MAIZE / CORN - BY PRODUCTS
#Maize / or #corn is a major staple food grain throughout the world, particularly in Africa, Latin America and Asia, and a major feedstuff in developed countries. The maize grain has many food (grain, flour, syrup, oil…) and non-food usages (cosmetics, adhesives, paints, varnishes). Maize starch and oil are also major products . The maize grain is a major feed grain and a standard component of livestock diets where it is used as a source of energy. Other grains are typically compared to maize when their nutritional value is estimated. Many by-products of maize processing for flour (hominy feed, bran, germs, oil meal), starch (corn gluten feed, corn gluten meal) and alcohol/biofuel industries (distillers’ dried grains and solubles) can be fed to animals.
Maize breeders have created many cultivars that correspond to specific climatic or agronomic conditions and uses. "Dent corn" maize is the most widely grown type of maize and the one typically used for feed. Other types (flint corn, popcorn, sweet corn, flour corn) are more intended for food uses. Some varieties have been created to improve the industrial or nutritional value: high lysine, high tryptophan, high oil, high amylose, low phytate, etc. Brown midrib maize has a lower lignin content resulting in an increased digestibility in livestock. Genetically-modified (GM) maize varieties have been designed to improve grain performances (herbicide resistance, pest resistance, higher yields).
Supply & Distribution
Maize is native to Central America (Oaxaca, Mexico) where it was domesticated, possibly as early as 5,500 to 10,000 BC. It later spread to Central America, the Caribbean, South America and North America. Through genetic selection and hybridation, it now grows worldwide between 58°N in Canada and Russia and 40°S in Chile and Argentina, from sea level up to an altitude of 3800 m in the Andean mountains . Optimal growth conditions are average day-temperature of 18-21°C, annual rainfall of more than 750 mm, and deep, well-drained rich soils.
Maize can withstand annual rainfall ranging from 230 to 4100 mm, with soil pH between 4.3 and 8.7, and a great variety of soils. Frost kills the plants. Drought is detrimental at flowering as it affects pollination and impairs yields. Maize has no tolerance to flooding (FAO, 2009; Duke, 1983).
Maize grain is fed as dry maize grain (less than 15% moisture) or high-moisture maize grain (22 to 28% moisture). When maize is dried, it should not be heated over 150°C, since this reduces nutritive value and acceptability to pigs (Patience et al., 1995).
Dry or high-moisture maize grain can be available as:
unprocessed = whole grain, shelled
finely ground = fine meal
cracked = medium particle size
steam-rolled = moistened and flattened grains
steam-flaked = heated, moistened and pressured grains (flakes)
Each form has its advantages and disadvantages when feeding livestock .
Maize grain yield averages 3.6 t/ha in the world (highest yields are 7-11 t/ha)
Maize crops drain nutrients from the soil, do not compete well with weeds after the seedling stage and are subject to many diseases and pests. In consequence, the cultivation of high-producing maize requires high fertilizer levels as well as herbicides, pesticides and fungicides, which are deleterious to biodiversity and soil conservation. Heavy fertilizer applications can cause nitrate leaching and soil erosion. Herbicides may contaminate the groundwater while pesticides alter biodiversity (European Commission, 2000). In developing countries where fertilizers are too expensive for general use, the nutrient uptake is higher than when fertilizers are regularly used, thus reducing soil fertility and causing further soil degradation .
Genetically modified maize
The debate about the environmental impact of GM crops is complex and a full discussion of the issue is beyond the scope of this datasheet. Genetically-modified (GM) maize varieties that are herbicide-resistant or pest-tolerant have been commercialised since 1996, and their potential environmental impact has been the subject of considerable debate. Some positive impacts have been reported for GM maize, notably a reduction in herbicide and pesticide use, and certain benefits for wildlife . However, potential negative effects have also been alleged, including the alteration of the DNA of soil microflora, and deleterious impacts on useful insects such as butterflies and bees, or on non-GM plants (including maize) through genome transfer .
