Buckwheat waste depolymerization using a subcritical ethanol solution for extraction of bioactive components: from the laboratory to pilot scale

Abstract

Buckwheat waste (BW) is rich in bioactive components such as antioxidants and saccharides. To effectively extract these compounds, subcritical ethanol solution treatment (SEST) was conducted from laboratory to pilot scale. Extraction at 80 °C with hot water and ethanol solutions, and at 120 °C with subcritical water and subcritical ethanol solutions were evaluated in laboratory scale. Then, the SEST was scaled up to the pilot level using a batch reactor with a volume scale factor of 1000. Degradation of lignin and dissolution of extractives increased the total phenolics yield. The increase in the temperature led to the degradation of some flavonoid components. Reducing sugars were mainly present as polysaccharides because of the low extraction temperature. Water and ethanol exhibited synergistic effects under subcritical conditions, which resulted in degradation of more lignin and extraction of more bioactive components than hydrothermal extraction, while retaining cellulose and hemicellulose. In the pilot-scale experiment, the total yields of phenolics, flavonoids, and reducing sugars were 29.8 ± 0.1, 13.9 ± 0.5, and 33.9 ± 0.5 g/kg, respectively. The turbidity and Brix values of the liquid samples obtained by SEST were high because of breakdown of the structure of the BW and the dissolution of the bioactive components. Additionally, compared with the laboratory scale, better results were obtained on the pilot scale because of greater feedstock homogeneity and equipment parameters. SEST is a promising approach that could be used on the pilot scale to depolymerize BW and extract bioactive components.