contaminants of grains

CONTAMINANTS OF GRAIN

J McLean, GrainCorp, Narrabri, NSW, AustraliaC Wrigley, Food Science Australia and Wheat CRC,North Ryde, NSW, Australia

2004, Elsevier Ltd. All Rights Reserved.

Introduction

Ideally, grain should be harvested in sound and cleancondition, without any form of defect or contamina-tion. Realistically, however, there is always the like-lihood that the grain will be harvested together withnongrain material and with weed or crop seeds, all ofwhich detract from the value of the harvested crop.The loss in value relates partly to the fact that theresulting consignment of grain does not contain100% of the type of grain ordered, but worse thanthat, it is likely that the nongrain materials will causeproblems with the processing of the grain, or that theymay even render the grain unfit for the designatedpurpose or for any use.

Historic Perspective

Primitive man, as the hunter-gatherer, had to acceptwhatever material grew with the seeds that were col-lected laboriously fromwherever they could be found.As a result, the presence of contaminants must havebeen considerable. Presumably, this unsatisfactorysituation was one of various stimuli for early manto progress to cultivation and seed sowing, therebyto improve the purity and quality of grain foods. Nev-ertheless, throughout the Middle Ages, the presenceof contaminating material was generally extensive,because of poor agricultural practice and also dueto the lack of purity of the seed for sowing.Significant improvements in grain quality have been

forced as a result of the progressive change from sub-sistence agriculture (the farmers family consumingwhat they produce) to trading in grain (provisionof the grain produced for sale, in competition withothers). The past century has seen the extension oftrading from the local situation to major internationalmarketing and transport on a large scale (see Cereals:Overview). As a result, standard specifications havebeen established for the various grades of grain, basedon quality, offered for trade within a country andinternationally. Examples of these specifications areprovided in Tables 13.

An important part of these specifications is the lev-els of contaminating materials, the higher-valuegrades being those with the least foreign material.Examples of these specifications can be examinedon the websites of the export corporations of majorgrain-trading countries. The first two examples inTable 1 contrast a premium Australian wheat grade(prime hard) with a lower grade (general purpose).The former has tighter specifications for all aspectsof physical quality, compared to the lower-valuegrade, including the requirement for less material inthe category of contaminants.

Types of Contaminants

Nongrain material goes under various names, depen-ding on local terminology and on the species of graininvolved. Common terms include extraneous mat-ter, unmillable material, dockage, besatz,and screenings. This last term alludes to the generalpractice of screening the grain through sieves of suit-able size to separate material that is larger or smallerthan the normal size range of the grain involved.The act of sieving to determine screenings is illus-trated in Figure 1. The amount of these screeningsis a significant measure of grain quality, as it indicatesthe proportion of the grain consignment that is not thegrain purchased. In addition, the nature of the non-grain material is very important, depending on whichof the following categories are involved.

Plant Material from the Grain Crop

Most obviously, nongrain contaminants are derivedfrom the plants that produced the harvested grain.This includes parts of the husks, leaves, and stalks.For the cereal grains, it is not uncommon for the tipsof the heads to be included with the harvested grain.This occurs for varieties that may not fragment asreadily as others during harvesting. This is due tothe dilemma facing the breeder in selecting the bestgenotypes for the harvest operation. On the onehand, it is desirable to have a variety that shattersreadily, so that the grain is released from the head onharvesting. However, this characteristic is likely tocarry the significant disadvantage that some of thegrain will be prematurely shed onto the ground beforeor during harvest, thus reducing the yield of availablegrain.

CONTAMINANTS OF GRAIN 331

In addition, if the settings of the grain-harvestingequipment are not correct, there will be excessiveinclusion of plant parts with the grain or damageto the grain. The resulting presence of shattered orhalf grains is undesirable, because they are more sus-ceptible to insect attack and to further damage duringgrain handling and transport. The risks of such un-desirable consequences during harvest and transportare greater in very dry, hot conditions.Hot, dry conditions are also conducive to the pro-

duction of grain dust fine particles, comminutedfrom the plant material and even from the grain itself.Ongoing handling and transport of dry grain is likely

to produce more grain dust, as grains rub against eachother when it is turned or moved from storage fa-cilities to transport containers (trucks or rail cars).Figure 2 shows that grain dust is largely composedof fragments broken from the surfaces of grains. Inthe wheat dust (Figure 2a), there are short hairs fromthe brush end of the grain, and also fragments of thebran layers, as well as starch from the endosperm ofgrains that have been completely broken. The dustfrom barley (Figure 2b) shows long spear-likestructures (broken pieces of rachilla hairs) as wellas fragments of awns, lemmas, and paleas (seeGrain and Plants, Morphology). It is a controversial

Table 1 Some of the specifications for physical aspects of grain quality for contrasting grades of wheat involved in international trade

Quality attribute Australian prime hard Australian general

purpose

Canadian No 1.

