sorghum: obliging alternative and ancient grain€¦ · well as flatbreads such as ethiopian...

12 / JANUARY–FEBRUARY 2014, VOL. 59, NO. 1

D. Lemlioglu-Austin1

NovozymesFranklinton, NC, U.S.A.

The recent growing i nterest in sorghum and sorghum-related

products has been manifested in presentations given at a number of conferences held during the last few years. Both paper and poster pre-sentations by students as part of product development competitions and by independent researchers from industry and academia have highlighted the interest in develop-ing new sorghum-based products. Examples of new products promot-ed by recent student product devel-opment competitions include

Simply Sweet Sorghum Treats: Both ice cream and cones are made with sorghum grain varieties. Cooking liquid is used as the medium for the ice cream, and cooking solids are added to whole sorghum flour to make ice cream cones. Phenolic-rich sorghum extracts provide an array of colors, enabling ice cream with red velvet, tart pink, and berry blue fla-vors to be produced.

Granotè—Pineapple & Orange Sor-ghum Herbal Tisane: This all-natu-ral, caffeine-free, high-antioxidant health-promoting beverage incorpo-rates in sorghum. Cracked and roast-ed red sorghum varieties are com-bined with a dried pineapple and orange fruit mix to appeal to a wide range of consumers.

Gluten-free Cereal Bar with Sor-ghum and Tropical Fruits: Thedevelopment of sorghum-based products specifically for incorpora-

tion into cereal bars is being spurred by the growing popularity of cereal bar products due to their conve-nience and association with health benefits.

Home-style Waffle Melts: These waffles are formulated with whole grain white sorghum flour and based on frozen waffle products.

In developing parts of the world, sor-ghum has remained a dietary mainstay since the earliest human settlementsbegan cultivating crops. Promotion of sorghum grains and their products isbecoming more commonplace in thedeveloped world with the growing aware-ness of the potential applications of this largely untapped food resource among the scientific community, food industry, and health-conscious consumers. This article focuses on the historical importance of this essential nutrient-rich grain and its potential role in modern food develop-ment. Specific product developmentexamples and a discussion of future trends are provided.

Background on Sorghum

Sorghum is a good source of dietary fiber and phenolic com-pounds and is an important food staple for people in many parts of the world. It is a true ancient grain and is known to have been col-lected 8,000 years ago in Nabta Playa in southern Egypt (52). Sor-ghum was domesticated in Ethio-pia and Sudan and from there cul-tivation spread throughout Africa, where it remains an important cereal grain. Sorghum likely trav-eled to India during the 1st millen-nium B.C. as food on ships and then continued to be disbursed along the silk trade routes. It most likely arrived in the Americas with slave traders from Africa in the 19th century A.D. (52).

If you ask a hundred people if they have ever eaten sorghum, chances are they’ll have no idea what you’re talking about. How-ever, sorghum (Sorghum bicolor (L.) Moench) is the fifth most

widely grown cereal crop in the world, following wheat, corn, rice, and barley. Due to its natural drought tolerance and versatility, sorghum is an important food staple for people in semiarid parts of the world with an uncertain food supply (55). Nigeria, Sudan, Ethiopia, and Burkina Faso account for nearly 70% of the sor-ghum grown in Africa. Throughout Africa, sorghum porridge or gruel is commonly consumed in almost every country, as well as flatbreads such as Ethiopian injera, which is made from sorghum, teff, or a combination of both. Sorghum also is used to make both alcoholic and nonalco-holic beverages. Most of these products incorporate fermented or sprouted sor-ghum, because these two processes make sorghum’s nutrients more available and increase their shelf life and food safety.

Although sorghum has fed people in developing parts of the world for centu-ries, there has been little interest in sor-ghum as a food source in the United States, where it has mainly been used for livestock feed and in a growing number of ethanol plants (1,46). However, there is a

1 E-mail: [email protected]; Tel:+1.479.790.3805.

Photo courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University

http://dx.doi.org/10.1094/CFW-59-1-0012

©2014 AACC International, Inc.

Sorghum: Obliging Alternative

and Ancient Grain

CEREAL FOODS WORLD / 13

growing interest in sorghum grain and its products by U.S. consumers and the food industry due, in part, to growth in the “gluten-free” trend.

Sorghum Production

Sorghum (or milo as it is sometimes referred to in the United States) represents the third-largest cereal grain crop grown in the United States, following wheat and corn. Its comparative advantage is its drought tolerance, resistance to mycotox-ins and fungi, and ability to grow under relatively harsh climate conditions (50).

Currently, sorghum production is 396.11 million bu (1 bu is 56 lb) world-wide. In 2012, leading producers around the world included Mexico, the United States, Nigeria, India, and Argentina (59). In the United States, sorghum is grown primarily on dryland acres; the “sor-ghum belt” stretches from South Dakota to southern Texas (Fig. 1).

Sorghum is grown in 14 U.S. states. Historically, Kansas and Texas have been the top two sorghum-producing states, harvesting 79% of the U.S. sorghum crop. In 2012, Texas produced 112.1 million bu valued at $703.1 million, and Kansasproduced 81.9 million bu valued at$582.5 million. Other states producing large quantities of sorghum include Loui-siana, Arkansas, South Dakota, and Okla-homa (59). The United States is the lead-ing exporter of sorghum. In recent years, it has accounted for more than 65% of world trade. The top importers during the 2010–2011 crop year were Mexico (60%), the European Union (22%), and Japan (9%) (60).

Characteristics of Sorghum Grain

Sorghum (S. bicolor) is a cereal ofremarkable genetic variability, which makes it difficult to classify. A few names for sorghum include milo, jowar, kafir corn, Guinea corn, and cholam. The seed or caryopsis of sorghum is a major source of calories and protein in the diets of mil-lions of people in Africa and Asia. Sor-ghum is grown from traditional hybrid seeds and does not contain traits gained through biotechnology, making it non-transgenic (non-GMO) (61).

