# Properties of Different Varieties of Durian
## 3 Results and Discussion
### Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) Studies  
The FTIR spectra and DSC peaks are presented in Figure 4. The main FTIR bands of three cultivars of durian polyphenol extracts were from wavelength numbers from 3200 to 500 cm\({}^{-1}\) (3258, 2922, 1741, 1593, 1406, 1039, 987, 923, 828, and 523 cm\({}^{-1}\)). Three durian cultivars showed similar spectra profile (Figure 4A). The wavelength numbers of FTIR spectra at 828 and 1039 cm\({}^{-1}\) were assigned to -C-H alkenes and -C-O alcohols of catechin [3]. A band at a wavelength number of 1617 cm\({}^{-1}\) was responsible for gallic acid. Additionally, a band at 923 cm\({}^{-1}\) of FTIR spectra was derived from polyphenols in durian extracts [3]. FTIR spectra of Monthong and Chane cultivars presented a band at 1741 cm\({}^{-1}\), which corresponds to the -CO (stretching) and the band at 2922 cm\({}^{-1}\) was related to the C-H bond of saturated carbons [9]. Some bands corresponded with the measurements of pineapple fruit [49]. The band presented at 3600-3000 cm\({}^{-1}\), with a maximum value close to 3300 cm\({}^{-1}\) was associated with the stretching vibration of O-H groups. Similar bands were shown in all durian cultivars at 3258 cm\({}^{-1}\). The peak at 1719 cm\({}^{-1}\) was estimated for carbonyl group C=O stretching [49]. According to the present procedure of preparation, the samples were lyophilized, and then the O-H stretching band has to show carboxylic acids, alcohols, and phenols, which are important for the bioactivity of the fruits. In the pineapple, the bands between 1800 and 1500 cm\({}^{-1}\) have been related to proteins as amide I and amide II ((1700-1600 cm\({}^{-1}\) and 1565-1520 cm\({}^{-1}\)), respectively, and fats (1745-1725 cm\({}^{-1}\)) [50]. This region was found in durian samples between 1741 and 1593 cm\({}^{-1}\). Several peaks were found in the spectral range of 1400-800 cm\({}^{-1}\) in pineapple and 1406-523 cm\({}^{-1}\) in durian fruits. These bands can be assigned to with the stretching and bending of carbohydrates,organic acids and colour pigments [49; 50]. The obtained results of FTIR spectra, showing similar patterns for all durian cultivars can be compared with some standards found in durian and used as well for fluorescence studies. In tannic acid, one peak was found between 3495 and 3280 cm\({}^{-1}\), which shows the stretching vibration for O-H group. For durian extracts, one peak at 3258 cm\({}^{-1}\) was assigned. The peaks (cm\({}^{-1}\)) were found for tannic acid and durians at 2929 and 2922, respectively, indicating CH\({}_{2}\) asymmetric and symmetric stretching of the compound. The peak at 1703 cm\({}^{-1}\) represents the stretching of the carbonyl (C=O) group in the compound. Such a peak does not appear at this number in durian extracts. The peak at 1500-1450 cm\({}^{-1}\) allocated the carboxylic acid (O-C-O) and at 1314-1187 cm\({}^{-1}\) suggested the bending vibration of the O-H group. In addition, a sharp absorption band at 1021, which assigned to the C-O group of molecules, corresponds with the durian extracts [35; 51]. In quercetin, the peak obtained in the range of 3398-3314 cm\({}^{-1}\) represented the O-H stretching vibration due to the intramolecular hydrogen bonding. The peak obtained at 1449-1400 cm\({}^{-1}\) is indicated of the C-O bond [52]. As it was shown in our previous results, FTIR was widely used for avocado, durian, mango [3], apple, strawberry, red grapefruit, and for the determination of different stages of ripening as well, different kiwifruit cultivars. [36]. Thus, FTIR was used for the determination of functional groups present in different phytochemicals in the plant samples. Figure 4: (**A**), Fourier transform infrared (FTIR) spectra of polyphenols of durian extracts from the top: Monthong, Chanee and Puangmanee. (**B**), Differential scanning calorimetry (DSC) measurements of Puangmanee, Chanee and Monthong. DSC profiles of three durian extracts are shown in Figure 4B.