IngredientsCorn, or maize (Zea mays L.), is the only cereal crop indigenous to the Americas and one of the most important food and industrial crops in the United States. Zein is the principal storage protein derived from this species. Zein belongs to the characteristic class of proteins known as prolamins, which occur specifically in cereals — the equivalent of hordein in barley and gliadin in wheat. In maize, prolamins are called zeins; in wheat, gliadins; in oat, avenins; in barley, hordeins; in rye, secalins; and in sorghum, kafirins.
Zeins, the seed storage proteins of maize, are synthesized during endosperm development by membrane-bound polyribosomes and transported into the lumen of the endoplasmic reticulum, where they assemble into protein bodies. Zein is located in 'zein-bodies' of approximately 1 µm distributed uniformly throughout the cytoplasm of corn endosperm cells between starch granules of 5–35 µm. Zein belongs to a class of proteins called prolamins, which are soluble in alcohol, and comprises approximately forty to fifty percent of the total protein in corn, or about four percent of the corn kernel.
Zein's defining characteristic is insolubility in water except in the presence of alcohol, high concentrations of urea, high concentrations of alkali (pH 11 or above), or anionic detergents. Zein is particularly rich in glutamic acid (21–26%), leucine (20%), and proline (10%).
Zein has been further divided into four subclasses: alpha-zein, beta-zein, gamma-zein, and delta-zein. Alpha-zein is the primary commercially used zein and accounts for about seventy percent of the zein in corn. Beta-zein accounts for about five percent. Gamma-zein accounts for approximately twenty to twenty-five percent, and delta-zein accounts for about one to five percent. Each zein type has a different amino-acid profile and exhibits slightly different physical properties.
By electrophoretic analysis, α-zein exhibits two major bands with molecular weights of 19 and 22 kDa, respectively; β-zein, which constitutes 1–5% of zein, is made of a polypeptide of 14 kDa; γ-zein, which constitutes 10–20% of zein, is made of two polypeptides of 16 and 27 kDa; and δ-zein accounts for 1–5% of zein with a molecular weight of 10 kDa. In Zea mays, the 22 kDa and 19 kDa zeins are encoded by a large multigene family and are the major seed storage proteins, accounting for 70% of the total zein fraction.
The circular dichroic spectrum of zein protein mixture in methanol solution showed the zein secondary structure to be largely helical. The polar, hydrophobic, and turn characteristics of the zein residues, as well as the homologous repeat units in their primary sequences, suggested a structure with nine adjacent, topologically antiparallel helices clustered within a distorted cylinder. The structure of alpha-zeins is largely defined by a series of tandemly repeated peptides of 20 amino acids, with nine repeats in the 19-kDa and ten repeats in the 22-kDa alpha-zeins.
Commercial extraction of zein results in a product with a molecular weight of 25,000 to 35,000. Zein contains a high proportion of hydrocarbon group side chains and has a high percentage of amide groups present with a relatively low amount of free carboxylic acid groups.
Most commercial zein is extracted from corn gluten, also referred to as corn gluten meal (CGM). Corn gluten is produced in the corn steep liquor process ("wet milling") used to separate corn starch from the corn kernel. Treatment of dry-milled corn with 0.55% lactic acid and 0.2% sulfur dioxide at 50°C for 6 hours before ethanol extraction resulted in a 50% increase in zein isolate yield with high solubility (98%). Commercial zein is available as a powder, as ethanolic solutions for coating applications, as micro- and nanoparticle preparations, and as films and fibers for pharmaceutical and food applications.
Zein is now used as a coating for candy, nuts, fruit, pills, and other encapsulated foods and drugs. In the United States, it may be labeled as "confectioner's glaze" and used as a coating on bakery products or as "vegetable protein."
First reports describing zeins date back to 1821, when J. Gorham named proteins isolated from maize "zeine." T.B. Osborne, the founder of seed storage protein research, classified zeins as prolamins and developed the first extraction methods based on their hydrophobic nature. Commercial production of zein was initiated in 1939, and many potential uses were subsequently identified.
Historically, zein has been used in the manufacture of a wide variety of commercial products, including coatings for paper cups, soda bottle cap linings, clothing fabric, buttons, adhesives, coatings, and binders. The dominant historical use of zein was in the textile fibers market, where it was produced under the name "Vicara." With the development of synthetic alternatives, the use of zein in this market eventually disappeared.
