materials (almond seed) in the previous study (Zhang et al., 2009).
Response surface plots were constructed to visualise significant
(p < 0.05) interaction effects of ultrasound extraction variables on
the yield (Fig. 1a–c).
The results revealed that the higher oil recovery was obtained
by the ultrasound extraction at higher ultrasound power for longer
time. The ultrasound extraction at the elevated temperature using
high proportion of solvent to sample ratio resulted in extra efficiency
for the oil recovery from papaya seed (Fig. 1a–c). In fact,
the yield increased with simultaneously elevating extraction temperature
and ultrasound power. Zhang et al. (2009) also reported
that the extraction yield significantly increased with prolonging
the extraction time. This could be explained by the fact that the
ultrasound extraction process at the elevated temperature could
facilitate the oil transfer from seeds powder into the warm media
(Zhang et al., 2009). The elevated extraction temperature softens
the plant tissues and enhances the diffusion, thus promoting the
elution of attached oil inside the solvent. This could be favourable