Seed microstructure and meal chemical composition
TEM microscopy of camelina seed cotyledon cells showed distinct
separation of OBs from protein-rich areas or protein storage vacuoles
(PSVs) that were, more or less, spherical in shape and evenly
distributed within the cytoplasm (Figures 1D and E). The discrete dark
areas inside PSVs may be globoids containing phytic acid crystals as
reported for other seeds (Weber and Neumann, 1980). Camelina OBs had an
average diameter of 0.68 μm with a packing density of ~3
OBs/μm2. The OBs of Brassica seeds, including
rapeseed, have diameters between ~0.2 and 3.0 μm
(Katavic et al., 2006). The comparatively small size of camelina OBs and
the high packing density may facilitate larger oil storage capacity
within the cotyledon cells. The distinct membrane of camelina OBs
(Figure 1E) may prevent coalescence and provide steric hindrance or
electrostatic repulsion that may stabilize the OBs similar to other
oil-bearing seeds (Tzen, 2012). Mechanical pressing during oil
extraction may rupture these membranes and allow oil leakage. Subsequent
extraction with non-polar solvents, such as hexane, removes any oil that
remains trapped within the cellular matrix. Cellular components
remaining after oil extraction, including organelle membranes, cell wall
membranes and proteins, collectively make up the spent meal.
The mucilage-reduced, oil-free meal contained 51.3% protein and 6.8%
ash (mineral) (Table 1); these levels were higher than those reported
for camelina pressed cake meal [~40-45% protein
(Boyle et al. 2018; Li et al., 2014) and 5% ash (Zubr, 1997)]. The
levels of phytate and phenolic compounds, which are considered
anti-nutrients in many seed -derived meals (Wanasundara, 2011), were at
6.1% and 1.0% (as sinapic acid equivalents), respectively (Table 1).