12 Wet Milling: Starch and gluten Purpose of wet milling gluten comprise the steps of extracting the crude Wet milling of cereal grains differs fundament. starch and crude protein, purifying, concentrating ally from dry milling in being a maceration and drying the two products. In order to obtain process in which physical and chemical changes gluten in a relatively pure form(in addition to occur in the nature of the basic constituents starch)it is necessary to separate the gluten from the bran and germ This may be done by first starch, protein and cell wall material-in order milling the wheat by conventional dry processes to bring about a complete dissociation of the endosperm cell contents with the release of the and using the white four as the starting material starch granules from the protein network in for the wet process which they are enclosed In dry milling, the Until the development of recent method endosperm is merely fragmented into cells or cell processes starting with flour were mostly variants fragments with no deliberate separation of starch on three long-established methods from protein (except in protein displacement Martin process: dough is kneaded under water milling by extension of dry milling; cf. p. 132). Although the grains of all cereals contain Batter process: a flour-water batter is dispersed starch, those most widely processed by wet milling in more water so that the gluten breaks down are wheat and maize. Other cereals which are less into small curds. The gluten Is separated frequently wet milled are rice, sorghum and the starch milk by screening millet, while experimental work has been carried Alkali process: four is suspended in an alkaline out to separate starch and protein from triticale solution(e. g 0.03 N sodium hydroxide)in which the protein disperses. Starch is removed by tabling and rye and centrifuging, and the protein precipitated by acidifying to pH 5.5. The protein product is in heat a denatured condition i.e. non-vital A number of modern processes start with flour: .. Means for separating starch from wheat by wet the Canadian process(1966)resembles the alkali milling processes have been known from classical process, but suspends the four in 0.2 M ammonium times. Marcus Porcius Cato (234-149 B.C. hydroxide; the Far-Mar-Co process(U.S. Pat described a process in which cleaned wheat was No. 3, 979, 375)is similar to the martin process, steeped for 10 days in twice its weight of water, but the dough moves through a tube in which the water poured off, the soaked wheat slurried, it is washed and mixed the Alfa-Laval/Raisio enclosed in a cloth, and the starch milk pressed process( Starke, 1978, 30: 8)resembles the batter out. The residue of gluten, bran and germ would process, but uses centrifuging, decantation and have been discarded or used as animal feed hydrocyclones for separating the starch from the All wet processes for manufacture of starch and gluten; the Koninklijke Scholten-Honig process 259
I2 Wet Milling: Starch and Gluten Purpose of wet milling Wet milling of cereal grains differs fundamentally from dry milling in being a maceration process in which physical and chemical changes occur in the nature of the basic constituents - starch, protein and cell wall material - in order to bring about a complete dissociation of the endosperm cell contents with the release of the starch granules from the protein network in which they are enclosed. In dry milling, the endosperm is merely fragmented into cells or cell fragments with no deliberate separation of starch from protein (except in protein displacement milling by air-classification, which is a special extension of dry milling; cf. p. 132). Although the grains of all cereals contain starch, those most widely processed by wet milling are wheat and maize. Other cereals which are less frequently wet milled are rice, sorghum and millet, while experimental work has been carried out to separate starch and protein from triticale and rye. gluten comprise the steps of extracting the crude starch and crude protein, purifying, concentrating, and drying the two products. In order to obtain gluten in a relatively pure form (in addition to starch) it is necessary to separate the gluten from the bran and germ. This may be done by first milling the wheat by conventional dry processes and using the white flour as the starting material for the wet process. Until the development of recent methods, processes starting with flour were mostly variants on three long-established methods: Martin process: dough is kneaded under water sprays. The gluten agglomerates, and the starch is washed out. Batter process: a flour-water batter is dispersed in more water so that the gluten breaks down into small curds. The gluten is separated from the starch milk by screening. Alkali process: flour is suspended in an alkaline solution (e.g. 0.03 N sodium hydroxide) in which the protein disperses. Starch is removed by tabling and centrifuging, and the protein precipitated by acidifying to pH 5.5. The protein product is in a denatured condition, i.e. non-vital. A number of modern processes start with flour: Wheat Means for separating starch from wheat by wet the Canadian process (1966) resembles the alkali milling processes have been known from classical process, but suspends the flour in 0.2 M ammonium times. Marcus Porcius Cat0 (234-149 B.C.) hydroxide; the Far-Mar-Co process (U.S. Pat. described a process in which cleaned wheat was No. 3,979,375) is similar to the Martin process, steeped for 10 days in twice its weight of water, but the dough moves through a tube in which the water poured off, the soaked wheat slurried, it is washed and mixed; the Alfa-Laval/Raisio enclosed in a cloth, and the starch milk pressed process (Starke, 1978, 30:8) resembles the batter out. The residue of gluten, bran and germ would process, but uses centrifuging, decantation and have been discarded or used as animal feed. hydrocyclones for separating the starch from the All wet processes for manufacture of starch and gluten; the Koninklijke Scholten-Honig process 259
(BP 1, 596, 742)also resembles the batter process is met by imports of gluten, chiefly from the and uses hydrocyclones. A process by Walon European continent. Imports of gluten in 1988/ U.S. Pat. No. 4, 217, 414)uses bacterial alpha- 89 amounted to 37,000 t, giving a total availability amylase to solubilize the starch; the gluten is not of about 57,000 t. World production of vital Some modern processes start with wheat but 1988), of which 130,000 t were produceda, denatured and can be separated as 'vital gluten,. gluten in 1986 is reported as 253, 000 t(Gode iffer from Cato's method in using a steep liquor western Europe and 54, 000 t in the u.s.A., containing 0.03-0.7% of sulphur dioxide to inhibit Canada, Mexico and Argentina development of micro-organisms. After draining off the steep liquor, the wet grain is coarsely milled and slurried with water. The bran and Uses for vital wheat gluten germ are separated by screening, and the heavy Vital gluten is used as a protein supplement tarch granules separated from the light gluten curd by sedimentation and centrifuging at levels of 0.5-3.0% to improve the texture In the Pillsbury process(Br. Pat. No. 1, 357, 669 and raise the protein content of bread, par grain is steeped in an acid medium with applica- ticularly 'slimming' bread, crispbread and tion of vacuum or carbon dioxide to remove the speciality breads such as vienna bread and air pocket at the base of the crease where micro- hamburger rolls organisms might develop. In the Far-Mar-Co to fortify weak flours, and to permit the use process(U.S. Pat. No. 4, 201, 708)wheat is soaked by millers of a wheat grist of lowered strong in water and faked. The flakes are disintegrated weak wheat ratio (particularly in the EC and the resulting bran-germ and endosperm countries) by raising the protein content of particles are hydrated and form a dough-like mass the milled four: which is tumbled and manipulated in water to - in starch-reduced high protein breads(cf.p separate and recover vital gluten, starch and bran 209), in which the gluten acts both as a source germ components of protein and as a texturizing agent; In all