Cereal 2

16Quality Evaluation of Cereals and Cereal Products

Vladimir F. RasperUniversity of Guelph, Guelph, Ontario, Canada

Charles E. Walker*

BRIAustralia Ltd., North Ryde, New South Wales, Australia

The quality of cereals and various cereal products is determined by a variety of characteristics that may be assigned different significance levels, depending upon the desired end product. These characteristics can be divided into chemical, enzymatic, and physical. Likewise, individual quality testing methodologies can be classified into those concerned with the chemical components of the tested material, assays for estimating enzymatic activity, and tests dealing with various physical or physicochemical properties. Procedures based on small-scale product preparation, e.g., laboratory milling and experimental baking tests, are also parts of the methodology. Tables 1 and 2 contain a list of the procedures most commonly employed as part of the Approved Methods of the American Association of Cereal Chemists [1] or Standards of the International Association for Cereal Chemistry and Technology [1823]. The expected ranges of values measured by these procedures for different types of wheat flour are given in Tables 35.

IChemical Tests

AMoisture

1

Moisture determination is an essential step in evaluating the quality of cereal grains and their products. The behavior of the grains in both storage and milling depends to a great extent on their moisture content. Moisture content also influences the keeping quality of flour and bakery products. The knowledge of moisture content is required for comparing production data at a uniform level of dry solids and for compliance with government regulations. Similarly, since compositional percentages are inversely related to moisture content in the analyzed material, results of chemical analyses have to be reported on a fixed-moisture basis. In North America, it has become a common practice to report the results on the 14% basis, whereas in Europe the dry solids basis is often preferred, and 12% is used in other countries for some products.

There are many methods for testing moisture content, and their results may vary considerably. It is therefore important that all tests are made by the same method when the results are intended for the same purpose or different laboratories are involved. In reporting the results, the method used should be indicated so that in comparing results of different methods, a proper correction factor can be applied.

*This work was co-authored by Dr. Walker while on leave from Kansas State University, Manhattan, Kansas.

Disclaimer: It is common practice in the Cereal Technology field to refer to equipment by manufacturer and/or by brand names. Where company names have been used in this article, it is for clarity and identification only. No endorsement of any particular company or its products in preference to other similarly suited equipment is implied.

TABLE 1 Some of the Most Commonly Used AACC Approved Methods and ICC Official Standards for Testing Grains and Flours

Tested property Principle AACC Methodsa ICC Standardb

Chemical constituent

Moisture

Oven-drying

44-15A

109/1

2

44-16 110/1

44-18

44-19

44-20

Dielectric meter 44-11

Vacuum drying 44-40

Distillation with toluene 44-51

Protein

Automated Kjel-Foss method 46-08

Automated colorimetric method 46-09

Improved Kjeldahl method 46-10 105/1

46-11

46-12

Micro-Kjeldahl method 46-13

Udy-dye method

46-14A

Biuret method 46-15

Combustion method 46-30

Gluten

Hand washing 38-10

Machine washing 38-11 137

Incineration 08-01 104

3

Mineral matter (ash)

08-02

08-03

Crude fiber

Chemical digestion 32-10 105/1

Dietary fiber (insoluble)

Enzymatic and chemical digestion 32-20

Crude fat

Solvent extraction 30-10 30-25 136

Fat acidity

Titration

02-01A

02-02A

02-03A

Starch

Enzymatic 76-11 128

Polarimetric 76-20 122

4

Starch damage

Enzymatic

76-30A

Enzymatic activity

-Amylase

Colorimetric 22-01 108

22-06

Nephelometric 22-07

Viscometric

Amylography 22-10 126

Falling number

56-81B

107

Pressuremetric 22-11

Volumetric 22-14

Chemical (incubation in situ) 22-15

22-16

Rapid Viscometric 22-08

61-02

Proteases

Chemical 22-60

5

22-61

Spectrophotometric 22-62

Colorimetric 22-63

46-11

46-12

(table continued on next page)

Continued

TABLE 1

Tested property Principle AACC Methodsa ICC Standardb

Physical properties

Farinography

Dough mixing 54-21 115

Mixography

Dough mixing 54-40

Extensigraphy

Dough stretching 54-10 114

6

Alveography

Dough stretching 54-30 121

Particle size

Centrifugation 50-10

Sedimentation 127

Physicochemical properties

Sedimentation value

Swelling and sedimentation 56-60 116

Oxidizing, bleaching, and maturing agents

Oxidizing agents

Chemical 48-02

Acetone peroxides

Chemical 48-05

Ascorbic acid

Chemical 86-10

Benzoyl peroxide

Chemical 46-06B

7

Chemical 48-07

Chlorine dioxide

Chemical 48-30

Azodicarbonamide

Chemical 48-42

Potassium bromate

Chemical 50-10

aApproved Methods of the American Association of Cereal Chemists, 9th ed., St. Paul, MN 1995.bStandard Methods of the International Association for Cereal Science and Technology.

When moisture is determined by drying, the measured value is defined as the percent loss in weight under the conditions of the specific procedure. The loss includes both water and other volatiles. If the original moisture content in the sample exceeds 16%, drying is usually carried out in two stages. The moisture content is first reduced to 16% or less (13% for rice) by keeping the sample in a well-ventilated and warm place. Then the sample is dried at an elevated temperature: 103°C for 72 hours [1] (AACC Method 44-15A) or at 135°C for 2 hours (AACC Method 44-19). An alternate procedure uses a partial vacuum equivalent to 25 mm mercury or less at 98100°C for approximately 5 hours (AACC Method 44-32). Other techniques such as measuring the dielectric constant (AACC Method 44-11), azeotropic distillation with toluene (AACC Method 44-51), and near-infrared reflectance (NIR) spectroscopy are also used. According to the ICC Basic Reference Method [22], sample moisture content is defined as the loss in weight sustained by the material when equilibrated in an anhydrous atmosphere at a temperature between 45 and 56°C and a pressure of 1.32.7 kPa (1020 mmHg).

BProtein

8

The protein quantity has historically been determined by the classical Kjeldahl analysis or one of its more recent modifications [1] (AACC Methods 46-10, 46-1 1, 46-12, 46-13). Protein nitrogen is reduced and transformed to ammonium sulfate by hot digestion of the dry sample with concentrated sulfuric acid in the presence of a catalyst. Ammonia is then liberated from the sulfate by distillation in the presence of sodium hydroxide and driven into a known volume of standard acid solution. From the quantity of unreacted acid determined by titration, the quantity of released nitrogen is established and converted to protein by multiplying the percentage of nitrogen with the appropriate conversion factor (5.7 for wheat and wheat flour, 6.25 for most foods and feeds). Another method is based on the dye-binding capacity of specific groups of amino acids in protein [1,47] (AACC Method 46-14A).

More recently, methods have been developed to determine protein by near-infrared reflectance spectroscopy [1,31,54] (AACC Method 39-10) and near-infrared transmission. NIR is a somewhat empirical method, however, and requires a set of previously analyzed reference samples to calibrate the instrument. As a result of the expense, hazards, and environmental pollution characterizing the Kjeldahl procedure, many laboratories now use methods that measure the nitrogen as a gas left after exhaustively combusting the sample in a 99.9% pure oxygen atmosphere at 950°C [1] (AACC Method 46-30).