CWRS

Canadian CW

feed

Test weight, kg hl1 74 68 75 65Varietal mix Specified Specified Specified Specified

Falling number 350 200

Sprouted grains Nil Nil 0.5 No limit

Unmillable material:

above 2 mm screen 0.6% max. 1.2% max.

below 2 mm screen Active scale Active scale

Small foreign seeds 0.6% max. 1.2% max. 0.05% 0.05%

Contaminants in 1/2 l measure

Seeds, see Table 4 From 1 to 50, acc.

to species

From 2 to 150,

acc. to species

Not stated Not stated

Tainting material Nil Nil

Chemicals, dyes, etc. Nil Nil

Ergot pieces 1 1 0.01% 0.10%

Loose smut pieces 3 3

Grain insects Nil Nil

Field insects 010 010 1.0 No limitEarth pieces 1 3

Sand grains 20 50

Earcockle 10 15

Head scab 1 2

Heat damaged or moldy Nil Nil

White-grain disorder 2 5

Dry green, sappy or

frosted/distorted grains

1 10 7.0% No limit

Smudge, black point 10.0% No limit

Shrunken, broken grains 7.0% No limit

Sclerotinia 0.01% 0.10%

Objectionable matter

(stone, sticks, glass, concrete)

0.03% 0.10%

Foreign material 0.2% 1.0%

Excreta 0.01% 0.03%

Vitreous kernels 65.0% No limit

Grass green 0.75% No limit

Fusarium damage 0.25% 5.0%

Fireburnt Nil 2.0%

Degermed 4.0% No limit

Dark, immature 1.0% No limit

Artificial stain, no residue 1 1 Nil 2.0%

Pink grain 2 5 1.5% No limit

Broken grain, seive #5, buckwheat 0.30% 0.50%

Sources: (1) AWB Ltd. Wheat Receival Standards (200203); (2) http://www.grainscanada.gc.ca Canadian Grains Commission Official Grain GradingGuide, dated 1 August, 2002.

332 CONTAMINANTS OF GRAIN

Table 2 Specifications for physical aspects of grain quality for grades of barley involved in international trade

Quality attribute Australian

malt 2 six-row

malting barley

Australian

malt 3 six-row

malting barley

Australian

food 1 six-row

malting barley

US no. 1

six-row blue

malting barley

US no. 4

six-row blue

malting barley

Test weight 65 kg hl1 65 kg hl1 68 kg hl1 47.0 lb bu1 43.0 lb bu1

Varietal mix Specified Specified Specified Specified Specified

Falling number 300 300 300 Not stated Not stated

Sprouted grains Nil Nil Nil 3.0% 13.0%

Unmillable material 38.0 below

2.5 mm screen

42.0 below

2.5 mm screen

30.0 below

2.5 mm screen

4.0% 10.0%

Small foreign seeds 0.6% 0.6% 0.6% 0.5% 3.0%


Seeds, specified species From Nil to 85,

acc. to species

From Nil to 85,

acc. to species

From Nil to 85,

acc. to species

2.0% 5.0%

Tainting material Nil Nil Nil Nil Nil

Chemicals, dyes, etc. Nil Nil Nil Not stated Not stated

Ergot pieces 0.5 cm 0.5 cm 0.5 cm Nil Nil

Loose smut pieces Nil Nil Nil Nil Nil

Grain insects Nil live, 10 dead Nil live, 10 dead Nil live, 10 dead Nil Nil

Field insects 3 3 3 Nil Nil

Earth pieces 3 3 3 0.5% 3.0%

Sand grains 50 50 50 0.5% 3.0%


(stone, sticks, glass, concrete)

Nil Nil Nil Not stated Not stated

Frosted 5 5 5 0.4% 0.4%

Dark tipped (per 100 g) 10 10 10 Not stated Not stated

Odors, moldy Nil Nil Nil Nil Nil

Chemical residues (chemicals

not approved for use on grain)

Nil Nil Nil

Heat damage 0.1% 0.1%

Sources: (1) Australian GrainCorp Receival Standards 2002/2003; (2) USDA (1995) USDA Grain Inspection Handbook.

Table 3 Specifications for physical aspects of grain quality for grades of oilseeds involved in international trade

Quality attribute Australian

canola

CSO-1

Australian

sunflower

CSO-4

Australian

soybean

CSO-9

US no. 1

grade

canola

US no. 3

grade

canola

US no. 1

grade

soybeans

US no. 4

grade

soybeans

US no. 1

grade

sunflowers

US no. 2

grade

sunflowers

Test weight 6.2 kg hl1 Not stated Not stated 56 lb bu1 49 lb bu1 25 lb bu1 25 lb bu1

