STRUCTURAL AND MORPHOLOGICAL CHARACTERIZATION OF BANANA PEELS (Musa spp.) SUBJECTED TO DELIGNIFICATION AND DEPECTINIZATION TREATMENTS

Banana peels (Musa spp.) are an abundant residual biomass suitable for biorefineries to obtain bioproducts. However, their complex structure inhibit access to hemicellulose, a polysaccharide of interest in the synthesis of enzymes and prebiotic compounds, requiring pretreatments. Among these, depectinization removes pectic fractions using acidic, saline, and alkaline solutions. Delignification involves chemical (alkaline) and physical (ultrasonic) treatments. This study aimed to to characterize the functional groups and morphology of banana peels subjected to depectinization and delignification, as well as the extracted pectin. Depectinization was performed by extraction with water and 0.5% (w/v) ammonium oxalate in a 1:30 (w/v) ratio at 60°C/2 h. The solubilized pectin was filtered, dialyzed and lyophilized, and the residue was dried and subjected to delignification pretreatments. The first (#1) was carried out with 1% (w/v) NaOH in autoclave (121ºC/30 min); the second (#2), with 7.5% (v/v) H₂O₂ (150 rpm, 25ºC/1 h); the third (#3) with ultrasound-assisted NaOH (90 W, 20 kHz, 20 min); and the fourth (#4) with a combination of #1 and #3. The residues were filtered, washed to neutrality and dried. The characterization of the functional groups was performed by Fourier Transform Infrared Spectroscopy (FTIR, 40 scans with 4 cm^-1 resolution in a frequency range of 4000-600 cm^-1). The morphology was evaluated by Scanning Electron Microscopy (SEM, gold sputtering, magnification 1000×). The FTIR spectrum of the extracted pectin showed bands similar to those reported in the literature, such as 2920 cm^-1 (C-H), 2300 cm^-1 (C≡C), and 1600 cm^-1 (carboxylate). These bands were less intense in the depectinized sample, confirming the efficiency of the process. For delignification, a decrease in the bands at 1700 and 1520 cm^-1, associated with lignin, was observed. Bands characteristic of hemicellulose and cellulose (1000 and 1070 cm^-1) were maintained. SEM micrographs revealed that the raw bark presented rigid and ordered fibrils, while the depectinized material was loose and bulky, resulting from the breaking of hydrogen bonds. Samples from treatments #1, #3, and #4 were disorganized, with broken fibrils, especially in #1 and #4, due to the severity of the treatment. Treatment #2 resulted in overlapping fibrils, confirming previous studies. In summary, pectin removal was satisfactory, favoring its use. Treatments #1 and #4 resulted in rigid material, limiting future applications. However, treatments #2 and #3, less aggressive and more effective in delignification, showed potential for bioprocesses, being recommended optimization and evaluation in submerged cultivation.