processes, the starch and gluten are dried n high-fibre breads (cf. p. 209)now being using, in the case of gluten, methods such as made in the U.s. A, to maintain texture and freeze-drying which do not denature the gluten 'Vital'gluten, or undenatured gluten, is gluten Vital gluten is also used as a binder and to raise separated from wheat by processes which permit the protein level in meat products, e.g. sausages, the retention of the characteristics of natural breakfast foods, pet foods, dietary foods and gluten, viz. the ability to absorb water and form textured vegetable products(t v.p. an extensible, elastic mass. Commercial glutens are produced in the U. K, Europe, Australia and Canada(McDermott, 1985). In the U. K, some Vital gluten in bread 260,000-270,000 tonnes of wheat were used in In the U. K, domestic bread consumption in 1988/89 for the manufacture of starch and vital 1988 averaged 30.28 oz/person/week. With a gluten, chiefly by the dough(Martin) or batter population of about 57 million, the total domestic processes, which start with four. So far as is bread consumption would have been about 2.5 known, processes such as the pillsbury and Far- million tonnes per year, or about 2.75 million Mar-Co processes that start with wheat grain are tonnes total consumption, allowing for about 10% not currently being used in the U. K consumed non-domestically. with about 45,000 With a yield of about 0.075 t of gluten from t of vital gluten used in bread in the U. K.in each tonne of wheat, the quantity of gluten 1988, the average level of use would have bee produced in the U. K. in 1988/89 would have been about 1.6%. The usual rates of addition are 1.5% some 20,000 t. The demand for vital gluten in for white bread and 4.5% for wholemeal bread the U. K. considerably exceeds this figure, and In the u.s. a. about 70% of all vital wheat
260 TECHNOLOGY OF CEREALS (BP 1,596,742) also resembles the batter process and uses hydrocyclones. A process by Walon (U.S. Pat. No. 4,217,414) uses bacterial alphaamylase to solubilize the starch; the gluten is not denatured and can be separated as ‘vital gluten’. Some modern processes start with wheat but differ from Cato’s method in using a steep-liquor containing 0.03-0.7°/~ of sulphur dioxide to inhibit development of micro-organisms . After draining off the steep liquor, the wet grain is coarsely milled and slurried with water. The bran and germ are separated by screening, and the heavy starch granules separated from the light gluten curd by sedimentation and centrifuging. In the Pitlsbury process (Br. Pat. No. 1,357,669) grain is steeped in an acid medium with application of vacuum or carbon dioxide to remove the air pocket at the base of the crease where microorganisms might develop. In the Far-Mar-Co process (U.S. Pat. No. 4,201,708) wheat is soaked in water and flaked. The flakes are disintegrated and the resulting bran-germ and endosperm particles are hydrated and form a dough-like mass which is tumbled and manipulated in water to separate and recover vital gluten, starch and brangerm components. In all processes, the starch and gluten are dried using, in the case of gluten, methods such as freeze-drying which do not denature the gluten. ‘Vital’ gluten, or undenatured gluten, is gluten separated from wheat by processes which permit the retention of the characteristics of natural gluten, viz. the ability to absorb water and form an extensible, elastic mass. Commercial glutens are produced in the U.K., Europe, Australia and Canada (McDermott, 1985). In the U.K., some 260,000-270,000 tonnes of wheat were used in 1988/89 for the manufacture of starch and vital gluten, chiefly by the dough (Martin) or batter processes, which start with flour. So far as is known, processes such as the Pillsbury and FarMar-Co processes that start with wheat grain are not currently being used in the U.K. With a yield of about 0.075 t of gluten from each tonne of wheat, the quantity of gluten producedin the U.K. in 1988/89 would have been some 20,000 t. The demand for vital gluten in the U.K. considerably exceeds this figure, and is met by imports of gluten, chiefly from the European continent. Imports of gluten in 1988/ 89 amounted to 37,000 t, givinga totalavailability of about 57,000 t. World production of vital gluten in 1986 is reported as 253,000 t (Godon, 1988), of which 130,000 t were produced in western Europe and 54,000 t in the U.S.A., Canada, Mexico and Argentina. uses for vital wheat gluten Vital gluten is used as a protein supplement: - at levels of 0.5-3.0% to improve the texture and raise the protein content of bread, particularly ‘slimming’ bread, crispbread and speciality breads such as Vienna bread and hamburger rolls; - to fortify weak flours, and to permit the use by millers of a wheat grist of lowered strong/ weak wheat ratio (particularly in the EC countries) by raising the protein content of the milled flour; - in starch-reduced high protein breads (cf. p. 209), in which the gluten acts both as a source of protein and as a texturizing agent; - in high-fibre breads (cf. p. 209) now being made in the U.S.A., to maintain texture and volume. Vital gluten is also used as a binder and to raise the protein level in meat products, e.g. sausages, breakfast foods, pet foods, dietary foods and textured vegetable products (t.v.p.). ,,ital gluten ;,, bread In the U.K., domestic bread consumption in 1988 averaged 30.28 oz/person/week. With a population of about 57 million, the total domestic bread consumption would have been about 2.5 million tonnes per year, or about 2.75 million tonnes total consumption, allowing for about 10% consumed non-domestically. With about 45,000 t of vital gluten used in bread in the U.K. in 1988, the average level of use would have been about 1.6%. The usual rates of addition are 1.5% for white bread and 4.5% for wholemeal bread. In the U.S.A., about 70% of all vital wheat
WET MILLING: STARCH AND GLUTEN Cleaning stepit Germ Fibre Dr ying Wet screening extracti gnd grindin 「oxh Evaporating Crystallizing FIG. 12. 1. Maize wet-milling process.(Adapted from Anon. (1958)Food, 27: 291; Con in Indust th edn, Corn Industries Resarch Foundation Inc, New York, and S A. Matz(Ed (1970) Cereal Technology, Avi Publ. Co Inc. Westport, Conn. U.S.A.)
Cleaning Steeping Evaporating concentrates I 1 1 1 Moisture Grinding expelling Moisture expelling * Drying Filtering I I 011 extracting * Germ cake Feed drying and grinding Bleaching 1 Oil - Deodorizing Gluten feed Gluten meal
TECHNOLOGY OF CEREALS luten is used in the manufacture of bread, and more slowly to 43-45%. The steeping softens olls, buns and other yeast-raised products. The the kernel and assists separation of the hull, germ remainder finds uses in breakfast cereals(.g. and fibre from each other. The sulphur dioxide Kellogg s Special K), breadings, batter mixes and in the steep may disrupt the -ss- bonds in pasta products(Magnuson, 1985) the matrix protein (glutelin), facilitating starch protein separation. Gluten flour After steeping, the steep water is drained off Gluten flour is a blend of vital wheat gluten is protein. The protein in the steep water is with wheat flour, standardized to 40% protein recovered by vacuum evaporation, allowed to content in the u.s.a settle out of the water in tanks and dried as 'gluten feed' for animal feeding The water recovered is re-used as steep water or, after aize concentration, as a medium for the culture of Maize is wet-milled to obtain starch, oil, cattle organisms from which antibiotics are obtainee feed(gluten feed, gluten meal, germ cake)and the hydrolysis products of starch, viz. liquid and solid glucose and syrup De-germing The maize, after steeping, is coarsely ground in de-germing mills with the objective of freeing the germ from the remainder of the grain without The sequence of operations in wet milling of breaking or crushing the germ. The machine maize is shown in Fig. 12.1 generally used for this purpose is a Fuss mill,a For safe storage, maize must be dried because bronze-lined chamber housing two upright metal the moisture content at harvest is generally higher plates studded with metal teeth. One plate rotates than the desirable m.c. for storage. Drying at 900 rev/min, the other is stationary. Water and temperature should not exceed 54@C; at higher maize are fed into the machine, which cracks temperatures changes occur in the protein where- open the grain and releases the germ by addition by it swells less during steeping, and tends to of a starch-water suspension, the density of the hold the starch more tenaciously, than in grain ground material is adjusted to 8-10.5 Be*(1. 