Milling
The silflower seed was milled to remove a fraction of the hulls to
obtain an enriched kernel fraction with higher oil content. The initial
attempt to remove the seed’s wing using a food processor with a blunt
blade, a method that worked well in dewinging milkweed seeds
(Evangelista, 2007), was not successful for silflower seeds. This could
be due to the fibrous nature of the wing. However, a corrugated roller
mill with differential speed was able to strip the hull from the kernel.
By decreasing the gap of the rollers after each pass of the +5M and +12M
fractions, the kernel particle size was reduced while most of the hulls
remained intact and stayed on top of the 5- and 12-mesh screens. An
enriched kernel fraction with oil content higher than 20%, accounting
for 66% of all fractions, was obtained from +18M and finer fractions
(Table 4). More hulls were removed from +18M and +25M fractions by air
classification and the heavier fractions were milled again to pass
through the 25-mesh screen. The combined -25M fractions had an oil
content of 24.85% (Table 2). Based on the oil contents of the hulls
(1.04%) and the kernel (31.00%), the full-fat kernel-rich fraction has
20.4% hulls, a significant reduction from 43.75% hull in whole seeds
(Table 1). After extracting the oil from the kernel-rich fraction, the
crude protein content of defatted meal increased to 63.41% (Table 2),
just two percentage points short of classifying as protein concentrate
(crude protein content from 65 to 89%).