ZEIN: THE INDUSTRIAL BIOPOLYMER FOR THE 21st CENTURY
- The United
States produces about 300-325 million tons of corn per year,
accounting for about 40-50% of the world's annual production. About
50% of US corn is used directly as animal feed, about 25% is used for ethanol production
and the rest for export and producion of food, feed, fiber and industrial products.
There are four basic methods for processing corn: Alkaline
Processing, Dry Milling, Wet Milling and Dry-Grind (for ethanol production). Corn wet milling is a
process that utilizes mechanical unit operations -- size
reduction (milling), aqueous extraction and separation
(filtration, centrifugation) -- for separating and purifying the
major corn components such as oil, starch, protein, fiber. Corn refiners take the process
further and convert the starch into a myriad of food and industrial products. Wet milling
generates large amounts of protein co-products : about 5-6% of
the corn becomes corn gluten meal (CGM, 60% protein) and 24% of
corn dry weight is corn gluten feed (CGF, 21% protein).
Much of the fuel ethanol produced today in the US is by the "Dry-Grind" process. This also generates
co-products (DDG or DDGS) that contain all the non-starch
components of corn, amounting to about 28% of the corn
processed. Most of these protein co-products are currently
marketed as animal feed at low prices. Another one-third of the corn becomes carbon dioxide which is another zero- or low-value coproduct.
The high demand for
corn starch and starch-based products -- sweeteners, syrups,
ethanol, bioproducts, organic acids, food ingredients -- will
create a disposal problem for the growing quantities of protein
co-products. In addition, the corn processing industry must also
consider increasingly tight environmental regulations and
limitations of international markets for CGF and CGM.
There are two possible alternate higher-value outlets for corn
(1) As an industrial polymer, e.g.,biodegradable plastics and films and
(2) As a functional ingredient in (human) food products.
Protein forms about 9% of the dry weight of corn. It is composed mainly of zein (a highly hydrophobic protein,
soluble in isopropanol or ethanol), glutelin (soluble in aqueous alkaline solutions), albumins and globulins.
Zein comprises about 40% of the total kernel protein on a dry basis.
Zein was first discovered by Gorham in 1821. Osborne developed the first patented
process for extraction of zein from corn gluten meal (CGM) using 95% ethanol. Swallen et al. were
granted a series of patents on zein production using different alcohols of varying
concentrations and additives. Zein became commercially available in 1938 and quickly
found application in coatings, fibers, films, plastics, adhesives and inks.
Zein (often combined with vegetable oils and glycerin as plasticizers) is used as a waxing
or glaze, to enhance shelf life of pharmaceutical tablets, nuts
and candies by acting as a water and oxygen barrier. This was part of the “chemurgy” movement where crop/farm by-products were utilized by
industry. Zein fibers with the commercial name of Vicara was produced by the Virginia-Carolina
Chemical Corporation in 1948. It was marketed for its claims of washability, the
warmth of wool and resistance to moths and mildew.
Zein reached a peak production of 7 million kg per year
in 1956 but with the development of cheaper synthetic materials, the market for
zein dropped significantly by 1960. Today there is one known manufacturer of zein in USA and one in Japan.
The cost of purified zein is $20-70 per kg depending
on the grade and purity. However, this price makes zein an
uneconomical material for large industrial uses such as biodegradable plastics, since petroleum-based polymer resins sell
for much lower prices ($0.35-0.70 per kg).
Even though there are several hundred patents on applications of zein and renewed
interest due to its biodegradability and potential nanotechnology applications, its
current high price is still a limitation.
The potential market for zein should now be good, considering:
(1) Increased demand for true 100% biodegradable packaging
(2) The low margins in some sectors of the corn processing
industry that are eager to find higher-value outlets for their
(3) Valuable lessons learned from previous
attempts at corn-based "biodegradable" plastics : these were
largely starch-based and did not fare well in the market for
Assuming that "biodegradability" and being "renewable" and "green" can
enhance the value of zein-based films and packaging, this market could use a substantial
portion of the zein in the 5 billion bushels (1 bushel = 25 kg)
of corn presently processed into food, feed and industrial products in USA today. However,
the cost of zein must be reduced and the quality improved over what is currently available.