Protein determination is particularly significant when testing wheat or flour. Wheat protein quantity and quality have long been recognized to have a decisive effect on the physicochemical properties of wheat flour dough and consequently on its handling properties and baking potential.

Page 508

TABLE 2 Procedures for Testing Baking Quality of Wheat Flour and Ingredients

Tested property Principle

Standard procedures

Bread flour quality

Straight-dough baking test with long fermentation; size: pup loaf

9

Bread flour quality Straight-dough baking test with optimized conditions; also suitable for evaluation of effects of environment, variety, dough ingredients, protein content, flour components; used for 10100 g flour and on 1-lb loaves; also used for blends of wheat and nonwheat flours

Bread flour quality

Sponge and dough baking tests; 800 g flour, 1-lb loaves

Baking test of flour quality for sweet yeast products

Preparation of coffee cakes using 100 g of mix

Baking property of self-rising biscuit flour

Preparation of biscuits

Baking quality of cookie flour

Baking sugar snap cookies and measuring cookie spread; 225 g flour

Baking quality of cookie flour

Same as above; 40 g flour

Baking quality of cake flour

Preparation of white layer cakes; 200 g flour

Baking quality of angel food cake flour

Preparation of angel food cakes

10

Baking quality of pie flour

Preparation of pie shells; 1000 g flour

Baking quality of rye flour Straight-dough process for rye bread; 100 g wheat (clear) and 100 g rye flour

Baking quality of nonfat dry milk (NFDM)

Straight-dough bread process with 6% NFDM

Nonstandardized procedures

Bread flour quality

Sponge dough method under optimized conditions, see Table 6

Cake flour quality

Yellow layer cake, see Table 7

aApproved Methods of the American Association of Cereal Chemists, 8th Edition, St. Paul, MN, 1983.bAmerican Institute of Baking, Manhattan, KS.

Since these relevant functions of wheat protein have been attributed primarily to gluten-forming proteins, protein determination in wheat or wheat flour is very often supplemented by a quantitative estimation of wet and dry gluten, especially in Europe. Gluten is prepared by washing out most of the starch and solubles from a piece of dough developed from flour and water [1] (AACC Method 38-10). This tedious and poorly reproducible procedure has been made easier by the introduction of automatic gluten washers (Fig. 1) [1] (AACC Method 38-11). The wet gluten can be examined visually for its color and elasticity. The difference between gluten weight before and after

11

drying can be taken as a rough estimate of its hydration capacity. Some other tests used for evaluating gluten quality are mentioned in Section IV.

CMineral Content

Mineral content, more commonly known as ash, has always been considered an important criterion in flour quality. Although not directly related to the baking performance of flour, it serves as an indicator of the degree of separation of starchy endosperm from the bran during the milling process because the aleurone and bran layers are higher in mineral matter than the endosperm. Thus, ash content determination not only provides a useful criterion for classifying flours, but is a tool for controlling the entire milling operation. Ash content may vary from less than 0.4% for high-quality, low-extraction flours to more than 2.0% for whole wheat flours. The conditions of the determination may vary with the type of the tested material and procedure used. According to AACC Method 08-01, ash is determined as a residue after incinerating the sample at 550°C (for soft wheat flour) or 575590°C (for hard wheat flour) until a light gray ash is obtained [1]. Using an accelerated method, applicable only to flour, the sample is wetted with magnesium oxalate solution and incinerated for 3045 minutes at 700°C [1] (AACC Method 08-02). The ICC Standard No. 104 (18) for ash determination in cereal materials prescribes incineration at ~900°C until the residue is white or nearly white.

For a rapid determination of ash without any incineration involved, NIR spectroscopy can be applied [53]. Most NIR instruments now used in mills can have this calibration included.

DFiber

12

Mineral content correlates very closely to fiber content. They are both related to the amount of bran in the kernel or in the flour. In cereal testing, fiber was traditionally determined as crude fiber in the form of a residue remaining af-

TABLE 3 Generally Used Criteria for Measuring Quality of Flour for Yeast Breads

Pan bread

Quality criterionWholesale,

conventionalContinuous

doughHearth breads

Variety breads, cracked wheat bread, rye bread Soft rolls Sweet goods

Wheat classa HS, HW, or blend HS, HW, or blend

HS HS HS, HW, or blend

HS, HW, or blend

Flour absorption (% by farinograph) Medium to high 6064

Medium 5964 High 6368 High 6575 High 5964 Medium to high 6064

Ash (%) 0.440.50 0.440.50 0.440.55 0.450.55 0.440.5 0.450.50

Alk. water retention NSb NS NS NS NS NS

Baking test Pan; straight or sponge

Pan; sponge Hearth; straight

Pan; straight Pan; sponge Pan; straight

Color Creamy white Creamy white Creamy white

NS Creamy white to white

Creamy white

Enzyme activity

Amylase

Amylograph (BU)

475625 525600 400600 350550 475625 475625

290350 280330 300360 300375 290350 290350

13

Maltose (mg)

Pressuremeter 5th-hour (mm)

500550 475550 500550 500550 500550 500550

Falling number

200300 200300 175275 200300 200300 200300

Amylase analyzer

300600 300600 350600 300600 300600 300600

Lipase

NS NS NS NS NS Low for prepared mixes

Protease

NS NS NS NS NS NS

Particle size

Range (SED)c = (m)

0150 0150 0150 0150 0150 0150

Protein

Quantity (%)

11.013.0 11.013.0 13.514.5

Quality (Farinograph recording

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mixer values)

Hydration

Medium Short to medium

Medium to long

Medium to long Medium Short to medium

Peak development (min)

68 57 79 79 68 58

Stability (min)

7.5 minimum 8 minimum 10 minimum 10 minimum 8 minimum 8 minimum

Extensibilityd Medium Medium Medium to long

Medium to long Medium to long Long

Resistance to extension Medium Medium Maximum Maximum Medium to low Medium to low

Starch damage (%) 5.57.7 5.57.8 7.08.5 Low as possible 5.57.8 5.57.8aHS = Hard spring, HW = hard winter.bNS = Not significant at present, or significance not known.cStokes equivalent diameter.dDescriptive terms in each instance refer to relative values for wheat variety involved.Source: Ref. 15.

TABLE 4 Generally Used Criteria for Measuring Quality of Flour for Chemically Leavened Breads and Biscuits

Crackers

Quality criterion Home baking Biscuits Sponge Dough Pastry

15

Wheat classa HW or HW-SW blend HW-SW blend or SW

SW or SW-HW SW SW

Flour absorption(% by farinograph)

Medium low5258

Low5054

Low4852

Low4852

Low 4852

Ash (%) 0.440.48 0.440.40 0.400.48 0.400.48 0.400.48

Alk. water retention NSb NS 5868 5868 5056

Baking test Biscuits; kitchen layer cakes

Biscuits AACC cookie; W/T 6.07.5

AACC cookie; W/T 7.58.5

AACC cookie; W/T 7.58.5

Color Creamy white White Creamy Creamy Creamy

Enzyme activity

Amylase

Amylograph (BU)

450600 NS 700800 NS NS

Maltose (mg)

290320 NS 200250 NS NS

Pressuremeter 5th-hr (mm)

400450 NS 300350 NS NS

Falling number

200300 250 minimum 250 minimum 250 minimum 250 minimum

16

Lipase

NS NS NS NS NS

Protease

NS NS NS NS NS

Particle size

Range (SED)c = (m)

0125 090 0125 0125 0125

Protein

Quantity (%)

9.511.0 9.010.0 9.010.0 8.09.0 8.09.0

Quality (recording mixer values)

Hydration

Short Short Short Short Short


35 23 13 13 13

Stability

36 13 13 12 12

17

Extensibilityd

Medium Medium short Medium Medium Medium

Resistance to extensiond

Medium to low Low Low Low Low

Starch damage Low as possible Low as possible Moderate Low as possible Low as possible

Viscosity

MacMichael

90120° 6090° 6590° 4560° 4560°

aHW = Hard winter, SW = soft winter.bNS = Not significant at present, or significance not known.cStokes equivalent diameter.dDescriptive terms in each instance refer to relative values for wheat variety involved.Source: Ref. 15.