Sprouted grains 5% 5% 5%

Unmillable material 5.0% 5.0% 1.0% 5.0%


Seeds, specified species From nil

to 200,

acc. to

species

From nil

to 200,

acc. to

species

From nil

to 200,

acc. to

species

Not stated Not stated

Ergot pieces 0.05% 0.05%

Oil content 42% 40%

Green seeds 5% Nil Nil 2.0% 20.0%

Chlorophyll 12 mg per kg

Impurities 3% 4% 4%

Broken seed 7% 7% 20%

Damaged seed 3% 3% 3% 2.0% 8.0% 5.0% 10.0%

Heat damaged 0.1% 2.0% 0.2% 3.0% 0.5% 1.0%

Sclerotinia 0.05% 0.15%


(stone, sticks,

glass, concrete)

0.05% 0.05%

Splits 10.0% 40.0%

Grains of other colors 1.0% 10.0%

De-hulled seed 5.0% 5.0%

Sources: (1) AOF Incorporated Technical and Quality Standards, December, 2001; (2) USDA (1995) USDA Grain Inspection Handbook.


matter in international trade as to whether the accu-mulated dust should be removed before shippinggrain, or whether it is a legitimate part of a graincargo. In any case, the dust generated during grainhandling is a significant health problem, causingirritation to the bronchial tract as well as to the

skin. Dust also creates safety concerns due to itsexplosive potential; therefore dust reduction isa high priority at grain storage centers.

Defective Grains

Defective grains may be regarded as undesirable con-taminants, even though of the same grain species.Such defects include:

Immature cereal grains these may have comefrom side tillers that formed at a late stage com-pared to the main tillers of the plant. Alternatively,it may indicate that varieties of different maturityhave been sown as amixture. These grains are likelyto be green in color and sappy in texture.

Sprouted grains (Figure 3) these are grains thathave become wet, and have thus started the germi-nation process (see Cereals: Grain Defects).

Sun-cracked rice grains these are grains that willprobably fall to pieces during rice milling (the re-moval of the outer bran layers), thereby reducingthe yield of whole rice grains.

Figure 1 Sieving of a grain sample to remove screenings(nongrain material).

(a) (b)

(c) (d)

100 m

400 m

100 m

10 m

Figure 2 Scanning electron micrographs of grain dust from (a) wheat and (b) barley. The photo of half a barley grain (c) shows wherethe rachilla hairs have been broken from the base of the rachilla. The rachilla hairs are also shown at greater magnification (d). In each

photo, the black bar at the bottom, near the right side is: (a) 100 m, (b) 100 m, (c) 400 m, and (d) 10 m.


Vitreous content, pinched grains, black point,frosted/distorted are very important but controver-sial defects. Ear cockle (seed-gall nematode), a dis-ease caused by Anguina tritici, must be detected asit is an object of exclusion due to quarantine incertain countries, especially in Iran.

Infected Grains

Various forms of infection with microorganismscause grains to become dangerous contaminants(see Cereals: Grain Diseases). For example, grainthat is harvested with a high moisture content(416% moisture) may be infected with molds, com-monly called field fungi, such as Fusarium and Alter-naria causing, in turn, the production of mycotoxins.Because these toxins are active at very lowconcentrations, e.g., a few ppb, their detection is dif-ficult. They are not necessarily present in visuallyspoiled grain (e.g., moldy), so there is the need forreadymeans of testing. Immuno-assay kits are ameansof doing so quickly and in field situations. If notdetected, mycotoxin-affected grain may cause severeillness or death to humans or animals. Grain affectedby field fungi may be dark brown, gray, or variousshades of black discoloration or pink, especially whenaffected by Fusarium spp.Ergot infection is another serious contaminant,

mainly present in rye, rye grass, canola, and to

a lesser extent, wheat. In this case, the ergot fungus(Claviceps purpurea) infects the flowers of the cerealgrain, producing an ergot body in place of the grain(Figure 4). The ergot bodies often thresh intact, easilyrecognizable in grain samples as black bodies (scler-otia) larger and longer than the normal grain length.The extent of ergot contamination is generallyspecified as a percentage by weight, but the lengthof ergot bodies placed end-to-end is a simple measureused in practical situations. Harvested grain of anyspecies may contain ergots from other species, espe-cially from rye grass (Lolium perenne). Any of thesesources of ergot produce toxic alkaloids, which maycause injury in cattle when present at a level as low as0.05%. On the other hand, some poultry species ap-pear to be much more tolerant to ergot poisoning (seeCereals: Grain Diseases).Another serious infection of cereal grains is bunt,

also known as ball smut or stinking smut, caused byTilletia caries or T. foetida. This defect also involvesthe replacement of the endosperm of the grain by buntspores, which have a pungent unpleasant odor. Asa result of this form of contamination, sound grainmay be tainted by admixture with bunt-affected grain(Figure 5). If these grains are broken, black buntspores spread through the grain as a further sourceof contamination. In the case ofwheat, the bunt sporescatch in the brush hairs of sound grains (Figure 6).In grain storage, excessive moisture can lead to

moisture migration and bin burn of the grain (caus-ing heat damage and moldy appearance) resulting

Figure 3 Sprouted heads of wheat. The heads have becomewet when harvest ripe. The one at left is a sprout-susceptible

variety and the grains have started to sprout inside the head.

