Oilseed Processing Methods and Nutritional Value

Oilseed Processing Methods

• Three main methods for removing oil from oilseeds:
  • Screw press or expeller
  • Direct solvent
  • Pre-press solvent

Screw Press (Expeller) Method

• Seeds are cracked, dried, cooked, and extruded through a die.
• Temperature is closely regulated during extrusion to inactivate antinutritional factors without reducing nutritional value.
• Excessive heat can reduce protein solubility and biological value through the Maillard or browning reaction.
  • Feedstuffs, including forages, are susceptible to the Maillard reaction when exposed to excessive heat.
  • The Maillard reaction creates linkages between carbohydrates and amino acids, reducing nutrient availability and nutritional value.
• Screw-pressed oilseed meals have the highest lipid content (4-5%).

Direct Solvent Method

• Soybeans are cracked, cooked, ground, and extracted with hexane or another solvent to remove lipids.
• The process is typically performed at low temperatures.
• During solvent recovery, the meal is heated to inactivate antinutritional factors.

Pre-Press Solvent Method

• A modified expeller process combined with solvent extraction.
• Resultant oilseed meals have the lowest lipid content.

Nutritional Value of Oilseeds

• Nutritional value varies:
  • Between different oilseeds
  • Within a variety of oilseed
  • Between different processing methods
• Oilseed meals are generally high in protein.
  • Minimum crude protein content is 40% on a dry-matter basis.
  • Protein content is standardized prior to marketing.
  • Most of the nitrogen is in the form of true protein.
  • The protein is highly digestible.
  • Moderate to good biological value, but generally lower than animal protein feeds.
  • Low in cystine and methionine.
  • Lysine content is variable and low in all except soybean meal.
• Energy value varies greatly between oilseed meals.
• Mineral content:
  • Low in calcium.
  • High in phosphorus, but at least 50% is relatively unavailable to monogastrics.
• Vitamin content:
  • Low to moderate in B vitamins.
  • Low in vitamin E and carotene.