TABLE 5 Criteria for Evaluating Flours for Cookies, Cakes, Soups, and Gravies

Cakes

Quality criterion Cookies Layer FoamSoups and gravies

(thickeners)

Wheat classa SW SW SW SW

Flour absorption(% by farinograph)

Low; 4852 Low; 4852 Very low; 4448 NSb

Ash (%) 0.420.50 0.340.40 0.290.33 0.400.58

Alk. water retention 5054 5462 5256 4855

Baking test AACC cookie; W/T White layer cake Angel food cake None

18

8.09.5

Color Creamy White White NS

Enzyme activity

Amylase

Amylograph (BU)

NSb NS NS 700+, high as possible

Maltose (mg)

NS NS NS 200, low as possible

Pressuremeter 5th-hr (mm)

NS NS NS NS

Falling number

250 minimum 250 minimum 250 minimum 250 minimum

Lipase

NS Low for prepared mixes

Low for prepared mixes

NS

Protease

NS NS NS NS

Particle size

0125 0125 2060 0150

19

Range (SED)c = (m)

Protein

Quantity (%)

7.09.5 7.09.5 5.57.5 9.010.5

Quality (recording mixer values)

Hydration

Short Short Short NS


13 12 11.5 NS

Stability (min)

12 11.5 11.5 NS

Extensibilityd

Medium Short Short NS

Starch damaged Low as possible High Low Low as possible

Viscosity

MacMichael

4065° 3565° 3045° NS

20

aSW = Soft winter.bNS = Not significant at present, or significance not known.cStokes equivalent diameter.dDescriptive terms in each instance refer to relative values for wheat variety involved.Source: Ref. 15.

ter treating the sample successively with hot concentrated acid and hot concentrated alkali [1] (AACC Method 32-10). In wheat grain, the crude fiber content ranges from 2 to 2.5% (14% m.b.). Flour crude fiber is directly related to the milling extraction and averages around 0.5% (14% m.b.) in white flour. Recently, fiber content in cereals and cereal products has more frequently been reported as ''dietary fiber." This term designates a residue indigestible by human digestive enzymes. A method based on a combined action of amylase and neutral detergent was designed to simulate the digestive process in vitro for the determination of insoluble dietary fiber [1] (AACC Method 32-20). For the determination of total dietary fiber, consisting of both soluble and insoluble fractions, the enzymatic method uses amylolytic and proteolytic enzymes as proposed by Prosky et al. [36]. Like crude fiber, total dietary fiber in flour will increase with higher milling extraction rates. It may range from approximately 3% in white wheat flour to over 9% in whole meal. In wheat bran, it accounts for more than 40% of the solids.

EStarch

Starch constitutes the main chemical component of the cereal grains and their products. However, when quality testing wheat flours, more attention is usually given to the physical condition of the starch granule rather than the actual quantity of this component. It is the degree of physical

21

Figure 1Gluten washers: (A) Glutomatic 2200.(Courtesy of Falling Number A.B. Stockholm, Sweden.)

22

(B) Glutinex MLI 500.(Courtesy of Bühler Brothers Ltd. Uzwil,Switzerland.)

damage to the granule inflicted by milling that is more important. Some positive contribution to the quality of some types of wheat flour can be expected from a limited amount of damaged granules. Cake flours often benefit by a high batter viscosity resulting from high starch damage. However, distinctly adverse effects will be noticed if the amount becomes excessive. The first attempt to measure the extent of starch damage involved microscopic examination of wheat flour after staining with Congo red. Physical damage enhances the absorption of dyes by the starch granule. Congo red was later replaced with 0.2% solution of crystal violet or chlorzinciodide [56]. Several methods exploit the higher susceptibility of damaged starch granules to amylolytic degradation and quantitatively estimate the level of products of this degradation [1,11] (AACC Method 76-30A). Other methods depend upon the development of color formed when iodine reagent is added to an extract of flour that contains amylose leached out from the damaged granules by a solution of ammonium sulfate, formamide, and sulfosalicylic acid [16,55].

An amperometric technique [29] measures the rate of iodine absorption by starch granules. The rate increases with higher degrees of damage. This principle is now used by the Chopin Starch Damage Analyzer (Fig. 2).

Specific methods are used in analyzing flours for added bleaching and maturing agents. The Approved Methods of the AACC [1] include procedures for the determination of acetone peroxide (Method 48-05), benzoyl peroxide (Method 48-07), chlorine dioxide (Method 48-30), potassium bromate (Method 48-42), ammonium persulfate (Method 48-62), and azodicarbonamide (Method 48-71A).

IIEnzyme Activity

In testing cereal grains and their milling products for enzymatic activity, amylolytic activity, i.e., the activity of starch-hydrolyzing enzymes, is considered of primary importance. While only small amounts of -amylase are present in sound grain, the activity of this

23

enzyme increases markedly during pre- or postharvest germination (sprouting). Some level of this activity is needed for sufficient gas development during fermentation in the early stages of baking yeasted doughs such as pan breads. If the -amylase concentration is insufficient, the flour can be supplemented with preparations from wheat or barley malt, fungi, or bacteria. Excessively high levels, however, impair the quality of both the dough and the final baked product because -amylase cleaves the starch molecules, reducing the paste viscosity, and can lead to sticky doughs. Unlike -amylase, -amylase is present even in sound (not field-sprouted) grain, but the quantity remains practically unchanged during germination. For that reason, the assays for amylolytic activity deal primarily with -amylase.

The AACC Method 22-07 [1] is a colorimetric assay based on the reaction of -amylase with a buffered solution of potato amylose dyed with Cibachrom blue F3GA. Another AACC method (Method 22-07) measures the rate of decrease in light-scattering ability of a dilute suspension of a -limit dextrin substrate treated with enzyme extracted from the tested flour. The ICC Standard No. 108 [19] is a similar colorimetric method. Other chemical procedures are based on quantitatively estimating the reducing sugars produced in situ in a buffered flour suspension after a standard incubation period [1] (AACC Method 22-15). Such methods measure the effects of the combined activity of -

24

Figure 2Chopin Rapid FT starch damage analyzer.

(Courtesy of Chopin SA, Villeneuve la Garenne, France.)

and -amylase, as well as the damaged starch granules' susceptibility to amylolytic activity. In that respect, the results are more a reflection of the total gas production ability of the tested flour than the actual amylolytic activity. A number of methods evaluate this combined effect by measuring the quantity of gas produced by the flour under the specific test conditions (see Section IV). Methods for indirectly estimating amylolytic activity from viscometric measurements on starch pastes are found in Section III.

