Journal of Scientific & Industrial Research Vol. 58, February 1999, pp 83-88

Maize Wet Milling Co-products as Feed Additives: Perspectives and Opportunities

Harish K Tekchandani, Fausto F Dias*, and Darshan Mehta

The Ani! Starch Products Ltd, Ahmedabad 380025

The nutriti onal value of the co-products produced during the manufacture o f starch from maize by the wet milling process is

described. The use of these co-products in the feed industry is described . The wet milling industry produces 170,000 MT (dry

substance basis) of these products per annum. The expected growth of the wet milling industry due to the increased demand for

starch by user indu stries will only succeed if the feed industry recognises the value of the co-products.

Introduction

India produces about 10 milli on MT of maize . Though not to the same extent as in the Uni ted States (the largest maize producer in the world), a major part of the maize grown is utili zed as feed l . Poultry feed consumes more maize than catt le feed. The remaining amount is used for other applications such as brewing and starc h manufacture . The relative proportion of maize used in various applications in India, vis-a-vis the United States is given in Table I .

Starch is normally manufactured by a process known as wet milling. Bes ides starch, the process yie lds four major co- products which are used as feed ingredi ents. Of the 6, 16,000 MT of maize which is processed by wet mi lling annually , it should be poss ible to recover about 170,000 MT (dry substance) of co- products. Four major co-products recovered during the wet milling of maize

are: • Condensed fermented maize (com) extractives

or com steep liquor • Maize (com) gluten meal • Maize (com) gluten feed • Maize (com) germ meal or maize oilcake

Based on current amount of maize be ing processed by wet millers in Indi a, the amount of feed co-products that are avai lable is given in Table 2. With the increased demand for starches in various industries such as paper manufacture and food process ing, it is likely that the availability of these co-products will increase. The suc­cess of the maize wet milling industry depends on the efficient recovery of co-products and their utilization.

"Present add ress: H2/G3 Navelkar Es tates , Haingui m, Old Goa, Goa 403 402

The Maize Wet Milling Process

Cleaned maize kemels are soaked in a so luti on of

sulphur di ox ide in water at about SO°C, in a process

referred to as steeping. (Figure I ). The solubles in the ,

Table I - The relative amounts of maize used in va rious

applications in India , vis-a-vis the United States

Maize Ut ili za- Uni ted States India tion

Million MT of Maize (% of maize consumed)

Feed 124.4 (58.8) 5.5 (55)

Feod 4.9 (2.3) 3.8 (38)

Milling and 34.7 ( 16.4) 0 .6 (6) refining

Others 47 .5(22.4) 0 .1 ( I)

Tabl e 2 - Avail ab ility of co-products from the wet - milling

industry in India

Co-Product Moi sture % Commercial, Dry TPA Substance,

TPA

Corn Gluten II 24640 21930, Meal

Oil cake 5 27720 26335

Corn Extrac- 50 70470 35235 tives

Husk 65 246400 86240

An nual grind 6, 16,000 MT (D ias and Mehta, 1997)

(Maize, in the United States, is referred to as corn . Many of the

co-products are beller known with the prefix corn, even in cou n­

tries where the grai n is referred to as maize)

84 J SCI IND RES VOL 58 FEBRUARY 1999

Figure I - Products and co-products of the maize wet milling industry

kernels leach out, and under the selective environmental pressures of temperature and su lphur dioxide, an ac tive lactic fermentation takes place. The lactic acid and sul­phur dioxide serve to soften the grain and to disrupt the starch-protein (gluten) matrix to permit their efficient separation in subsequent steps. When steeping is com­plete, the water (light steep water) is drained off and concentrated to give condensed com extractives (corn steep liquor) . The maize grains are then coarsely milled to separate out the germs which are collected, dried, and further processed to recover oil. The residue is com germ meal (maize oilcake) . After the germ has been removed, the rest of the maize kernel is re-milled and the bran (the outer hull) is collected by screening. This mayor may not be mixed with the corn extractives and/or oilcake to give corn gluten meal, which is mar­keted after drying or drying and pelletising, or in wet condition. In India, oilcake is normally not mixed with the bran . The remaining mixture of starch and gluten is separated in centrifuges, taking advantage of their dif­ferences in density . The gluten is collected on filters and dried to give corn gluten meal. The starch is either dried, or modified and dried . Or it can be further processed to produce nutritive sweeteners like crystalline glucose (dextrose), glucose syrup or high fructose syrup. Or it

can used for the manufacture of ethanol , or other fer­mentation products such as lysine or xanthan gum.