Figure 4 Ergot-infected heads, in which ergot bodies have re-placed grains in the head. (Reproduced with permission from

Ferns GK, Fitzsimmons RW, Martin RH, and Wrigley CW (1978)

Australian Wheat Varieties: Supplement No 1. Melbourne,

Australia: CSIRO.)


from the development of field fungi, which may pro-duce dangerous toxins and offensive odors.

Other Crop Seeds

Commonly found contaminants are the seeds of othercrop plants. These are likely to be species whoseplants are of similar size and maturity to the targetseed. It is thus difficult to avoid harvesting themtogether with the intended crop. Such foreign seeds

are likely to be other agricultural species (e.g., barleyor rye in a wheat crop) that has been present in theseed sown, or that have been carried over froma previous crop at this growth site. Such contaminantsmay not be critical unless they interfere with the sub-sequent processing of the grain, such as milling intoflour. A further consideration is how readily they canbe removed, if their removal is essential, because thisexercise will add to processing costs. Oilseeds, forexample, pose the threat of disrupting wheat-millingequipment with the build-up of oil residues, althoughcontaminants such as canola are relatively easy toseparate from wheat before milling.For a wheat consignment, there may be no need to

removeminor contamination with other cereal grains,such as barley and oats (up to 5%). Canadian re-search has shown that flour yield decreased by0.4%for each addition of 1% of barley added to a wheatsample. Milling stocks fed well during flour milling,despite the barley contamination. Likewise, the ef-fects of contamination of wheat with cultivatedoats (or even wild oats) were similar to that of barley,except that at 5% addition, oats caused difficulty withthe milling process.

Weed Seeds

Weed seeds present problems of greater severity thancrop seeds (Table 4). Some weed seeds are the samesize as grain kernels, which make it virtually impos-sible for them to be sieved out of a parcel of grain (e.g.,Phalaris). For a start, agricultural authorities mustrestrict the seeds of noxious weeds, due to the threatthat they pose to cropping and grazing. However, insmall amounts, their presence may not be serious toagriculture because they are likely to be destroyed byprocessing, such as flour milling. If wheat containsseeds with a dark seedcoat, they are likely to causedark specks in flour, which can decrease the visualappeal of the end product for the market. On theother hand, some weed seeds cause serious problemsbecause some are toxic to humans and animals. In thiscategory are species such as castor oil seed (Ricinuscommunis), Mexican poppy (Argemone species), andthornapple (Datura species). Ricin, the toxic principlein the castor oil seed, is reported to be one of the mosttoxic plant substances known.Tainting seeds, whose scent may taint a whole con-

signment of grain, must be avoided, and they aregenerally specified as nil tolerance, i.e., none ofthis type is allowed. In Australia, for example,seeds called Hexham scent (Melilotus indicus) im-part their scent to the grain with which they may bemixed, with the risk of a large consignment of grainbeing tainted by the presence of a relatively small

Figure 5 Bunt of wheat. (Reproduced with permission fromFerns GK, Fitzsimmons RW, Martin RH, and Wrigley CW

(1978) Australian Wheat Varieties: Supplement No 1. Melbourne,

Australia: CSIRO.)

Figure 6 Bunt spores caught in the brush hairs of sound grains.(Reproduced with permission from Ferns GK, Fitzsimmons RW,

Martin RH, and Wrigley CW (1978) Australian Wheat Varieties:

Supplement No 1. Melbourne, Australia: CSIRO.)


contribution of grain with this contamination; similarproblems may be produced by the presence of euca-lyptus leaves. Animals will probably reject feed grainif it is tainted. Alternatively, if they do consume it,the taint may be passed through to the animalby-products, such as milk.There is naturally great variation in the range of

weed-seed species that are relevant to specific regionsand grain species. Regional and national booklets arepublished for many grain-growing regions, illustrat-ing a relevant range of weed and crops seeds. Exam-ples of weed seeds that must be identified andrestricted are shown in Figure 7.

Insects

Insects that attack grains are a serious case ofcontamination (Figure 8). Accordingly, there isa nil tolerance for live insects in many regions(Tables 13). This specification may be relaxed toa small extent in the cases of dead insects and forspecies of insects that do not attack grains, (ona case-by-case basis only) such as field insects. Infes-tation with grain-attacking insects (previously or cur-rently present) may be indicated by the presence ofgrains that have been partly eaten by insects (Figure 9).There are two main types of grain insects. Primary

insects are more destructive as they can attack soundgrain, while secondary insects can only attack grainthat has been damaged. Insects can deplete the energyvalue of the grain, greatly reducing its value even forstock feed. Insect infestations are often associatedwith bad odors. Due to the serious threat that some

insects can impose, there is a strict nil tolerance onspecific species. For example, the Khapra beetle, Tro-goderma granarium, is the worlds most serious insectpest. This insect does not occur in some countries(e.g., Australia). However, the warehouse beetle,T. variable, is often mistaken for the Khapra beetleand this can jeopardize not only the acceptance ofa parcel of grain but the whole countrys reputation.