06- not dried or dried at lower temperatures. In 1.08 sp gr. at this sp. gr. the germs foat while addition, if dried at temperatures above 54C the the grits and hulls settle germ becomes rubbery and tends to sink in the ground maize slurry(whereas the process of germ separation depends on the floating of the germ), Germ separation and the starch tends to retain a high oil content The ground material flows down separating troughs in which the hulls and grits settle, while Steeping the germ overflows. More modern plants use hydrocyclones which require less space and are The cleaned maize is steeped at a temperature less costly to maintain than flotation equipment of about 50oC for 28-48 h in water containing Moreover, the germ separated on hydrocyclones 0. 1-0. 2% of sulphur dioxide. Steeping is carried is cleaner than that separated by flotation out in a series of tanks through which the steep The germ is washed and freed of starch on water is pumped counter-current. The moisture reels, de-watered in squeeze presses and dried on ontent of the grain increases rapidly to 35-40%, rotary steam driers. The dry germ is cooked by Baume Scale: a hydrometer scale on which 0 represents the sp, gr. of water at 12. 5.C and 10 the sp. gr. of a 10% solution of NaCl at 12.5 C, It is also known as the lunge
262 TECHNOLOGY OF CEREALS gluten is used in the manufacture of bread, and more slowly to 4345%. The steeping softens rolls, buns and other yeast-raised products. The the kernel and assists separation of the hull, germ remainder finds uses in breakfast cereals (e.g. and fibre from each other. The sulphur dioxide Kellogg's Special K), breadings, batter mixes and in the steep may disrupt the -SS- bonds in pasta products (Magnuson, 1985). the matrix protein (glutelin), facilitating starch/ protein separation. After steeping, the steep water is drained off. It contains about 6% of solids, of which 3545% Gluten flour Gluten flour is a blend of vital wheat gluten is protein. The protein in the steep water is with wheat flour, standardized to 40% protein recovered by vacuum evaporation, allowed to content in the U.S.A. settle out of the water in tanks, and dried as 'gluten feed' for animal feeding. The water recovered is re-used as steep water or, after Maize concentration, as a medium for the culture of Maize is wet-milled to obtain starch, oil, cattle organisms from which antibiotics are obtained. feed (gluten feed, gluten meal, germ cake) and the hydrolysis products of starch, viz. liquid and De-germing solid glucose and syrup. The maize, after steeping, is coarsely ground in de-germing mills with the objective of freeing the germ from the remainder of the grain without Operations The sequence of operations in wet milling of breaking or crushing the germ. The machine maize is shown in Fig. 12.1. generally used for this purpose is a Fuss mill, a For safe storage, maize must be dried because bronze-lined chamber housing two upright metal the moisture content at harvest is generally higher plates studded with metal teeth. One plate rotates than the desirable m.c. for storage. Drying at 900 rev/min, the other is stationary. Water and temperature should not exceed 54°C; at higher maize are fed into the machine, which cracks temperatures changes occur in the protein where- open the grain and releases the germ. By addition by it swells less during steeping, and tends to of a starch-water suspension, the density of the hold the starch more tenaciously, than in grain ground material is adjusted to 8-10.5" BC* (1.06- not dried, or dried at lower temperatures. In 1.08 sp.gr.): at this sp.gr. the germs float while addition, if dried at temperatures above 54°C the the grits and hulls settle. germ becomes rubbery and tends to sink in the ground maize slurry (whereas the process of germ Germ separation separation depends on the floating of the germ), and the starch tends to retain a high oil content. The ground material flows down separating troughs in which the hulls and grits settle, while the germ overflows. More modern plants use hydrocyclones which require less space and are Steeping The cleaned maize is steeped at a temperature less costly to maintain than flotation equipment. of about 50°C for 2848 h in water containing Moreover, the germ separated on hydrocyclones 0.1-0.2°/~ of sulphur dioxide. Steeping is carried is cleaner than that separated by flotation. out in a series of tanks through which the steep The germ is washed and freed of starch on water is pumped counter-current. The moisture reels, de-watered in squeeze presses and dried on content of the grain increases rapidly to 35-40%, rotary steam driers. The dry germ is cooked by * Baume Scale: a hydrometer scale on which 0" represents the sp. gr. of water at 12.5"C and 10" the sp. gr. of a 10% solution of NaCl at 12.5"C. It is also known as the Lunge Scale
ET MILLING: STARCH AND GLUTEN steam, and the oil extracted by hydraulic rotary or fash driers. Further fractionation to or by solvent extraction. The germ oil is so obtain the alcohol-soluble zein, which comprises filtered and stored The extracted germ about 50% of the maize gluten, by solvent extrac- used for cattle feed tion and precipitation may be carried out. Zein nds a use as a water-protective coating material for nuts and confectionery and as a binder for pharmaceuticals The de-germed underflow from the germ separ- A combined dry-wet milling process for refin ator is strained off from the liquor and finely ing maize has been described (U.S. Pat. N ground on impact mills, such as an entoleter, or 4, 181, 748; 1980) in which the maize is dry- milled attrition mills, such as the Bauer mill. After this to provide endosperm, germ, hull and cleaning process, the starch and protein of the endosperm fractions. The endosperm fraction is wet-milled are in a very finely divided state and remain inin two steps which respectively precede and suspension. The hulls and fibre, which are not follow an impact milling step. The principal reduced so much in particle size, can then be products are prime maize starch, corn oil and an separated from the protein and starch on reels animal feed product fitted with 18-20 mesh screens. Fine fibres which interfere with the subsequent separation of starch from protein, are removed on gyrating shaker Maize wet-milling in the U.s.A fitted with fine nylon cloth The processing of maize into wet-processed products has increased greatly in the U.S.A. in Separation of starch from protein recent years. In 1960/61, 3.94 Mt were processed rocessed products, but by 1984/85 the In the raw grain the starch granules are em- figure had increased to 20.7 Mt, representing bedded in a protein network which swells during 10.6% of the entire maize harvest in 1984 of 195 teeping stage and tends to form tiny globules Mt. Of this, 7.9 Mt were used to produce high of hydrated protein(Radley, 1951-1952). Disper- fructose corn syrup(HFCS),4.8 Mt for glucose sion of the protein, which frees the starch, is and dextrose, 3. 8 Mt for starch and 4.3 Mt for accelerated by the sulphur dioxide in the steep alcohol (Livesay, 1985). water The growth of the industry in the 1970s The effect of the sulphur dioxide, according to followed the development of a process to convert Cox et al.(1944), is due to its reducing, not to starch into high-fructose corn syrup(HFCS). The its acidic, property. The sulphur dioxide also has sweetness of hfcs allows it to be used as a a sterlizing effect, preventing growth of micro- substitute for sucrose in soft drinks and other organisms in the steep processed foods The suspension of starch and protein from the wet screening is adjusted to a density of 6 Be Products of wet-milling filters, and the starch separated from the protein The wet-milling of maize yields about 66% of in continuous high-speed centrifuges such as the starch, 4% of oil, and 30% of animal feed Merco centrifugal separator comprising about 24% of gluten feed of 21% The starch is re-centrifuged in hydrocyclones protein content(made up of about 13% of fibre to remove residual protein and is then filtered 7% of steep water solubles and 4% of germ and dried to 10-12% m.c. in kilns or ovens, or residue), plus about 5.7% of gluten meal of 60% in tunnel or fash driers. The moisture content is protein content. The composition of products further reduced by vacuum drying to 5-7%m c. from the wet-milling of maize is shown in table in the u.s.A., or to 1-2%m c. in Britain. 12. 1(Wright, in Watson and Ramstad, 1987 The separated protein is filtered and dried in most of the starch is further processed to make
