MONGUBA STARCH (Pachira aquatica) AS AN UNCONVENTIONAL SOURCE: INFLUENCE OF EXTRACTION METHODS ON COMPOSITION AND STRUCTURAL AND THERMAL PROPERTIES

Brazil has vast biodiversity, including unconventional food plants. The monguba (Pachira aquatica) stands out for its nutritious fruits, rich in protein and lipids. The objective of this study was to compare four methods of starch extraction from monguba seeds and to characterize the starches obtained in terms of chemical, thermal, structural and mineral properties, in order to provide information for their industrial use. The fruits were collected in the city of Barra do Garças-MT (June and July 2025) and stored at -18 °C. The following methods were used for starch extraction: (A) water, (B) 0.1N NaOH, (C) 0.2% SO2 and (D) 0.2% SO2 + 0.1 N NaOH. The starches obtained were evaluated in relation to mineral composition (X-ray Fluorescence - XRF), molecular structure (X-ray Diffraction - XRD), functional groups (Fourier Transform Infrared Spectroscopy - FTIR) and thermal properties were evaluated by TG (Thermogravimetry) and DSC (Differential Scanning Calorimetry). The FTIR spectra of Monguba starch exhibited typical polysaccharide bands (~3400 cm⁻¹ O–H, 2920 cm⁻¹ C–H, 1640 cm⁻¹ bound water, and 1200–900 cm⁻¹). The starch extracted in water showed greater intensity at 1047 cm⁻¹, indicating a predominant crystalline structure. NaOH increased the amorphous phase (1022 cm⁻¹), SO₂ caused moderate changes at 1640 cm⁻¹ and the combination NaOH + SO₂ generated greater structural disorganization, with a more amorphous spectrum. TGA and DSC analyses of monguba starch indicated that starch extracted with water degrades between 300–480 °C after moisture loss (~120 °C).The extraction with SO₂ anticipated decomposition to ~250 °C, with a peak between 350–450 °C, while NaOH 0.1 N increased thermal stability, starting at ~320 °C and degrading between 370–500 °C. The combination of SO₂ + NaOH showed an intermediate profile, beginning at ~280 °C with a peak between 350–480 °C. XRF revealed selective changes in mineral composition: starch extracted with SO₂ had higher Ca content; extraction with NaOH favored P and Mg; the combined SO₂ + NaOH process increased K and Rb; whereas aqueous extraction maintained high levels of Fe and Si. XRD diffractograms showed main peaks between 17.2–17.4°, indicating crystalline regions. Starch crystallinity was preserved in all treatments. The choice of extraction method allows tailoring the properties of monguba starch, which may expand its potential applications in the food, pharmaceutical, and cosmetic industries.