When synthetic materials became cheaper in the 1950s, zein products were not cost-effective and lost use. Today, because of environmental concerns, interest in zein utilization is again growing. Currently, much of the zein from corn gluten meal is used for food, the medical, and pharmaceutical fields.
Zein is a food substance Generally Recognized as Safe (GRAS) by FDA [21 CFR 184.1984] as a direct human food ingredient, for use as a surface-finishing agent, and for technical effects — as an anticaking agent or free-flow agent, a drying agent, and a humectant. Zein has been considered GRAS by FDA since about 1960, confirming its long-standing safety record.
Based on the long history of zein usage in food and related evaluation data, zein was approved in 1985 by the US-FDA as a GRAS excipient for film coating of pharmaceuticals, mainly involving tablets. For pharmaceutical coating, zein is preferred over food shellac, since it is all natural and requires less testing per the USP monographs.
Zein is characterized by a high proportion of nonpolar amino acids, which contributes to its hydrophobicity and insolubility in water. It is notably rich in glutamine, proline, alanine, and leucine, while being deficient in essential amino acids such as lysine and tryptophan. This compositional bias has significant nutritional implications but also offers unique physicochemical properties for material science and pharmaceutical applications.
Zeins account for more than 50% of total seed proteins but are deficient in several essential amino acids. As a result, the corn grain is considered nutritionally poor for monogastric animals with respect to key essential amino acids, most notably lysine, tryptophan, and methionine. Zeins, in general, contain extremely low levels of the essential amino acids lysine, tryptophan, and to a lesser extent methionine.
The four subfamilies differ substantially in their amino-acid profiles. Alpha-zein (19 & 22 kDa) is very high in glutamine and leucine and high in alanine and proline, while being very low in lysine and tryptophan. Beta-zein (15 kDa) is high in cysteine and methionine. Gamma-zein (27 & 16 kDa) is high in cysteine and proline, and moderately rich in glutamine. Delta-zein (10 kDa) is notably high in methionine relative to the other subfamilies.
Over half of the amino acids in zein are hydrophobic, which makes it dissolvable in aqueous ethanol solutions (60–90%, v/v), but not in water. Polymeric zein nanoparticles (ZNP), derived from corn protein, are biodegradable drug carriers with high stability and low synthesis costs. Their amphiphilic nature allows efficient encapsulation of both hydrophilic and lipophilic drugs, making them promising for drug delivery. However, their instability under physiological pH can limit therapeutic efficacy, necessitating protective coatings for improved absorption.
Zein, a plant-based protein obtained from the endosperm of corn (Zea mays L.), has received considerable attention in recent years due to its promising features of being economical, mucoadhesive, gastro-resistant, and biocompatible, and its ability to load both hydrophilic and hydrophobic therapeutic agents.
Zein protein-based films, once degraded by proteolytic enzymes, lead to the production of amino acids that are non-toxic and easily re-absorbable by the body.
Zein-coated tablets exhibit stronger resistance to abrasion, high humidity, and high temperatures than a variety of commercial sugar-coated tablets. The primary technical function or purpose of zein is as a food coating that can enhance food quality. Because zein is water-insoluble, it helps prevent moisture loss from the food, thus preserving food quality. These barrier properties also allow for modified, extended, or delayed release of drug substances in pharmaceutical formulations.
Zein, despite its inherent hydrophobicity, has the ability to self-assemble into various structures, such as microspheres, films, fibers, nanoparticles, and composites. This differential solubility characteristic can be utilized to fabricate nutraceutical-loaded nanoparticles from zein using an antisolvent precipitation approach. In this approach, the zein and nutraceuticals are first dissolved in a concentrated ethanol solution. This solution is then injected into water, which serves as an antisolvent, promoting the self-assembly of the protein and nutraceutical molecules into nanoparticles.
Zein, a vegetable protein extracted from corn (Zea mays L.), forms a gastro-resistant and mucoadhesive polymer that is cheap and easy to obtain and facilitates the encapsulation of bioactives with hydrophilic, hydrophobic, and amphiphilic properties. The mucoadhesive properties of zein increase nanoparticle residence time in the gut mucosa. Engineered zein-based nanocarriers overcome key barriers such as enzymatic/chemical protection via hydrophobic encapsulation, enhanced mucus penetration or adhesion through surface engineering, and improved epithelial transport via ligand conjugation.
