High-Value-Added Compound Recovery with High-Temperature Hydrothermal Treatment and Steam Explosion, and Subsequent Biomethanization of Residual Strawberry Extrudate

This study was on the comparison of hydrothermal treatments at 170 degrees C (steam injection) and 220 degrees C (steam explosion) to solubilize the organic matter contained in residual strawberry extrudate, focusing on phenolic compounds that were susceptible to be extracted and on sugars. After the extraction step, the remaining strawberry extrudate phases were subjected to anaerobic digestion to generate biogas that would compensate the energy requirements of the suggested hydrothermal treatments and to stabilize the remaining waste. Hydrothermal treatment at 220 degrees C allowed the recovery of 2053 mg of gallic acid eq. per kg of residual strawberry extrudate. By contrast, after hydrothermal treatment at 170 degrees C, only 394 mg of gallic acid eq. per kg of residual strawberry extrudate was recovered. Anaerobic digestion processes were applied to the de-phenolized liquid phase and the solid phase together, which generated similar methane productions, i.e., around 430 mL CH4/g volatile solids, after both 170 degrees C and 220 degrees C hydrothermal treatments. Considering the latest observation, hydrothermal treatment at 220 degrees C is a preferable option for the valorization of residual strawberry extrudate (RSE) due to the high solubilization of valuable phenolic compounds that can be recovered.