## 3 Results
### Molecular Characteristics  
FT-IR spectra of red and white untreated and treated sorghum flours with different particle sizes are shown in Figure 2. Many peaks can be observed on the FT-IR spectra that could be associated with the molecular bindings of sorghum chemical compounds such as starch, proteins, and polyphenols. Particle size reduction, sorghum variety, and dry heat treatment led to changes in the intensities of absorption band and the appearance of peaks in some regions. There can be observed two prominent peaks in the region 1700-1600 cm\({}^{-1}\) (at 1649 cm\({}^{-1}\)) and in the region 1060-960 cm\({}^{-1}\) (997 cm\({}^{-1}\)), the first one being ascribed to Amide I expression of proteins, while the second band to carbohydrates fingerprint [45]. The peaks found in 3800-3600 cm\({}^{-1}\) may be attributed to the O-H groups of phenols intermolecular bonded [36], while the peak found at about 3296 cm\({}^{-1}\) was given by the O-H stretching vibration [46].  
Figure 1: Effect of dry heat treatment on sorghum flour fractions foaming capacity: CW—Control white sorghum, CR—control red sorghum, T1—dry heat treatment at 121 \({}^{\circ}\)C, T2—dry heat treatment at 140 \({}^{\circ}\)C, L/M/S—particle sizes, I—integral. Means with distinct letters are significantly different (\(p<0.05\)).  
Figure 2: FT-IR spectra of untreated (C) and treated (T1, T2) red (R) and white (W) sorghum flows at different particle sizes: integral (I), large (L), medium (M), and small (S).  
The absorption bands found at about 2923 and 2352 cm\({}^{-1}\) could be due to the C-H stretching vibration and could suggest the presence of the alkane group and/or cis-olefinic group [2]. Interesting changes of FT-IR spectra were observed in the 2352 cm\({}^{-1}\) region, in CR_L, CW_S, CW_M, T2R_M, and integral flours samples which showed higher peak absorbances compared to other samples (Figure 3). The absorption bands found at about 1151 and 1077 cm\({}^{-1}\) could be attributed to the fiber fractions such as small hemicellulose and cellulose [45]. On the other hand, 1154 and 1416 could be due to the P-H, P-H banding, phosphine, and phosphoric acid which may be associated with the presence of phytic acid [43]. In the integral flours, the reduction of absorption intensity in 1154 and 1416 cm\({}^{-1}\) was observed with the increase of sorghum grain dry heat treatment temperature. The peaks observed in 750-880 cm\({}^{-1}\) region and 1150-1500 cm\({}^{-1}\) zone could be associated with aromatic rings deformation, revealing the presence of phenols, with stretching given by them and C-C, C-H, O-H deformations suggesting the presence of phenolic acids and flavonoids [42]. The decrease of particle size led to higher absorbances in these regions, while white sorghum exhibited higher absorbances compared to the red one, except for L particle size. Dry heat treatment showed differential contribution in absorbances intensities, higher values compared to the controls being observed in the case of L, M, and S particle sizes. For the L particle size sample, the highest absorption intensities were observed for T1R_L, while for M and S particle sizes T2W samples exhibited the highest absorbances compared to the other studied samples.