Animals and Animal Products

Further contaminants include snails, rodents, urine,feces, rodent hairs, birds, bird feathers, and snakes.Snails rarely live more than 2 weeks in storage, so thatthey are unlikely to reproduce during storage. Mostanimals contaminate grain through the grain-storagesystem (with the exception of snails) due to their re-production and spread throughout the grain store.Rodents and birds are attracted to the grain as afood source and they will often nest there. As a result,there can be the added contamination from the accu-mulation of their urine, feces, rodent hairs, feathers,eggs, and decaying carcasses. For example, a single ratcan produce 12 000 droppings, 2.9 l of urine, and 0.9million shed-hairs in 6 months. Rodents thus becomean important issue, especially when there is a plague.Animals and birds are also potential vectors for dis-eases. Snakes and some bird species will be presentaround storage sites, preying on rodents and otherbirds. All of these animals can become included ina consignment of grain accidentally if present onone of the transport belts or elsewhere on thegrain-transport path when it is turned on.

Table 4 Groupings of contaminating seeds (a few examples only) used by the Australian wheat industry to indicate their severityas contaminants

Seed type Botanical name Local common name Maximum number allowable in 1/2 l

Most grades GP1a Feed

1 Ricinus communis Castor oil plant Nil Nil Nil

Coriandrum sativum Coriander

Allium vineale Crow garlic

2 Datura spp. Thornapple 1 1 1

Gossypium spp. Cotton seed

3 Zea mays Maize 1 50 100

Lupinus spp. Lupin

Helianthus annuus Sunflower

4 Melilotus indicus Hexham scent 5 50 50

Argemone spp. Mexican poppy

5 Sorghum halepense Johnson grass 20 80 200

Lolium temulentum Drake, darnel

6 Secale cereale Cereal rye 50 200 500

Sorghum bicolor Sorghum

Avena sativa Oats

aGeneral Purpose 1.Source: AWB Ltd., Melbourne, Australia.


Agricultural Chemicals

Pickling compounds (fungicides) applied to seed grainrender the grain unfit for consumption (human oranimal). Pickling colors range from bright pink orgreen through to a slight pink or green coloration.There is a strict nil tolerance for pickled grain asa small amount can render a whole stack unusable.Parcels are regularly checked for pesticide residue lev-els (obtained through the application of herbicidesand/or insecticides). There are tolerances by nationalregulatory bodies, known as maximum residue limits(MRL). Grain with levels above these limits cannot beused or sold legally.Grain that is fed to cattle and chickens can transfer

the chemicals, thus posing a threat to their markets,with the likelihood that the resulting meat will beprohibited from human consumption. Examplesinclude endosulfan in cottonseed hulls and wheat

resulting from spray drift. It is necessary to observeand follow chemical instructions for correct applica-tion rates and withholding periods to ensure thatMRL levels are not exceeded and to reduce the chanceof insect resistance building up.Heavy metals (mercury, cadmium, and lead) are

contaminants that must be tested for routinely asa precautionary measure, especially in industrializedcountries.

Inanimate Materials

Sticks, stones, and other inanimate materials causeproblems in both analysis and processing, as theycan damage grinders and technical equipment. Theseverity of the material depends on their size. If thematerial is a similar size to the grain, it cannot besieved out easily and this can become a seriousissue. Such materials can be picked up during the

Silybum marianumvariegated thistle

Carthamus lanatussaffron thistle

Emex spp.double geethreecornered Jackspiny Emexcats heads

Galium tricornutum(Galium tricorne)threehorn bedstraw

Figure 7 Weed seeds that are likely to cause problems if identified in grain consignments. (Reproduced with permission from FernsGK, Fitzsimmons RW, Martin RH, andWrigley CW (1978)AustralianWheat Varieties: Supplement No 1.Melbourne, Australia: CSIRO.)


harvesting process or introduced through the storageand handling processes if equipment is not carefullycalibrated and cleaned prior to use.

Tainting Contaminants

In addition to the contamination of grain with taint-ing materials as a result of harvest, tainting of a grainconsignment can occur during storage and transport ifa taint or odor is acquired from materials with thegrain. One such source can be the packaging materialused, in the case of grain that is stored and transportedin bags, for example, hessian bags.

GM Grain

With the introduction of genetically modified (GM)grain (initially involving maize, canola, and cotton),and in response to various international market de-mands, the presence of GM grain within conventionalgrain delivered can lead to rejection of that grain.Methods are being put into place that will permit

Sitophilus granariusGranary weevil

Sitophilus oryzaeRice weevil

Rhyzopertha dominicaLesser grain borer

Tribolium castaneumRust-red flour beetle

Cryptolestes spp.Flat grain beetle

Oryzaephilus surinamensisSaw-toothed grain beetle

Figure 8 Insect species that attack grains. (Reproduced with permission from Ferns GK, Fitzsimmons RW, Martin RH, and WrigleyCW (1978) Australian Wheat Varieties: Supplement No 1. Melbourne, Australia: CSIRO.)