25

Some amylase preparations used for adjusting wheat flour's amylolytic activity contain appreciable quantities of proteolytic enzymes. In flour unsupplemented with such preparations, higher levels of proteolytic activity indicate sprouted grain. In order to assay this activity, the nitrogen released from a buffered hemoglobin substrate when it is incubating with the enzyme-containing flour extract is estimated quantitatively by Kjeldahl analysis [1] (AACC Method 22-60). Solubilized hemoglobin can also be measured spectrophotometrically (Method 22-62) or colorimetrically (Method 62-63).

Unfavorable storage conditions may enhance the lipase action, especially in materials high in fat. Since higher lipase activity leads to an increase in fat acidity, the extent of the lipase action can be expressed in terms of milligrams of potassium hydroxide required to neutralize the free fatty acids extracted from a 100-g sample [1] (AACC Methods 62-01A, 62-02A, and 62-03A). Fat acidity may range from about 20 for sound wheat to over 100 if the grain was stored under adverse conditions.

IIIPhysical Testing

APhysical Grain Testing

1Test Weight

Test weight, measured as weight of grain per unit volume, is the simplest and most widely used predictor for a grain's milling quality. Although many factors may influence the relationship between test weight and milling yield, the latter usually increases with increasing test weight unless the weight value exceeds 75 lb per bushel (96 kg/hl) [15].

26

In countries using Imperial units, test weight is expressed in terms of lb per bu. In the United States, the Winchester bushel (2150.42 in3) is used, which differs slightly from the Imperial bushel (2219.36 in3). In countries using the metric system, test weight is defined in terms of kilo-

grams per hectoliter. For conversion, the following factors can be used:

From To Multiply by

lb/Winchester bu lb/Imperial bu 1.032

lb/Winchester bu kg/hectoliter 1.282

lb/Imperial bu kg/hectoliter 1.247

27

2Hardness

Grain hardness constitutes a comparative measure for distinguishing between soft and hard wheats. The criterion is widely used in testing corn (maize) for hardness and breakage susceptibility [33]. Methods used for testing hardness employ either a single grain or a bulk sample [34]. The single grain tests involve abrasion, cutting, crushing, or penetration. In bulk tests hardness is estimated from the power or time required to grind a given quantity of grain, from the quantity of abraded material, or from the particle size of the ground material. The latter is determined by sieving [59], sedimentation [23] (ICC Standard No. 127), centrifugation [1] (AACC Method 50-10), light-diffraction technique [2], Coulter counter, or NIR spectroscopy [54]. Many laboratories now use a single kernel characterization system to simultaneously measure several factors including hardness [32].

When grading wheat, other physical criteria are considered. Kernel weight, which is usually expressed in g per 1000 kernels, is a function of kernel size and density. It may be a reliable predictor of milling yields, because large, dense kernels usually have a higher ratio of endosperm to nonendosperm components than smaller, less dense kernels. U.S. hard red winter and spring wheats range in kernel weight from 20 to 32 g/1000 kernels. Soft red winter, white, and durum wheats average approximately 35 g/1000 kernels [15].

Milling yield can also be predicted from kernel size and shape [43]. Based on bran pigmentation, wheats are classed as either red or white. These two colors are varietal characteristics but may be influenced by environmental factors. Inspection of grain for damaged kernels and impurities is also part of the grading procedure. The ICC system adopted for the evaluation of wheat intended for milling includes testing for extraneous material referred to as ''Besatz" [20]. "Besatz" includes dockage, foreign material, damaged kernels, shrunken and broken kernels, and wheat of other classes.

3Experimental Milling

28

Experimental milling provides the miller with advance information on the probable performance of a grain in a commercial scale process. In breeding programs, it serves as a useful tool to evaluate the milling potential of the tested lines and helps to predict their end-use quality.

Prior to any experimental milling, the grain must be cleaned and conditioned (tempered) [1] (AACC Method 26-10). Numerous milling devices exist for the actual milling operation. They all work on the principle of grinding and sifting and differ only in the extent of these operations. The Bühler Laboratory Mill (Bühler Bros, Inc., Uzwil, Switzerland) is a continuous automatic mill with pneumatic conveying and a milling system consisting of three breaks and three reductions (Fig. 3). It can produce straight-grade flour comparable in quality to commercially milled flour. Some modifications such as the addition of a bran finisher are required to achieve typical commercial extraction rates, however [5].

Another automatic mill is the Brabender Quadrumat Senior (Fig. 4) with two four-roll system units, one for breaking and one for reduction, and a two-section plansifter. The Brabender Quadrumat Junior (Fig. 5), a compact unit with four 3-inch-diameter corrugated rolls, is well suited for milling small quantities of wheat, down to about 20 g. It is often used in early-generation testing

29

Figure 3The Bühler experimental mill MLU 202.(Courtesy of Bühler Brothers Ltd., Uzwil,

Switzerland.)

when only limited sample sizes are available from the plant breeder.

Some millers prefer batch-operated experimental mills such as the Allis-Chalmers or Ross Mill Stands because the milling procedure

30

can be adjusted at each stage on the basis of a visual examination, the yields, and stock quality throughout the mill flow. When evaluating the results of experimental milling, two factors are usually considered: flour extraction (the percentage of the wheat recovered as flour) and flour ash. The lower the flour ash and the brighter the flour color, the more desirable the wheat for milling. The following two formulas are used to evaluate wheat milling quality from experimental milling data [40]:

Figure 4The Brabender Quadrumat Senior laboratory mill.

(Courtesy of C. W. Brabender Instruments Co., SouthHackensack, NJ.)

31

Figure 5The Brabender Quadrumat Junior laboratory mill.(Courtesy of C. W. Brabender Instruments Co., SouthHackensack, NJ.)

Higher milling ratings and milling values are preferred. The milling quality of different wheats can also be judged by comparing their cumulative ash curves [28]. Cumulative ash curves are constructed by arranging mill streams in ascending order of ash on a constant moisture basis and by plotting cumulative ash against cumulative extraction for each successive blend of millstreams. Wheats that exhibit the lowest initial flour ash

32

and the slowest rate of ash increase with increasing flour extraction are preferred. The results of this comparison can be expressed in terms of a single numerical score, the curve index. A line is drawn from the 30% extraction point on the cumulative curve to the 70% extraction point (Fig. 6). The distance on the 50% extraction level from the curve to the drawn line, when measured at right angle to the line, is called depth, D. It is used in the calculation of the curve index:

where L is the length of the line between the 30% and 70%

extraction points. A lower curve index indicates better milling quality.

BFlour Color Testing

Flour is tested for color for evaluating either its whiteness, which primarily determines the extent of the oxidation of carotenoid pigments by bleaching compounds, or the presence of bran particles, indicating milling performance. Testing flour for whiteness may be based on measuring light reflectance of the sample within the blue range of the light spectrum. Since improvement in flour color results from the oxidation of the pigments by the bleaching agents as well as natural oxidation during storage, the measured values vary not only with the extent of bleaching but the age of the flour. Correlation between color measured in the blue range of light spectrum and ash content in flour is rather limited. If color is to be taken as a measure of contamination with bran particles, reflectance meters with a light source in the green band of the light spectrum should be used. Among them, the Kent-Jones Grader [25] and the Agtron Color Meter set on ''green mode" [1,12,44] (AACC Method 1430) are the most common. NIR analyzers have also been employed for this purpose, though tri-stimulus reflected color instruments such as the Minolta or Hunter devices using the L*a*b* system are now more routinely used.

