Quality of oil and meal obtained by cold-pressing and hexane extraction of industrial hemp grain with different maturity

Harvested hemp grain exhibits varying degrees of maturity, which can be attributed to the plant’s indeterminate flowering trait, extent of seed shattering, and post-harvest cleaning. In this study, six fractions with different thousand seed weights (TSW) were obtained from bulk hemp grain by density-grading. TSW ranged from 17.8 g (heaviest) to 7.1 g (lightest). The oil content decreased (31.0% to 14.1%) with decreasing TSW as did cold-pressing oil yields (21.5% to 14.0%), but overall oil recovery after hexane extraction was the same ( >99.4%). Cold-pressed oils from fractions with TSW ≥ 12.6 g (mature seeds) were lighter in color (CIE L*a*b* scale, L* > 77 vs < 10) and had lower chlorophyll contents (14 to 37 ppm vs 75-80 ppm) than their corresponding hexane-extracted oils. The oil’s fatty acid profile is typical of hemp oil with linoleic (53%), linolenic (18%) and oleic (13%) as major components. Due to the long storage time of the bulk grains at room temperature, the oils obtained were of poor quality. Acid values ranged from 2.7 to 47.5 mg KOH/g for cold-pressed oils and 5.0 to 64.4% mg KOH/g for hexane-extracted oils. No discernible trend was observed in the oil’s peroxide values, which varied from 28.5 to 55.1 meq/kg. The protein contents of the grain fractions were not significantly different (25.3% to 21.2). Glutelins were the major soluble proteins (50-70%) followed by similar amounts of albumins and globulins (7-9% and 11-13%, respectively). SDS-PAGE showed similar molecular weight distribution of the polypeptides in each fraction, however, the 47 and 35 kD bands (associated with vicilin and edistin) were fainter in the lighter fractions. The oils can still be refined and processed into other products like fatty acids and mono- and diglycerides, which can be used in various industrial applications.