Zein can hydrate, and has therefore been used in swellable matrices for controlled drug release. Zein nanoparticles can improve drug stability, increase oral bioavailability, control drug release, and enhance drug targeting, thereby improving the pharmaceutical effect effectively. Zein nanoparticles can be engineered to provide sustained and controlled release of encapsulated drugs.
The use of zein as a bioavailability-enhancing carrier is the most extensively studied area of its pharmaceutical science. Oral administration remains the preferred drug delivery route but faces formidable gastrointestinal barriers, including enzymatic degradation, solubility limitations, and poor epithelial absorption. Zein-based nanocarriers (ZBNs), derived from maize prolamin, provide a transformative platform to address these challenges. This area of research has highlighted the intrinsic advantages of ZBNs: structural stability across pH gradients, self-assembly versatility, and surface functionalization capacity.
Numerous studies have demonstrated the ability of ZNPs to significantly enhance the oral bioavailability of hydrophobic drugs. Scientists have encapsulated cyclosporine A, a poorly water-soluble immunosuppressant, in zein nanoparticles and observed a significant increase in its oral bioavailability in rats compared to the unformulated drug.
Evidence strength: The body of evidence for enhanced oral bioavailability from zein nanoparticle formulations is substantial at the preclinical (animal and in vitro) level. More efforts are required to promote the scale-up production and clinical application of zein nanoparticles. No large-scale human clinical trials specifically testing zein nanoparticle formulations as stand-alone agents have been reported in the peer-reviewed literature to date.
Many kinds of nutraceuticals and other bioactive agents can be dissolved in ethanol solutions and therefore encapsulated into zein nanoparticles, including curcumin, resveratrol, quercetin, and thymol. The encapsulation of hydrophobic nutraceuticals (curcumin or resveratrol) in zein-based delivery systems can increase their antioxidant activity, anti-inflammatory activity, bioaccessibility, and cellular uptake.
In one preclinical study using zein/pectin core-shell nanoparticles, resveratrol was nanoencapsulated and its anticancer activity was assessed by its anti-proliferative activity against hepatocarcinoma cells using the MTT assay. The results showed that nanoencapsulated resveratrol exhibited significantly greater cytotoxicity than free resveratrol, with a lower half-maximal inhibitory concentration (IC50) value of 77.2 µM compared to 112.0 µM for non-encapsulated resveratrol.
Optimized zein/carboxymethyl chitosan nanoparticles exhibited a small particle size (201.6 nm), high encapsulation efficiency (72.90% for curcumin and 78.23% for resveratrol), and superior radical scavenging capacity. Structural characterization confirmed that hydrophobic interactions, electrostatic attraction, and hydrogen bonding were the main forces maintaining nanocomplex integrity. The coating significantly improved storage and digestion stability of both encapsulated bioactives.
Studies have also shown improved oral bioavailability of curcumin, resveratrol, and artemether when formulated as zein nanoparticles.
Evidence strength: This body of evidence is predominantly in vitro and in animal models. Increased bioaccessibility and cellular uptake have been demonstrated consistently in laboratory settings. Well-powered human pharmacokinetic studies demonstrating meaningful clinical improvement in the bioavailability of curcumin or resveratrol via zein nanoparticles specifically have not yet been published.
Zein was approved as a generally recognized as safe (GRAS) excipient in 1985 by the US-FDA for film coating of pharmaceuticals, including tablets. Despite its long-term application in tablet production, effects of zein coating on tablet properties are still not fully understood. Many studies have also been conducted to illustrate its potential as an active ingredient of direct compressed tablets and film-based delivery carriers.
In the pharmaceutical industry, zein is primarily used as an excipient in drug formulations, especially for tablet coatings and controlled-release systems, due to its film-forming and biocompatible properties. Zein must comply with USP (United States Pharmacopoeia) standards for excipients, which outline specifications for excipient quality, including limits for contaminants and compatibility with active pharmaceutical ingredients (APIs).
