Route exploration of valorization of buckwheat waste based on subcritical liquid treatment

概要

Buckwheat waste (BWW), which includes husks, leaves, and straw, is usually
thrown away or burned. This leads to serious pollution problems and a waste of
resources. BWW is rich in cellulose, hemicellulose, antioxidants, and various sugars;
thus, it can be considered as a potential source to improve the economic benefits of
buckwheat cultivation. However, components such as sugars and antioxidants in
BWW are often cross-linked with structural compounds via chemical bonds.
Therefore, it is vital to develop a strategy to facilitate depolymerization of these
structures and improve the utilization efficiency of BWW.
In this study, subcritical water has been developed to improve the yields of
saccharides from BWW. Subcritical ethanol solution was used to increase the yields
of bioactives components. The scale-up to an industrial level was tested on a pilot
scale. The hydrolysate prepared from subcritical seawater treatment of BWW has also
been tested as a liquid fertilizer to promote lettuce growth.
1. Subcritical water treatment of BWW for sugar extraction
A subcritical water treatment (SWT) was chosen for cellulose and hemicellulose
degradation to produce saccharides from raw BWW. The sum of saccharides yields in
the liquid sample were compared. A higher sum of saccharides yields of 4.10 % was
obtained at a relatively lower severity factor of 3.24. The contents of cellulose,
hemicellulose, and lignin were analyzed in the residue after SWT. The result shows
that lignin was dominant in the residue. The irregular pores were observed by SEM
after SWT due to the removal of some hemicellulose, and lignin. Finally, an overall
mass conversion based on saccharides production was carried out. The result reflects
a considerable yield of saccharides from BWW by SWT.
2. BWW depolymerization using a subcritical ethanol solution for extraction of
bioactive components: from the laboratory to pilot scale
Subcritical ethanol solution treatment (SEST) was used to depolymerize BWW
and extract bioactive components such as phenolics, flavonoids, and sugars on both
the laboratory and the pilot scale. On the laboratory scale, various treatment
conditions were compared. Depolymerization of the microstructure was evaluated by
the detection of solid components, and the extraction of bioactive compounds was
studied by the detection of liquid components. The mechanism of SEST
depolymerization of BWW and the extraction of bioactive components is discussed. ...

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