Controlled water immersion as a post-harvest strategy for the valorization of underripe Coffea arabica L. fruits

Underripe coffee fruits are frequently associated with reduced beverage quality; however, they represent an underutilized fraction with potential for valorization through post-harvest processing. This study evaluated the physicochemical, structural, chemical, and sensory changes in underripe Coffea arabica L. fruits subjected to different water-immersion regimes, aiming to identify processing conditions capable of improving the technological use of this fraction. Underripe fruits were subjected to static immersion, immersion with daily water renewal, or a combined regime consisting of daily water renewal up to 96 h followed by static immersion, for periods ranging from 24 to 192 h. After immersion, two fractions were evaluated: underripe fruits successfully hulled during processing and fruits that remained unhulled because of their greater resistance to mechanical hulling. Physicochemical properties of the immersion water, bioactive compounds, visual characteristics, multivariate relationships, and beverage sensory quality were assessed. Static immersion resulted in a marked accumulation of soluble electrolytes in the medium, with electrical conductivity increasing from approximately 2,000 µS cm⁻¹ at 24 h to more than 7,000 µS cm⁻¹ at 192 h, whereas daily water renewal maintained substantially lower values. The pH of the static system increased from approximately 4.0 to 5.7 over the immersion period. Caffeine, trigonelline, and chlorogenic acid showed treatment- and time-dependent variations, indicating that water management and fruit structure affected the relative distribution of these compounds during processing. Hulled underripe coffees showed sensory scores ranging from 79.00 ± 3.60 to 81.21 ± 0.44, with treatment means of 80.44–80.69, whereas unhulled coffees ranged from 78.03 ± 0.89 to 79.47 ± 1.08, with treatment means of 78.53–78.79. No significant differences among immersion times were detected within each treatment ( p > 0.05). The ripe-coffee control scored 80.75 ± 0.65. Overall, controlled water immersion, particularly when associated with water renewal and hulling, maintained sensory quality while modulating physicochemical and compositional characteristics of underripe coffee fruits, supporting its potential as a post-harvest strategy for the technological valorization of this underutilized fraction.