The official definitions of corn-wet milling derived feed ingredients, as established by The Association of American Feed Control Officials, are as follows:

Com Gluten Feed is that part of the commercially shelled corn that remains after the extraction of the larger portion of the starch, gluten, and germ by the processes employed in the wet- milling manufacture of corn starch or syrup. It mayor may not contain one or more of the following: fermented corn extractives, corn germ meal.

Com Gluten Meal is the dried residue from corn after the removal of the larger part of the starch and germ, and the separation of the bran by the process employed in the wet-milling manufacture of corn starch or syrup, or by enzymatic treatment of the endosperm. It may con­tain fermented corn extractives and/or corn germ meal.

Corn Germ Meal (Wet Milled) are ground corn germ from which most of the solubles have been removed by steeping and most of the oil removed by hydraulic, expeller, or solvent extraction processes, and is obta ined in the wet-milling process of manufacture of corn starch, corn syrup, or other corn products .

Condensed Fermented Corn Extractives are obtained by the partial removal of water from the liquid resulting from steeping corn in a water and sulphur dioxide solu­tion which is allowed to ferment by acti on of naturally occurring lactic acid producing microorganisms as prac­ticed in the wet-milling of corn.

It should be noted that Corn Gluten Feed can have varying compositions depending on the amount of con­densed fermented corn extractives added, and whether it contains de-oiled germ or not. In Indi a, most wet-mill­ers add neither corn extractives or dc-oiled germ . The husk, as it comes out of the process, at about 65 per cent moisture, is sold directly as a feed fo r cattle. In the discussion below corn gluten feed will refer to the product to which corn extractives have been added to give a protein value of about 20 per cent (dry substance basis). This product is the most commonly available and is an item of international trade. Indian wet-millers cou ld produce this product if the demand exists. And demand will on ly grow if its nutritional value vis-a-vis other feed-stuff is better recognised.

Nutritional Value

Nutrition is of primary concern to the feed manufac­ture. Each of the corn wet milling co-products contrib-

TEKCHANDANI e/ at.: MAIZE WET MILLING CO-PRODUCTS 85

Table 3 - Nutritional characteristics of various corn wet - milling co-products

Unit Corn Gluten Corn Gluten Corn Germ Condensed Fermented Feed Meal 60% Meal Corn Extractives

