Napin-enriched fraction
The α-helix content of 32.1% ± 0.4% (Figure 6) determined for camelina
napin was similar to that reported for B. napus napin
(Pantoja-Uceda, 2003; Wanasundara, 2011). The spectral peaks resembling
β-sheets (1627-1638 cm-1) and β-turns (1674-1684
cm-1) most likely originated from bond vibrations
responsible for short, extended chains attached to helical motifs. These
peaks resembled those observed for cruciferin (Figure 6); however, they
do not originate from true β-structures in napin. This phenomenon is
commonly observed in other helical proteins, such as hemoglobin and
cytochrome C (Byler and Susi, 1986). Camelina napin showed far-UV CD
spectra typical of a helical protein similar to described by Greenfield
(2006) with -θ peaks at ~222 nm and ~208
nm and a + θ peak at ~195 nm (Figure 7B). The secondary
structural features of napin did not show differences in magnitude with
changes in pH (Figure 7B and Table 4). Napin from B. napus is
also structurally stable in response to changes in pH (Perera et al.,
2016). The increase in S0 at pH 3 and the decrease at pH
10 (Table 4), although much less than that observed with cruciferin,
suggested some degree of structural change for napin. Use of intrinsic
fluorescence to probe napin tertiary structure details during pH changes
was not possible due to the very low number of Trp and Tyr residues. No
thermal transition peak above or below 100°C was observed for camelina
napin dry powder or slurries at pH 3, 7 and 10. However, Boyle et al.
(2018) reported that temperatures of ~104-107°C with
lower enthalpy values (ΔH = ~0.2-3.0 J
g-1) are required for denaturation of camelina napin.
The high thermal-stability nature of crucifer napin at a temperature of
>100°C (ΔH = ~9-14 J g-1)
is reported elsewhere for B. napus (Krzyzaniak et al., 1998). The
lower sensitivity of napin structure to changes in pH and its high
stability in response to heat is a distinct contrast to the properties
of cruciferin found in the SSPs of Brassicas, including camelina.
Cruciferin and napin, and to a lesser extent vicilins and OBPs, comprise
the bulk of the camelina meal proteins. Camelina protein is rich in
S-containing amino acids, contains proteins that are soluble at acidic
pH, and is structurally stable at low pH and high temperatures, making
camelina seed protein similar to that from other economically-important
crucifers. Protein products rich in cruciferin and/or napin could be
obtained from camelina using scalable processes described forBrassica oilseeds to benefit camelina value chain development.
Unique properties of individual proteins (cruciferin and napin) could
position camelina alongside commercial ventures being developed for
canola/rapeseed protein
(https://www.meritfoods.com/canola.protein/;
https://napiferyn.com/;
https://www.dsm.com/corporate/solutions/nutrition-health/canolapro-plant-protein.html).
The ability to change the camelina seed protein profile and consequently
influence the quality attributes of SSP fractions (Lyzenga et al, 2019)
may cater to specific nutritional or functional applications. Seed coat
mucilage is also a valuable hydrocolloid (Soukoulis et al., 2018);
however, removal or reduction of camelina seed coat mucilage is critical
for high protein recoveries. Therefore, effective technologies for
recovering seed coat mucilage are necessary to bring this valuable
co-product into an integrated valorization scheme. OBs that are
stabilized by OBPs may also have economic value in food, feed and
personal care applications
(https://www/botaneco.com/food-and-feed).