Flaxseed (Linum usitatissimum) low temperature processing: Oil quality and fatty acids profile

Flaxseed consumption has been prioritized by health-conscious people all over the world. Its consumption raises interest to it both from a personal and an industrial prospect due to its remarkable fatty acids profile. Besides its high content of unsaturated fatty acids, flaxseed oil is known for its low omega 6/omega 3 ratio, which may possess health improving properties because this oil is precursor of anti-inflammatory molecules. However, the high amount of polyunsaturated fatty acids in flaxseed oil causes its high sensitivity to high temperatures, to light and to oxygen, which may lead to its oxidation and quality degradation. Screw pressing can produce high quality oil but in lesser volume, which could be disadvantage. Therefore, the extraction process must be optimized for maximizing oil recovery, while maintaining oxidation indicators within limits specified by regulations, as well as a potentially health beneficial fatty acid profile. Optimization of screw press parameters for pressing out the flaxseed oil were investigated by Response Surface Methodology. Both size of the cake outlet and the speed of the screw pressing were optimized, and the values that provided the highest experimental oil recovery, 41.4%, were of 1 mm and 155.89 rpm respectively. Although the overall trend in oil extraction showed a rising oil recovery when screw speeds increased from 98.73 up to 213.05 rpm, certain fluctuations were observed in oil extraction with varying outlet cake sizes. However, there was an inversely-proportional function between the oil recovery and the size of the cake outlet, therefore, screw speed provided a minor, non-significant effect while the size of the cake outlet proved to have a strong effect on oil recovery. The highest acid value and peroxide value accounted to 0.71 mg KOH/g and to 7.71 meq/kg respectively. Sediment content (SC) of screw pressed flax oil ranged between 9.12~14%. During the oil extraction at the maximum yield, temperature increased, however the ratio of omega 6 to omega 3 in the obtained oil still remained low.