Dry Matter % 90.0 90.0 95 .0 50.0 Protein % 21.0 60.0 22.0 25.0 Fat % 2.5 3.0 * 0 Fiber % 10.0 3.0 12.0 0 NDF % 37.6 14.0 0 ADF % 12.4 5.0 14.0 0 TDN % 80.0 86.0 67.0 40.0 Starch % 23.0 nla 0 0 ME (poultry) kcal/kg 1826 3872 1694 1595 NE-L** mcal/kg 1.914 2.046 1.54 NE-G** mcal/kg 1.298 1.518 0.99 NE-M** mcallkg 2.112 2.2 1.54 Alanine % 1.5 5.2 1.4 1.8 Arginine % 1.0 1.9 1.3 1.1 Aspartic Acid % 1.2 3.6 1.4 1.4 Cystine % 0.5 1.1 0.4 0.8 Glutamic Acid % 3.4 13.8 3.2 3.5 Glycine % 1.0 1.6 1.1 1.1 Histidine % 0.7 1.2 0.7 0.7 Isoleucine % 0.6 2.3 0.7 0.7 Leucine % 1.9 10.1 1.8 2.0 Lysine % 0.6 1.0 0.9 0.8 Methaionine % 0.5 1.9 0.6 0.5 Phenylalanine % 0.8 3.8 0.9 0.8 Proline % 1.7 5.5 1.3 2.0 Serine % 1.0 3.1 1.0 1.0 Threonine % 0.9 2.0 l.l 0.9 Tryptophan % 0.1 0.3 0.2 0.05 Tyrosine % 0.6 2.9 0.7 0.5 Valine % 1.0 2.7 1.2 1.2 Vitamin A (equiv) *** mg/kg 0 66-143 0 0 Beta-Carotene mg/kg 0 44-66 0 0 Choline mg/kg 2420 2200 1408 3498 Niacin mg/kg 74.8 81.4 41.8 83.6 Pantothenic Acid mg/kg 17.16 2.86 4.4 14.96 Pyriodoxine mg/kg 14.96 6.16 5.94 8.8 Riboflavin mg/kg 2.42 2.2 3.74 5.94 Thiamine mglkg 198 0.22 6.16 2.86 Biotin mg/kg 0.22 0.22 0.22 0.33 Inositol mg/kg 5390 1892 NA 2730 Total ash % 7.8 1. 8 3.8 7.8 Potassium % 1.3 0.45 0.34 2.4 Phosphorus % 0.9 0.70 0.5 1.8 Magnesium % 0.42 0. 15 0.16 0.71 Chloride % 0.23 0. 10 0.04 0.43 Calcium % 0.2 0.02 0.04 0. 14 Sulfur % 0. 16 0.83 0.32 0.59 Sodium % 0.12 0.03 0.04 0.11 Iron ppm 304 167 330 110 Zinc ppm 88 42 106 66 Manganese ppm 22 Trace 3.7 29 Copper ppm 9.9 22 4.4 15.6 Chromium ppm < 1.5 < 1.5 < 1.5 < 2.0 Molybdenum ppm 0.8 0.6 0.5 1.0 Selenium ppm 0.22 0.66 0.33 0.35 Cobalt ppm 0.09 0 0 0. 14 * About I % if solvent extracted, 10 % if expelled. In India Corn Germ Meal has oil in excess of J 0 % . *"Dry Maller Basis "* *As retinol (0.15 mg retinol corresponds to 5000 LU. Vitamin A)

86 ] SCI lND RES VOL 58 FEBRUARY 1999

utes different nutritional characteristics to the fini shed feed . The four co- produc ts are broadly c lassified as "protein supplements" with protein levels in excess of

20 per cent. However, bes ides variations in protein levels , the four products have di fferent levels of various amino acids, minerals , and vitamins. These are indicated

in Table 3. With several feed ingredients to choose from , the feed

manufactures today employs computer soluti ons to feed formul ation questions. Based on the analytical data fed, the most cos t effective formulation is decided on. How­ever, though most formulations are done on the least cost bas is, specific properties of the mai ze wet-milling co­products contribute much to the ir usage.

Poultry Feed

Depending on the type of bird (chicks , broi ler, lay­ers, etc.) and the stage of production, the needs of poultry feed manufacturers vary widely. Gluten meal is the most

common wet- milling product used in poultry feeds. Its high protein and energy content makes it ideal for nutri­ent-dense, high-efficiency rations needed by broiler pro­

ducers . In fact, the energy content of gluten meal is second on ly to that of fats and oils, among common ly available feed ingredients. The xanthophyll content (50 to 100 mg per kg) imparts an yellow colour to the skin of the birds and the yolk of eggs,. traits which are

considered desirable. A recent report2 on the Indian

consumers' preferences in the purchase of eggs indicates that this is also true in India. The methionine and cystein in corn gluten meal have biological activit ies of98.5 per

cent to poultry. The high linoleic acid content assists in meeting the essential fatty acid requirement of pou ltry .