WET MILLING: STARCH AND GLUTEN 263 steam, and the oil extracted by hydraulic presses rotary or flash driers. Further fractionation to or by solvent extraction. The germ oil is screened, obtain the alcohol-soluble zein, which comprises filtered and stored. The extracted germ cake is about 50% of the maize gluten, by solvent extracused for cattle feed. tion and precipitation may be carried out. Zein finds a use as a water-protective coating material for nuts and confectionery and as a binder for pharmaceuticals. Milling The de-germed underflow from the germ separ- A combined dry-wet milling process for refinator is strained off from the liquor and finely ing maize has been described (U.S. Pat. No. ground on impact mills, such as an entoleter, or 4,181,748; 1980) in which the maize is dry-milled attrition mills, such as the Bauer mill. After this to provide endosperm, germ, hull and cleaning process, the starch and protein of the endosperm fractions. The endosperm fraction is wet-milled are in a very finely divided state and remain in in two steps which respectively precede and suspension. The hulls and fibre, which are not follow an impact milling step. The principal reduced so much in particle size, can then be products are prime maize starch, corn oil and an separated from the protein and starch on reels animal feed product. fitted with 18-20 mesh screens. Fine fibres, which Maize wet-milling in the U.S.A interfere with the subsequent separation of starch from protein, are removed on gyrating shakers fitted with he nylon cloth. The processing of maize into wet-processed products has increased greatly in the U.S.A. in recent years. In 1960/61,3.94 Mt were processed into wet-processed products, but by 1984/85 the Separation of starch from protein In the raw grain the starch granules are em- figure had increased to 20.7 Mt, representing bedded in a protein network which swells during 10.6% of the entire maize harvest in 1984 of 195 the steeping stage and tends to form tiny globules Mt. Of this, 7.9 Mt were used to produce highof hydrated protein (Radley, 195 1-1952). Disper- fructose corn syrup (HFCS), 4.8 Mt for glucose sion of the protein, which frees the starch, is and dextrose, 3.8 Mt for starch and 4.3 Mt for accelerated by the sulphur dioxide in the steep alcohol (Livesay, 1985). water. The growth of the industry in the 1970s The effect of the sulphur dioxide, according to followed the development of a process to convert Cox et al. (1944), is due to its reducing, not to starch into high-fructose corn syrup (HFCS). The its acidic, property. The sulphur dioxide also has sweetness of HFCS allows it to be used as a a sterlizing effect, preventing growth of micro- substitute for sucrose in soft drinks and other organisms in the steep. processed foods. The suspension of starch and protein from the Products of wet-milling wet screening is adjusted to a density of 6"BC (1.04 sp.gr) by de-watering over Grinco or string filters, and the starch separated from the protein The wet-milling of maize yields about 66% of in continuous high-speed centrifuges such as the starch, 4% of oil, and 30% of animal feed, Merco centrifugal separator. comprising about 24% of gluten feed of 21% The starch is re-centrifuged in hydrocyclones protein content (made up of about 13% of fibre, to remove residual protein and is then filtered 7% of steep water solubles and 4% of germ and dried to 10-12O/0 m.c. in kilns or ovens, or residue), plus about 5.7% of gluten meal of 60% in tunnel or flash driers. The moisture content is protein content. The composition of products further reduced by vacuum drying to 5-7% m.c. from the wet-milling of maize is shown in Table in the U.S.A., or to 1-2% m.c. in Britain. 12.1 (Wright, in Watson and Ramstad, 1987). The separated protein is filtered and dried in Most of the starch is further processed to make
TECHNOLOGY OF CEREALS Composition of Maize Wet-Milled Products* Fibre Protein NDF+ h NFES Starch Corn gluten feed 22 0.1 low 62.0 2.5 Germ meal Steep liq 23.0 19.2 TNX6.Anon 1982;Wright, KN,1987. 5 Nitrogen-free extract modified starch, sweeteners and alcohol (Long, modified starch for particular purposes, or by 1982) enzymic hydrolysis, to yield maltose, which can Other uses for corn gluten include cork-binding be further treated to make dextrose(D-glucose) agent, additive for printing dyes, and in pharma- regular corn syrup, high-fructose corn syrup ceuticals. It is perhaps misleading that the protein (HFCS), and malto-dextrins product obtained from maize should be called In modifying starch, the objectives are to alter 'gluten,, because maize gluten in no way resembles the physical and chemical characteristics in order the vital gluten that is obtained from wheat(cf. to improve functional characteristics, by oxida tion, esterification, etherification, hydrolysis Ethanol can be made by yeast fermentation of or dextrinization. The methods used are acid naize starch, and has articular advantage thinning, bleaching or oxidation, cross-linking because the yeast can be re-cycled. About 85% substitution or derivatization, instantizing of the ethanol produced from maize starch is In acid thinning, or conversion, the glucosidic blended with gasoline, in which it acts as an linkages joining the anhydroglucose units are octane enhancer for unleaded fuel (May, 1987). broken, with the addition of water. The resulting An edible film has been made from maize starch thinning reduces the viscosity of the starch paste mylose obtained from high-amylose maize(cf. and allows such starches to be cooked at higher p. 99). Suggested uses for the film include the concentrations than the native starch. In a wet packing of gravies, sauces and coffee process of conversion, the starch is treated wit The starch obtained from the milling of waxy 1-3% of hydrochloric or sulphuric acids at about maize(cf. p. 99), called'amioca', consists largely 50oC, then neutralized and the starch filtered off of amylopectin. Amioca paste is non-gelling and Acid-thinned starches are used in confectionery has clear, fluid adhesive properties products, particularly starch jelly candies(Moore Heated and dried maize starch/water slurries et aL. 1984). Non-food uses include paper -sizing yield pregelatinized starch, known as 'instant calendering, coating applications(Sanford and starch, as it thickens upon addition of cold water. Baird, 1983; Bramel, 1986). In a dry process onversion, in which dry starch powder is roasted with limited moisture and a trace of hydrochloric Uses for wet-milled maize products acid, the main product is dextrins, used for Uses for maize starch include paper manufac- adhesives and other non-food pur ture, textiles, adhesives and packaged foods, and In bleaching, or oxidation, aqueous slurries as the starting material for further processing by of starch are treated with hydrogen peroxide chemical treatment, to make various kinds of peracetic acid, ammonium persulphate, sodium