Maize grain is palatable and suitable for all livestock. It is the most valuable energy source among cereals. It has a high starch content (about 65%), about 4% oil and a low fibre content (10% NDF) .
Maize starch is less readily fermentable than other cereal starches (30% escapes rumen fermentation). Proteins in maize grain are mainly zein and glutelin, and are situated in the endosperm and germ respectively. Zein, the most important, is deficient in lysine and tryptophan so amino acid supplementation is often necessary. Maize varieties such as Opaque-2 or Flour-2 have been designed to have a better amino acid profile.
Maize grain is low in calcium and supplementation is required. 75% of phosphorus is bound in phytate, which is not readily available to livestock and also reduces calcium availability . Low-phytate hybrids have been developed to increase P availability in monogastrics
Yellow maize has a higher vitamin A content than white maize. Vitamin A deficiency is of little importance in ruminants but it may have deleterious effects in pigs and poultry if not adequately supplemented with a source of vitamin A. Yellow maize is best for monogastrics . Maize grain is generally poor in available niacin.
Ruminants ( FOOD FOR THOUGHTS )
Maize grain is a valued energy source in ruminants. In dairy cows, it can support high milk yields because of its high starch content. Providing adequate amounts of starch also promotes rumen bacterial growth, thus enhancing forage digestibility, rumen cycling and subsequent feed intakes. As it contains a slowly degrading starch in the rumen, maize grain has a low acidogenic value and provides by-pass starch, allowing glucose absorption in the small intestine. However, because it is low in protein, maize grain has to be properly complemented with a protein source to fulfil dairy cattle requirements. High yielding cows fed on maize grain require high quality forage such as alfalfa or a combination of low quality forage (hay) and soybean meal (as a protein source). For high milk production, steam-flaked maize grains are fed to cows since it is more digestible and more palatable, and improves milk yield and milk protein yield .
In steers, maize grain is frequently the main concentrate: it is highly digestible and it is the most palatable cereal for cattle. High moisture maize and steam-flaked maize were reported to give better growth rates than dry-rolled maize when fed in finishing rations to steers.
In pigs, maize is the reference to which other energy sources are compared. It is of utmost value for growing and fattening pigs, for sows and breeding stock, provided that its protein, vitamin and mineral deficiencies are counterbalanced by appropriate feed supplements (with proteins able to correct the amino acid imbalances of the maize).
Maize grain can be fed whole or ground to pigs. If ground, medium-sized particles will be preferred. Yellow maize contains poly-unsaturated fatty acids and may cause soft fat in pigs as well as yellower fat (due to cryptoxanthin) that may be considered undesirable (Patience et al., 1995).
In poultry, maize is appreciated for its highly digestible starch, low fibre and relatively high oil content, resulting in high metabolizable energy values. It is fed at high levels in broilers and laying hens. Maize oil is a good source of polyunsaturated fatty acids (linoleic acid). In poultry, white and yellow maize have equivalent energy, protein and mineral values. Yellow maize contains more carotene and cryptoxanthin which are beneficial to yolk pigmentation. Moreover, birds are attracted to the yellow colour of the grain that can be ground, medium-size or fine, for inclusion in pelleted diets.
In hot climates it is often possible to replace maize by less expensive and more easily available feedstuffs. Barley can totally replace maize in broiler diets, as can sorghum grain, pearl millet and broken rice, but triticale should only partially replace maize since it reduces growth rates .
In hot and tropical countries, maize grain is the most common cereal used in rabbit feeds. Maize grain was present in 34% of all experimental diets presented during the 3 last World Rabbit Congresses (Lebas et al., 2017; Lebas et al., 2013; Lebas et al., 2009). When used, the average incorporation level of maize grain is 20-22% depending of the studies and the highest level of incorporation is generally about 50-55% ; However in some special studies it was incorporated without problem up to 84% in a "control" diet .
