Waxy corn

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Waxy corn (maize) was found in China in 1909. As this plant showed many peculiar traits, the American breeders long used it as a genetic marker to tag the existence of hidden genes in other maize breeding programs. In 1922 a researcher found that the endosperm of waxy maize contained only amylopectin and no amylose in opposition to normal dent maize varieties that contain both. Until World War II, the main source of amylopectin was cassava but when Japan severed the supply lines of the States, they forced processors to turn to waxy maize. Amylopectin is used in food products, in the textile, adhesive, corrugating and paper industry.

Feeding trials later showed that waxy maize produces more efficient gains than normal dent. Interest in waxy maize suddenly mushroomed. Geneticists could show that waxy maize has a defect in metabolism precluding the synthesis of amylose in the endosperm. It is coded by a single recessive gene (wx). Waxy maize yield about 3.5% less than their normal dent counterparts and has to be isolated from any nearby normal maize fields by at least 200 meters.

Contents

[edit] History

The exact history of waxy maize is unknown. The first mentions of it were found in the archives of the U.S. Department of Agriculture (USDA). In 1908, the Rev. J. M. W. Farnham, a Presbyterian missionary in Shanghai, sent a sample of seeds to the U.S. Office of Foreign Seed and Plant Introduction. A note with the seeds called it: “A peculiar kind of corn. There are several colours, but they are said to be all the same variety. The corn is much more glutinous than the other varieties, so far as I know, and may be found to be of some use, perhaps as porridge.” These seeds were planted on May 9, 1908, near Washington, D.C., by a botanist named G.N. Collins. He was able to grow 53 plants to maturity and made a thorough characterisation of these plants, including photographs, which were published in a USDA bulletin issued in December of 1909.[1] In 1915, the plant was rediscovered in Upper Burma and in 1920 in the Philippines. Kuleshov,[2] when screening the distribution of maize in Asia, found it in many other places.

The discovery in China of a distinct type of maize bears the historical question whether maize was known in the Orient before the discovery of America. The question was closed at the end of the 19th century by De Candolle[3] who stated: ”Maize is of American origin, and has only been introduced into the old world since the discovery of the new. I consider these two assertions as positive, in spite of the contrary opinion of some authors.“ But the finding of this unique variety of maize suggested a re-examination of the question. He also states that Portuguese arrived in China in 1516, simultaneously introducing maize.

Collins supposed that waxy maize has arisen by a way of mutation in Upper Burma [4]. In this case, it was difficult to conceive that from 1516 on the American plant had had time to penetrate into a wild country inaccessible to foreigners, to produce a mutation, and as such a mutant to spread from the Philippines to Northern Manchuria and the Primorsky region within three to four hundred years.[5] We are able to counterpart both of these arguments nowadays. At first we know that the waxy mutation is quite common (see #Genetics). Secondly, the fact that maize, if introduced into Asia in Post-Columbian times, must have been rapidly accepted merely indicates that, like the potato in Ireland, it met an acute and pressing need.[6] Goodrich[7] states that there are now in China some 6000 local histories called gazetteers written from A.D. 347 on. Maize was first accurately described in one of them, published in the sixteenth century.

Ho [8], an eminent Chinese historian, stated: “Summing up the introduction of maize into China, we may say that maize was introduced into China two or three decades before 1550 . . . ” It might be, as various students concluded, that maize reached Asia before 1492, but currently we are not aware of a single plant fragment, artifact, illustration, or written record to prove it. Therefore, any undocumented statement about its occurrence there in earlier times is to be regarded with scepticism until substantiated.[9][10] Thus, the two assertions of De Candolle are still valid.

In his publication, Collins characterised the new plants as possessing a number of unique characters. No indications of these characters in any recorded form of Zea mays had thus far been found. Several of the unique features combine to enable the plant to resist the drying out of the silks by dry, hot winds at the time of flowering. Although the plants produced such small ears that they could find no place in direct competition with the improved varieties, the possession of this adaptation gave the new type an economic interest, particularly in some parts of the semiarid Southwest. Consequently, the effort has been made to combine by hybridising the desirable characters of this small variety with those of larger and more productive types.[11]

When Collins found such a distinct difference in the appearance of normal and waxy maize endosperm, he suspected a difference in chemical composition, but the analysis did not yield any unusual results. The percentages of starch, oil, and protein were all within the normal range. Yet, he was intrigued by the physical nature of the starch, and wrote: “In view of the recent development of specialised maize products as human food, the unique type of starch may be of some economic importance."

