Hydrothermolysis of rapeseed cake in subcritical water. Effect of reaction temperature and holding time on product composition

•Utilization of rapeseed cake- a residual biomass rich in protein and fat.•Hydrothermal decomposition of rapeseed cake as a new method of its conversion.•Amino acids and fatty acids as a valuable products of the studied reaction.•Experimental design method to optimize conditions for higher amino acids and fatty acids yields.

We have investigated the hydrothermolysis of rapeseed cake, which is a residual biomass with high protein and fat content. The effects of the process parameters, reaction temperature and holding time, on the composition of the products (amino acids and fatty acids) contained in the separated liquid fractions (water and ether, respectively) were studied. To model the hydrothermal process the experimental design methodology was used. Based on this, optimized operational parameters were determined yielding highest amounts of amino acids and high conversion of triacylglycerols to fatty acids. A maximum estimated yield of amino acids of 135.9 g kg-1 of rapeseed cake was obtained at 215 °C after 36 min. A further increase of both reaction temperature and holding time would lead to the Maillard reaction and the decomposition (deamination and decarboxylation) of the amino acids. Maximum conversion of triacylglycerols to fatty acids of 0.91 was predited at 246 °C during 65 min. In this case, a further increase of both reaction parameters would lead to enhanced cis–trans isomerization of the unsaturated fatty acids produced.