264 TECHNOLOGY OF CEREALS TABLE 12.1 Composition of Maize Wet-Milled Products* Fibre Moisture Proteint Fat Crude NDF* Ash NFES Starch (Oh) (%) (%) (Yo) (”1 (%) (Yo) (Oh) Maize 15.5 8.0 3.6 2.5 8.0 1.2 69.2 60.6 Corn gluten feed 9.0 22.6 2.3 7.9 25.4 7.8 50.1 low Corn meal 10.0 62.0 2.5 1.2 4.1 1.8 22.5 low Germ meal 10.0 22.6 1.9 9.5 41.6 3.8 52.2 low Steep liquor 50.0 23.0 0 0 0 7.3 19.2 low * Sources: Anon. 1982; Wright, K. N., 1987. t N X 6.25. $ Neutral detergent fibre. $ Nitrogen-free extract. modified starch, sweeteners and alcohol (Long, modified starch for particular purposes, or by 1982). enzymic hydrolysis, to yield maltose, which can Other uses for corn gluten include cork-binding be further treated to make dextrose (D-glucose), agent, additive for printing dyes, and in pharma- regular corn syrup, high-fructose corn syrup ceuticals. It is perhaps misleading that the protein (HFCS), and malto-dextrins. product obtained from maize should be called In modifying starch, the objectives are to alter ‘gluten’, because maize gluten in no way resembles the physical and chemical characteristics in order the vital gluten that is obtained from wheat (cf. to improve functional characteristics, by oxidap. 260) tion, esterification, etherification, hydrolysis Ethanol can be made by yeast fermentation of or dextrinization. The methods used are acid maize starch, and has a particular advantage thinning, bleaching or oxidation, cross-linking, because the yeast can be re-cycled. About 85% substitution or derivatization, instantizing. of the ethanol produced from maize starch is In acid thinning, or conversion, the glucosidic blended with gasoline, in which it acts as an linkages joining the anhydroglucose units are octane enhancer for unleaded fuel (May, 1987). broken, with the addition of water. The resulting An edible film has been made from maize starch thinning reduces the viscosity of the starch paste, amylose obtained from high-amylose maize (cf. and allows such starches to be cooked at higher p. 99). Suggested uses for the film include the concentrations than the native starch. In a wet packing of gravies, sauces and coffee. process of conversion, the starch is treated with The starch obtained from the milling of waxy 1-3% of hydrochloric or sulphuric acids at about maize (cf. p. 99), called ‘amioca’, consists largely 5OoC, then neutralized and the starch filtered off. of amylopectin. Amioca paste is non-gelling and Acid-thinned starches are used in confectionery has clear, fluid adhesive properties. products, particularly starch jelly candies (Moore Heated and dried maize starch/water slurries et al. , 1984). Non-food uses include paper-sizing, yield pregelatinized starch, known as ‘instant calendering, coating applications (Sanford and starch’, as it thickens upon addition of cold water. Baird, 1983; Bramel, 1986). In a dry process conversion, in which dry starch powder is roasted with limited moisture and a trace of hydrochloric acid, the main product is dextrins, used for Uses for wet-milled maize products Uses for maize starch include paper manufac- adhesives and other non-food purposes. ture, textiles, adhesives and packaged foods, and In bleaching, or oxidation, aqueous slurries as the starting material for further processing by of starch are treated with hydrogen peroxide, chemical treatment, to make various kinds of peracetic acid, ammonium persulphate , sodium
VET MILLING: STARCH AND GLUTEN 265 hypochlorite, sodium chlorite, or potassium per- high viscosity, cohesiveness, and stability to manganate and then neutralized with sodium retrogradation. They are used as emulsifiers in bisulphite. The xanthophyll and other pigments foods and for many non-food uses(Orthoefer, are bleached, thereby whitening the starch which 1987) then becomes suitable for use as a fluidizing agent Dextrose is made by enzymic hydrolysis of in,e.g. confectioners'sugar. Starch, in aqueous starch and crystallization; HFCs by partial slurry, can be oxidized with about 5.5%(on d wt. enzymic isomerization of dextrose hydrolysates of chlorine as sodium hypochlorite. Hydroxyl regular com syrup and malto dextrins by partial COH)groups are oxidized, forming carboxyl hydrolysis of corn starch with acid, acid -C=O)or carbonyl (OH-C=O) groups, with enzyme, or enzyme only(Hebeda, 1987) cleavage of glucosidic linkages. The bulkiness of In making dextrose, thermostable bacterial the -C=o groups reduces the tendency of the alpha-amylase from B subtilis or B licheniformis starch to retrograde. Bleached starch finds uses is used for liquefying starch to 10-15 DE n batter and breading mixes in fried foods (dextrose equivalent followed by saccharification Mooreet aL., 1984), to improve adhesion Oxidized with glucoamylase from Aspergillus niger to starch finds non-food uses in paper sizing, due 95-96% dextrose(dry basis). The glucoamylase to its excellent film-forming and binding properties releases dextrose step-wise from the non-reducing (Bramel, 1986 end, cleaving both alpha-l→4 and alpha-l→6 Cross- linking improves the strength of swollen bonds. The hydrolysate is clarified, refined, and ranules, preventing rupture. Granular starch is processed to crystalline dextrose, liquid dextrose cross-linked by treatment with adipic acid and high-dextrose corn syrup or HFCS feed acetic anhydride, forming distarch adipate, or Glucose and dextrose are used in beer, cider with phosphorus oxychloride, forming distarch soft drinks, pharmaceuticals, confectionery, baking phosphate. The slurry is neutralized, filtered, and jams washed and dried. The viscosity of cross-linked The refined dextrose hydrolysate can be treated starch is higher than that of native starch with immobilized glucose isomerase of bacterial Derivatization or substitution consists of the origin. This enzyme catalyzes the isomerization introduction of substitution groups on starch by of dextrose to D-fructose. a product containing acting the hydroxyl groups (-Oh) with mono- 90% of HFCS may be obtained by chromatographic functional reagents such as acetate, succinate, separation octenyl succinate, phosphate or hydroxypropyl Dextrose and HFCS are important sweeteners groups. Derivatization retards the association dextrose has 65-76% of the sweetness of sucrose of gelatinized amylose chains, improves clarity, while HFCS is 1. 8 times as sweet as sucrose and reduces gelling and improves water-holding 2. 4 times as sweet as dextrose (Orthoefer, 1987). Substitution may be combined The use of maize in the U. S A. to produce with cross-linking to yield thickeners with par- HFCS increased from 0. 25 Mt in 1971/72 to 8.1 ticular processing characteristics(Moore et al., Mt in 1985/86. The explosive growth of HFCS 1984). Starch esters - acetates, phosphates, production between 1972 and 1985 was due to octenyl succinates -find uses as thickeners in the technical breakthrough in the process for foods, e.g. fruit pies, gravies, salad dressings, making HFCS, the high cost of sugar in the filled cakes, because they withstand refrigeration U.S.A., and the availability of abundant stocks and freeze/ thaw cycles well. Non-food uses include of relatively low-cost maize in the U.SA(May warp sizing of textiles, surface sizing of paper, 1987). By 1991, HFCS had become the largest and gummed tape adhesives( sanford and Baird, product category of the U. s. corn wet-milling 1983; Bramel,1986) industry, accounting for more than one-third Phosphate mono-esters of starch, made by of the industrial grind. When reporting world roasting starch with orthophosphates at pH 5- production, however, the U.S. Dept. Agric. now 6.5 for 0.5-6 h at 120%-160oC, have good clarity, refers to HFSS(high-frucose starch syrup) rather
