Process optimization for the extraction of bioactive compounds from defatted flaxseed cake (Linum usitatissimu) using ultrasound-assisted extraction method and its characterization

The purpose of this study was to use an ultrasound-assisted approach to maximize the extraction of polyphenols from defatted flaxseed cake. Response surface methodology (RSM) was used to optimize the power intensity (757, 1010, 1262 W/cm(2)), solid-liquid ratio (1: 10, 1:20, and 1:30 g/ml), and sonication time (15, 20, and 25 min), using a three-factor Box-Behnken design. The optimization was done on the basis of different responses viz. extract yield, total phenolics content (TPC), and DPPH radical scavenging activity. The linear effect of power intensity was significant (p < .01) on all the responses. However, TPC assay and DPPH radical scavenging activity was only significantly affected by power intensity in a negative linear fashion. The interactive effect of power intensity with sonication time was also significant (p < .05) on all the responses. The optimized values obtained for extract yield, TPC assay, and DPPH antioxidant activity were 19.126%, 51.984 mg GAE/g, and 72.149%, respectively, under the optimal condition of power intensity 1013.69 W/cm(2), solid-liquid ratio 22.83 g/ml, and sonication time 22.22 min. In addition, scanning electron microscopy (SEM) analysis revealed that ultrasound-assisted extraction effectively disrupted the defatted flaxseed cake powder, thereby improving polyphenol yield.