Fourier Transform Mid-Infrared (FTIR) Spectroscopy to Identify Tannin Compounds in The Panicle of Sorghum Mutant Lines

Abstract

G5 and G8 are two sorghum mutant lines projected as sorghum varieties for ruminant’s feed. However, most of the sorghum panicles contains phenolic compounds, especially in the form of condensed tannins. The objective of this research was to investigate the phenolic and tannin compounds from the panicles of two sorghum mutant lines. The second objective was to identify tannin content by Fourier Transform Mid-Infrared (FTIR) Spectroscopy in the sorghum panicles. The two mutant lines were compared with Pahat variety. This research was arranged into a randomized complete block design with two factors. The first factor was the sorghum variety/mutant lines, whereas the second factor was the generative phase of harvesting time (flowering, soft dough and hard dough). The results showed that the panicles of G5 sorghum contained the lowest total phenol compounds (P<0.01). The average mean of G5 and G8 mutant lines produced lower total tannin content (27.3 and 18.2%, respectively) than Pahat variety (P<0.01). Generally, total phenol and total tannin in all variety/mutant lines increased with the increasing maturity stage (P<0.01). All the spectra of the sorghum panicle samples in different harvesting age investigated shared certain special similarities. A band due to alkane medium (C-H) stretch was observed at 2937-2854 cm−1. At 1521-1514 and 1446-1408 cm−1, a band due to the C-C aromatic compounds was observed. Based on those findings, it can be concluded that G5 and G8 mutant lines produced less total phenol and total tannin contents than Pahat variety. Meanwhile, FTIR could be used to describe the profile of tannin compounds qualitatively.

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“…This confirms the presence of carbon hydrogen chains in the char structure. The peak at 1630 cm -1 is for aromatic structure, the peak at 1400 cm -1 is for C-N and C=N groups, the peak at 1160 cm -1 is for P-O, the peak at 1050 cm -1 is for P-O-C, the peak at 984cm -1 is for polyphosphate and/or pyrophosphate, the peak at 881 cm -1 is for alkene, the peak at 492cm -1 is for O-P-O group (Abdelkhalik et al 2020(Abdelkhalik et al , 2019Wahyono et al 2019;Makhlouf et al 2017a,b;Viswanath et al 2015;Chen and Wang, 2007).…”

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“…Hasil analisis FTIR ditunjukkan pada Gambar 2 yang dibandingkan dengan hasil analisis tanin standar yang dilakukan Wahyono,dkk. [14] pada Gambar 3.…”

“…Gambar 3. Analisis FTIR pada Tanin Standar [14] Hasil analisis FTIR pada Gambar 2 menunjukkan adanya karakteristik tanin yaitu puncak vibrasi fenolik (O-H stretching) pada 3391,97 cm -1 . Selain itu, terdapat juga gugus-gugus lainnya seperti gugus alkana (C-H stretching) pada puncak 2983,35; 2926,53 dan 2855,61 cm -1 , gugus karbon dioksida (O=C=O stretching) pada puncak 2360,81 cm -1 , gugus aldehid (C=O stretching) pada 1737,98 cm -1 , gugus alkena (C=C stretching) pada puncak 1613,64 cm -1 , gugus nitrogen (N-O stretching) pada puncak 1539,32 cm -1 , gugus alkana kelompok metil (C-H bending) pada puncak 1448,49 cm -1 , gugus fenol (O-H bending) pada puncak 1373,27 cm -1 , gugus aromatik ester (C-O stretching) pada puncak 1302,21 cm -1 , gugus alkil aril eter (C-O stretching) pada puncak 1236.37 cm -1 , gugus anhidrida (CO-O-CO stretching) pada puncak 1043,23 cm -1 dan gugus alkena (C=C bending) pada puncak 938,38; 847,39 dan 766,57 cm -1 .…”

“…Hasil analisis FTIR pada penelitian ini telah memiliki kemiripan dengan hasil analisis tanin standar yang dilakukan Wahyono, dkk. [14]. Dari Gambar 3 diketahui terdapat karakteristik tanin yaitu pada puncak vibrasi fenol (O-H stretching) pada 3275,54 cm -1 .…”

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“…. A strong absorption in the range of 3200-3600 cm -1 , 2850-3000 cm -1 , 1720-1740 cm -1 , and 1680-1700 cm -1 due to hydroxyl groups, alkane group, carbonyl group, and acid group respectively represent the tannins (Wahyono et al, 2019). .…”