The use of water in subcritical conditions for extraction has several drawbacks. These include the safety features, higher production costs and possible degradation of the bioactive compounds. To overcome these problems, sonic energy and an entrainer were used as external interventions to decrease the polarity of water at milder operating conditions. The effect of low (28 kHz) and high (800 kHz) frequencies of sonication in the extraction of the main ginger bioactive compound (6-gingerol) were compared. Six parameters were studied: mean particle size (MPS, mm), time of extraction, applied power, sample to solvent ratio (w/v), temperature of extraction, and the percentage of entrainer. The optimum conditions for high frequency SAWE prototype were MPS 0.89–1.77 mm, 45 min, 40 W applied power, 1:30 (w/v), 45 °C, and 15% of ethanol as entrainer. Two-way analysis of variance (ANOVA) gave the most significant parameter, which was power with F (1, 45.07), p < 2.50 × 10−9. Although the effect of low frequency was stronger than high frequency, at the optimum conditions of the sample to solvent ratio 1:30 (w/v) with 700 mL solvent and temperature 45 °C, the concentration and recovery of 6-gingerol from high frequency of SAWE prototype was 2.69 times higher than at low frequency of SAWE. It was found that although the effects of high frequency (800 kHz) were negligible in other studies, it could extract suitable compounds, such as 6-gingerol, at lower temperature. Therefore, the effects of sonication, which cause an enlargement in the cell wall of the ginger plant matrix, were observed using a Scanning Electron Microscope (SEM). It was found that the applied power of sonication was the most significant parameter compared to the other parameters.
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