Figure 9 Wheat grains that have been partly eaten by insects,indicating previous (or current) infestation. (Reproduced with per-

mission from Ferns GK, Fitzsimmons RW, Martin RH, andWrigley

CW (1978) Australian Wheat Varieties: Supplement No 1.

Melbourne, Australia: CSIRO.)


the detection of such contamination thereby guaran-teeing the required grain quality required by specificmarkets.

Analysis of Contaminating Materials

Given the wide range of contaminants that may beharvested with grain, plus the variations in allowablelevels, it is important that there should be rapid meansof identifying them. This requirement applies espe-cially to identifying the species of contaminatingseeds, since the range of species varies considerablyfrom one region to another. Accordingly, manualsillustrating the range of contaminants are providedfor staff training, to inform growers and for usewhen grain is delivered.

Sampling

However, an essential prerequisite of valid analysis isthe initial step of taking a representative subsample ofthe load being analyzed. Sampling procedures are gen-erally specified together with the manuals illustratingthe contaminants. Procedures are also published bygrain-trading authorities. The website of the US De-partment of Agriculture (www.usda.gov/gipsa/pubs/farm-proc/practical_proc.htm) specifies standardsampling procedures for various grain-productionsituations. Standard procedures for sampling are pro-vided in the Methods of the American Associationof Cereal Chemists (AACC) and the InternationalAssociation for Cereal Science and Technology

(ICC) (see Appendix: Test Methods for Grain andGrain-Based Products).A critical stage of grain sampling is taking a rep-

resentative set of samples from a truck when grain isfirst delivered from harvest to the elevator (Figure 10).In this case, sampling is done so that a whole truckscontents can be observed from above. Routinely, thegrain in the truck is sampled by pushing a samplingspear into the grain at several points. This form ofsampler is designed to take grain from several verti-cally separated points throughout the depth of grain.Alternatively, vacuum probes are used to spear thetruck in a straight vertical line right down throughto the bottom of the load. If the grain is deliveredby road, train, or other vehicle with multiplecompartments, each bin is sampled three times.

Sieving

An example of the use of mechanical sieving isprovided by the routine practice of GrainCorp ineastern Australia using the Agtator (Figure 11).Forty shakes are automatically performed to andfro, as specified by Australian receival standards.The use of a mechanical sieve such as this ensuresrepeatable movement, speed, and duration. Thefollowing screen sizes are appropriate: wheat,2.0mm slotted; for barley, 2.5mm and 2.2mmslotted; for sorghum, 2.0mm slotted (wheat screen);for sunflowers, 2mm round; for chickpeas, top3.97mm slotted over bottom 2mm slotted; and forcanola, top 2.58mm round over bottom 1.00mmround.

Figure 10 Sampling grain from a truck using a spear sampler.


Visual Examination and On-the-SpotInstrumental Analysis

Traditional methods of analyzing contaminants in-volve visual inspection, and this approach is stillthe best with respect to providing an immediate out-come and requiring no expensive equipment. How-ever, this approach is subjective and highly dependenton the experience of the inspector. This expertise isacquired and maintained by ongoing training, the useof illustrated manuals and actual samples, requiringongoing monitoring to ensure the standards are ap-plied consistently. By this approach, grain samples arefirst evaluated visually at the site of grain receival, andthen a representative portion may be sent back toa regional laboratory for a second cross-reference as-sessment. In addition, a further portion may be pre-sented to buyers of the grain for their additionalevaluation. The identification of the species of insectsis also an important part of this process, because thevarious insect species differ in the severity and con-sequences of infestation.The immediate detection of serious contaminants is

critical at the time of delivery, so that defective grainloads are not combined with sound grain, as thismight downgrade the grain to which it is added. Sub-sequent analysis in the laboratory provides results toolate to prevent damage of a large grain consignmentby, for example, the incorporation of a relativelysmall load of grain that is tainted or insect infested.On-the-spot analysis is thus critical.It has become usual for visual inspection to be

complemented by on-the-spot testing to provide ob-jective results for specific critical aspects of contam-ination. Image analysis has great potential forreplacing the subjectivity of human involvement byanalysis of the image of grains and contaminantsprovided by a television camera. However, the

introduction of image analysis is a slow process dueto the expense and technical input required to developmethods and monitoring procedures.NIR analysis has been used to detect the presence of

insect infestation, probably due to the ability of thisspectroscopic method to detect the distinctive pres-ence of insect protein and/or chitin. The use of NIRmethodology has the potential advantage that NIRequipment is already in routine use to determinemoisture, protein content, and oil content, but theNIR units in routine use may not be adequate formore complex analyses. Ultraviolet light inspectionprovides an immediate means of checking for rodenturine, which fluoresces with a blue-green color (seeAppendix: Test Methods for Grain and Grain-BasedProducts; AACC Method 2885). Rapid immuno-assay kits are now available to detect and quantifya range of chemical contaminants, aflatoxins, anddamage from sprouting.