Condensed Fermented Corn Extractives are an excel­lent poultry feed ingredient, rich in energy, proteins and amino acids, and minerals. Its deficiency is that the main commercial form in which it is available is a 50 per cent so lution, and thi s makes formulation difficult. Drying corn steep, except for speciality feeds, i not economi­ca l. Investigators at the Gujarat Agricultural University at Anand have studied, and are continuing to study, the value of corn steep concentrate as a poultry feed ingre­dient. Patel3 studied the use of corn steep in broiler starter and fini sher rations. He replaced de -o iled grou nd­nut cake and soyabean meal with e ither 4,6 or 8 per cent of corn steep concentrate in starter feeds (crude protein

adjusted to 23 per cent and metabolisable energy to about 2800 kcal per kg) and finisher feeds (crude prote in

20 per cent and metabolisable energy about 2900 kcal ). The main ingred ients in the formulation s are given in Table 4. The formulations a lso contained vitamin and mineral supplements. Patel's results indicate that the substitution of groundnut cake and soyabean mea l by corn steep did not impact the body weight or body weight gain adversely. The addition of corn steep had no deleterious effect on the feed conversion efficiency .

Neither was there a difference in carcass quali ty or

Table 4 - Broiler starter and fini sher feed compositions tested

Ingred ient Broiler starter feed Broil er finisher feed

TI T2 To T4 TI T2 T1 T4

Maize 44 44 44 44 47 47 47 47

Rice polish 6 6 6 6 12 12 12 12

De-oil ed groundnut cake 20 18 17 16 18 16 15 14

Soyabean meal 12 10 9 8 7 5 4 3

Sunflower cake 5 5 .5 5 5 5 5 5

Fish meal 6 6 6 6 4 4 4 4

Mutton tallow 2 2 2 2

Corn steep concentrate 4 6 8 4 6 8

Metabolisable energy, 2782 2786 2788 2790 2917 2921 2923 2925 Kcal per kg

Crude protein. % 23.02 23.07 23.09 23 . 11 20.00 20.05 20.07 20.09

TEKCHANDANI et 01.: MAIZE WET MILLING CO-PRODUCTS 87

dress ing characteristics . Patel concluded that corn steep concentrate was a cost effective substitute for other commonly used protein poultry feed ingredients . Hi s findings led to the utilization of corn ex tractives in

Central Gujarat. Besides the ir good nutritional profile, corn ex trac­

ti ves have the advantage that when added to feeds in mash form it prevents dusting and renders the feed more acceptable to birds. Thi s prevents dusting losses and results in better utilization. When making pe lleted feeds, corn extractives act as a nutritional binder which im­proves the flavour and makes the feed more acceptable .

Corn gluten feed may have potential in rations meant for commercial laying hens and growing pullet rations. A high dietary energy level is not as critical for obtaining optimum performance of pullets and hens as it is for broilers. In fact, lower energy levels (555-573 kca l/lb)

have been recommended for growing pullets . Corn glu­ten feed has al so been tested as an ingredient for induced moulting programmes for layers. Work done at the University of Illinois indicates that hens fed 100 percent corn gluten feed or 50 per cent maize and 50 per cent corn gluten feed returned to moulting faster than birds fed maize alone4.

There are several reports that wet-milling co-prod­ucts such as corn gluten meal and corn g luten feed contained unidentified factors that produce unexplained positi ve response 'in poultry performance. Examples of these responses include reduced liver fat accumulation in layers and improved egg qualityS

Cattle Feed

Considerable work has been done on both beef and dairy cattle. Only some re ferences to the earlier work on beef cattle are included as in the Indi an context this work is of less importance6- 11 . Essentially most of the studies indicate that corn gluten feed can be fed instead of corn and still maintai n performancc. In fact, Richards6 re­ported that the energy value for corn gluten feed is 110-120 per cent that of corn. The only negative report is that feeding excess corn gluten feed may result in polioencephalamalacia (PEM) associated with thiamine deficiency in the rumen due to the hi gh sulphur content. Testimonial ev idence has been strong enough that sup­plemental thiamin is routine ly added to wet corn gluten

feed diets. In the recent study by Scott, Klopfenstcin, Stock, and

Klemesrud I 0 sixty yearl ing Herefo rd steers were used to evaluate thc effect of replacing of dry ro lled maize

