Extraction of polyphenols from oilseed cakes by subcritical water

Pumpkin, flax and hemp seed oils have been recommended for human nutrition due to their high content of essential fatty acids. Oil extraction from oilseeds generates tonnes of processing wastes, referred to as oilseed cakes. The oil seed cakes are most often further processed into animal feed due to their high protein and energy contents. However, these matrices represent low-cost renewable resources of high added-value compounds, such as phenolic acids and flavonoids. In this work, polyphenolic compounds from pumpkin, flax and hemp seed cakes were extracted by subcritical water in a homemade extractor. Operational parameters included the pressure of 20 bars, temperature of 160 ºC and convective mass transfer defined by vibration frequency of the extraction vessels of 3 Hz. The sample to solvent ratio was 1 : 30. Total phenolic and total flavonoid contents were determined by spectrophotometric method. Hemp seed cake extract showed the highest content of total phenolics (36.8±0.41 mg GAE/g dry weight) and total flavonoids (10.3 ±0.01 mg CE/g dry weight), while pumpkin seed cake extract had the lowest content (32.61±1.29 mg GAE/g dry weight and 4.55±0.04 mg CE/g dry weight) of total phenolics and flavonoids, respectively. Presented work demonstrates that subcritical water can be used as safe and green alternative for the extraction of polyphenolic compounds from oilseed cakes, applicable in food and pharmaceutical industries.