Analysis in the Laboratory

Contaminant identificationmay continue by visual ex-amination at a regional or central laboratory, wherea higher level of expertise may be expected of theinspectors. There is also a role for image analysisand sophisticated NIR equipment at a central site,where the volume of samples would warrant the ex-pense and need for operator expertise. Awide range oflaboratory methods is available for the detection ofspecific contaminants. For example, the AACCMeth-ods provide many standard procedures in section28 AACC Method Group (see Appendix: TestMethods for Grain and Grain-Based Products).Laboratory methods include gas or liquid chro-matography to analyze for agricultural chemicalsand ELISA immuno-assays for many contaminants,especially aflatoxins.

Avoidance of Contaminants

Purity of Seed Sown

An obvious source of contaminants is the seed orig-inally sown. If it contains foreign seeds, these arelikely to multiply and downgrade the harvestedgrain. Additional risks include the presence of dis-eased seed, which will lead to the spread of diseasesduring growth. It is thus important to obtain seed ofguaranteed purity at the time of purchase.

Farm Management

Use of best farm-management practices includescleaning and calibrating of harvester and sowingequipment before use, proper preparation of fieldsbefore sowing, ensuring that the crop is mature before

Figure 11 Agtator equipment for sieving grain.


harvesting, and storage of the grain so that it does notbecome contaminated. During growth of the crop,weeds must be controlled. In addition, it is valuableto use crop rotations as bio-fumigants to avoid thebuildup of microbial spores in soils.

Quality Assurance Methods

All these methods of contaminant avoidance shouldbe combined for implementation via a system of qual-ity assurance, to provide systematic recognition ofpotential hazards, intentional approaches to avoidthe hazards, and records to indicate how and whenthe preventive measures were taken. This approachextends beyond the farm, to involve, for example, theuse of traceable and repeatable methods of appropri-ate farm practices, working only with companies thatare themselves quality-assurance certified.

International Regulations onContaminants

International regulations on many food matters areadministered by parts of the Codex Alimentarius. TheCodex Committee on Food Additives and Contami-nants (CCFAC) establishes or endorses maximum orguideline levels of contaminants in food and animalfeed, as well as dealing with food additives and nat-urally occurring toxicants. CCFAC is developingrisk-analysis approaches to be applied to all foods.The resulting document is the General Standard forContaminants and Toxins in Foods. Further details ofthe latest developments are available at the USDAwebsite: www.fsis.usda.gov/oa/codex/fac.htm.

Future Prospects

Traditionally, the presence of contaminants of anytype in a grain consignment has prompteda reduction in its market value, because any variationin appearance can provide grounds for bargaining andfor price reduction. More recently, there has beena growing awareness that some defects and contam-inants may have relatively small financial conse-quences. In some instances, the economic effectscan readily be assessed. For example, the presenceof 2% screenings (by weight) at a 5% reduction inprice would be a worthwhile bargain, if the cost ofcleaning is more than covered in the price difference.Similar considerations apply to other innocuous con-taminants, if their dimensions make them easily re-movable. Another approach to overcoming suchproblems may involve the intelligent blending of di-verse grain samples. Relatively simple research activ-ities can establish the extent of economic penalties for

the presence of one grain type as a contaminant inanother, e.g., oilseed in cereal or the reverse.There is a continuing need for more effective meth-

ods of analysis to characterize and quantify the pres-ence of contaminants in grain deliveries at the point ofreceival and during grain handling. New screeningmethods should preferably be deployable on-the-spot and be nondestructive of the grain. Most ofall, they need to be cost-effective, the cost of deploy-ment warranting the benefits, and the risks therebyavoided. Detection of contaminants by image analysisis likely to increase in its application. We can expectthat large grain sorters will be placed into grain-storage sites and cleaning facilities.Increases in quality demands will mean the need to

increase the efficiency of detection and measurementrequirements at the receival point. In summary, thesenew methods must be rapid (taking less than 5min),easy to operate with minimal operator skill required,nondestructive and cost-effective, being able tooperate in a wide range of temperature variation,under dusty conditions, occupying minimal benchspace . . . but the fulfillment of these requirements isa tall order.

See also:Cereals: Grain Defects; Grain Diseases.Plants:Diseases and Pests.

Further Reading

AOF Incorporated Technical and Quality Standards,December, 2001.

American Association of Cereal Chemists (1983) ApprovedMethods of the American Association of CerealChemists, 8th edn. St. Paul, MN: American Associationof Cereal Chemists.

