ULTRASOUND AND YEAST FERMENTATION MODULATE THE NUTRITIONAL COMPOSITION, BIOACTIVE CONTENT, AND ANTIOXIDANT POTENTIAL OF CASHEW APPLE BAGASSE FLOUR

The valorization of fruit-processing by-products as food ingredients requires processing strategies that preserve their bioactive compounds and nutritional properties. This study evaluated the effects of ultrasound pretreatment and controlled yeast fermentation on the proximate composition, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant potential of cashew apple bagasse flour. Ripe cashew apples (Anacardium occidentale L., clone CCP 76; 25 kg) were purchased from CeasaMinas, Brazil. After sanitization and juice extraction, the bagasse was divided into five treatments in triplicate: control (C), ultrasonic bath (UB), probe ultrasound (PU), 48-h fermentation with Saccharomyces cerevisiae (SCF), and 96-h fermentation with Starmerella meliponinorum (SMF). Samples were dried at 55 °C and ground (32 mesh). Unprocessed wet cashew bagasse (WCB) was evaluated as an initial reference. Proximate composition was determined using AOAC-recommended methods, TPC and TFC by spectrophotometric assays, and antioxidant potential using ABTS and DPPH methods. Phenolic and antioxidant data were analyzed by ANOVA followed by Tukey's test (p ≤ 0.05). WCB contained 72.90% moisture, 2.12% protein, and 0.46% ash. Following processing, flour moisture ranged from 7.51% to 11.79%, while fermented flours exhibited higher protein contents (12.18–13.04%) than C (5.91%) and ultrasound-treated flours (8.44–10.37%). Ash contents were also higher in fermented flours (1.96–2.75%) than in ultrasound-treated samples (1.17–1.22%). These differences may reflect microbial biomass accumulation, substrate utilization, and changes in dry matter composition during fermentation. Regarding bioactive compounds, WCB exhibited TPC and TFC values of 1.44 mg GAE/g and 0.27 mg CE/g, respectively, and antioxidant values of 13.33 and 7.32 µmol TE/g for ABTS and DPPH. Among flours, fermentation resulted in higher TPC (3.63–3.76 mg GAE/g) than ultrasound pretreatment (2.52–2.59 mg GAE/g), without significant differences from C (3.16 mg GAE/g). TFC was highest in C (1.04 mg CE/g) and SMF (1.00 mg CE/g). ABTS values were higher in fermented flours (35.79–39.69 µmol TE/g) and C (35.10 µmol TE/g) than in ultrasound-treated flours (24.40–27.64 µmol TE/g). DPPH values followed a similar pattern, with C and SMF exhibiting the highest values (21.08 and 20.91 µmol TE/g, respectively). Although acoustic cavitation may enhance compound extractability, oxidative transformations could explain the lower values after ultrasound treatment. Conversely, yeast-mediated metabolism may modify phenolics and generate metabolites with distinct antioxidant properties. Overall, controlled fermentation, particularly with S. meliponinorum, showed promise for producing cashew apple bagasse flour with favorable nutritional composition and preserved antioxidant potential, supporting its further investigation as a sustainable food ingredient with potential functional applications.