3.6. Microstructural analysis
To
better understand the influence of different extraction methods on the
characteristics of RBO, microstructure of native and samples after
extraction were investigated by
SEM.
The
images showed that the internal tissue of the rice bran seems to undergo
a process of destructing and restructuring. In Fig. 3a, natural rice
bran had a relatively complete structure, regular or dense shape and
smooth surface, meanwhile, the intact oil cells on the surface of bran
tissues before extraction were
observed.
Fig. 3b showed the expansion process caused the disruption of cell walls
and loose cell arrangement of expanded rice bran, making conventional
extraction or enzymatic extraction more accessible to organelle.
After
AEE, the oil was almost extracted together with aleurone grains and the
substances in the cell gradually were decreased, therefore, the
structure of rice bran cell was further destroyed (Fig.
3c).
In
Fig. 3d, the surface of rice bran treated with n-hexane became more
fragmented, dried and cracked, and some lipids and starches were dragged
away (Alcázaralay, Cardenastoro, Santos & Meireles,
2015).
In
the process of SE, the chemical affinity between organic solvent and
oils affected the mass transfer process which caused a high oil
extraction yield, but it could also damage the protein and starch in the
extraction process. The process of enzymatic extraction was based on the
insolubility of oils in water and the efficiency was lower than that of
SE. However, AEE could simultaneously separate solid phase (mainly
starches and proteins) and an oil phase, so the development of these
by-products could also make full use of rice bran.