In temperate countries, as the main parts of Europe, were maize grain is harvested before complete drying, many mycotoxins may be produced by various fungi in the grain before final drying in the fields or during storage. It's well known that all potential sources of mycotoxins must be discarded from rabbit diets . For this reason, in Europe, nutritionists are suspicious when considering maize grain, classified as a raw material with high sanitary risk. In addition, contrary to values observed for pigs or poultry, the energy value of maize grain for rabbits (14.6 MJ/kg DM) is lower than that of wheat grain (15,2 MJ/kg DM) and only equivalent to that of barley grain (14.5 MJ/kg DM), while the price of these 2 low-risk cereals is generally lower than that of maize grain. For these reasons, maize grain is generally not used in most of the European rabbit diets as it is considered a high sanitary risk material with poor economical interest.
Maize is used in fish diets. It is mostly ground to make meal or pellets. It is easy to pelletize but pellets are prone to abrasion. Digestible energy of maize meal is rather low for rainbow trout (Oncorhynchus mykiss) while it is high for carp (Cyprinus carpio). Digestible energy and other nutrient digestibilities can be improved through gelatinization of maize starch. Feeding rainbow trout fingerlings with maize meal increased animal performance .
CORN DISTILLERS GRAIN
Corn distillers grain is the main by-product of the distillation of alcohol from maize grain. Distilleries produce alcoholic beverages, industrial ethanol and ethanol biofuel with the following by-products :
Spent grains, wet grains, wet distillers grain (WDG), wet distillers grain with solubles (WDGS)
Dried distillers grain (DDG), dried distillers grain with solubles (DDGS)
Condensed distillers solubles (CDS), dried distillers solubles (DDS)
There are two main distillery processes: dry-milling distillery and wet-milling distillery. The dry-milling (or dry-grind) process is the main process for producing ethanol. This process starts with removing the bran by grinding before steeping the grain in water and results in ethanol and various "distillers" by-products. The wet-milling process starts with steeping the grains and then separates the kernel into various fractions, which allows for the production of multiple food and industrial products, including starch, fructose, oil and ethanol. This process yields numerous by-products including maize gluten meal, maize gluten feed and maize germ meal .
While official and trade definitions exist for the different maize distillery by-products, the boundaries between these products may be somewhat fuzzy. Particularly, the amount of solubles blended back to the distillers grain to create DDGS can be variable. In fact, many research studies do not designate whether the product used was with or without solubles, and virtually all corn distillers grain available are DDGS, so the practical distinction between corn distillers grain with or without solubles is rarely useful
This datasheet will deal primarily with the DDGS of maize-based, dry-milling ethanol production, which are now the dominant distillery by-product. The changes in this industry have been tremendous. In the USA, distilleries produced in 1992 two million tons of corn distillers grain, with 40% from the production of alcoholic beverages and 60% from biofuel production. In 2010, the USA were the main world producer of maize-based ethanol biofuel and American maize distilleries yielded more than 34 million tons of corn distillers grain. Biofuel production accounted for 97% of the corn distillers grain produced in the USA. Projections for US corn distillers grain are about 38.6 million tons by 2020 . The situation is different in Europe and Canada, where wheat is the main cereal grain used for biofuel production, followed by maize, rye, sorghum and grain mixtures .
Distillery by-products have a long and rich history in animal feeding. They used to be considered offals and were dumped in sewers and rivers. Spent grains were sold a low price to local farmers as animal feed . Corn distillers grain only became an important by-product in the middle of the 19th century in the UK, when the Coffey-patent still (continuous distillation column) replaced pot stills, allowing the use of maize in grain whisky production, partly replacing barley . In New York in the 1850s, the large-scale feeding of dairy cows with distillery mash in unsanitary conditions resulted in the "swill milk" scandal, a major food scare that led to better regulations of the dairy industry . The first study about feeding distillers grains to cattle was published in 1907 .
Corn distillers grains are valuable feed ingredients, rich in protein, moderately rich in fat and relatively poor in fibre, and can be fed to all classes of livestock . It should be noted that, as of 2012, maize ethanol by-products are not only relatively recent but are still evolving due to changing technologies and demand in biofuel.
