Proximate Composition, Antioxidant Capacity, and Dietary Fiber Functional Properties of Pulp and Peel of Two Oenocarpus bataua Morphotypes from the Bolivian Amazon: Effects of Preservation Methods and Frozen Storage

Oenocarpus bataua Mart. (Arecaceae) (known as “majo” in Bolivia) is an Amazonian palm fruit with considerable potential for the development of functional foods; however, its rapid postharvest deterioration limits its utilization. This study evaluated the effects of preservation methods and frozen storage on the physicochemical properties of two morphotypes of its fruits (dark-purple and pale-colored). Proximate analysis of pulp and peel fractions revealed a lipid-rich composition, with crude lipid contents close to 49% (dry basis), moderate protein levels (7.1–9.7%), and crude fiber contents around 15%. Dietary fiber characterization showed exceptionally high total dietary fiber (61.6%), predominantly insoluble dietary fiber (56.3%) under short-term frozen storage. Fresh pulp exhibited high antioxidant capacity, as determined by the DPPH assay (2003–2070 µmol TE/g dry matter), while freeze-drying preserved significantly higher antioxidant activity than hot-air drying. Functional properties were strongly affected by storage duration, with water-holding capacity decreasing from (4.43–3.17) g H2O/g dry matter and swelling capacity from 13.95 to 9.62 mL H2O/g dry matter after prolonged freezing. FTIR spectroscopy confirmed the presence of characteristic polysaccharide and lignocellulosic structures and indicated structural disruption of the insoluble fiber matrix during long-term storage. These findings support the use of Bolivian majo as a promising source of functional ingredients and provide a basis for developing value-added Amazonian food products and optimizing preservation strategies.