33

Color must be used rather than ash content when the flour is fortified with calcium because the calcium salt contributes more ash than does the naturally occurring mineral material.

Figure 6Measurement of the curve index.

(From Ref. 28.)

The "slick" (Pekar) test is a rough but simple guide for assessing flour color visually [1] (AACC Method 14-10). Flour is placed on a flat piece of wood or metal, pressed down, trimmed, and immersed in water. The color may be judged at several stages: (1) before immersion in water (dry), (2) shortly after immersion, and (3) after the flour has been dried. Bran shows up as fine brown flecks more obviously when it is wet. It is common to "slick" several flours immediately beside each other.

34

More recently, image analysis has been used, in which computer software examines the brightness of the pixels in a digitized image. The more sophisticated instruments use a low-power microscope and illuminate the sample with UV light. Since bran and aleurone fragments fluoresce differently under UV light, producing different colors, it is possible to obtain rather accurate estimates of the fraction of each component in the flour sample [51].

Simple systems can also be based on a small TV camera using visible light or on an inexpensive flatbed scanner. The Branscan equipment (Fig. 7) is an example of such an application. It can measure "speckyness" directly rather than mineral ash content. Models are available for use in either a laboratory situation or for on-line quality monitoring and control purposes. An automatic sampler compresses a flour sample against a flat glass window and a series of fields are digitally analyzed. Visible range light is used, and the gray scale threshold can be set to select the size and darkness of the pixels that are to be denoted as "specs." The number and total area of the specs can be determined and used as indicators of milling efficiency or flour baking quality [52].

The procedure can also be used to identify flour specks in noodles, for example.

CPhysical Dough Testing

Dough physical properties not only determine performance at the various stages in the manufacturing process but also have a pronounced effect on finished product qualities. Since the physical condition of dough depends to a large extent on the quality of the flour used, testing doughs for their physical properties has become an essential part of the quality evaluation of wheats and their flours. The methodology can be considered in three phases that reflect the relevance of the individual physical qualities of dough at different stages in the baking process (Fig. 8).

1

35

Recording Mixers

The first phase is concerned with the behavior of dough when it is developed from flour and water and subsequently subjected to overmixing. Recording mixers are used to measure and record the changes in the resistance to mixing

Figure 7The Branscan image analysis system for determining bran

specks in flour.(Courtesy of Parascan Technologies, Ltd., Redditch,

Worc., UK.)

with time. The mixing curves are characterized by an ascending part that indicates changes during the dough-development process, while the subsequent decline in resistance is taken as a sign of a steady breakdown of the dough structure upon mixing beyond the point of optimum development. Optimum development from the standpoint of bread quality may occur slightly past the ''mixing peak," depending upon what equipment follows.

36

(a)Farinograph

The Brabender farinograph (Fig. 9) is one of the most widely used recording dough mixers [7]. The two Z-shaped blades of the farinograph mixer rotate at constant but different speeds and subject the dough to a relatively gentle mixing at constant temperature. A representative farinograph record, or farinogram, with the commonly measured indices as defined by ICC method [21] is shown in Figure 10. Dough-development time and stability increase with increasing strength of flour, whereas mixing tolerance index and degree of softening are inversely related to increasing strength. The AACC method [1] (AACC Method 54-21) uses additional indices. Arrival time is defined as the elapsed time required for the top of the curve to reach the 500 FU (farinograph units) line on the recording chart and serves as a measurement of the rate at which water is taken up by the flour. Departure time equals the sum of the arrival time plus the stability. Longer arrival and departure times indicate stronger flour. The 20-minute drop is measured as the difference between the height of the center of the curve at its peak and 20 minutes after the first addition of water. The larger the value, the weaker the flour. To express the strength of the tested flour as a single score, the valorimeter value may be determined from the dough-development time and the descending slope of the curve by means of a special nomograph known as the valorimeter. The higher the value, the stronger the flour.

Water absorption by flour is another relevant property that can be determined by means of a farinograph. It is defined as the amount of water required for dough to reach a definite consistency (normally 500 FU) at the point of optimum development. Stronger flours with higher protein content and better gluten quality are characterized by higher absorptions. Figure 11 presents an example of how the farinograms and water absorption values change with increasing flour strength.

More information about the dough-mixing characteristics may be obtained if the standard farinograph mixing bowl is replaced with the resistograph mixer. The resistograph combines mixing with stretching, pressing, and kneading, thus imparting high shear and high work input to the dough. The resistograms have two maxima, which become more pronounced with medium and weak flours (Fig. 12). The first maximum is related to binding water; the second one measures the stickiness and extensibility at breakdown of the dough. Another variant of the farinograph, the Brabender Do-Corder mixer (Fig. 13), was designed to simulate conditions of

37

mechanical dough development [30]. It has a nearly closed mixer in which dough can be subjected to mixing at variable speeds and with work-input levels higher than in an ordinary farinograph mixer (Fig. 14). This variant was developed in response to the implementation of short-time, high-speed bread processes and the new mixer designs they required.

(b)Mixograph

The mixograph (TMCO, Lincoln, Nebraska), originally designed by Swanson and Working [46], is another widely used recording mixer (Fig. 15). The mixing action is provided by four planetary pins revolving about three stationary pins attached to the bottom of the mixing bowl. The mixing can be described as a pull, fold, and repull action, which is more severe than that produced by the farinograph. As a result, the main advantage of the mixograph is the speed with which a test can be conducted [26]. The mixograph is especially popular with hard wheat plant breeders and in mill and bakery quality-control laboratories, and in laboratories doing research on the proteins that control mixing quality. It is available in several sizes, including 35 g, 10 g, and a computerized model requiring

38

Figure 8Three-phase system of physical flour testing.

(Courtesy of C. W. Brabender Instruments Co., South Hackensack, NJ.)

only 2 g of flour. However, in comparison with the farinograph, the mixograph is more difficult to standardize and requires more operator skill to determine the ''proper" flour water absorption [49].

The shape of a mixogram (Fig. 16) can be characterized by indices similar to those defined for the farinogram [1] (AACC Method 54-

39

40). Peak time is similar to farinograph dough development time. Peak height provides information about flour strength and absorption. Height of curve at a specified time past the peak is similar to the farinograph tolerance index. Higher values indicate a greater tolerance to overmixing. The same applies to the values of the angle between the ascending and descending portions of the curve at the peak. A higher tolerance to overmixing and overall flour strength can also be judged from the area under the curve. Examples of mixograms milled from different classes of wheat are shown in Figure 17.

Like other empirical dough-testing instruments, the mixograph has been modernized by redesigning it and by incorporating computerized data acquisition and interpretation. A particularly challenging feature was the development and introduction of the 2-g model [17,38].

(c)Consistograph

The Chopin Consistograph is a new recording dough mixer (Fig. 18). It consists of two parts: a mixer equipped with a pressure sensor in the mixing bowl, along with a special double arm mixing blade, and the Alveolink NG recorder-calculator, fitted with a color printer and dedicated software for data collection, graphing, and analysis. The consistograph can (1) record in real time the pressure in the mixing bowl during mixing, (2) determine the water-absorption capacity of a flour with a mixing test at constant absorption, and (3) characterize the behavior of a dough with a mixing test at varying absorption. A consistograph testing method achieved AACC First Approval status in September 1998.