In the United States, four distinct vari-eties of sorghum are grown for different uses: 1) grass sorghum is used as cattle feed; 2) broom sorghum, which is not a food source, makes good brooms; 3) sweet sorghum, like sugar cane, yields syrup; and 4) grain sorghum is ground for flour and is used in beer.

Sorghum grain characteristics have been documented in detail by Rooney and Miller (47). The kernel or grain is consid-ered a naked caryopsis, although some African varieties retain their glumes after threshing. Sorghum caryopses differ wide-ly in weight (3–80 mg), test weight (708–785 g/L), and density (1.15–1.38 g/cm3). Commercial U.S. sorghum varieties have kernels that are generally 4 mm long,2 mm wide, and 2.5 mm thick, with akernel weight of 25–35 mg, test weightof 747–772 g/L, and density of 1.28–1.36 g/cm3 (47).

The appearance and quality of sorghum are affected significantly by genetically controlled characters (61). The caryopsis

consists of three distinct anatomical com-ponents: pericarp (outer layer), endo-sperm (storage tissue), and germ (embryo) (Fig. 2). The outer layer (pericarp) origi-nates from the ovary wall (19) and isdivided into three histological tissues: epicarp, mesocarp, and endocarp (16). The outermost layer of the pericarp(epicarp) is generally covered with a thin layer of wax, is two or three cell layers thick, and consists of rectangular cells that often contain pigmented material. Unlike most cereals, the sorghum meso-carp contains starch granules. A thick pericarp usually contains three or four mesocarp cell layers filled with small starch granules (Fig. 3).

Fig. 2. Sorghum grain structure. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)

Fig. 1. U.S. Sorghum production (U.S. Grains Council & Chicago Board of Trade 2013;www.grains.org/index.php/buying-selling/sorghum#sthash.PkboB5mK.dpuf ).


Sorghum endosperm proteins have equal or lower in vitro pepsin digestibil-ity in raw flour and substantially lowerdigestibility in cooked products than those of other cereals (25). The reasons sorghum proteins are less digestible than those of other cereals have not yet been completely elucidated. However, several factors have been identified that may play a role in determining the digestibility of sorghum endosperm proteins, including physical grain structure, protein body structure, protein cross-linking, starch properties, and phenolic content or com-position of the grain. The majority ofproteins contained in the sorghum endo-sperm are found in digestion-resistant spherical protein bodies that have highly cross-linked outer layers. Disulfide bond-mediated cross-linking increases during cooking of sorghum, resulting in the for-mation of highly cross-linked web-like protein structures. Protein digestibility has a substantial impact on the nutritional properties of sorghum utilized in the pro-duction of human foods, animal feeds, and bioindustrial applications such as ethanol (4).

Mycotoxins are less of a problem in sorghum than in maize (Zea mays L.). In contrast to maize, fumonisin has not been found at significant levels in sorghum. In similar drought-prone environments,aflatoxin levels can be excessive in maize, while sorghum has nonsignificant afla-toxin levels. Although aflatoxin is not found at significant levels on sorghum in the field, it can be found on improperly stored, high-moisture sorghum (45).

U.S. Sorghum Grain Standards

Sorghum grain is marketed in the United States according to established U.S. grain standards (58):

Sorghum grade: Sorghum does not contain more than 3% sorghum with a pigmented testa or undercoat.

White sorghum grade: White sor-ghum contains sorghum with a white pericarp without a pigmented testa. It cannot contain more than 2% sor-ghum with a pigmented pericarp or testa.

Mixed sorghum grade: Mixed sor-ghum contains mixtures of sorghum with and without pigmented testa.

Tannin sorghum grade: Tannin sor-ghums contain proanthocyanidins as part of their phenolic compounds but do not contain tannic acid or hydro-lyzable tannins. Tannin sorghums have a pigmented testa on the inner-most layer of the pericarp. The pig-mented testa is seen as a dark layer between the light endosperm and pericarp when the caryopsis is scraped to remove the pericarp.

When damaged immature pericarp tissues respond with antimicrobial phe-nolic compounds that form pigments that stain the pericarp and endosperm. Insect and mold damage to the pericarp com-monly occurs together when caryopses mature in hot, humid environments (61) (Fig. 4).

Some specialty sorghum varieties con-tain substantial quantities of phenolic

compounds, which are generally located in the outer layers of the kernel in theepicarp and testa (2,40). Common spe-cialty sorghum varieties include red, tan-nin (sumac and high-tannin), and black (Fig. 5).

Nonfood Sorghum Applications

In addition to feed and food applica-tions, sorghum can be manufactured into a wide variety of products. For example, because of its poor conductivity sorghum is well-suited to biodegradable packaging material applications (53). In addition, it is being utilized in housing wallboard (35).

Ethanol. Sorghum is increasingly being used in ethanol production because it pro-duces approximately the same amount of ethanol per bushel as corn while requiring one-third less water. Sorghum is a good fit for different types of ethanol production, including traditional starch from grain; sugar from pressed juice; and biomass production. In fact, the entire sorghum plant can be used as biomass. Currently, ≈12% of the U.S. sorghum crop is utilized in ethanol production. Sweet sorghum in particular is being pursued as feedstock for half of the planned ethanol plants in Florida (18).

Animal Feed. Globally, ≈50% of the sorghum consumed is consumed byhumans, but in the United States more than 90% of the sorghum consumed is consumed as a component in livestock feed. Corn (maize) is the main alternative ingredient for sorghum in livestock feed (9). Although corn and sorghum have similar chemical makeups, corn is easier for livestock to digest and utilize than sorghum. Certain processing techniques have been developed, however, to break down the sorghum kernel so it is as easy for livestock to digest and utilize as corn. Many studies have compared the effects of different processing techniques on the

Fig. 3. Sorghum grain thin and thick pericarp. P: Pericarp; Al: aleurone layer. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)

Fig. 4. When damaged, immature pericarp tissues respond with antimicrobial phenolic compounds that form pigments that stain the pericarp and endosperm. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)


ability of different types of livestock to digest and utilize sorghum in feed. Stud-ies on cattle show that steam-flaked sor-ghum was preferable to dry-rolled sor-ghum because it improved daily gain and feed efficiency (37).

