Soybean Meal and Products Descriptions and Photomicrographs
Sponsored LinksSoybean products are widely used in animal feeds. These are solvent extracted or mechanically pressed soybean meal and various methods of heat processed fullfat soybeans. Soybean protein concentrates may be occasionally used in specially prepared feed formulas. Identification of soybean products in a feed is generally made by the characteristics of the hulls and hilum or seed scar.
Macroscopic Features
1. Soybean seed is a typical legume seed, elliptic in outline, having thickness less than the breadth, 6 to 10 mm in length and 3 – 4 seeds are nested in a 1.5 – 2.5 inches long hairy pods.
2. The seed coat or hull is smooth, often shiny and firm in texture.
3. Seed color is generally buff, but it can range from green through yellow and black.
4. When the seed coat is removed, the embryo remains, consisting of the two cotyledons, the hypocotyls, and the plumule. The major portion of soybean meal is made up to cotyledons.
Stereomicroscopic Features
1. The hull, about 0.1 mm thick, consists of three distinct layers of which, the middle layer is not distinguishable at low magnification.
2. The outer surface is slightly pox-marked. The marks are light depressions, like minute pin-pricks, 0.1 – 0.2 mm apart.
3. The inner surface is almost white and has a straight porous, spongy appearance.
4. The hilum is the black to brown oval seed scr where the bean attaches to the pod. There is a longitudinal slit in the middle of the hilum. The slit as well as the edge of the oval are distinct and raised. At one end of the hilum is a small groove, the chalaza, the point where seed coat was joined to the ovule. At the other end is the micropyle, a small orifice through which the primary root of the young seedling emerges.
5. The meal consists of oil-extracted particles of bean proper and conglomerated bean and hull particles.
6. Solvent extracted meal particles are irregular and flat in shape with round edges. They appear translucent, having a glazed or waxy surface, and varying colors from cream to pale reddish-brown. The texture is hard and brittle. Expeller meal is darker in color and appears in rough, granular chunks.
Histological Features
The seed coat and hour-glass or column cells are the most useful characteristics in identifying soybean products under a high powered microscope.
1. The seed coat consists of four layers of cell: palisade cells; hour-glass cells; spongy parenchyma and the aleurone layer.
2. The hour-glass cells form the second inner layer, generally readily separated in mounting media. The cells have the hour-glass liked shape, each being hexagonal and ranging from 30 to 70 microns long. Both the cells and intercellular spaces are empty.
3. On the seed coat or hull, there are pox-marks, rough-edged depressions with an irregular polka dot on a colorless to tan, translucent background. These dots may join to give oddly shaped, connecting sinuses.
4. The surface of cotyledons consists of small cubical cells filled with aleurone. The inner part of cotyledons made up of elongated palisade-like cells with thin walls filled with aleurone and small amounts of oil. The large meal particles are irregular, shiny, semi-translucent, round chunks, colorless at the edges, buff to dark tan or brown in denser portion.
March 13 2008 09:21 am | Article