SOLID-STATE FERMENTATION OF PEACH PALM BY-PRODUCT: A STRATEGY FOR THE PRODUCTION OF PHENOLIC COMPOUNDS

The generation and underutilization of agro-industrial waste present significant environmental and economic challenges. Processing peach palm hearts (Bactris gasipaes Kunth) generates a substantial volume of lignocellulosic by-products (Bolanho et al., 2014), which can be converted into sources of bioactive compounds through solid-state fermentation. This study aimed to optimize the production of total phenolic compounds (TPC) via solid-state fermentation of peach palm by-products. The stem portion of the peach palm was dried in a forced-air oven at 60 °C, until final moisture of 10 g 100g⁻¹, ground, and sieved to establish the particle size. This substrate was subjected to solid-state fermentation using Rhizopus oryzae. A Box–Behnken design was employed, with three factors and 15 experimental runs (including three center-point replicates), varying particle size (32, 48, and 100 mesh), moisture content (30, 50, and 70 g 100g⁻¹), and nitrogen supplementation (0, 5, and 10 g kg⁻¹ of urea). Fermentation was conducted in tray-type reactors at 30 °C for 48 hours. Phenolic compounds were extracted using 80% ethanol under orbital agitation and quantified via the Folin–Ciocalteu method, with results expressed as gallic acid equivalents (GAE). Under optimized conditions, antioxidant activity was evaluated using free radical scavenging assays (DPPH and ABTS) and the ferric reducing antioxidant power (FRAP), in comparison to the unfermented by-product. Total phenolic content (TPC) values ​​ranged from 19.60 to 53.27 mg GAE g⁻¹. TPC mean obtained at the center point was 47.96 ± 1.13 mg GAE g⁻¹, indicating adequate experimental repeatability. The quadratic model explained 97% of the result variability, showing an adjusted R² of 0.95 and no significant lack of fit (p = 0.13). Effects were positive for particle size (quadratic) and nitrogen supplementation (linear), whereas moisture content showed a negative linear effect and a positive quadratic effect. Interactions between moisture and nitrogen, and between particle size and nitrogen, showed negative effects, demonstrating that nitrogen supplementation depends on the other variables studied. Based on the desirability profile, the fermentation condition using intermediate particle size (48 mesh), lower moisture (30 g 100g⁻¹), and higher nitrogen supplementation (10 g kg⁻¹) yielded the highest TPC (53.27 mg GAE g⁻¹), representing a 47.5% increase compared to the unfermented byproduct (36.12 ± 0.90 mg GAE g⁻¹). Furthermore, under this condition, fermentation led to significant increases in antioxidant activity of 15.0%, 119.4%, and 137.1% as measured by the DPPH, ABTS, and FRAP methods, respectively. Thus, it was possible to identify fermentation conditions favorable for increasing TPC, demonstrating the process's potential for valorizing the peach palm by-product as a source of antioxidant compounds.

Acknowledgments: to CNPq and Araucaria Foundation for financial support.