Sorghum Food Applications

and Benefits

Flavor. Sorghum grains offer nutri-tional and functional benefits as well as unique flavors in food applications. Sor-ghum varieties vary in composition, ker-nel structure, and unique phytochemical contents. Sorghum grains are consumed as porridges, flatbreads, cooked whole grain (similar to rice), and a wide variety of fermented products. Sorghum syrup is pressed from the stalks of sweet sorghum plants, similar to sugar cane, and then boiled down into concentrated syrup. As it cooks, the syrup develops a rich, earthy, honey-like flavor. It can be used on itsown as a topping for pancakes and oat-meal or, like honey or molasses, in des-serts and baked goods. This syrup can also be used like malt extract to brew gluten-free beer (50).

Gluten-free. Sorghum is naturally glu-ten-free and may be used as an alternative ingredient in food products that tradi-tionally contain gluten. Over the lastdecade, there has been increasing interest in utilization of sorghum products for development of products that are safe for people with celiac disease or wheat aller-gies (1). Although it has long been thought that sorghum is safe for those with celiac disease, no clinical testing was done until 2007. Italian researchers (8) first conduct-ed laboratory tests. After the tests estab-lished the likely safety of sorghum, they fed celiac patients sorghum-derived food products for 5 days. The patients experi-enced no symptoms, and the level of dis-ease markers (antitransglutaminase anti-bodies) was unchanged at the end of the5 day trial (8).

Celiac disease is a disorder caused by an abnormal immune response to gluten proteins found in wheat, rye, barley, and possibly oats (64). Gluten triggers inflam-matory reactions in people with celiac disease or gluten sensitivity that can cause abdominal pain and digestive issues and can eventually lead to joint pain andintestinal damage. The only treatment for individuals with celiac disease is to avoid all foods containing gluten. The FDAallows a product to be labeled as gluten-free if it contains <20 ppm gluten. Accord-ing to the latest research, ingesting 50 mg

of gluten/day causes intestinal damage in people with celiac disease (42). This means that at least 5 lb of gluten-free foods con-taining <20 ppm gluten must be consumed per day for damage to occur.

Initial consumer perceptions of gluten-free foods were that they were bland, bor-ing substitutes for more appealing gluten-containing products. With improvements in product formulations and alternative ingredients, perceptions of gluten-free products have begun to improve as well. Three-quarters (75%) of consumers sur-veyed who do not have celiac disease ora sensitivity to gluten eat these foodsbecause they believe they are healthier, despite the lack of scientific research con-firming the validity of this theory. Almost one-third of U.S. adults (29%) surveyed say they want to cut down on the gluten they consume or follow a gluten-free diet. In 2010 sales of gluten-free products reached more than $2.6 billion and are expected to exceed $5 billion by 2015 (43). These numbers suggest the gluten-free market is here to stay. With so many people needing to avoid foods that con-tain gluten, a need for special products

has arisen, and more and more gluten-free products are finding their way onto supermarket and health-food store shelves or are being offered via the Internet.

Nutrients in Whole Grain. Sorghum is a grain with many attractive features and, as a whole grain, provides many nutri-tional benefits. Unlike refined grains, whole grain foods contain dietary fiber (soluble and insoluble), resistant starches, vitamins, minerals, phytoestrogens, and antioxidants that may protect against non-communicable diseases (NCDs). The epi-demiologic evidence for the association between whole grain intake and NCDs is largely consistent, with most studies sug-gesting diets high in whole grains areinversely associated with risk of type 2 diabetes, cardiovascular diseases, and cer-tain cancers (29).

According to the 2010 USDA Dietary Guidelines for Americans report, at least half of daily grain food intake should be in the form of whole grains. The FDA allows health claim labels for foods con-taining 51% whole grains by weight when the whole grains contain ≥11% dietary fiber. Despite these recommendations,

Fig. 5. Specialty sorghum varieties. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)


most consumers fall short of the recom-mended intake of whole grain foods (30).

Sorghum grain, which unlike like some grains does not have an inedible hull, is commonly eaten with all its outer layers intact, thereby retaining the majority of its nutrients. Sorghum kernels vary in color from white and pale yellow to deep reds, purples, and browns; however, white, bronze, and brown kernels are the most common (Fig. 6) (2). Sorghum can be used in whole kernel form in dishes and soups or as whole grain flour in foods such as breads and other baked goods, pastas, breakfast cereals, and snacks (Fig. 7).

Lipids. The wax surrounding the sor-ghum grain contains compounds called policosanols that may have an impacton human cardiac health (2,7). Sor-ghum grain lipids have been consistentlyreported to contain valuable phytochem-icals, such as phytosterols, policosanols, unsaturated fatty acids, aldehydes, and steryl/wax esters, with potential health benefits (7). Lee et al. (31) observed that sorghum is a rich source of phytochem-icals and decided to study sorghum’spotential for managing cholesterol. They reported that different levels of lipids from sorghum significantly reduced “bad” (non-HDL) cholesterol in hamsters when they were fed these lipids for 4 weeks. Reductions ranged from 18% in ham-sters fed a diet including 0.5% lipids from sorghum to 69% in hamsters fed a diet including 5% lipids from sorghum. “Good” (HDL) cholesterol was notaffected. The researchers concluded that

“grain sorghum contains beneficial com-ponents that could be used as food ingre-dients or dietary supplements to manage cholesterol levels in humans” and also reported that lipids from sorghum exert-ed beneficial effects on the cholesterolmetabolism and intestinal microbiota of hamsters (31). Exact mechanisms and bioactive compounds related to theseeffects have not been elucidated. Studies are in progress to understand the pos-sible beneficial mechanisms, as well asto determine the bioactive compounds responsible.