WET MILLING: STARCH AND GLUTEN 265 hypochlorite, sodium chlorite, or potassium per- high viscosity, cohesiveness, and stability to manganate and then neutralized with sodium retrogradation. They are used as emulsifiers in bisulphite. The xanthophyll and other pigments foods and for many non-food uses (Orthoefer, are bleached, thereby whitening the starch which 1987). then becomes suitable for use as a fluidizing agent Dextrose is made by enzymic hydrolysis of in, e.g. confectioners' sugar. Starch, in aqueous starch and crystallization; HFCS by partial slurry, can be oxidized with about 5.5% (on d.wt.) enzymic isomerization of dextrose hydrolysates; of chlorine as sodium hypochlorite. Hydroxyl regular corn syrup and malto-dextrins by partial (-OH) groups are oxidized, forming carboxyl hydrolysis of corn starch with acid, acid + (-C=O) or carbonyl (OH-C=O) groups, with enzyme, or enzyme only (Hebeda, 1987). cleavage of glucosidic linkages. The bulkiness of In making dextrose, thermostable bacterial the -C=O groups reduces the tendency of the alpha-amylase from B. subtilis or B. lichenifomis starch to retrograde. Bleached starch finds uses is used for liquefying starch to 10-15 D.E. in batter and breading mixes in fried foods (dextrose equivalent) followed by saccharification (Moore et al. , 1984), to improve adhesion. Oxidized with glucoamylase from Aspergillus niger to starch finds non-food uses in paper sizing, due 95-96% dextrose (dry basis). The glucoamylase to its excellent film-forming and binding properties releases dextrose step-wise from the non-reducing (Bramel, 1986). end, cleaving both alpha-1-4 and alpha-1-6 Cross-linking improves the strength of swollen bonds. The hydrolysate is clarified, refined, and granules, preventing rupture. Granular starch is processed to crystalline dextrose, liquid dextrose, cross-linked by treatment with adipic acid and high-dextrose corn syrup or HFCS feed. acetic anhydride, forming distarch adipate, or Glucose and dextrose are used in beer, cider, with phosphorus oxychloride, forming distarch soft drinks, pharmaceuticals, confectionery, baking phosphate. The slurry is neutralized, filtered, and jams. washed and dried. The viscosity of cross-linked The refined dextrose hydrolysate can be treated starch is higher than that of native starch. with immobilized glucose isomerase of bacterial Derivatization or substitution consists of the origin. This enzyme catalyzes the isomerization introduction of substitution groups on starch by of dextrose to D-fructose. A product containing reacting the hydroxyl groups (-OH) with mono- 90% of HFCS may be obtained by chromatographic functional reagents such as acetate, succinate, separation. octenyl succinate, phosphate or hydroxypropyl Dextrose and HFCS are important sweeteners: groups. Derivatization retards the association dextrose has 65-76% of the sweetness of sucrose, of gelatinized amylose chains, improves clarity, while HFCS is 1.8 times as sweet as sucrose and reduces gelling and improves water-holding 2.4 times as sweet as dextrose. (Orthoefer, 1987). Substitution may be combined The use of maize in the U.S.A. to produce with cross-linking to yield thickeners with par- HFCS increased from 0.25 Mt in 1971/72 to 8.1 ticular processing characteristics (Moore et al., Mt in 1985/86. The explosive growth of HFCS 1984). Starch esters - acetates, phosphates, production between 1972 and 1985 was due to octenyl succinates - find uses as thickeners in the technical breakthrough in the process for foods, e.g. fruit pies, gravies, salad dressings, making HFCS, the high cost of sugar in the fdled cakes, because they withstand refrigeration U.S.A., and the availability of abundant stocks and freeze/thaw cycles well. Non-food uses include of relatively low-cost maize in the U.S.A. (May, warp sizing of textiles, surface sizing of paper, 1987). By 1991, HFCS had become the largest and gummed tape adhesives (Sanford and Baird, product category of the U.S. corn wet-milling 1983; Bramel, 1986). industry, accounting for more than one-third Phosphate mono-esters of starch, made by of the industrial grind. When reporting world roasting starch with orthophosphates at pH 5- production, however, the U.S. Dept. Agric. now 6.5 for 0.5-6 h at 12O0-16O"C, have good clarity, refers to HFSS (high-frucose starch syrup) rather
266 TECHNOLOGY OF CEREALS than HFCS, acknowledging that alternative starch The de-germed endosperm and sources, such as wheat and potatoes, can be wet-screened on a nylon cloth witl iverted to fructose-rich syrups using enzymic apertures, through which the free 品买 conversions, refining and separation technologies protein pass. The residue, mostly horny endo- which are currently applied in the U.S.A. to sperm, is re-ground in an entoleter, impact mill starch separated from maize. On this basis, world or other suitable mill, to release more starch, and production of HFSS increased from 0.65 Mt in is again screened 1975 to 7.1 Mt in 1988. Production of hfss in the U.S. A similarly increased from 0.48 Mt in De-watering 975 to 5.3 Mt in 1988. Over this period, HFSS production as a percentage of total world sugar The washed tailings of the screen are de plus HFSS consumption increased from 0. 9% in watered to about 60% m.c. by continuous screw 1975to6.3%in1988( Meyer,1991) presses. The product is known as 'fibre. the fibre, blended with concentrated steep water Sorghum (containing solubles leached out during the steep ing)and spent germ cake, is dried in a continuous The methods used for the wet-milling of fash drier to yield ' milo gluten feed orghum closely resemble those described for maize(cf. p. 262), but the process is more difficult with sorghum than with maize. The problems are Starch/protein separation associated with the small size and spherical shap The de- fibred starch granules and protein f the sorghum kernel, the large proportion of particles are separated in a merco continuous horny endosperm, and the dense high-protein centrifuge by a process of differential sedimenta peripheral endosperm layer Varieties with dark- tion; the starch granules, with a density of 1.5 coloured outer layers are not satisfactory for wet- settle out of an aqueous slurry at a faster rate milling because some of the colour leaches out than the protein particles, density 1. 1. The starch nd stains the starch slurry is dried on a Proctor and schwartz moving belt tunnel drier, or by flash drying Steeping The cleaned sorghum is first steeped in water Sorghum gluten (1.61-1. 1/kg) for 40-50 h in a counter-current The gluten'(protein) is concentrated, filtered process. Part of the water is charged with 0. 1- and fiash dried. The protein content of milo 0. 16%of sulphur dioxide, which is absorbed by gluten is 65-70% on dry basis. a blend of milo the grain and weakens the protein matrix in which the starch granules are embedded TABLE 12.2 milling of Sorghum*(dy basler De-germing he steeped grain, in slurry form, is ground Product If protein Fat Starch in an attrition mill. The mill has knobbed plates, Ge 118 38.818.6 one static, one rotating at about 1700 rev. min. fibre 176 The milling detaches the germ and liberates about Tailings 39.2 half of the starch from the endosperm. The germ, squeegee 10.6 which contains 4045% of oil, floats to the surface St of the slurry, and is removed from the heavier Solubles 43.7 endosperm and pericarp in a continuous liquid Source: Freeman and Bocan (1973) t percentage of dry substance in whole grain
266 TECHNOLOGY OF CEREALS than HFCS, acknowledging that alternative starch sources, such as wheat and potatoes, can be converted to fructose-rich syrups using enzymic conversions, refining and separation technologies which are currently applied in the U.S.A. to starch separated from maize. On this basis, world production of HFSS increased from 0.65 Mt in 1975 to 7.1 Mt in 1988. Production of HFSS in the U.S.A. similarly increased from 0.48 Mt in 1975 to 5.3 Mt in 1988. Over this period, HFSS production as a percentage of total world sugar plus HFSS consumption increased from 0.9% in 1975 to 6.3% in 1988 (Meyer, 1991). The de-germed endosperm and pericarp are wet-screened on a nylon cloth with 70-75 ym apertures, through which the free starch and protein pass. The residue, mostly horny endosperm, is re-ground in an entoleter, impact mill, or other suitable mill, to release more starch, and is again screened. De-watering The washed tailings of the screen are dewatered to about 60% m.c. by continuous screw presses. The product is known as ‘fibre’. The fibre, blended with concentrated steep water (containing solubles leached out during the steeping) and spent germ cake, is dried in a continuous Sorghum sorghum closely resemble those described for Starch/protein separation maize (cf. p. 262), but the process is more difficult with sorghum than with maize. The problems are associated with the small size and spherical shape The de-fibred starch granules and protein of the sorghum kernel, the large proportion of particles are separated in a Merco continuous horny endosperm, and the dense high-protein centrifuge by a process of differential sedimentaperipheral endosperm layer. Varieties with dark- tion; the starch granules, with a density of 