Milling of Legumes and Oilseeds

• Legumes and oilseeds are important sources of plant-based proteins and oils globally
• Processing techniques enhance their nutritional value, palatability, and shelf life
• Milling, a key process, involves particle size reduction for various applications
• Understanding the structure and nutritional composition, including anti-nutritional factors (ANFs), is crucial for effective processing

Milling of Legumes and Oilseeds

• Milling is a mechanical process that reduces the particle size of legumes and oilseeds
• Milling improves texture and increases surface area
• Milling facilitates further processing like oil extraction or flour production
• Different milling methods affect particle size distribution differently, including hammer milling, roller milling, and pin milling
• Hammer mills use rotating hammers to impact and shatter the material
• Roller mills crush the material between rotating rollers
• Pin mills use high-speed rotating pins to shear the material
• The choice of milling method depends on the desired particle size, the physical properties of the seed, and the intended use of the milled product
• Milling affects the functional properties of legume and oilseed flours like water absorption capacity, oil absorption capacity, and emulsification properties
• Fine milling can lead to increased protein solubility and improved baking performance
• Excessive milling can damage starch granules and protein structures, negatively impacting product quality
• Proper milling is crucial for efficient oil extraction in oilseeds

Structure of Legumes

• Legumes consist of the seed coat (testa), cotyledons, and embryo (germ)
• The seed coat protects the seed and is rich in fiber
• Cotyledons are the main storage tissues containing proteins, carbohydrates, and lipids
• The embryo contains the embryonic shoot and root, responsible for germination
• The hilum is a scar on the seed coat where the seed was attached to the pod
• Cell walls in legumes are complex, containing cellulose, hemicellulose, and pectin
• Protein bodies are structures within the cotyledon cells that store proteins
• Starch granules are also present in the cotyledons, providing energy upon germination
• The microstructure of legumes affects water absorption, cooking time, and texture
• Differences in cotyledon cell size and arrangement influence the hardness and cooking properties of different legume varieties

Structure of Oilseeds

• Oilseeds typically consist of the seed coat (hull or husk), the endosperm (in some oilseeds), and the embryo
• The seed coat protects the seed and can be a significant source of fiber
• The endosperm, when present, provides nutrients to the germinating seedling
• The embryo is rich in oil and protein
• Oil bodies (oleosomes) are specialized structures within the cells that store lipids
• Protein bodies are also present, storing proteins
• The structure of the seed coat affects dehulling efficiency and oil quality
• The arrangement and size of oil bodies influence the efficiency of oil extraction
• Cell wall structure impacts seed hardness and the ease of cell rupture during oil extraction

Anti-Nutritional Factors (ANFs) in Legumes

• ANFs are compounds that interfere with nutrient absorption and utilization
• Common ANFs in legumes include trypsin inhibitors, lectins, phytates, tannins, and cyanogenic glycosides
• Trypsin inhibitors inhibit the activity of trypsin, an enzyme required for protein digestion
• Lectins (hemagglutinins) bind to the intestinal lining, interfering with nutrient absorption
• Phytates (phytic acid) bind to minerals like iron, zinc, and calcium, reducing their bioavailability
• Tannins bind to proteins and reduce their digestibility
• Cyanogenic glycosides release hydrogen cyanide (HCN) upon hydrolysis, which can be toxic
• Processing methods like soaking, cooking, autoclaving, fermentation, and germination can reduce ANF levels
• Soaking helps to leach out water-soluble ANFs
• Cooking and autoclaving denature heat-labile ANFs like trypsin inhibitors and lectins
• Fermentation breaks down ANFs and improves nutrient bioavailability
• Germination reduces phytate levels and increases the levels of some vitamins
• Genetic selection can also be used to develop legume varieties with lower ANF levels

Anti-Nutritional Factors (ANFs) in Oilseeds

• Common ANFs in oilseeds include glucosinolates (in rapeseed), gossypol (in cottonseed), and trypsin inhibitors
• Glucosinolates are present in rapeseed and related species and can produce undesirable flavors and thyroid-inhibiting compounds
• Gossypol is found in cottonseed and is toxic to monogastric animals
• Trypsin inhibitors are also present in some oilseeds, interfering with protein digestion
• Processing methods like heat treatment, solvent extraction, and enzymatic treatment can reduce ANF levels in oilseeds
• Heat treatment denatures trypsin inhibitors and reduces glucosinolate levels
• Solvent extraction removes gossypol from cottonseed oil
• Enzymatic treatment can break down glucosinolates
• Proper processing is essential to ensure the safety and nutritional quality of oilseed-based products

Processing Technologies for Legumes

• Soaking hydrates the seed, reduces cooking time, and helps remove some water-soluble ANFs
• Blanching applies brief heating to inactivate enzymes and soften the seed coat
• Dehulling removes the seed coat to improve texture and reduce fiber content
• Cooking denatures proteins, gelatinizes starch, and reduces ANF levels
• Autoclaving is high-pressure cooking that effectively reduces ANFs and improves digestibility
• Fermentation uses microorganisms to break down complex compounds, reduce ANFs, and enhance flavor
• Germination (Sprouting) increases vitamin content and reduces phytate levels
• Extrusion is a high-temperature, short-time process that texturizes legume proteins and produces various products
• Milling reduces particle size for flour production and other applications

Processing Technologies for Oilseeds

• Dehulling removes the seed coat to improve oil quality and reduce fiber content in meal
• Crushing/Flaking ruptures the oil-bearing cells to facilitate oil extraction
• Cooking/Conditioning adjusts moisture and temperature to optimize oil yield
• Oil Extraction separates oil from the solid material using mechanical pressing or solvent extraction
• Mechanical Pressing uses pressure to squeeze oil from the seeds (e.g., expeller pressing)
• Solvent Extraction uses solvents like hexane to dissolve and extract oil
• Refining removes impurities from the crude oil, such as gums, free fatty acids, and pigments
• Degumming removes phospholipids (gums) from the oil
• Neutralization removes free fatty acids to improve flavor and stability
• Bleaching removes pigments to lighten the oil's color
• Deodorization removes volatile compounds that cause undesirable odors and flavors
• Winterization removes waxes to prevent cloudiness at low temperatures