Phenolic Compounds. Some specialty sorghums, which contain a variety of phe-nolic compounds, are high in antioxidants that are believed to help lower the risk of certain cancers, diabetes, heart disease, and some neurological diseases. Evidence suggests that the phenolic compounds in sorghum produce specific health benefits that are not observed for other grains such as corn, rice, and wheat (2). Phenolic com-pounds are concentrated in the bran, along with high levels of antioxidants, dietary fiber, and luteolinidins and api-geninidins that are relatively rare innature (14,26). Awika and Rooney (2) reported that high-tannin sorghum bran contains more antioxidant phytochemi-cals than other grain brans, such as rice, wheat, and oat, which contain relatively low phenolic compounds and antioxi-dants. The researchers found that the bran of certain varieties of sorghum has greater antioxidant and anti-inflammatory prop-erties than foods such as blueberries and

pomegranates. They also reported that levels of polyphenolic compounds in high-tannin sorghum varieties ranged from 23 to 62 mg of polyphenols/g com-pared with ≈5 mg of polyphenolics/g of blueberries and 2–3.5 mg/g of pomegran-ate juice (2).

In sorghum, phenolic compounds are generally located in the outer layers of the kernel, in the epicarp and testa (2,16), and can be divided into three major categories: phenolic acids, flavonoids, and condensed tannins (24). All sorghums contain phe-nolic compounds. The amount of phe-nolic compounds is influenced by both genotype and environment (15). Although condensed tannins are considered antinu-tritional compounds, tannin sorghums have been consumed and preferred for centuries in breads, porridges, and alco-holic beverages in Africa and Asia. Awika and Rooney (2) stated that tannin sor-ghums can and should be considered a source of natural antioxidants, dietary fiber, and color compounds.

Breeders have developed specific sor-ghums with unique combinations of these components. Specialty and white sorghums have been incorporated into a wide array of food product formulations, including dark purple tortillas; chips; naturally col-ored, high-fiber baked products; and cooked whole grain (similar to rice). The high levels of compounds such as thestable 3-deoxyanthocyanin (3-DXA) pig-ments, condensed tannins, flavones, and flavanones found in some sorghum vari-eties is of special interest from both com-mercial and health-benefit perspectives. Stable 3-DXA compounds are present in darker colored sorghums and to a lesser extent in white sorghum (15).

Although whole grain consumption has long been correlated with reduced risk of certain forms of digestive tract cancers, especially colon cancer, how much of these effects are contributed by dietary fiber and/or phytochemicals concen-trated in the grain bran is still unknown. Additional in vitro data, as well as con-trolled animal studies, are necessary to understand how the levels and composi-tion of polyphenols in sorghum affect certain cancers and which specific com-ponents are responsible.

Sorghum has been widely consumedas a staple food and in beverages through-out Africa for centuries. More recently, corn has replaced sorghum in someareas. Researchers from the University of Witwatersrand Medical School in SouthAfrica (28) have suggested that the change

Fig. 6. Sorghum varieties and colors. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)


in the staple diet of South Africans from sorghum to maize (corn) is the cause of an epidemic of squamous carcinoma of the esophagus seen in South Africans. They linked the cancer to Fusarium fungi that grow freely on maize but are far less common on sorghum, stating that coun-tries in Africa in which the staple food is sorghum have a low incidence of squa-mous carcinoma of the esophagus (28).

Although, data on cancer relating to sorghum are too limited to draw firm conclusions, in vitro studies have revealed that sorghum has some anticarcinogenic properties. Grimmer et al. (23) found that high molecular weight (MW) procyani-dins (tannins) had higher antimutagenic activity compared with lower MW tan-nins. Gómez-Cordovés et al. (20) showed that sorghum tannins had anticarcino-genic activity against human melanoma cells, as well as positive melanogenicactivity (melanogenesis is believed to help protect human skin against UVirradiation damage). McDonough et al. (38) found that tannin sorghum branresisted oxidative damage due to high-energy irradiation. Yang et al. (63) tested the effects of black, red, and white sor-ghums and found that extracts from all three had strong antiproliferative activity

against human colon cancer cells. In addi-tion, Burdette et al. (6) measured thedegree to which extracts from four differ-ent varieties of sorghum reduced inflam-mation in mice. They found that black and sumac varieties showed significantly higher polyphenolic contents and antioxi-dant levels than the two low-tannin vari-eties tested, which did not reduce inflam-mation. Gómez-Cordovés et al. (20) also studied the effect of three different com-ponents from wine and one from sor-ghum to gauge their effects on the growth of human melanoma cells. They conclud-ed that all four components (phenolic fractions) “have potential as therapeutic agents in the treatments of human mela-noma,” although the mechanism by which each slows cancer growth may differ.

Many fruits also contain these com-pounds; however, sorghum bran may prove to be the richest and cheapest source of phenolic compounds. Use of sorghum may provide a way to reintro-duce a quality source of nutrients into many products that now use bleached and refined flours. Because most chronic dis-ease states in humans are associated with chronic inflammation and high oxidative stress, a food ingredient such as phenolic-rich sorghum bran could potentially

improve the nutritional benefits of certain processed foods and the overall diet.