(d)Commercial Implementation

Unlike many of the procedures used in cereal quality evaluations, mixing properties can be easily related to commercial practice, and

40

the principles have been directly transported. Equipment is available from several sources to monitor the electrical power demand by large-scale mixers [37]. A power draw transducer produces a signal that may be interpreted by appropriate software, often producing a mixing curve resembling that from a farinograph or a mixograph. Furthermore, some systems are sufficiently automated that they can actually stop the mixer at the appropriate time, usually shortly after the dough has reached maximum resistance to mixing (just past the peak on the mixing curve) and direct it to automatically empty and to begin the next mixing cycle. An example of the graphical output from such sensing equipment and software is shown from the Easy Mix system available from BRI-Australia (Fig. 19).

Figure 9The Brabender Farinograph/Resistograph.


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2Stress-Strain Instruments

Techniques constituting the second phase of the three-phase testing system provide information on the potential behavior of dough during its rise due to the development and expansion of gas during the fermentation and early baking stages. Load-extension instruments are applied to measure the resistance of dough to extension.

(a)Extensograph

The Brabender extensigraph (Fig. 20) stretches a cylindrically shaped dough piece until it ruptures while the resulting force on the test piece is transmitted through a balanced lever system to a recorder. The dough (with 2% salt based on flour weight) is prepared in a farinograph mixer, usually at 2% less than its optimum absorption to compensate for the salt addition. According to the AACC procedure [1] (AACC Method 54-10), the dough is developed until its consistency reaches its maximum, whereas the ICC method (ICC Standard No. 114) uses mixing for a fixed 5-minutes period. When the dough test piece is stretched, a curve of force versus time, an extensigram, is recorded (Fig. 21). Several extensigram indices provide a practical guide to general dough strength. They include:

1. The maximum resistance, Rm, or the resistance at a fixed extension usually corresponding to 50 mm transposition on the chart paper, R5. The latter has the advantage of measuring the resistance at the same extension for all tested doughs.

2. The dough extensibility, E, which is the distance it stretched before rupture.

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Figure 10Representative farinogram showing some commonly measured indices.

(From Ref. 3.)

43

Figure 11Farinograms of flours with different strengths. Farinograph absorptions:

flour A54%, flour B57%, flour C64.5%, flour D62.7%.(From Ref. 35.)

Figure 12Comparison of farinograms and resistograms for identical flours: (B) farinogram of soft flour, (C) farinogram of strong flour,

(D) resistogram of soft flour, (E) esistogram of strong flour.(Courtesy of C. W. Brabender Instruments Co., South Hackensack, NJ.)

3. The ratio of resistance to extensibility.

44

4. The area under the curve, which is proportional to the energy required to stretch the test piece to its rupture point. This index is a convenient single figure for characterizing flour strength. The stronger the flour, the more energy is required to stretch the dough.

The extensigraph response by different flours and the ways in which the extensigram shape may relate to the dough's behavior can be seen from Figure 22.

Apart from differentiating among flours, the extensigraph is also used to evaluate the effects of oxidizing agents on dough's physical qualities. For example, Figure

45

Figure 13The Brabender Do-Corder.


23 shows how the extensigram changes after the addition of ascorbic acid to the dough, when it is allowed to react for different times. Ascorbic acid (vitamin C) is often added to commercial bread dough to produce a finer crumb grain and larger loaf volume.

(b)Extensometer

46

The Halton (or Simon ''Research") extensometer of the Association of British Flour Millers [14] is similar to the Brabender extensigraph. The extensometer is part of a three-unit device that also includes a water absorption meter and a mixer-shaper unit. The absorption meter determines the optimum absorption of the dough (generally yeasted) from the extrusion time values measured on several doughs prepared from the same flour sample with varying amounts of water. Optimum absorption has been empirically linked to an extrusion time of 50 seconds. After the doughs are shaped in the mixer-shaper unit, they are stretched between two pegs. The force exerted on the stationary peg is transmitted and recorded in the form of a curve that resembles the Brabender extensigram.

(c)Alveograph

Another load-extension apparatus, until recently more popular in several European countries than in North America, is the Chopin alveograph. Unlike the Brabender extensigraph or Halton extensometer, which both stretch the test dough piece in only one direction, the

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Figure 14Two views of the developer head for the Brabender

Do-Corder.(Courtesy of C. W. Brabender Instruments Co., South

Hackensack, NJ.)

alveograph subjects dough to extension in two dimensions by blowing a molded and rested sheet into a bubble [1,10,24] (AACC

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Method 54-30). From the physical viewpoint, such an extension mode is well linked with the gas cell expansion in rising dough. The instrument records the air pressure in the bubble as a function of inflation time. A typical alveograph record, an alveogram, is shown in Figure 24. Its interpretation is similar to that of the extensigram. The maximum height of the curve is taken as a measure of resistance to extension, and its length as a measure

Figure 15The National Mixograph.

(Courtesy TMCO, Lincoln, NE.)

of extensibility. The area under the curve is usually converted into a W value, referred to as deformation energy, which represents the total work input in blowing up the test piece into a bubble. The W value is the most commonly used alveogram index, much like the area under the extensigram. Alveograms for flours with distinctly different properties are shown in Figure 25.

Alveograph flour tests have traditionally been conducted on doughs prepared with a constant water addition to the flour (51.4%). Now it is possible to carry out Alveograph tests at varying absorptions, better reflecting actual baking absorptions. This is done by utilizing water absorptions previously determined with the recently developed recording dough mixer, the Chopin Consistograph (see above).

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A new alveograph modification is the Alveograph NG (Fig. 26). This unit has three components: a mixer for dough preparation, the alveograph for deformation of the dough sample, and a recorder-calculator for data acquisition, visualization, analysis, and printout of data functions. Yet another alveograph version is the Alveo-Consistograph, which combines capabilities of the Alveograph NG and the Consistograph.

(d)Dobraszczyk/Roberts Attachment

Many instruments can be modified to provide a stress-strain type record. For example, a recent attachment developed for the Stable Microsystems TA-XT2 Texture Analyzer mimics the bubble-blowing action of the alveograph (Fig. 27). The crosshead movement is proportional to the bubble volume, and the resisting force encountered is related to the pressure in the bubble. The area under the resulting curve that is produced is a measure of the total work input [9].

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Figure 16Representative mixogram showing the commonly measuredindices: peak time = line CD; maximum height = line CH.Angle between ascending and descending portion of curve

at peak (lines BC and CE, angle 1). Alternately, anglesformed by lines with horizontal lines (angles 2 and 3) have

been used to describe curves.(From Ref. 26.)

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(e)Dynamic Rheometry

Conventional applied dough-stressing systems are destructive. They extend the structure to failure, and the extension is usually far greater than occurs during normal dough rising and oven spring. Such instruments cannot be easily characterized in terms of fundamental rheological properties. An alternative approach is to apply a much smaller strain of the order of a few percent, repeating the strain several times per second in a regular vibratory or oscillatory manner. By measuring the stress transmitted through the dough piece and its phase angle lag, it is possible to measure both the elastic and viscous components. Unfortunately, though this approach is important to someone studying fundamental rheological properties, the results are often difficult to relate to the dough's actual behavior in practical situations [27] (Fig. 28).