Australian GrainCorp Receival Standards 2002/2003.AWB Ltd. (2001) Australian Graincrop Receival Standards

2002/03. Melbourne, Australia: AWB Ltd.AWB Ltd. (2001) Wheat Receival Standards 2002/03

Season. Melbourne, Australia: AWB Ltd.CCFRA (2002) Manual of Methods for Wheat and Flour

Testing. Guideline No. 3, (3rd edn.). Chipping Camp-den, Gloucestershire, UK: CCFRA Technology.

Ferns GK, Fitzsimmons RW, Martin RH, and Wrigley CW(1978) Australian Wheat Varieties: Supplement No 1.Melbourne, Australia: CSIRO.

Fitzsimmons RW and Wrigley CW (1979) AustralianBarleys: Identification of Varieties, Grain Defects andForeign Seeds. Melbourne, Australia: CSIRO.

National Institute of Agricultural Botany (2000) BotanicalDescriptions of Cereal Varieties. Cambridge, England:National Institute of Agricultural Botany.

USDA Grain Inspection, Packers and Stockyard Adminis-tration (1995) Grain Inspection Handbook: Book 1.Washington, DC: USDA (http://www.usda.gov/gipsa).


Wrigley CW (ed.) Identification of Food-Grain Varieties.St. Paul, MN: American Association of Cereal Chemist.

Relevant Websites

http://www.grainscanada.gc.ca Canadian GrainsCommission Official Grain Grading Guide, dated 1August 2002.http://www.aaccnet.org American Association ofCereal Chemists.http://www.aocs.org American Oil ChemistsSociety; Standard Methods.http://www.awb.com.au AWB Ltd, Melbourne,Australia.http://www.campden.co.uk Campden and Chor-leywood Food Research Association.

http://www.cgc.ca; www.grainscanada.gc.ca Ca-nadian Grains Commission, Winnipeg.http://www.fsis.usda.gov Codex Committee onFood Additives and Contaminants.http://www.pi.csiro.au CSIRO Plant Industry,Australia.http://www.wheat.pw.usda.gov Graingenes.http://www.icc.or.at International Association forCereal Science and Technology.http://www.seedtest.org International Seed TestingAssociation.http://www.crop.cri.nz New Zealand Institute ofCrop and Food Research.http://www.sgrl.csiro.au Stored Grain ResearchLaboratory, Canberra, Australia.http://www.usda.gov United States Department ofAgriculture.

Corn see Maize: Genetics; Breeding; Quality Protein Maize; Dry Milling; Wet Milling; Foods from Maize.

COTTONSEED

E Hernandez, Texas A&M University, College Station,TX, USA

2004, Published by Elsevier Ltd.

Introduction

Most vari eties of co tton ( Gossypium hirsutum L., G .aboreum L., G. barbadense L., or G. herbaceum L.)are grownmainly in warm climates around the world.Over 98.5 million tons (Mt) of cotton were producedworldwide in 200102 and over 33.6Mt of cotton-seed. Cotton is grown for its fiber (over 80% of itsvalue) and the seed is used mostly for oil recovery andfeed. Whole cottonseed can be fed to dairy cattle, andthe meal resulting from oil extraction is fed primarilyto ruminants and, in limited amounts, to poultry andswine.Traditional varieties of cottonseed contain gossy-

pol, a yellow-green polyphenolic compound consid-ered toxic to man and monoga stric an imals ( Figure 1),reportedly affecting the heart, liver, and reproductive

organs. It has been used in China as a male contra-ceptive but the practice was abandoned because ofpermanent side effects. Gossypol is dispersed in theplant as deposited structures or glands, which canbe seen as black specks in the stems, leaves, and seed( Figure 2). The glands in the seed are ov oid structure scontaining 3550% gossypol and are 0.0250.178mm in diameter. These gossypol glands aredifficult to break by mechanical means, but heatgenerated in extraction of oil by pressing, binds gos-sypol to protein, turning it nontoxic. Switching tosolvent extraction with hexane, where no appreciableheat is generated, increases the free gossypol contentin the meal over ten times.Raw cottonseed kernels may contain 0.62.0%

free gossypol. The Food and Drug Administrationin the US (FDA) limits free gossypol in human foodproducts and ingredients at 450 ppm, and the ProteinAdvisory Group of the United Nations Food andAgriculture Organization (FAO) and World HealthOrganization (WHO) has set maximum guidelinesof 600 ppm for free gossypol and 12 000 ppm total

COTTONSEED 343

Contaminants of Grain Introduction Historic Perspective Types of Contaminants Plant Material from the Grain Crop Defective Grains Infected Grains Other Crop Seeds Weed Seeds Insects Animals and Animal Products Agricultural Chemicals Inanimate Materials Tainting Contaminants GM Grain

Analysis of Contaminating Materials Sampling Sieving Visual Examination and On-the-Spot Instrumental Analysis Analysis in the Laboratory

Avoidance of Contaminants Purity of Seed Sown Farm Management Quality Assurance Methods

International Regulations on Contaminants Future Prospects Further Reading Relevant Websites

contaminants of grains

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