Zein can hydrate so it has been used in swellable matrices for controlled drug release. Other pharmaceutical applications of zein in oral drug delivery include its incorporation in solid dispersions of poorly soluble drugs and in colonic drug delivery systems.
Evidence strength: The use of zein as a pharmaceutical excipient and tablet coating is well-established, with regulatory approval and decades of commercial application. The performance of zein as a coating or matrix former for controlled-release systems is backed by extensive pharmaceutical science literature, though clinical outcomes tied specifically to the zein coating (as opposed to the active drug) are not typically reported separately in clinical trial literature.
The success of tissue engineering has been mainly related to the right selection of nano-sized biocompatible materials for the development of matrices with excellent anatomical structure, functionality, mechanical properties, and histocompatibility. Today, the research community has paid particular attention to zein as a potential biomaterial for tissue engineering applications and nanotechnological approaches.
The zein protein fulfills the criteria of the ideal wound dressing, which include non-toxicity and non-inflammatory stimulation. Zein gels containing rutin were prepared without any chemical refinement in order to obtain a natural formulation characterized by antioxidant and anti-inflammatory properties to be proposed for the treatment of burns and sores. In vitro scratch assay showed that the proposed gel formulations promoted cell migration and a rapid gap closure within 24 hours (~90%).
In a preclinical study, in vivo activities of rutin-loaded zein gel showed a greater therapeutic efficacy in Wistar rats, with a decrease of the wound area of about 90% at day 10 with respect to the free form.
An earlier foundational study reported that zein films were prepared for culturing human liver cells (HL-7702) and mice fibroblast cells (NIH3T3), while the Corning microplate and polylactic acid (PLA) were chosen as controls. The surface morphology of zein films revealed they were composed of particles of diameter 100–500 and 500–2500 nm, respectively. The biocompatibility of zein films was assessed by attachment, extensibility, and proliferation of cells on them. Over 60% of both HL-7702 cells and NIH3T3 cells could attach to the Corning microplate, zein films, and PLA at 3 hours after seeding.
Zein, a vegetable protein, has garnered considerable attention owing to its inherent traits such as biocompatibility, biodegradability, antibacterial properties, and economic viability. It has found wide acceptance across various domains, including biomedicine, pharmaceuticals, and packaging.
Evidence strength: Tissue engineering and wound healing evidence is primarily preclinical (in vitro and animal models). No human clinical trials examining zein-based materials specifically for wound healing have been identified in the peer-reviewed literature.
Zein, a corn-derived prolamine protein, has become a subject of research in cancer therapy, particularly non-small cell lung cancer (NSCLC). Its unique attributes, enriched by modifiable hydroxyl and amino groups, have led to the development of advanced functionalised drug delivery systems.
Zein nanoparticles (ZNP) have demonstrated significant potential in overcoming limitations associated with conventional drug delivery systems, such as poor drug solubility, rapid degradation, non-specific targeting, and systemic toxicity.
In one in vivo study examining beta-carotene co-delivery with methotrexate, in vivo pharmacokinetics analysis yielded a 2.3- and 2.7-fold increase in maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC), respectively, for zein-loaded beta-carotene. The authors credited these findings to the enhancing effect of the nanosized formulation and the mucoadhesive properties of zein that increase nanoparticle residence time in the gut mucosa.
Evidence strength: All anticancer evidence for zein nanoparticle-based delivery is preclinical — confined to cell lines (in vitro) and animal models (in vivo). No human clinical trials of zein nanoparticle anticancer drug delivery systems have been completed and reported.
Zein nanoparticles exhibit antioxidant, anticancer, anesthetic, antidiabetic, hypoglycemic, and immunogenic properties, as demonstrated in both in vitro and in vivo studies. Their ability to enhance bioavailability, reduce toxicity, and enable targeted drug delivery highlights their potential in nanomedicine. These properties, however, reflect the properties of the encapsulated bioactive compounds rather than the zein protein itself.
Zein nanoparticles are promising nanocarriers that can encapsulate various bioactives with anti-inflammatory, antioxidant, antimicrobial, anticancer, and antidiabetic properties.
