Abstract
This study was on the comparison of hydrothermal treatments at 170 °C (steam injection) and 220 °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 °C allowed the recovery of 2053 mg of gallic acid eq. per kg of residual strawberry extrudate. By contrast, after hydrothermal treatment at 170 °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 °C and 220 °C hydrothermal treatments. Considering the latest observation, hydrothermal treatment at 220 °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.
Highlights
The strawberry sector has seen exponential growth in recent years, reaching 8.3 million tonnes in2018 [1]
Most of these soluble compounds were displaced to the liquid phase (LP) after the hydrothermal treatments, which retained around 75% and 85% of the CODs, at 170 and 220 ◦ C, respectively (Table 1)
The hydrothermal treatment at 220 ◦ C for 5 min allowed obtaining a double concentration of soluble organic matter and up to three times more phenolic compounds than at 170 ◦ C for 60 min
Summary
The strawberry sector has seen exponential growth in recent years, reaching 8.3 million tonnes in2018 [1]. The strawberry sector includes a direct marketing of fresh fruit and obtaining by-products derived from strawberries, such as yogurts, juices, or jams [2]. RSE is formed by achenes, fibers, and part of the juice of strawberries that is retained and rejected during the extrusion of the fruits to obtain a strawberry concentrate. This waste as well as the strawberry contains a wide variety of interesting bioactive compounds, with high concentrations of nutrients and phytochemicals, which could be recovered [3,4]. The great variety of nutrients and phytochemicals that strawberry contains is of great interest in our diet because they are beneficial to avoid or prevent different cardiovascular, neurological, cancerous, and other diseases [4,5]
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