_{2}\)- and -CH\({}_{3}\) groups [74]. A medium-intensity absorption band centered at approximately 1400 cm\({}^{-1}\) arises from C-N stretching vibrations [73].  
In the fingerprint region, spanning from 1200 to 900 cm\({}^{-1}\), the stretching vibrations of C-C, C-O-C, and C-O bonds, along with the bending vibrations of the C-O-H bond, are observed in various carbohydrate groups. The peak observed at 1040 cm\({}^{-1}\) indicates the presence of galacturonic acid and glucuronic acid [75,76]. The region below 900 cm\({}^{-1}\) in the FTIR spectrum is mainly associated with conformational changes caused by specific molecular vibrations in carbohydrates [73,74].