Figure 17Mixograms of flours milled from different wheat

classes (using farinograph optimimum absorption).(From Ref. 26.)

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3Pasting Tests

The third phase of the three-phase testing system concentrates on changes in physical properties taking place during the baking stage, the most striking of which result from the gelatinizing of starch and its degradation by amylolytic enzymes either inherent in or added to flour. Continuously measuring the sample's viscosity while it is being heated in a controlled manner is well suited for this purpose.

(a)Amylograph

The Brabender amylograph (Fig. 29) is a torsion viscometer, which provides a continuous record of the changes in the viscosity of a buffered flour suspension during a uniform temperature increase (fixed at 1.5°C/min) under constant stirring [1,45] (AACC Method 22-10). The starch granules swell upon reaching the gelatinization temperature and, together with the increased solubles concentration in the surrounding liquid due to the amylose starch molecules leaching out from the swollen granules, cause the suspension viscosity to rise.

Gelatinized (pasted) starch becomes highly susceptible to the action of thermostable amylases that are activated by the higher temperatures. They hydrolyze and liquefy part of the total starch, thus reducing its viscosity. The recorded maximum viscosity is therefore a result of two simultaneous processes (Fig. 30). Since there is little variability in the viscosity of gelatinizing wheat starch in the absence of amylases, the height of the viscosity curve is primarily a reflection of the amylolytic activity in the flour being tested. The higher the activity of the starch-liquefying enzymic system, the lower is the peak viscosity. Although both -amylase and -amylase contribute to this reduction in viscosity, the -amylase is predominantly responsible for the final viscosity. Because it is more heat sensitive, -amylase is largely inactivated before the starch substrate becomes sufficiently susceptible to its action. Similarly, the lower heat stability of fungal -amylases renders the test unsuitable for testing flours supplemented with such enzymes.

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A modified amylographic procedure had to be designed for these flours. Using a pregelatinized substrate eliminates the need for test temperatures above the optimum performance range of the enzyme [1] (AACC Method 22-12).

The classical amylograph typically requires about 4060 g to conduct a test. Brabender has recently introduced a new model, the visco-amylo-graph R, which requires only about one-tenth that amount, and it can be programmed to heat at different rates (Fig. 31).

(b)Falling Number

The principle of viscometry in determining the amylolytic activity of wheat flour is applied in the Falling Number test [1] (AACC Method 56-81B) (Fig. 32). The test is based on measuring the time required to stir and to allow a specified viscometer-stirrer to fall a standard distance. Only a single value is obtained, not a complete pasting curve as provided by the amylograph or the RVA (below). It is intended to rapidly screen small-sized wheat samples for sprout damage. Whole grain samples that have lower than 250 s FN are generally considered to be damaged, with too much -amylase present. On the other hand, samples above 400 s FN may need malt or some other -amylase preparation added to them for satisfactory bread fermentation (Fig. 33).

(c)Rapid Visco Analyzer

The Newport Scientific Rapid Visco Analyser is a stirring, temperature-controlled viscometer. It was originally developed to be a fast and robust field-use replacement for the Falling Number test, yielding a single number to indicate the extent of -amylase activity induced by preharvest sprouting in wheats. It still serves that purpose but has rapidly developed into a versatile instrument that can perform complete heating and cooling pasting curves as well. The device typically uses 35 g of starch, flour, or whole meal,

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suspended in 25 mL of water, held in a thin aluminum cup that is clamped in a temperature-controlled split copper block. The solution is stirred with a plastic paddle and heated at a programmable rate while its viscosity is being measured as the torque required to maintain the paddle's speed at a constant 160 rpm. The data is collected and analyzed by the computer that controls the instrument. Its uses now extend beyond wheat meal to modified starches, rice, maize, breakfast ce-

Figure 18The Chopin Consistograph.


real manufacture, etc. (AACC Methods 22-08, 61-02) [1,8,48,50,57] (Fig. 34).

IVPhysicochemical Tests

A number of tests were designed for predicting a flour's potential bread-baking strength from its gluten behavior. The Berliner and

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Koopman method [4] measures the swelling ability of wet gluten when immersed in a 0.1 N lactic acid solution. Higher ''specific swelling factors" can be obtained with stronger glutens. A modification to this method measures the turbidity of the suspension, which is inversely related to gluten strength.

The Pelschenke test (or dough-ball test) uses a small ball of yeasted dough that is prepared from whole wheat meal and then immersed in water at constant temperature [1] (AACC Method 56-50). The length of time before it starts to disintegrate is called the "test number." It is a measure of both gluten quantity and quality. It varies from less than 30 minutes for soft wheats to more than 6 hours for very strong wheats. By dividing the "test number" by the wheat protein content, an index to gluten quality, separated from quantity, may be obtained. The higher the index, the higher is the gluten strength.

The sedimentation test [1] (AACC Methods 56-60, 56-61A, 56-63) originally developed by Zeleny [60], measures the volume of sediment (predominantly swollen protein and occluded starch) from a crude white flour suspended in dilute acetic acid. Like the "test number," the "sedimentation value" is a reflection of both gluten quantity and quality but can be turned into an index of gluten quality alone if divided by sample protein content. It is then referred to as "specific sedimentation value."

The alkaline water-retention test [58] has been useful in predicting performance of wheat flours in cookie (biscuit) manufacture. Another widely used test to evaluate soft wheat flour quality is the MacMichael viscosity test. The special MacMichael viscometer measures the increase in viscosity of acidulated soft flourwater suspensions due to swelling of gluten proteins and, to some extent, of starch [1] (AACC Method 56-80). Starch swelling becomes more pronounced if the granules are damaged. Thus, if the range in protein content is relatively narrow, the measurements reflect primarily the condition of the starch. On the other

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Figure 19Mixing curve obtained from a spiral mixer by the Easy-Mix system.(Courtesy of BRI-Australia Ltd., North Ryde, NSW, Australia.)

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Figure 20The Brabender Extensigraph.


hand, if the changes in viscosity due to starch are more or less constant, the increase in viscosity is in direct relation to the swelling properties and quantity of gluten present. (The Brookfield viscometer is now often used for a similar test because the MacMichael viscometer is no longer manufactured and the torsion wires are no longer available.) A rapid lactic acid swelling procedure has also been developed, using the RVA [6].

Physicochemical testing also includes tests evaluating a dough's gas production and retention capacity. The National pressuremeter method [1] (AACC Method 22-11) measures the pressure of gas produced by a yeasted suspension of flour in an airtight and pressure gaugeequipped container after a 5-hour fermentation at 30°C. National has computerized the instrument so that up to eight pressure cells can be monitored simultaneously and the pressure changes are continuously graphed (Fig. 35). Other methods for measuring gas production and/or gas retention use special instruments such as the Demaray gasograph [39] or the Chopin rheofermentometer (Fig. 36). The latter, apart from measuring the total and retained gas, also monitors the changes in dough volume during fermentation (Fig.

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37). The Brabender maturograph (Fig. 38) measures the net results of gas production and gas loss by recording the changes in height of fermenting dough subjected to periodic punching at 2-minute intervals (Fig. 39). From the shape of the curve, optimum proofing conditions and fermentation tolerance can be established. The difference between top and bottom envelopes of the curve band reflects the changes in the height of the dough due to peri-

Figure 21Representative extensigram with the most commonly measured indices.

(From Ref. 3.)

odic punching and recovery and is often referred to as elasticity [41].