Evidence strength: The antioxidant and anti-inflammatory effects observed in zein nanoparticle studies are predominantly attributable to the encapsulated payloads (e.g., quercetin, resveratrol, curcumin) rather than to zein itself. Evidence is limited to in vitro and preclinical models.
In the United States, the FDA classifies zein as Generally Recognized as Safe (GRAS) for use in food applications such as coatings for fruits, vegetables, and confectionery, as well as in food packaging. Zein has been investigated as an encapsulant for probiotics and heat-sensitive bioactives to protect them during food processing and gastrointestinal transit. The evidence in this area remains largely preclinical and technology-development focused.
Zein as a dietary ingredient or excipient does not carry a standardized human therapeutic dosage. Reported forms and concentrations from published research include the following:
No human clinical dosage guidelines for zein as a dietary supplement have been established by any regulatory or pharmacopeial body.
In the United States, the FDA classifies zein as Generally Recognized as Safe (GRAS) for use in food applications. This means that zein does not require pre-market approval but must comply with 21 CFR 184.1400, which outlines the criteria for GRAS substances. In the European Union, the European Medicines Agency (EMA) oversees the use of excipients like zein in drug formulations, ensuring compliance with European Pharmacopoeia standards.
Identified maize allergens in double-blind placebo-controlled maize-challenge-positive patients included a 14-kDa alpha-amylase inhibitor, 30-kDa endochitinases A and B, 19 kDa zein-beta precursor, and 26 kDa zein-alpha precursor. Lipid transfer protein (LTP) was found to be the only major allergen in Italian patients with either positive maize challenge or a history of maize-induced anaphylaxis.
Two maize allergens belonging to the prolamin superfamily — Zea m 27 kDa Zein and Zea m 50 kDa Zein — have also been found in maize seeds. By use of sera from patients who tested positive by ImmunoCAP assay for elevated IgE to maize proteins, specific IgE binding to the 27 kDa γ-zein has been demonstrated. Bioinformatic analysis identified significant sequence homology of the 27 kDa γ-zein with several known allergens.
Research has shown that inhaling zein dust could induce type 1 hypersensitivity reactions, leading to asthma. This is relevant to occupational exposure scenarios, such as in workers processing corn protein powders.
The Celiac Sprue Association, the largest non-profit celiac disease support group in the USA, reported that the zein protein of corn does not cause any allergic reaction in people with celiac disease, and corn flour is quite safe as an ingredient in the formulation of gluten-free products. However, this is not the entire picture. Zein is hydrolyzed by gastrointestinal proteases and still causes allergic reactions in some celiac patients, which is related to IgA antibodies in celiac disease patients recognizing digested α-zein as celiac disease antigens.
One study confirmed the improvement of some patients with refractory celiac disease on a gluten-free diet when a corn-free diet was prescribed. This suggests that a minority of celiac patients may react to corn zein, though zein is not classified as a trigger under standard gluten-containing grain definitions.
The route of administration affects the antigenicity of zein. Experimental data showed that intramuscular injection of zein triggers a systemic immune response. The oral administration of zein nanoparticles did not cause a systemic immune response but induced systemic tolerance without mucosal tolerance. These findings, though based on animal experiments, are relevant to the design of injectable or implantable zein-based devices versus oral formulations.
Although zein nanoparticles are biocompatible and can be easily prepared, they tend to form aggregates during freeze-drying (lyophilization) and cannot be redispersed in water. The low colloidal stability after centrifugation and lyophilization limits the applications of zein-based colloidal carrier systems. This is a manufacturing and formulation concern rather than a direct safety concern for consumers.
Zein isolate is not used directly for human consumption due to its negative nitrogen balance and poor solubility in water. These deficiencies result in a negative dietary nitrogen balance, limiting its use in human food products. Overdependence on a cereal, notably corn, for dietary protein is in part responsible for the condition of malnutrition known as kwashiorkor. This risk is associated with a corn-dominant diet, not with isolated zein in pharmaceutical or food coating applications.
Maize lipid transfer protein and endochitinase were found to be cross-reactive with grape LTP and one grape endochitinase, indicating that individuals with zein or maize protein sensitization may be at risk for cross-reactive reactions to other plant foods. The clinical significance of specific zein subclass cross-reactivity requires investigation in larger patient populations.
Health conditions that Zein may help support.
Body systems that Zein may help support.
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