Starch Digestibility. Phenolic com-pounds complex with proteins and carbo-hydrates, generating insoluble compounds that are resistant to digestive enzymes. Specialty sorghum varieties contain vari-ous types of phenolic compounds, includ-ing condensed tannins (polymers of fla-van-3-ols) and anthocyanins (luteolinidin and apigeninidin). There has been increas-ing interest in applications for starches that are more slowly digested in mini-mally cooked or processed foods and their potential role in reducing calories, increasing dietary fiber, and providing energy over extended periods. Readily digestible carbohydrates lead to rapidly elevated blood glucose levels and insulin secretion, both of which contribute to the health complications caused by diabetes. Starch digestibility depends on the plant source, extent of starch–protein interac-tion, physical form of the granule, inhibi-tors such as tannins, and starch type (27,48,51,62).

Postprandial blood glucose changes can be used to categorize the glycemic index (GI). GI can be estimated based on in vitro rate and extent of starch digestibility, known as the estimated glycemic index

Fig. 7. Sorghum products. (Courtesy of Cassandra McDonough, Cereal Quality Lab, Texas A&M University)


(EGI). GI ranks foods based on how quick-ly and how much they elevate blood sugar levels. Foods can be classified as havinga low (<55), intermediate (55–70), orhigh GI (>70). Foods with a low GI and higher resistant starch (RS) content can slow absorption of carbohydrates andprevent extreme blood glucose fluctua-tions (21). Resistant starches are notdigested in the small intestine (although they may be digested in the large intes-tine) and, thus, do not cause a glycemic response. These starches can ferment in the colon, promoting growth of “good” bacteria, and have many other beneficial effects (57).

Among cereals, sorghum generally has the lowest starch digestibility, yet digest-ibility of isolated sorghum starch is simi-lar to that of raw or cooked corn starch (48,62). Sorghum starch is also biologi-cally equivalent to corn starch (49). The major differences between corn and sor-ghum starches are the type and distribu-tion of proteins surrounding starch in the endosperm (50). Experience with live-stock feeding (44) and brewing (22) sug-gests that starch in whole sorghum grain may be slightly less digestible due to its hard peripheral endosperm layer, which limits access to the interior (25,48). Pro-cessing methods that break open kernels and expose the interiors, such as steam-flaking and reconstitution, are effective in raising sorghum digestibility to that of corn (2).

Some specialty sorghum varieties are less digestible than other cereals (48). In particular, varieties that contain con-densed tannin have been reported to be less digestible than other depauperate varieties (5,10–12,48). Davis and Hoseney (11) reported that condensed tannins iso-lated from sorghum grain inhibited the enzyme -amylase and that condensed tannins also bound to starch granules to varying degrees. Barros et al. (3) alsoreported that condensed tannins in sor-ghum strongly interacted with amylose and linear fragments of amylopectin in starch, resulting in decreased starchdigestibility. Daiber (10) and Beta et al. (5) found that condensed tannins inacti-vated malt amylases, reducing starch breakdown and sugar production dur-ing brewing.

Thompson and Yoon (56) investigated the relationship between polyphenolintake and blood glucose response in healthy and diabetic volunteers. They found a negative correlation between GI and concentration or total intake of poly-

phenols. Polyphenols, especially large polymeric compounds or condensed tan-nins, appeared to be responsible, in part, for a reduced glycemic response to carbo-hydrate foods and relatively low blood glucose response to legumes compared with cereal products (56).

Farrar et al. (17) found that phenolic-rich sorghum brans inhibited protein gly-cation (restriction of advanced glycation improves insulin resistance), whereas wheat, rice, oat, and low-phenolic sor-ghum brans did not. Hargrove et al. (26) reported that certain varieties of sorghum bran may affect critical biological pro-cesses that are important in diabetes and insulin resistance. They also compared the ability of simple flavonoids and con-densed tannins in tannin sorghum bran extracts to inhibit enzymes in vitro and found that sumac sorghum bran extract, which is high in condensed tannin, inhib-ited -amylase at a much lower concen-tration than did black sorghum branextract, which does not contain con-densed tannin. However, Mkandawireet al. (39) reported that condensed-tan-nin content was not correlated with the in vitro starch digestibility of cooked grain sorghum.

Phenolic compounds complexing with starch and inhibiting enzymes may also lead to an increase in RS content in por-ridges. Lemlioglu-Austin et al. (32,33) and De Castro Palomino Siller (12) found that phenolic-rich whole sorghum por-ridges had significantly higher RS con-tents than white sorghum porridges.De Castro Palomino Siller (12) also showed that tannin sorghum extrudates and porridges had reduced starch digest-ibility and EGI and increased RS contents compared with corn extrudates and por-ridges, reporting that the addition of12% tannin bran to a bread formulation significantly (P < 0.05) decreased starch digestibility and EGI values.

Among specialty sorghum varieties, the digestibility of tannin sorghum has been studied the most (12,13,34,36,41,54). In contrast, Lemlioglu-Austin et al. (32,33) studied the effect of condensed tannins, anthocyanins, and both together on the starch digestibility of sorghum and corn starches in porridges. They found that specialty sorghum brans (32) and their extracts (33) containing condensed tan-nin or tannin, as well as anthocyanins, have the potential to lower starch digest-ibility and increase the amount of RS in foods. Specifically, bran extracts high in condensed tannin lowered the EGI (32)

and increased the RS content (12%)of porridges containing corn starchcompared with bean starch (EGI = 60;RS = 5.5%). Approximately 3–6 g of RSis consumed per day as part of the typical American diet. Considering RS is a type of dietary fiber, phenolic-rich sorghum bran extracts have the potential to beused in starchy foods to not only reduce starch digestibility but also improve fiber intake.

Conclusions

Sorghum grain composition and qual-ity varies from white grain varieties, which have a bland flavor, to black, red, and brown grain varieties, which have an array of stronger flavors. It can be easily processed into food products using extru-sion, steam-flaking, micronization, and other processes. Sorghum can also be substituted for wheat flour in a variety of gluten-free baked goods, and its neutral, sometimes sweet, flavor and light color make it easily adaptable to a variety of dishes. Because it does not contain gluten, bakers often incorporate a binder such as xanthan gum or corn starch to improve elasticity in doughs containing sorghum flour. Sorghum can be substituted forother ingredients in existing formula-tions as well.