Wet corn distillers grain is mainly found in the vicinity of ethanol plants. In the USA, it was estimated that 86% of the corn distillers grains are transported by road within 80 km from the ethanol plant (US EPA, 2010).
Distillers dried grain is a commodity. In 2008, the USA exported 4.5 million tons (81%) of the brewery and distillery by-products traded worldwide. The other main exporters were China, Canada, Germany and Poland. The main importers of brewery and distillery by-products were Mexico, Canada, Turkey, South Korea and Japan (FAO, 2011).
Ethanol manufacturing process (dry milling)
The ethanol manufacturing process starts by the cleaning and then the dry-milling of maize grains. The ground grains are mixed with water and enzymes (amylases) to produce a mash where starch hydrolysis occurs (liquefaction step). This mash is cooked to kill the bacteria that produce undesirable lactic acid. Enzymes are added to the mash to transform starch into dextrose (saccharification step). After saccharification, yeast is added to start the fermentation process, which produces a "beer" and CO2. The beer passes through a continuous distillation column to yield alcohol at the top of the column.
The product that remains at the bottom (whole stillage) is centrifuged and yields wet grains (also called spent grains) and thin stillage. Wet grains may be fed to livestock directly or they can be dried to produce dried distillers grain (DDG). Thin stillage can be sold as high-moisture feed or it can be dehydrated to produce condensed distillers solubles (CDS, also called syrup). Condensed distillers solubles and distillers grain are often blended together to prepare wet or dried distillers grain and solubles (WDGS or DDGS).
While ethanol manufacturing usually follows the process described above, the nature of the end products (beverages, industrial alcohol, biofuel), local know-how and innovation may require specific adaptations, resulting in slightly different by-products.
High protein distillers grain
The increasing use of maize as a raw material for ethanol production led in some cases to modifications of the processes, as there is a constant need for more value-added products to fit the economical model of biofuel production. New processes have been designed to separate valuable maize fractions before or after distillation. The grain can be primarily separated into germ (which will yield food-grade, high-value oil), bran and endosperm, which is subjected to distillation. Because fats and fibre are removed in the early steps of the process, protein is concentrated in the final distillers dried grain, called high protein distillers grain (HPDG) .
Reduced fat DDGS
The extraction of maize oil from distillers dried grain is less costly than direct extraction from the grain. It produces an oil unsuitable for food and feed but usable for biodiesel, as well as reduced fat DDGS .
In some whisky distilleries, the mash is filtered after the liquefaction step, producing wort and a solid by-product called draff or distillers spent grain. The wort undergoes further fermentation while the draff is dried or pressed before being fed to animals. The alcohol-free effluent that remains at the bottom of the distillation column is called spent wash or spent lees. This product, that contains enzymes and yeast, can be dried to yield dried distillers solubles. It can also be centrifuged so that the solids can be further dried into distillers concentrate. As in ethanol production, the spent grains are often mixed with the solubles, resulting in distillers dark grain . It is important to note that whiskies are often the result of the distillation of blended grains that may include maize, wheat, barley and rye. The by-products are therefore not corn distillers grain in the strict sense. Single malt whisky is usually made from barley (and sometimes rye), but not from maize .
Maize distillery by-products are the result of the extraction of starch from the maize grain, and tend to concentrate the other nutrients, notably protein, fibre, soluble sugars and oil. Concentrations of these nutrients may be up to 3 times higher than in the grain (Pedersen et al., 2007).
As noted in Processes, variations in the inclusion of solubles, extraction (or not) of oil, and technical innovations in fermentation and fractionation result in DDGS that contains more (or less) protein, energy, fat, fibre and phosphorus . The composition of maize DDGS is therefore extremely variable, depending on the ethanol plant . It is actually difficult to provide a typical composition for DDGS, because, unlike most industrial by-products, its composition is not driven by the rate of extraction of a single end product (such as starch, sugar or oil) but depends on multiple factors. The following table presents the proximal composition of several groups of DDGS .