1.5, coloured outer layers are not satisfactory for wet- settle out of an aqueous slurry at a faster rate milling because some of the colour leaches out than the protein particles, density 1.1. The starch and stains the starch. slurry is dried on a Proctor and Schwartz movingbelt tunnel drier, or by flash drying. Steeping Sorghum ’gluten’ The cleaned sorghum is first steeped in water (1.61-1.96 l/kg) for 40-50 h in a counter-current The ‘gluten’ (protein) is concentrated, filtered process. Part of the water is charged with 0.1- and flash dried. The protein content of milo 0.16% of sulphur dioxide, which is absorbed by gluten is 65-70% on dry basis. A blend of milo the grain and weakens the protein matrix in which the starch granules are embedded. TABLE 12.2 Composition of Products From Wet Milling of Sorghum* (dry basis) De-gerrning Product Yieldt Protein Fat Starch The methods used for the wet-milling of flash drier to yield ‘milo gluten feed’. The steeped grain, in slurry form, is ground (“h) (Yo) (Yo) (OK) in an attrition mill. The mill has knobbed plates, Germ 6.2 11.8 38.8 18.6 one static, one rotating at about 1700 rev./min. Fibre 7.4 17.6 2.4 30.6 The milling detaches the germ and liberates about Tailings 0.8 39.2 - 25.3 Gluten 10.6 46.7 5.1 42.8 half of the starch from the endosperm. The germ, Squeegee 1.2 14.0 0.6 81.6 which contains 4045% of oil, floats to the surface Starch 63.2 0.4 - 67.3 endosperm and pericarp in a continuous liquid cyclone. of the slurry, and is removed from the heavier Solubles 6.6 43.7 - - * Source: Freeman and Bocan (1973). t Percentage of dry substance in whole grain
WET MILLING: STARCH AND GLUTEN 267 gluten with milo gluten feed, reducing the protein content to 45%d b, is known as'milo gluten meal filling of Pearl (dry basis) Product Yield Fat Starch %)(%) thum 10,4 11.8 6.013.5 9.044.0 12.2. 0.875.5 0.1575 Solubles 16.8 6.1 Millet irl millet as raw t Percentage of dry substance in whole grain naterial for a wet-milling process has been invest igated(Freeman and Bocan, 1973). The small residual grain, is virtually fat-free, and is thus millet grains were much more difficult to de-germ much more stable than that separated in the than were sorghum or maize, although the poten- conventional dry milling process tial yield of oil from millet exceeded those from In the sEM process(U. S. Pat. No. 3, 261, 690) the other cereals. Separation of protein from rice oil is applied to brown rice(de-hulled rough starch was also more difficult with millet than rice) in controlled amounts, and softening of the from sorghum or maize, and the products of bran is accomplished The bran is removed by separation were somewhat less pure than those milling machines of modified conventional design obtained from the other cereals. The starch from in the presence of an oil solvent-rice oilhexane millet resembled that from sorghum and maize miscella. The miscella acts as a washing or rinsing in most respects, but the granule size was slightly medium to aid in flushing bran away from the smaller(cf. p. 57), and the starch had a slightly endosperm, and as a conveying medium for lower tendency to retrograde continuously transporting detached bran from The composition of products from the wet- rice. The miscella lubricates the grains, prevents milling of pearl millet is shown in Table 12. 3. rise of temperature, and reduces breakage The de-branned rice is screened, rinsed and drained, and the solvent removed in two stages flush Solvent extraction milling (sEM) evaporate the bulk of the hexane remaining in the rice, and the rice is subjected to a flow of This is a process applied to rice in order to inert gas which removes the last traces of the obtain de-branned rice grain, and also rice bran solvent nd rice oil as separate products. The SEM The bran/oil miscella slurry is pumped to process cannot strictly be described either as a vessels in which the bran settles, and is then dry-milling or as a wet-milling process, although separated centrifugally, while being rinsed with it involves stages which could be included in each hexane to remove the oil. The last traces of solvent of these categories are removed from the bran by flash de-solventizing The customary method for milling rice uses and the bran is coole abrasion of the rice grain in a dry condition The oil/hexane miscella from the bran-settling remove bran from the endosperm (cf p 160). In vessels is pumped to conventional solvent re- he sem process(also called X-M)the bran layers covery plant, where the hexane is stripped from are first softened and then 'wet-milled in thethe oil presence of a rice oil solution. The separated bran SEM(X-M)plants are operated at abbeyville has a higher protein content than that of the Louisiana, U.S. A. and in many asian countries
WET MILLING: STARCH AND GLUTEN 2 67 gluten with milo gluten feed, reducing the protein content to 45% d.b., is known as 'milo gluten meal'. Products of sorghum wet milling The yield and composition of products from the wet milling of sorghum are shown in Table TABLE 12.3 Composition of Products From Wet Milling of Pearl Millet* (dry basis) Product Yieldt Protein Fat Starch ("/.) ("1 (Yo) (Oh) Germ 7.5 10.4 45.6 10.4 Fibre 7.3 11.8 6.0 13.5 Tailings 1.5 34.1 1.9 34.2 Gluten 12.1 37.8 9.0 44.0 12.2. Squeegee 4.1 17.7 0.8 75.5 Starch 49.3 0.7 0.1 57.5 Solubles 16.8 46.1 - - * Source: Freeman and Bocan (1973). t Percentage of dry substance in whole grain. Millet The possibility of using pearl millet as raw material for a wet-milling process has been investigated (Freeman and Bocan, 1973). The small millet grains were much more difficult to de-germ than were sorghum or maize, although the potential yield of oil from millet exceeded those from the other cereals. Separation of protein from starch was also more difficult with millet than from sorghum or maize, and the products of separation were somewhat less pure than those obtained from the other cereals. The starch from millet resembled that from sorghum and maize in most respects, but the granule size was slightly smaller (cf. p. 57), and the starch had a slightly lower tendency to retrograde. The composition of products from the wetmilling of pearl millet is shown in Table 12.3. Rice residual grain, is virtually fat-free, and is thus much more stable than that separated in the conventional dry milling process. In the SEM process (U.S. Pat. No. 3,261,690), rice oil is applied to brown rice (de-hulled rough rice) in controlled amounts, and softening of the bran is accomplished. The bran is removed by milling machines of modified conventional design in the presence of an oil solvent - rice oivhexane miscella. The miscella acts as a washing or rinsing medium to aid in flushing bran away from the endosperm, and as a conveying medium for continuously transporting detached bran from rice. The miscella lubricates the grains, prevents rise of temperature, and reduces breakage. The de-branned rice is screened, rinsed and drained, and the solvent removed in two stages. Super-heated hexane vapour is used to flushevaporate the bulk of the hexane remaining in the rice, and the rice is subjected to a flow of inert gas which removes the last traces of the solvent. The bradoil miscella slurry is pumped to vessels in which the bran settles, and is then separated centrifugally, while being rinsed with hexane to remove the oil. The last traces of solvent are removed from the bran by flash de-solventking, and the bran is cooled. The oiuhexane miscella from the bran-settling vessels is pumped to conventional solvent recovery plant, where the hexane is stripped from the oil. SEM (X-M) plants are operated at Abbeyville, Louisiana, U.S.A. and in many Asian countries. Solvent extraction milling (SEM) This is a process applied to rice in order to obtain de-branned rice grain, and also rice bran and rice oil as separate products. The SEM process cannot strictly be described either as a dry-milling or as a wet-milling process, although it involves stages which could be included in each of these categories. The customary method for milling rice uses abrasion of the rice grain in a dry condition to remove bran from the endosperm (cf. p. 160). In the SEM process (also called X-M) the bran layers are first softened and then 'wet-milled' in the presence of a rice oil solution. The separated bran has a higher protein content than that of the