Sorghum also offers several potential functional and health benefits. Sorghum starch is digested more slowly and has a lower GI, so it lingers in the digestive tract longer than starches from other grain flours or flour substitutes. In addi-tion, specialty sorghum varieties are rela-tively inexpensive sources of phenolic compounds and have favorable storage stability, drought tolerance, high grain yield, and anti-inflammatory properties. Both tannin and black sorghum varieties can be used to formulate functional foods that offer potential health benefits. Sor-ghum bran is not only a good source of dietary fiber but provides a number of unique nutritional components as well. If interest in sorghum continues, sorghum bran extracts could easily be incorporated into a variety of foods and beverages as a liquid concentrate or dried powder.

References

1. Asif, M., Rooney, L. W., Acosta-Sanchez, D., Mack, C. A., and Riaz, M. N. Uses of sorghum grain in gluten-free products. Cereal Foods World 55:285, 2010.

2. Awika, J. M., and Rooney, L. W. Sorghum phytochemicals and potential impact on human health. Phytochemistry 65:1199, 2004.


3. Barros, F., Awika, J. M., and Rooney, L. W. Interaction of tannins and other sorghum phenolic compounds with starch andeffects on in vitro starch digestibility.J. Agric. Food Chem. 60:11609, 2012.

4. Bean, S. R., Ioerger, B. P., Smith, B. M., and Blackwell, D. L. Sorghum protein structure and chemistry: Implications for nutrition and functionality. Pages 131-147 in: Advances in Cereal Science: Implications to Food Processing and Health Promotion. Vol. 1089, ACS Symposium Series. J. M. Awika, V. Piironen, and S. Bean, eds. American Chemical Society, Washington, DC, 2011.

5. Beta, T., Rooney, L. W., Marovatsanga, L. T., and Taylor, J. R. N. Effect of chemical treatment on polyphenols and malt qual-ity in sorghum. J. Cereal Sci. 31:295, 2000.

6. Burdette, A. P., Garner, L., Mayer, E. P., Hargrove, J. L., Hartle, D. K., and Greens-pan, P. Anti-inflammatory activity ofselect sorghum (Sorghum bicolor) brans.J. Med. Food 13:879, 2010.

7. Carr, T. P., Weller, C. L., Schlegel, V. L., Cuppett, S. L., Guderian, D. M., Jr., and Johnson, K. R. Grain sorghum lipid extract reduces cholesterol absorption and plas-ma non-HDL cholesterol concentration in hamsters. J. Nutr. 135:2236, 2005.

8. Catassi, C., Fabiani, E., Iacono, G., D’Agate, C., Francavilla, R., et al. A prospective, double-blind, placebo-controlled trial to establish a safe gluten threshold for patients with celiac disease. Am. J. Clin. Nutr. 85:160, 2007.

9. Dahlberg, J., Berenji, J., Sikora, V., and Latković, D. Assessing sorghum [Sorghum bicolor (L) Moench] germplasm for new traits: Food, fuels and unique uses. Pub-lished online at www.maydica.org/articles/56_165.pdf. Maydica 56:165, 2011.

10. Daiber, K. H. Enzyme inhibition by poly-phenols of sorghum grain and malt. J. Sci. Food Agric. 26:1399, 1975.

11. Davis, A. B., and Hoseney, R. C. Grain sorghum condensed tannins. I. Isolation, estimation, and selective adsorption by starch. Cereal Chem. 56:310, 1979.

12. De Castro Palomino Siller, A. In vitro starch digestibility and estimated glyce-mic index of sorghum products. M.S. the-sis. Texas A&M University, College Sta-tion, TX, 2006.

13. de Oliveira, S. G., Berchielli, T. T., dos San-tos Pedreira, M., Primavesi, O., Frighetto, R., and Lima, M. A. Effect of tannin levels in sorghum silage and concentrate supple-mentation on apparent digestibility and methane emission in beef cattle. Anim. Feed Sci. Technol. 135:236, 2007.

14. Dykes, L., and Rooney, L. W. Review: Sor-ghum and millet phenols and antioxidants. J. Cereal Sci. 44:236, 2006.

15. Dykes, L., Rooney, L. W., Waniska, R. D., and Rooney, W. L. Phenolic compounds and antioxidant activity of sorghum grains

of varying genotypes. J. Agric. Food Chem. 53:6813, 2005.

16. Earp, C. F., and Rooney L. W. Fluorescence characterization of sorghum caryopsis. Food Microstruct. 5:257, 1986.

17. Farrar, J., Hartle, L., Hargrove, D. K., and Greenspan, P. A novel nutraceutical prop-erty of select sorghum (Sorghum bicolor) brans: Inhibition of protein glycation. Phytother. Res. 22:1052, 2008.

18. Glauber, J. W. Outlook for U.S. Agriculture in 2013. In: USDA Agricultural Outlook Forum. Published online at http://usda.gov/oce/forum/presentations/Glauber.pdf. Office of the Chief Economist, Washing-ton, DC, 2013.

19. Glennie, C. W., Liebenberg, N. W., and Van Tonder, H. J. Morphological develop-ment in sorghum grain. Food Microstruct. 3:14, 1984.

20. Gómez-Cordovés, C., Bartolomé, B., Vieira, W., and Viradir, V. M. Effects of wine phe-nolics and sorghum tannins on tyrosinase activity and growth of melanoma cells.J. Agric. Food Chem. 49:1620, 2001.

21. Goñi, I., Garcia-Alonso, A., and Saura-Calixto, F. A starch hydrolysis procedure to estimate glycemic index. Nutr. Res. 17:427, 1997.