VBakingThe Ultimate Test

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Flour and ingredient qualities are generally determined in industrial practice by experimental baking tests. The standard procedures developed by the American Association of Cereal Chemists are listed in Table 2. They are used to evaluate flour quality and may be adopted for determining the influence on quality of other bread ingredients and treatments. The same approach is used to evaluate soft wheat flours for cookies, cakes, pies, etc. The standard methods do not always produce results that correlate with industrial practice in a particular application. Therefore, many modifications to the formulas and procedures have been made in various laboratories. The baking methods for bread and cake testing used at the American Institute of Baking are given as examples in Tables 6 and 7. The baked products are scored for various quality parameters as specified by the respective methods (see Table 2).

Test baking can be done on several scales. For example, routine flour mill and plant bakery quality-control laboratories often bake one-pound bread loaves, whereas new wheat variety screening laboratories often bake ''pup" loaves requiring 100 g of flour each. When the flour is even more limited, a mini-pup size can be baked, requiring only 35 g of flour. Even smaller 10-g loaves have been developed to help the plant breeder make decisions at an even earlier generation [42].

An especially interesting system has been developed to evaluate the bread-baking quality of individual gluten protein components following their extraction and recombination. Two grams of flour are mixed in a 2-g mixograph, then baked in small metal thimbles [13] (Fig. 40).

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Figure 22Extensigrams of different types of flour and their relation

to the baking behavior of their doughs.

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TABLE 6 White Pan Bread Control Formulaa

Ingredients Weight (g)

Sponge:

Bread flour

700

Compressed yeast

20

Yeast Food (no oxidants) 5

Water

420

Dough:

Bread flour

300

Granulated sugar

70

30

62

Bread shortening (plastic, no emulsifier)

Salt

20

Calcium Propionate 1.2

Water or ice (variable)

180

Total

1746.2

Procedure

SpongeMixing:b 1 minute at low speed; 1 minute atmedium speedTemperature: 2526°CFermentation: 4 hours at 29°C in covered container

DoughMixing: 1/2 minute at low speed; 45 minutes atmedium speed. (To full gluten development.)Temperature: 2526°C.

Floor time: 20 minutes at 29°C (covered).

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Scaling weight525 g of dough per loaf.

Intermediate proof10 min at room temperature.

MoulderStraight grain. Head roll 0.87 cm, sheeter roll 0.67cm. Pressure plate 3.1 cm, width 22.9 cm.

Pan size10.8 cm × 25.4 top inside, 9.5 cm × 24.1 bottom outside dimensions; 7.0 cm depth.

ProofTo 1.6 cm above pan top at 43.0°C ± 0.5°C and 81.5% relative humidify.

Bake22 minutes at 216°C.

CoolOne hour at ambient temperature.

MeasureWeight and volume by rapeseed displacement.

ScorePackage loaves in polyethylene bags for evaluation of internal and external characteristics on following morning.

aProcedure of the American Institute of Baking, Manhattan, KS.bHobart A-200 or A-120 mixer with McDuffee bowl and 2-prong fork agitator.

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Figure 23The effect of ascorbic acid on extensigrams recorded after different resting periods.

(Courtesy of C. W. Brabender Instruments Co., South Hackensack, NJ.)

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Figure 24Representative alveogram showing the commonly usedindices, where P is overpressure (mm), L is abscise atrupture mm), G is swelling index (ml), V is volume of air(ml), and W is deformation energy (10-4) (J).(Courtesy of Chopin SA, Villeneuve la Garenne, France.)

Figure 25Alveograms of different flour types.(A) Normal dough,(B) Short dough with little stretching properties,(C) Soft dough with excess stretching properties.(Courtesy of Chopin SA, Villeneuve la Garenne, France.)

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Figure 26The Chopin Alveograph NG.


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Figure 27The Dobraszczyk/Roberts Dough Inflation system for the

stable Microsystem TA-XT2.(Courtesy Texture Technologies, Scarsdale, NY.)

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Figure 28A dynamic stress rheometer.(Courtesy Rheometric Scientific, Piscataway, NJ.)

Figure 29

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The Brabender Viscograph-E.(Courtesy of C. W. Brabender Instruments Co., South Hackensack, NJ.)

TABLE 7 Yellow Layer Cake Formulaa

IngredientWeight

(g) Mixing methodb

A. Cake flour 400 Blend dry ingredients for 1 minute at low speed.

Granulated sugar

480

Egg solids, whole

80

Nonfat dry milk

10

Salt

12

Baking powder

23

Shortening, plastic, emulsified

160

Add shortening, emulsifier, and water 1 and incorporate. Mix 1 minute at low speed and scrape. Mix 3 minutes at medium speed and scrape.

Emulsifier

10

70

Water 1

230

Flavor 2

Egg color liquid 1

B. Water 2 120

Add water 2. Mix 1 minute at low speed and scrape, then 1 minute at medium speed.

C. Water 3 150

Add water 3 on low speed and scrape bowl. Mix 1 minute at low speed and scrape. Mix 1 minute at speed 1 and scrape.

RecordSpecific gravity and temperature of batter. Desired Temperature 24 ± 1°C.

Scale400 g of batter per 8-inch (20 cm) round layer cake pan.

Bake28 min at 185°C until fully baked. Drop pans from 10 cm immediately out of oven.

CoolOne hour on wire rack at ambient temperature. Depan cakes after 10 min.

MeasureWeight and volume of baked cakes.

ScoreInternal and external characteristics of cakes 1 day after baking.aProcedure of the American Institute of Baking, Manhattan, KS.bHobart N-50 mixer with 5-qt bowl and paddle beater.

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Figure 30Regular amylogram of malted wheat flour by AACC method. Peak viscosity is 600 A.U. (amylograph units).

(From Ref. 45.)

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Figure 31Brabender Visco-Amylograph-R.

(Courtesy of C.W. Brabender Instruments Co., SouthHackensack, NJ.)

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Figure 32The Hagberg Falling Number apparatus.(Courtesy of Falling Number A.B., Stockholm, Sweden.)

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Figure 33The falling number procedure: (1) sample preparation; (2) weighing; (3) dispensing; (4) shaking;

(5) stirring; (6) measuring; (7) result.(Courtesy of Falling Number A.B., Stockholm, Sweden.)

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Figure 34The Rapid Visco Analyzer.(Courtesy of Newport Scientific, Warriewood, NSW, Australia.)

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Figure 35National Pressuremeter for AACC Method 22-11.(Courtesy of National Manufacturing Div., TMCO, Lincoln, NE.)

Figure 36The Chopin Rheofermentometer.


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Figure 37Standard rheofermentograms indicating the changes in dough volume and gas production (line 1) and retention (line 2).

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(A and A) Dough with good fermentation power and good tolerance. (B and B) Dough with good fermentationpower but poor tolerance. (C and C) Dough with poor fermentation power and poor tolerance.(Courtesy of Chopin SA, Villeneuve la Garenne, France.)

Figure 38The Brabender Maturograph.(Courtesy of C. W. Brabender Instruments Co., SouthHackensack, NJ.)

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Figure 39A maturogram.(From Ref. 3.)

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Figure 40Thimble-sized bread loaves being checked for volume.(Courtesy Dr. Peter Gras, CSIRO Grain Quality Lab., North Ryde, NSW, Australia.)

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Cereal 2

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