CORN GLUTTEN FEED
Corn gluten feed is the by-product of the wet-milling of maize grain for starch (or ethanol) production . Corn gluten feed consists mainly of maize bran and maize steep liquor (liquid separated after steeping) but may also contain distillers solubles, germ meal, cracked maize screenings, as well as minor quantities of end-products from other microbial fermentations . The chemical composition of corn gluten feed varies hugely, as it depends on the milling process and on the relative proportions of bran, steep liquor and other components. Particularly, the energy and protein content of corn gluten feed are positively correlated to the proportion of steep liquor in the blend .
The wet-milling process of maize is described in the figure above. The process yields 5 main products: maize starch, maize germ oil meal, corn gluten meal, corn gluten feed and maize steep liquor. After cleaning and removal of foreign material, the maize grain is usually steeped in water with sulfur dioxide (SO2) for 24-40 hours at a temperature of 48-52°C. The role of sulfur dioxide is to weaken the glutelin matrix by breaking inter- and intramolecular disulfide bonds. Steeping at 45-55°C favours the development of lactic acid bacteria that produce lactic acid, lowering the pH of the medium and thereby restricting growth of most other organisms. At the end of steeping phase, the maize kernels contain about about 45% water, have released about 6.0-6.5% of their dry substance as solubles into the steepwater and have become sufficiently soft to be pulled apart easily with the fingers . After steeping, the maize kernels are coarsely ground so that the germs are separated from the endosperm and used for oil extraction which yields maize germ oil meal. The remaining steeping water is condensed into a steep liquor. The endosperm undergoes further screenings that separate the fibre from gluten (protein fraction) and starch slurry. Fibre (bran) can be mixed with steep liquor and maize germ oil meal to create corn gluten feed . The fibre-free endosperm is centrifugated in order to separate the starch fraction and the gluten, which have different densities, resulting in almost pure starch (99% starch), and corn gluten meal (CRA, 2006).
Corn gluten feed is a feed ingredient mostly used in cattle diets as a source of energy and protein. Its economic value depends upon the relative price of whole grain and protein feeds. In the United States, it is usually considered as a source of protein . However, in the late 1980s, corn gluten feed was one of the several duty-free Non Grain Feed Ingredients that the European feed industry imported massively from the USA as a source of energy, to substitute for EU cereal grains that were very expensive at the time. Corn gluten feed imports declined after the Common Agricultural Policy (CAP) reforms reduced EU grain prices .
Corn gluten feed is usually sold after drying, but maize processors may save on drying cost by selling wet corn gluten feed.
Note: it is important to note that corn gluten feed should not be mistaken for corn gluten meal, which contains about 65% crude protein instead of 22% and is nutritionally completely different. The name similarity of these products is an occasional source of confusion, particularly in papers written by non-native English speakers.
Dried corn gluten feed is traded worldwide. Corn gluten meal and corn gluten feed production is relatively constant since ethanol is now mainly produced in dry mills . The consumption of corn gluten meal and corn gluten feed together was about 14.9 million t from October 2010 to September 2011. The main consumers of both products are the USA (5.6 million t), EU (3 million t), South Korea (1 million t), Japan (0.94 million t) and other Asian countries (1.6 million t). The USA supply 60% (2.1 of 3.5 million tons) of the corn gluten feed traded worldwide. The main importers for 2010-2011 were the EU, South Korea, Turkey, China, Japan, Israel, Egypt and Indonesia (Oil World, 2011).
Unlike dried corn gluten feed, wet corn gluten feed spoils easily and is usually distributed nearby maize processing plants.
Storage of wet corn gluten feed
Wet corn gluten feed spoils very quickly and must either be fed within 6-10 days or stored in anaerobic conditions in a sealed structure . Good results have been obtained by mixing it with other feedstuffs such as maize grain, maize silage or haylage. Packing the material into silo bags is an excellent means for maintaining its quality. The material undergoes little apparent fermentation because of the relatively low pH (4.3). Wet corn gluten feed stored in a silage bag for one year maintained its composition. In cold climates, freezing temperatures actually extend the storage life of wet corn gluten feed and it was even possible to store unprotected wet corn gluten feed on the ground in winter (North Dakota) with little spoilage for up to three to four weeks. However, high summer temperatures reduce freshness to only three to four days, causing palatability problems .