22. Goode, D., and Arendt, E. K. Pilot scale brewing with unmalted sorghum. J. Inst. Brew. 10:208, 2003.

23. Grimmer, H. R., Parbhoo, V., and McGarth, R. M. Antimutagenicity of polyphenol-rich fractions from sorghum bicolor grain.J. Agric. Food Chem. 59:25, 1992.

24. Hahn, D. H., Rooney, L. W., and Earp, C. F. Tannins and phenols of sorghum. Cereal Foods World 29:776, 1984.

25. Hamaker, B. R., and Bugusu, B. Overview: Sorghum proteins and food quality. In: Workshop on the Proteins of Sorghum and Millets: Enhancing Nutritional and Func-tional Properties for Africa. University of Pretoria, Pretoria, South Africa, 2003.

26. Hargrove, J. L., Greenspan, P., Hartle, D. K., and Dowd, C. Inhibition of aromatase and -amylase by flavonoids and proan-thocyanidins from Sorghum bicolor bran extracts. J. Med. Food 14:799, 2011.

27. Hasjim, J., Lee, S.-O., Hendrich, S., Setiawan, S., Ai, Y., and Jane, J.-L. Characterization of a novel resistant-starch and its effects on postprandial plasma-glucose and insu-lin responses. Cereal Chem. 87:257, 2010.

28. Isaacson, C. The change of the staple diet of black South Africans from sorghum to maize (corn) is the cause of the epidemic of squamous carcinoma of the esophagus. Med. Hypotheses 64:658, 2005.

29. Jones, J. M., Klurfeld, D. M., Slavin, J., and Waybright, S. Preparing for the 2015 die-tary guidelines: Attributes of refined grains, added fibers, and bran. Cereal Foods World 57:86, 2012.

30. Lee, B. H. Effects of grain sorghum wax and oil on cholesterol levels, gut micro-biota, and tissue metabolic fingerprints/

profiles of a hamster model with diet-induced hypercholesterolemia. Ph.D. the-sis. University of Nebraska, Lincoln, NE, 2013.

31. Lee, B. H., Weller, C. L., Cuppett, S. L., Carr, T. P., Walter, J., Martínez, I., and Schlegel, V. L. Grain sorghum lipids:Extraction, characterization, and health potential. Pages 149-170 in: Advances in Cereal Science: Implications to Food Pro-cessing and Health Promotion. Vol. 1089, ACS Symposium Series. J. M. Awika,V. Piironen, and S. Bean, eds. American Chemical Society, Washington, DC, 2011.

32. Lemlioglu-Austin, D., Turner, N. D.,McDonough, C. M., and Rooney, L. W. Effects of brans from specialty sorghum varieties on in vitro starch digestibility of soft and hard sorghum endosperm por-ridges. Cereal Chem. 89:190, 2012.

33. Lemlioglu-Austin, D., Turner, N. D.,McDonough, C. M., and Rooney, L. W. Effects of sorghum [Sorghum bicolor (L.) Moench] crude extracts on starch digest-ibility, estimated glycemic index (EGI), and resistant starch (RS) contents of por-ridges. Molecules 17:11124, 2012.

34. Mariscal-Landin, G., Avellaneda, J. H., Reis de Souza, T. C., Aguilera, A., Borbolla, G. A., and Mar, B. Effect of tannins in sor-ghum on amino acid ileal digestibility and on trypsin (E.C.2.4.21.4) and chymotryp-sin (E.C.2.4.21.1) activity of growing pigs. Anim. Feed Sci. Technol. 117:3, 2004.

35. Marston, K. G. Effect of sorghum flour treated with ozone and heat on the quality of gluten-free bread and cake. M.S. thesis. Kansas State University, Manhattan, KS, 2009.

36. Matuschek, E., and Svanberg, U. Enzy-matic treatment of high-tannin sorghum increases the bioaccessibility of iron.Abstract Th37. Page 60 in: Report of the 2004 International Nutritional Anemia Consultative Group Symposium: Iron Defi-ciency in Early Life: Challenges and Prog-ress. Available online at http://pdf.usaid.gov/pdf_docs/PNADE459.pdf. INACG, Washington, DC, 2004.

37. McDonough, C. M., Anderson, B. J., and Rooney, L. W. Structural characteristics of steam-flaked sorghum. Cereal Chem. 74:542, 1997.

38. McDonough, C. M., Awika, J. M., Turner, N. D., Xu, L., and Rooney, L. W. The poten-tial for use of antioxidants from sorghum bran in foods as countermeasures against radiation damage in space. In: 2004 AACC/TIA Joint Meeting Abstracts. Published online at www.aaccnet.org/meetings/Documents/Pre2009Abstracts/2004Abstracts/a04ma391.htm. AACCI, St. Paul, MN, 2004.

39. Mkandawire, N. L., Kaufman, R. C., Bean, S. R., Weller, C. L., Jackson, D. S., and Rose, D. J. Effects of sorghum (Sorghum bicolor (L.) Moench) tannins on -amy-lase activity and in vitro digestibility of


starch in raw and processed flours. J. Agric. Food Chem. 61:4448, 2013.

40. Netzel, M., Sopade, P. A., and Fanning, K. Characteristics of sorghum phenolic com-pounds and how they may influence nutri-tional value. In: Proceedings of Improving Sorghum as a Feed Grain Conference. Uni-versity of Queensland, Brisbane, Australia, 2012.

41. Nyamambi, B., Ndlovu, L., Read, R. J. S., and Reed, J. D. The effects of sorghum proanthocyanidins on digestive enzyme activity in vitro and in the digestive tract of chicken. J. Sci. Food Agric. 80:2223, 2000.

42. Packaged Facts. 2011 Consumer insights and trends: Packaged Facts forecasts the product and social trends that will make their mark in 2011. Published online at www.packagedfacts.com/about/inthenews.asp?id=1850. Packaged Facts, Washington, DC, 2010.

