Facilities available for
preparation of various protein products from oilseeds, cereals
and grains. These include:
Protein concentrates
Protein isolates
Modified protein products
Hydrolyzed protein products
Capabilities exist for process design of
commercial facilities for production of protein products used
in meat, dairy, beverage and bakery applications.
MANUFACTURING PROCESSES
I. Soy Protein Concentrates
Soy protein concentrates are prepared by removing soluble
sugars from defatted soy flakes or flours. The remaining components
are mainly proteins and insoluble polysaccharides.
By the removal of soluble sugars from defatted flakes , the
protein content of the resulting soy product is increased
and the undesirable oligosaccharides, which cause flatulence,
are eliminated. Flatus is gas formed in the gut by bacterial
fermentation of nondigestible carbohydrates. During extraction,
most sucrose and most nondigestible oligosaccharides consisting
of stachyose, raffinose, and a small amount of other carbohydrates
are not removed. Sucrose and the total nondigestible oligosaccharides
each constitute 8% of defatted flakes.
Different leaching methods are available to remove soluble
sugars to yield concentrates. The basic approach is to extract
the sugars while not solubilizing the protein portion. The
major parameters in leaching or fractionation that affect
yield and product quality are the starting material, extracting
solvent, and extracting conditions.
Soy concentrate can be prepared from full-fat flakes produced
by employing hexane as the oil-extracting solvent.
The amount of heat treatment during the preparation of defatted
flakes influences the quality as well as yield of soy protein
concentrate. Excessive toasting of defatted flakes, as indicated
by a lower Nitrogen Solubility Index (NSI), reduces the amount
of soluble sugars leached, resulting in a lower protein content
in the final product. In addition, heating of flakes reduces
the rate of soluble leaching. Because extraction is a continuous
process, slow leaching has a major impact on production speed.
There are three common processes for manufacturing soy protein
concentrate: aqueous alcohol wash, acid wash, and hot water
leaching. In general, concentrate preparation involves countercurrent
extraction.
1. Aqueous Alcohol Process
This process is commonly employed for producing commercial
soy protein concentrates. Soluble sugars along with a small
amount of soluble proteins are extracted by 50 to 70% aqueous
alcohol. Due to the denaturation of protein by aqueous alcohol,
most of the proteins become insoluble and remain with the
insoluble polysaccharide. The alcohol was recovered by flash
desolventizing.
The preferred alcohol concentration is 60% by weight. Soy
proteins appear to be least soluble in about 50% aqueous alcohol;
their solubility increases on either side of that concentration.
Excess water in the extraction solvent is to be avoided because
of additional energy costs for removal and because an extremely
wet soy protein cake tends to agglomerate, clogging the process
system. The aqueous alcohol removed by evaporation from the
alcohol water soy solubles is recycled to the extraction step.
The nitrogen solubility of soy protein concentrate made by
the aqueous alcohol process is low, in the NSI range of 5
to 10. This low NSI is not necessarily related to functionality
because the denaturation mechanism is different from that
of toasting used to produce low-NSI soy meals. However, extraction
with aqueous alcohol removes objectionable flavor and color
to yield desirable soy protein concentrate products.
2. Acid Wash Process
The majority of soy proteins are globulins, which are insoluble
in water in the regions of their isoelectric points. By the
washing of defatted soy flakes with water near the isoelectric
point of pH 4-5, soluble sugars are removed from the matrix
of proteins and polysaccharide. After acid-water washing,
the remaining materials are adjusted to near neutrality and
dried. Usually, these products are spray-dried. Because some
of the soy proteins are soluble at pH 4-5 , there is a reduction
in the protein yield.
The acid wash process yields soy protein concentrate products
with a relatively high NSI (about 65-75%) because severe denaturation
steps are not introduced in the process and the proteins are
neutralized before drying.
3. Hot Water Leaching Process
Proteins, including soy proteins, are easily denatured by
heat and become insoluble in water. Moist heat is more effective
for denaturation than dry heat. With water of high temperature,
the small molecular weight materials, including soluble sugars,
are extracted from the insoluble protein and polysaccharide
matrix.
4. Other Processes
Another modified, "second-generation" soy protein
concentrate of improved functionality is produced by successive
pressure and cavitation, such as centrifugal homogenation
at elevated temperatures and slightly alkaline pH, a high-NSI
soy protein concentrate can be obtained from one that originally
had a low NSI value. The highly soluble soy concentrate has
functional properties similar to those of milk protein's.
II. Manufacture of Isolated Soy Protein
It includes aqueous extraction of soluble proteins and carbohydrates
from defatted soybean flakes or soy flour; separation of the
insoluble residue, followed by precipitation of protein at
mildly acidic conditions; separation and removal of the soluble
carbohydrates, proteins, and salts; and washing and drying
of the protein. The protein can be neutralized and further
processed into isolates with a variety of forms and functional
properties.
III. SOY ISOLATE
Soybean flour is added to deionized water. The temperature
and pH of the mixture during the extraction is kept at 55
degrees C. The pH of the mixture is kept at 8.5 9.5
using NaOH. After an hour the mixture is pumped into a centrifuge
to separate the solids and the liquids. The liquid is held
in a container while the solids were extracted again. (The
difference between the beginning balance and the balance after
centrifugation is attributed to the extra water used to clean
the centrifuge baskets.) The solid residue is re-extracted
using the same conditions. The proteins are precipitated out
by HCI by bringing the pH to 4.55. All of the liquid fractions
are pasteurized at 65 degrees C for a hour. The solution was
then pumped into the centrifuge to separate the solids and
the liquids. Then, separated solids are neutralized and spray
dried to produce protein isolates.