CORN GLUTEN MEAL
Corn gluten meal is a by-product of the manufacture of maize starch (and sometimes ethanol) by the wet-milling process . Corn gluten meal is a protein-rich feed, containing about 65% crude protein (DM), used as a source of protein, energy and pigments for livestock species including fish. It is also valued in pet food for its high protein digestibility . In the USA and Canada, corn gluten meal is also used as a fertilizer and pre-emergent weed killer.
The wet-milling process of maize is described in the figure above. The process yields 5 main products: maize starch, maize germ oil meal, corn gluten meal, corn gluten feed and maize steep liquor. After cleaning and removal of foreign material, the maize grain is usually steeped in water with sulfur dioxide (SO2) for 24-40 hours at a temperature of 48-52°C. The role of sulfur dioxide is to weaken the glutelin matrix by breaking inter- and intramolecular disulfide bonds. Steeping at 45-55° C favours the development of lactic acid bacteria that produce lactic acid, lowering the pH of the medium and thereby restricting growth of most other organisms. At the end of the steeping phase, the maize kernels contain about 45% water, having released about 6.0-6.5% of their dry matter as solubles into the steepwater, and have become sufficiently soft to be pulled apart easily with the fingers . After steeping, the maize kernels are coarsely ground so that the germs are separated from the endosperm and used for oil extraction. The extraction of oil from the germs yields maize germ oil meal. The remaining steeping water is condensed into a steep liquor. The endosperm undergoes further screenings that separate the fibre from gluten (protein fraction) and starch slurry. Fibre (bran) is mixed with steep liquor and maize germ oil meal to create corn gluten feed . The fibre-free endosperm is centrifugated in order to separate the starch fraction and the gluten, which have different densities, resulting in almost pure starch (99% starch), and corn gluten meal
Note: it is important to note that corn gluten meal should not be mistaken for corn gluten feed, which contains about 22% crude protein rather than 65% and is nutritionally completely different. The name similarity of these products is an occasional source of confusion, particularly in papers written by non-native English speakers.
Corn gluten meal is obtained wherever maize is used for starch extraction. It is distributed worldwide. Its production has become relatively constant since ethanol is now mainly produced by dry-milling, which yields corn distillers rather than corn gluten meal and corn gluten feed (RFA, 2008). In 2010-2011, feed consumption of both corn gluten meal and corn gluten feed (statistics do not differentiate between the two products) was about 14.9 million t. The biggest consumers were the USA (5.6 million t), the European Union (3 million t), South Korea (1 million t), Japan (0.94 million t) and other Asian countries (1.6 million t). The USA was the major supplier: they provided 2.1 million t of the 3.5 million t exported worldwide. Main importers were the EU, South Korea, Turkey, China, Japan, Israel, Egypt and Indonesia (Oil World, 2011).
In the European Union, the ban on genetically-modified (GM) maize and maize by-products resulted in a spectacular decrease in the importation of maize grain, corn gluten meal and corn gluten feed in the early 2000s (European Commission, 2007). The importation of GM maize and GM maize by-products is now strictly regulated in the EU, and the EFSA examines every new demand for GM maize products (European Union, 2003).
Corn gluten meal can be fed wet or dried, but dried is more common.