43. Poutanen, K. Past and future of cereal grains as food for health. Trends Food Sci. Technol. 25:58, 2012.

44. Riley. J. G. Comparative feedlot perfor-mance of corn, wheat, milo, and barley. Pages 9-18 in: Proc. Feed Util. Symp. Texas Tech University, Lubbock, TX, 1984.

45. Rooney, L. W. Overview: Sorghum and millet food research failures and successes. In: Workshop on the Proteins of Sorghum and Millets: Enhancing Nutritional and Functional Properties for Africa. Published online at www.afripro.org.uk/papers/Paper09Rooney.pdf. University of Preto-ria, Pretoria, South Africa, 2003.

46. Rooney, L. W., Kirleis, A. W., and Murty, D. S. Traditional foods from sorghum: Their production, evaluation, and nutri-tional value. Pages 317-353 in: Advancesin Cereal Science and Technology, vol. 8.Y. Pomeranz, ed. AACCI, St. Paul, MN, 1986.

47. Rooney, L. W., and Miller, F. R. Variation in the structure and kernel characteristics of sorghum. Pages 143-162 in: Proceedings of the International Symposium on Sor-ghum Grain Quality. L. W. Rooney andD. S. Murty, eds. ICRISAT, Patancheru, India, 1982.

48. Rooney, L. W., and Pflugfelder, R. L. Fac-tors affecting starch digestibility withspecial emphasis on sorghum and corn.J. Anim. Sci. 63:1607, 1986.

49. Rooney, L. W., and Riggs, J. K. Utilization

of sorghum, PR-2945 and -2946. In: Grain Sorghum Research in Texas. Texas Agricul-tural Experiment Station, College Station, TX, 1971.

50. Rooney, L. W., and Waniska, R. D. Sor-ghum food and industrial utilization.Pages 689-730 in: Sorghum: Origin, His-tory, Technology, and Production. C. Wayne Smith and R. A. Frederiksen, eds. John Wiley & Sons, New York, NY, 2000.

51. Singh, J., Dartois, A., and Kaur, L. Starch digestibility in food matrix: A review. Trends Food Sci. Technol. 21:168, 2010.

52. Smith, C. W., and Frederiksen, R. A. Sor-ghum: Origin, History, Technology, and Production. John Wiley & Sons, New York, NY, 2000.

53. Stroade, J., and Boland M. Sorghum pro-file. Published online at www.agmrc.org/commodities__products/grains__oilseeds/sorghum/sorghum_profile.cfm. Agricul-tural Marketing Resource Center, Ames, IA, 2008.

54. Taylor, J., Bean, S. R., Ioerger, B. P., and Taylor, J. R. N. Preferential binding of sorghum tannins with -kafirin and the influence of tannin binding on kafirin digestibility and biodegradation. J. Cereal Sci. 46:22, 2007.

55. Taylor, J. R. N., and Belton, P. S. Sorghum and millets: Protein sources for Africa. Trends Food Sci. Technol. 15:94, 2004.

56. Thompson, L. U., and Yoon, J. H. Starch digestibility as affected by polyphenol and phytic acid. J. Food Sci. 49:1228, 1984.

57. Turner, N. D., and Lupton, J. R. Dietary fiber. Adv. Nutr. 2:151, 2011.

58. U.S. Department of Agriculture, Federal Grain Inspection Service, Grain Inspec-tion, Packers & Stockyards Administra-tion. The official United States Standards for Grain. USDA- FGIS-GIPSA, Washing-

ton, DC, 2006.59. U.S. Department of Agriculture, National

Agricultural Statistics Service. Crop pro-duction annual summary. Published on-line at http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1047. USDA-NASS, Wash-ington, DC, 2013.

60. U.S. Grains Council and U.S. Department of Agriculture, Foreign Agricultural Ser-vice Global Agricultural Trade System. Sorghum—Production and exports. In: Buying/Selling. Published online at www.grains.org/index.php/buying-selling/sorghum. U.S. Grains Council, Washing-ton, DC, 2013.

61. Waniska, R. D. Structure, phenolic com-pounds, and antifungal proteins of sor-ghum caryopses. Page 72 in: Technical and Institutional Options for Sorghum Grain Mold Management: Proceedings of an Inter-national Consultation. A. Chandrashekar, R. Bandyopadhyay, and A. J. Hall, eds. ICRISAT, Patancheru, India, 2000.

62. Wong, J. H., Lau, T., Cai, N., Singh, J.,Pedersen, J. F., Vensel, W. H., Hurkman, W. J., Wilson, J. D., Lemaux, P. G., and Buchanan, B. B. Digestibility of protein and starch from sorghum (Sorghum bicolor) is linked to biochemical and structural features of grain endosperm. J. Cereal Sci. 49:73, 2009.

63. Yang, C. S., Landau, J. M., Huang, M.-T., and Newmark, H. L. Inhibition of carcin-ogenesis by dietary polyphenolic com-pounds. Annu. Rev. Nutr. 21:381, 2001.

64. Zarkadas, M., Dubois, S., MacIsaac, K., Cantin, I., Rashid, M., Roberts, K. C., La Vieille, S., Godefroy, S., and Pulido, O. M. Living with coeliac disease and a gluten-free diet: A Canadian perspective. J. Hum. Nutr. Diet. 26:10, 2013.

Dilek Lemlioglu-Austin is a baking application scientist at Novo-zymes North America in Franklinton, NC. Dilek has worked as a food engineer in the Ministry of Agriculture of Turkey for 10 years, taught and led research at the University of Nebraska-Lincoln, Texas A&M University, and, most recently, North Carolina State University,Department of Food Science. She also has taught online courses on nutrition, health, and wellness through the University of Phoenix. Dilek has been an active member of AACC International, IFT, and a number of other organizations. She can be reached at [email protected].