Removal of seed coat mucilage
Camelina seeds are oblong in shape and comparatively small in size
(Figure 1A) with average dimensions of 2.2 mm in length and 1.2 mm in
width. Specialized cells in the seed coat of crucifers, such asArabidopsis thaliana, Capsella bursa-pastoris andLepidium flavum (Soukoulis et al., 2018), produce extracellular,
pectinaceous mucilage that absorbs water and expands and forms a gel
around the seed coat. Mucilage aids in fruit and seed dispersal, defends
against pathogens, enhances water uptake during germination and acts as
a barrier to water and oxygen diffusion into inner tissues to prevent
seed germination during undesirable environment conditions (Soukoulis et
al., 2018). Interference of seed coat mucilage with protein extraction
and recovery has been reported for flax (Wanasundara and Shahidi, 1997)
and yellow mustard (Wanasundara et al., 2012), and the same was expected
for camelina as the seed contains about 6.7% mucilage by weight.
Li et al. (2016) showed that camelina mucilage is composed of galactose
(58.1%), glucose (25%), rhamnose (11.6%) and xylose (5.2%), whereas
arabinose, glucose and xylose are more abundant in flax, yellow mustard
and chia mucilage, respectively (Soukoulis, et al., 2018). Viscozyme®,
an enzyme complex derived from Aspergillus spp. containing
arabinase, cellulase, β-glucanase, hemicellulase and xylanase, was more
effective in breaking down camelina seed coat mucilage than other
carbohydrases (pectinases and cellulases) or mild alkaline
(NaHCO3) solutions (data not shown). The optimum
conditions for Viscozyme® pre-treatment for camelina seeds were 3 h of
soaking with 0.1 mL enzyme/g seed with vigorous stirring to
remove/reduce seed coat mucilage. Microscopic examination of soaked,
untreated seed showed water-absorbed mucilage as a halo around the seed
(Figure 1B) compared to dry, non-hydrated seed (Figure 1A) or hydrated
seed after enzyme treatment (Figure 1C). Although non-enzymatic
approaches such as heating of hydrated camelina seed (as slurries) to
temperatures up to 85°C to reduce slurry viscosity have been used, the
possibility of partial denaturation of proteins at ~50°C
during hot-pressing of camelina seed, as has been reported by Boyle et
al. (2018), indicates the importance of low temperatures (<
50°C) during seed pre-treatments to minimize heat-induced alterations in
proteins.