Table 5 - Results of Feeding Wei Corn Gluten Feed to Lactating Dairy Cows

0 % 10 % 20 % 30 % WCGF WCGF WCGF WCGF

Dry Matter 103.84 103.84 10 1.86 101.86 intake(kg)

Milk Yield 50.50 50.70 50.90 51.10 (% )

Milk fat 3.7 1 3.80 3.71 3.89 (% )

Milk 3.36 3.n 3.23 3.28 protein (% )

3.5 % Fat 114.84 116.82 115.94 11 9.9 Corrected Milk (kg)

Table 6 - Recommendations for use of maize wet milling co-products in aquacu lture

Speciesrrype Corn Gluten Feed Corn Gluten Meal

Catfi sh up to 16 % uptolS %

Trout upt07 .S % upto 10 %

Salmon up to 7.5 % lip to 7.5 %

Freshwater prawns; up to 5 % up to 5 % shrimp

Tilapia upto 16 % up to 16 %

with various levels of maize bran and/or corn steep in

finishing diets. Steers fed 15 per cent bran , 15 or 30 per

cent corn extractives or any combination of bran and

extractives gained weight faster than steers fed the dry

rolled maize diet or the 30 per cent bran diet. Corn

extractives have a higher energy level than bran and

there is an associative effect between steep liqu or and II .

bran . Scott et af. used three hundred and twenty steer

calves to evaluate corn gluten feed and corn extractables

as degradable intake prote in sources re lative to soy-bean

meal and to determine the need for rumen degradable

protein. Among other things, they found that wet corn

gluten feed provided better daily gain effici ency than

. soybean meal. Steep liquor has a higher value than corn . Talpada et al. 12 reported that Corn Extractives pro­

vides 75.79 per cent TDN and 39.20 per cent DCP on

dry matter basis. The study was carried out at Gujarat

Agriculture Univers ity on bullocks. Gupta et af. 13 re­

ported that up to 15 per cent corn ex tracti ves can be

incorporated to feed without affecting the rate of body

1)8 J SCI IND RES VOL 58 FEBRUARY 1999

weight ga in s ignificantly. These ex periments were con­

ducted on growin~ cross-bred ca lves. Many trials 14-2 with wet (WCGF) or dry corn gluten

feed (DCGF) have indicated that both are excellent feeds fo r lac tating dairy cattle, result ing in similar levels of intake and production of fat-correc ted mil k. The results

indicate that up to 25-30 per cent (on a dry matter bas is) can be incorporated in the diets o f lactat ing da iry cows without any decrease in milk y ie ld . Hence, the dec ision of incorporating corn g luten feed into the rati ons of lactating animals is based on economi cs. T he results of one of the studi es l 6 are indicated in Table 5.

In milk production, the cos t of feed is the most important vari able fro m one producer to the another and

hence is of primary concern to da iry producers. Devel­opment of a profit able dairy enterprise depends on mak­in g nutr iti o na l a nd eco no mi ca l assess me nt s of feeds tu ffs. Tes timoni al evidence indicates that feeding germ meal results in enhanced milk producti on. No

published data is ava ilable. In the Indi an contex t, the use of corn ex trac ti ves as a

liqu id feed adju vant seems an attracti ve propos iti on. Roughages can be made nutritionall y adequate by en­richment with com extracti ves.

Other Animals

Ma ize g luten meal (and sometimes maize g luten feed) are used in the manufacture of aquaculture feeds. Fish require a higher proporti on of protein in the ir diet as they have a lower energy requirement. G luten meal,

because of its consistent quality, is a cost-effec ti ve sub­stitute fo r fish meal, the traditional maj or component of aquaculture feeds. Reco mmend ati ons5 f o r u se in aquaculture are given in Table 6.

Maize g luten meal is an excellent ingredient for cat food . The cyste ine enhances the palatability of extruded dry food, while the methi onine and lino le ic ac id improve the quality of the coat. A max imum of 7 .5 per cent can be added to ex truded cat foods. Both maize meal and com g luten feed can be used in dog food. An excellent source of fi bre, com gluten feed is an effective feed ingredient fo r o lder dogs and obese dogs.

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r