268 TECHNOLOGY OF CEREALS Advantages of the SEM process over the McDERMOTT, E E (1985)The properties of commercial ional milling process are glutens Cereals Fds wld, 30(2): 169-171 MEYER, P. A(1991)High fructose starch syrup production 1. An increase of up to 10% on head rice yield nd technology growth to continue. 2. a decrease in the fat content of the rice, which MooRE, C.O., TUSCHHOFF, J. V, HASTINGs, C. w and improves its storage life SCHANFELT, R. V (1984) Applications of starches in foods. 3. An increase in stability of the bran product In: Starch: chemistry and technology, pp 579-592 2nd edn 4. A yield of 2kg of rice oil from each 100kg of E.F.(Eds). Academic Press, Orlando, FL, U.S.A unmilled rice(2% yield on rice wt ORTHOEFER, F. T (1987)Corn starch modification and uses 479499 WATSON breakfast cereals, baby foods, baked goods. The Chem., St Paul, MN, USd Eds). Amer.AssocCereal has potential application in s. A, and ramstad p.e oil has edible and industrial applications, and is ADLEY,J. A.(1951-2) The manufac a rich source of a wax with properties similar to SANFORD, P. A. and BAIRD, J.(1983)Industrial utilization hose of myricyl cerotate, or carnauba wax. Other of polysaccharides. Pp. 41l-490 in: The polysacchardes applications are in margarine, cosmetics, paints York, U.S.A Edwards, 1967) WRIGHt, K. N.(1987) Nutritional 447-478 WATSON and RAMSTAD, References P. E.(Eds). Amer. Assoc Cereal St Paul, MN ANON. (1982)Corn Wet-Milled Feed Products, 2nd BRAMEL, G. F(1986) d starches for surface coatings Further Reading Cox, M.J., MACMASTERs, M.M. and HIlBERT, G E(1944) ANDRES, C.(1980) Corn- a most versatile grain. Fd the sulphurous steep in corn wet milling. Cereal Chem.,21:447 EDWARDS, J. A. (1967) Solvent extraction milling. Milling, e Fds wid,(1989)Soft wheat: view from France. Cereal AUTRAN 34(Sept):667-668,671-672,674,676 Ftat a cop od bet miling. C01%z SP a amal s: FINE, P. L. (1989) Soft wheat: view from Eastern United GoDON, B.(1988) Les debouches du gluten travaux LEATH PIRTAC et de l'INRA Inds aliment, agric. 105 HEBEDA, R. E(1987) nd technology. WATSON, S. A and RAMSTAD, P. E(Eds) and Technology, pp 501-534 WATSON, S A andr. St Paul, mn, u.s.a P. E(Eds ) Amer. Assoc. Cereal Chem. St Paul, MN, LINKO, P.(1987) Immobilized biocatalyst systems in the LIVESAY, J.(1985) Estimates of corn usage for major food pp 107-118 MORTON, I D (Ed )Ellis Horwood, Lond MITTLEIDER, J. F. ANDERSON, D, E, MCDONALD, C. E gton D. C, Fc and FISHER, N.(1978)An analysis of the econom LONG,J. E.(1982) Food sweeteners from the maize wet North Dakota. Bull. 508, North Dakota Agricultural Expe industry. In: Processing, Utilisation and Marketing hent Station, Fargo, N. D. and U.S. Dept Comm Maize. pp. 282-299 SWAMINATHAN, M. R, SPRAGUE, RAO, G. V.(1979)Wet wheat milling. Cereal Fds wld, NGH,J.(Eds). Indian Council of Agric (8):334335 U. S. Pat. Spec Nos. 3, 261, 690(SEM process); 3, 958,016 MAGNUSON, K. M.(1985)Uses and functionality of vital Pillsbury Co );3, 979, 375(Far- Mar-Co process); 4, 181, 748 wheat gluten. Cereal Fds wld, 30(2):179-181 ling);4, 201, 708(Far-Mar-Co process); MAY, J. B. ( 1987)Wet milling: process and 4,217,414(Wal 377-397 WATSON. WATSON S. A S. A. and RAMSTAD, P. E.(Eds). Amer. Assoc. Cereal d Technology. Amer. Assoc Cereal Chem. St them.. St Paul, mN U.S.A U.S.A
268 TECHNOLOGY OF CEREALS Advantages of the SEM process over the MCDERMOTT, E. E. (1985) The properties of commercial glutens. Cereals Fds Wld, 30 (2): 169-171. MEYER, P. A. (1991) High fructose starch syrup production and technology growth to continue. Milling and Baking News, March 26, 70 (4): 34. SCHANFELT, R. V. (1984) Applications of starches in foods. In: Starch: chemistry and technology, pp. 579-592 2nd edn. WHISTLER, R. L., BEMILLER, J. N. and PASCHALL, E. F. (Eds). Academic Press, Orlando, FL., U.S.A. ORTHOEFER, F. T. (1987) Corn starch modification and uses. In: Corn: chemistry and technology. pp. 479-499 WATSON, S. A. and RAMSTAD, P.E. (Eds). Amer. Assoc. Cereal Chem., St Paul, MN, U.S.A. RADLEY, J. A. (1951-2) The manufacture of maize starch. Food Manuf. 26: 429, 488; 27: 20. SANFORD, P. A. and BAIRD, J. (1983) Industrial utilization of PolYsaccharides. PP. 41 1-490 in: The Pob'sacchahdes, Vol. 2. ASPINALL, G. 0. (Ed.). Academic Press, New York, U.S.A. WRIGHT, K. N. (1987) Nutritional properties and feeding value of corn and its by-products. In: Corn: Chemistry and Technology. pp. 447478 WATSON, S. A. and RAMSTAD, P. E. (Eds). Amer. Assoc. Cereal Chem., St Paul, MN, U.S.A. conventional milling process are: 1. An increase of up to 10% on head rice yield. 2. A decrease in the fat content of the rice, which MOORE, c. o., TUSCHHOFF, J. v., HASTINGS, C. W. and improves its storage life. 3. An increase in stability of the bran product. 4. A yield Of 2kg Of rice Oil from each lookg Of unmilled rice (2% yield on rice wt). The bran product has potential application in breakfast cerea1sy baby foodsy baked goodso The oil has edible and industrial applications, and is a rich source of a wax with properties similar to those ofmyricyl cerotate, or carnauba wax. Other applications are in margarine, cosmetics, paints (Edwards, 1967). References ANON. (1982) Corn Wet-Milled Feed Products, 2nd edn. Corn Refiners Assoc., Washington, D.C. U.S.A. or paper. Tappi, 69: 54-56. Cox, M. J., MACMASTERS, M. M. and HILBERT, G. E. (1944) ANDRES, C. (1980) Corn - a most versatile grain. Fd. Effect of the sulphurous steep in corn wet milling. Cereal Processing, May: 78. Chem., 21: 447. AUTRAN, J-C. (1989) Soft wheat: view from France. Cereal EDWARDS, J. A. (1967) Solvent extraction milling. Milling, Fds Wld, 34 (Sept.): 667-668, 671-672, 674, 676. 21 July: 48. Brit. Pat. Spec. No. 1,596,742 (Koninklijke Scholten-Honig FREEMAN, J. E. and BOCAN, B. J. (1973) Pearl millet: a NV) . potential crop for wet milling. Cereal Sci. Today, 18: FINNEY, P. L. (1989) Soft wheat: view from Eastern United 69. States. Cereal Fds Wld, 34 (Sept.): 682, 684, 686-687. GODON, B. (1988) Les debouches du gluten travaux de LEATH, M. N. and HILL, L. D. (1987) Economics, producI'IRTAC et de I'INRA. Inds. aliment. agric., 105: 819-824. tion, marketing and utilization of corn. In: Corn: chemistry HEBEDA, R. E. (1987) Corn sweeteners. In: Corn: Chemistry and technology. WATSON, S. A. and RAMSTAD, P. E. (Eds). and Technology, pp 501-534 WATSON, S. A. and RAMSTAD, Amer. Assoc. Cereal Chem., St Paul, MN, U.S.A. P. E. (Eds.). Amer. Assoc. Cereal Chem., St Paul, MN, LINKO, P. (1987) Immobilized biocatalyst systems in the U.S.A. context of cereals. In: Cereals in a European Context. LIVESAY, J.(198.5) Estimates of corn usage for major food pp. 107-118 MORTON, I.D. (Ed.) Ellis Honvd, London. and industrial products. In: Situation Rep., pp 8-10 U.S. MITTLEIDER, J.F., ANDERSON, D. E., MCDONALD, C. E. Dept. Agric., Econ. Res. Serv., Washington D.C., FdS- and FISHER, N. (1978) An analysis of the economic 296, March. feasibility of establishing wheat gluten processing plants in LONG, J. E. (1982) Food sweeteners from the maize wet- North Dakota. Bull. 508, North Dakota Agricultural Experimilling industry. In: Processing, Utilization and Marketing ment Station, Fargo, N.D. and U.S. Dept. Commerce. of Maize. pp. 282-299 SWAMINATHAN, M. R., SPRAGUE, RAo, G. V. (1979) Wet wheat milling. Cereal Fds Wld, 24 E. W. and SINGH, J. (Eds). Indian Council of Agric. (8): 334-335. Technol., New Delhi. U.S. Pat. Spec Nos. 3,261,690 (SEM process); 3,958,016 MAGNUSON, K. M. (1985) Uses and functionality of vital (Pillsbury Co.); 3,979,375 (Far-Mar-Co process); 4,181,748 wheat gluten. Cereal Fds Wld., 30 (2): 179-181. (dry-wet milling); 4,201,708 (Far-Mar-Co process); MAY, J. B. (1987) Wet milling: process and products. In: 4,217,414 (Walon). Corn: chemistry and technology. pp. 377-397 WATSON, WATSON, S. A. and RAMSTAD, P. E. (Eds) (1987) Corn: S. A. and RAMSTAD, P. E. (Eds). Amer. Assoc. Cereal Chemistry and Technology. Amer. Assoc. Cereal Chem., St Chem., St Paul, MN, U.S.A. Paul, MN, U.S.A. BRAMEL, G. F. (1986) Modified starches for surface coatings Further Reading