Maize bran is a by-product of various maize processing industries, including starch and ethanol production, and the production of maize-based foods. While maize bran theoretically consists of the bran coating removed in the early stages of processing, the maize bran sold for livestock feeding is usually a mixture of the bran fraction and other by-products and is, therefore, a very loosely defined product of highly variable composition. In the case of ethanol production, maize bran is defined as the mixture of the bran fraction and distillers solubles . In the starch extraction process, maize bran is usually mixed with steep liquor to produce corn gluten feed. In the production of maize grits by the dry milling process, maize bran is mixed with broken kernels, germ residue after oil extraction, and inseparable fractions of germ, pericarp and endosperm to produce hominy feed (Stock et al., 1999). Maize bran and hominy feed are presented together in this datasheet since both products are closely related and form a continuum in terms of chemical composition. It must be noted that hominy feed is sometimes referred to as "hominy" although hominy is a distinct food product, and not a by-product.
Maize bran and hominy feed are feed commodities traded worldwide. However, while maize bran is often mixed with other maize processing by-products in industrialized countries, it is a major commodity in developing countries. In Malawi, for instance, maize bran is in high demand both for human and livestock consumption, and can become scarce and expensive .
Maize bran has a relatively low protein content varying between 9 and 15% of DM, higher than maize grain but lower than corn distillers and corn gluten feed. Fibre content (crude fibre 5-20% DM, NDF 20-60% DM) tends to be higher than for other maize by-products, and much more variable. Protein and cell wall content are poorly related in maize bran, but crude fibre and ash are positively related (R = 0.65). NDF and ADF can be predicted from crude fibre and ash (all data in % of DM) from the following equations :
NDF = 20.9 + 2.31 CF - 0.88 Ash (n = 31, R2 = 0.56, RSD = 8.2) (CF: crude fibre)
ADF = 2.54 + 0.97 CF (n = 32, R2 = 0.90, RSD = 1.3)
The starch content is also quite variable (17-54% of DM), closely and negatively related to the cell wall contents. It can be expressed as a function of crude fibre, ash and crude protein:
Starch = 63.7 - 1.43 CF - 1.43 Ash - 0.46 CP (n = 394, R2 = 0.70, RSD = 5.8) (CP: crude protein)
Maize bran usually contains less than 10% oil in the DM. Ash content is about 6% DM and similar to that of corn gluten feed and DDGS (dried corn distillers grain with solubles), but more variable.
Hominy feed is comparable to maize bran but less variable and richer in protein (15 vs. 12% DM in average) and starch (40 vs. 35%), and poorer in fibre (crude fibre 6.5 vs. 12% of DM), and, therefore, of a higher nutritional value. In the USA, hominy feed is required to contain more than 4% fat (as fed) .
Maize germ meal, maize germ cake, maize germ oil meal, maize germ oil cake, maize oil cake, maize oil meal, corn germ oil meal, corn germ oil cake, corn oil cake, corn oil meal, spent germs [English]; tourteau de germes de maïs [French]; germen desgrasado del maíz [Spanish]; farelo de gérmen de milho desengordurado [Portuguese]
Maize germ, corn germ, full-fat maize germ, full-fat corn germ, high-fat corn germ [English]; germes de maïs [French]; germen de maíz [Spanish]; gérmen de milho, gérmen integral de milho [Portuguese]
Maize germ meal (corn germ meal) is the by-product of oil extraction from maize germs obtained from maize processing. It is a product of moderate to good nutritive value suitable for all classes of livestock but its composition is highly variable.
Maize germ meal is considered a good ingredient for all livestock species . Maize germ meal readily absorbs liquids such as molasses and tallow and is, therefore, a useful carrier for liquid nutrients . It is a very variable product: its protein, oil, fibre and starch contents depend on the processes used for producing the germs and for extracting the oil, together with the amount of other maize by-products mixed with the spent germs. The residual oil, for instance, may be lower than 5% DM or higher than 14% DM, which will affect the energy value of the product. Likewise, the amount of residual bran will affect the fibre content and thus the suitability of the germ meal for pigs and poultry . As a result, the nutritive value of a given batch may differ from values published in feed composition tables by a large margin; if possible, maize germ meal should be analysed on a case-by-case basis, or at least by origin (processing plant).