The COPE Project
We have developed methods for producing low-cost zein for the food and industrial markets. Our
COPE (Corn Oil and Protein Extraction) process uses ethanol for
the initial extraction of zein from corn or corn co-products.
This is then combined with membrane
technology for the separation, isolation and purification of
zein from the ethanolic zein solution. Membrane technology
offers the possibility of selective low-energy low-cost
separation of zein and for recycle of the ethanol solvent
without the substantial evaporation costs that now limit other
zein extraction processes. Additional economies are possible if COPE-zein production is carried out in
dry-grind ethanol plants, since they already have the two key raw materials (corn and ehanol).
Further refinements of the COPE process have been
developed to extract additional high-value coproducts such as a "healthy" corn oil loaded
with nutrients such as carotenoids, vitamins and phytosterols,
and nutraceuticals such as xanthophylls (lutein and zeaxanthin).
Our preliminary economic analysis shows a net revenue of $2-4/bushel corn, depending on the coproduct(s). This
translates into an additional income of $75-150 million per year for a plant producing 100 million gallons of ethanol/year (380 million liters/year)
without any additional raw materials being used (we "borrow" in-house ground corn and ethanol).
Considering that US corn-based ethanol capacity is over 10 billion gallons per year, the potential impact of our
research is significant.
This technology has resulted in several US and Canadian patents and has been licensed through the
University of Illinois to Prairie Gold Inc., Bloomington, Illinois for commercialization.
2. Zein as a functional food ingredient
The main obstacle to utilization of zein in human food
products is their poor "functionality". Functional
properties refer to those attributes that provide the desired
physical or sensory properties to the food. For example,
proteins contribute not only nutritional quality to a food, but
also to textural properties such as gelation (important in
meats, cheeses, gels, etc.), adhesion (meats, bakery, pasta),
emulsification (Deli meats, soups, cakes), foaming/whipping
(cakes, frozen desserts) and moisture sorption (intermediate
moisture, shelf-stable foods).
Poor functionality of corn proteins is generally related to
their insolubility in aqueous systems; proteins generally have
to be in solution or fine suspension in order to exert their
desirable functional properties in foods.
In the mid-1980s, our group at the University of Illinois set about to
improve the water solubility of corn proteins and some of its
functional properties. The approach was enzymatic modification
combined with membrane technology to produce specific protein
fractions or peptides from corn gluten meal. With zein (one of
the two major proteins in corn), this involved a unique two
phase sequential process: an organic phase enzyme reaction
followed by an aqueous phase enzyme reaction.
What are the results?
- A successful
combination of enzymatic modification and fractionation by
membrane technology has created two new corn protein products: a
water-soluble zein and an enzyme treated corn gluten meal (in
which the glutelin fraction has been modified). Functional
properties were dramatically improved by this treatment. For
example, for zein:
- Protein solubility in water increased from 0% to 99%
over the pH range expected in foods.
- Protein solubility could be partially controlled by
membrane pore size: solubility decreased with larger membrane
- Clarity, solubility and foaming properties increased
with Degree of Hydrolysis. Ultrafiltration increased foam volume
and decreased foam stability.
- Moisture sorption properties of Illinois-process zein
fractions were vastly superior to unmodified proteins, and
better than soy protein hydrolysates produced in a similar
- Similar improvements were also observed for the
enzyme treated CGM. This development should enhance the
utilization of corn proteins for food products.
Major funding for the above corn projects have come from the Illinois Corn
Marketing Board . the Illinois Department of Commerce and Economic Opportunity, US Department of Agriculture
NRICGP program, several membrane companies and MAFMA. Partnerships and collaborations were established with engineering companies,
membrane manufacturers, food companies and ingredient manufacturers to research, develop and market the various processes.
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Updated July 2009 by email@example.com