3.1.2. Ethanol concentration
The effect of ethanol concentration on ultrasound extraction of oligosaccharides from scallion is shown in Fig. 1B. The concentration of oligosaccharides increased with the increment of ethanol concentration up to 60% v/v (7.49 ± 0.82 g/100 g FW). After this point, the concentration of oligosaccharides gradually declined reaching 5.60 ± 0.69 g/100 g FW at ethanol concentration of 96%v/v. Similarly, Ekvall et al. [29] reported that maximum yield of raffinose
family oligosaccharides from immature green peas was obtained at about 50% v/v ethanol followed by a decreased yield with further increase of ethanol concentration. Knudsen and Li[13] also found that increased ethanol concentration beyond 60% v/v noticeably reduced the amount of raffinose oligosaccharides extracted from plant material. A remarkable drop in oligosaccharides content at 96% v/v ethanol revealed that concentrated solvent did not ensure a good recovery of oligosaccharides compared to aqueous ethanol. Thus, ethanol concentrations of 35%, 60% and
85% v/v were selected as the lower, middle and upper level, respectively,to be employed in RSM optimization.
3.1.2. Ethanol concentrationThe effect of ethanol concentration on ultrasound extraction of oligosaccharides from scallion is shown in Fig. 1B. The concentration of oligosaccharides increased with the increment of ethanol concentration up to 60% v/v (7.49 ± 0.82 g/100 g FW). After this point, the concentration of oligosaccharides gradually declined reaching 5.60 ± 0.69 g/100 g FW at ethanol concentration of 96%v/v. Similarly, Ekvall et al. [29] reported that maximum yield of raffinosefamily oligosaccharides from immature green peas was obtained at about 50% v/v ethanol followed by a decreased yield with further increase of ethanol concentration. Knudsen and Li[13] also found that increased ethanol concentration beyond 60% v/v noticeably reduced the amount of raffinose oligosaccharides extracted from plant material. A remarkable drop in oligosaccharides content at 96% v/v ethanol revealed that concentrated solvent did not ensure a good recovery of oligosaccharides compared to aqueous ethanol. Thus, ethanol concentrations of 35%, 60% and85% v/v were selected as the lower, middle and upper level, respectively,to be employed in RSM optimization.
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