It is important to note that while there are official definitions for maize germ meal and maize germs, these products are actually part of a continuum of loosely named by-products yielded by the wet milling and dry milling maize industries (see Processes below). Products sold under these names may contain variable, or even substantial, amounts of bran, endosperm fragments and other residues. Maize germ meal from the wet milling industry can be very close to corn gluten feed, and from the dry milling industry very close to maize bran or hominy feed. Likewise, it is difficult to tell poorly extracted maize germs from low-oil maize germs from dry milling. The names themselves can also be a source of confusion: in French, "tourteau de germes de maïs" (maize germ meal) sounds like "tourteau de maïs" (hominy feed); in English, "maize germ meal" can easily be mistaken for "maize germs" and studies of "maize germ meal" (a product containing 1 to 20% oil) may actually concern full-fat maize germs (50% oil). Unlike most ingredients, maize germ meal is not a single product but a group of products of widely differing nutritional value.
Maize germ meal and maize germs are feed commodities traded worldwide.
Maize germ, which contributes about 11% of the kernel weight, contains 45-50% oil and about 85% of the oil kernel (CRA, 2009). The germ is a distinct entity that can be easily separated and then extracted to produce maize oil, yielding maize germ oil meal as the main by-product . The germs themselves are obtained from maize processing from wet milling (starch production) or dry milling (maize grits, maize flour, maize meal and ethanol production) . Germs are removed in the wet milling process to facilitate starch extraction, whereas they are removed in the dry milling process to improve the stability of maize grain products for use as food . In the wet milling process, maize grain is steeped in water and then separated into kernels, from which starch is later extracted, and germs. The germs are washed, dried, and extracted first by mechanical extraction and then by solvent (hexane). Maize germ meal consists of the spent germs and other maize grain fragments . In the dry milling process, abrading action strips away the germ and pericarp while leaving the endosperm intact. While the endosperm continues through the milling process, the combined bran and germ are aspirated to remove the bran, allowing the germ to be extracted, yielding oil and maize germ meal (Stock et al., 1999).
Maize germ meal is usually mixed with other by-products to create a final feed ingredient. In the wet milling process, spent germs are mixed with maize bran and maize steep liquor to make corn gluten feed (CRA, 2006). In the dry milling process, the spent germs are mixed with broken kernels and inseparable fractions of germ, pericarp and endosperm to produce hominy feed . However, maize germ meal is also sold as a separate product.
While maize germs are usually extracted, non-extracted (full-fat, high-fat) maize germs are sometimes available, either from the wet milling or the dry milling process. Because germs from dry milling have not been subjected to steeping, they should retain more soluble protein, phosphorus and starch than germs obtained from wet milling. However, they contain much less residual oil . The production of beer from maize (chicha) in South America also yields maize germs .
Maize germ meal
Maize germ meal obtained from the wet milling process for starch production has a relatively high protein content (22-31% DM). The crude fibre content is moderate (10% DM) but the NDF content is high and variable (30-60% DM). Residual oil ranges from less than 3% to more than 10%, reflecting differences in oil extraction efficiency. Oil-rich maize germ meal from wet milling is slightly poorer in protein than well defatted maize germ meal (25-32% vs. 22-30% DM). Like other maize by-products, maize germ meal tends to be poor in lysine (about 4% of the protein), though richer than maize grain (3%). Maize germ meal from wet milling is relatively close to corn gluten feed but contains more protein, more oil, less fibre and about the same amount of starch and is, therefore, of higher nutritional value. Maize germ meal is particularly rich in phosphorus, since the germ contains much of the P in the grain .
Maize germ meal obtained from dry milling has a lower protein content (10-20% DM), less fibre and more starch than maize germ meal obtained from wet milling. Residual oil depends on the extraction method and can also vary between less than 1% up to more than 20% DM.
Maize germ obtained from wet milling usually contains 11-16% of protein in the DM and 40-50% oil (Miller et al., 2009). Maize germ from dry milling contains a little more protein (13-18% DM) and much less oil (20-30% DM) . The residual oil contains 16% palmitic acid (16:0), 28% oleic acid (18:1) and 56% linoleic acid (18:2) .