Actually, for many years the main use of waxy maize was a genetic marker for other maize breeding programs. Breeders were able to use some of the traits to “tag” the existence of hidden genes and follow them through breeding programs. It is possible that waxy maize would have become extinct again in the USA without this special application in breeding.

In 1922, another researcher, P. Weatherwax of Indiana University in Bloomington, reported that the starch in waxy maize was entirely of a “rare” form called “erythrodextrin”, known today as amylopectin[12]. He found that this rare starch stained red with iodine, in contrast to normal starch which stained blue. Bates, French et al.[13] and Sprague, Brimhall, et al.[14] confirmed that endosperm starch of waxy maize consists nearly exclusively of amylopectin. The presence of amylopectin in rice had been demonstrated previously by Parnell.[15]

In 1937, just before World War II, G.F. Sprague and other plant breeders at what was then called Iowa State College had begun a crossbreeding program to attempt to introduce the waxy trait into a regular high-yielding hybrid maize. By this time, the waxy plant no longer had the peculiar structural traits noted by Collins, probably due to years of crossing into various genetic stocks. Only the unique endosperm had been retained.

At this time, waxy maize was not so important because the main source of pure amylopectin still was the cassava plant, a tropical shrub with a large underground tuber.[16] This situation maintained until World War II, when the Japanese severed the supply lines of the States and forced processors to turn to waxy maize.[17] Waxy maize appeared to be especially suitable for this purpose because it could be milled with the same equipment already extensively used for ordinary maize. [18]

H. H. Schopmeyer has advised that the production of waxy maize in Iowa for industrial use amounted to approximately 356 metric tons in 1942 and 2540 tons in 1943.[19] In 1944, there were only 5 varieties of waxy maize available for waxy starch production. In 1943, to cover all the special requirements for amylopectin, approximately 81650 tons of grains were produced. From World War II until 1971, all the waxy maize produced in the U.S. was grown under contract for food or industrial processors. In fact, most of the maize was grown in only a few counties in Iowa, Illinois, and Indiana.[20] But in 1970, as most maize growers remember well, the Southern corn leaf blight epidemic (Helminthosporium maydis Nisik. and Miyake) swept the U.S. corn belt.

At the same time, at least 80% of the maize being grown in the U.S. was susceptible to the blight because this maize contained the “Texas type” male-sterile cytoplasm, which allowed production of hybrid seed without mechanical or hand detasseling. So quite naturally, there was a mad scramble in 1971 to find any kind of maize that had normal cytoplasm – cytoplasm that would resist the blight. Consequently, some seed of waxy maize worked its way into the market.

Backcrossing also has been used extensively to transfer individual genes such as wx (waxy), o2 and the Ht gene for resistance to the leaf blight.[21] Some farmers who fed this waxy grain to their beef cattle observed that animals thrived on it. Feeding trials were set up which suggested that the waxy maize produced more efficient weight gains than normal dent. Interest in waxy maize suddenly mushroomed, and this maize type abandoned the status of botanical curiosity and speciality product to become the subject of major research importance.[22] In 2002, an estimated 1,200,000 to 1,300,000 tonnes of waxy maize was produced in the United States on about 2,000 km², representing only 0,5% of the total maize production.[23]

[edit] Biology

[edit] Chinese Maize

Collins noted, among others, these unusual traits of the Chinese maize:

  • Several unique structural features that enabled the plants to resist the drying out of the silks by wind at the time of flowering
  • Unusual growth behaviour in that the top four or five leaves all appeared on the same side of the main stem of the plant. Extremely erect leaves of the upper nodes, while the lower leaves were more spread and drooping
  • One of the main things he noted was the composition of the endosperm of the maize kernels. He wrote:

“The texture of the endosperm is one of the unique features of this maize. Cut in any direction it separates with a sort of cleavage, exposing a dull, smooth surface. The texture suggests that of the hardest waxes, though it is still harder and more crystalline. From this optical resemblance to wax the term cereous or waxy endosperm is suggested.”

The moisture content of the kernel must be 16% or lower before the waxy trait can be recognised visually.[24] The starch of normal dent maize is characterised by a content of about 25% amylose with the remainder being amylopectin and the intermediate fraction (see 3.5 Biochemistry). But these percentages vary among cultivars and with kernel development. For example, amylose percentage ranged from 20 to 36% for 399 cultivars of normal maize.[25][26] There are maize germplasm sources available that range from less than 20 to 100% complement of amylopectin.[27] Waxy maize contains 100% amylopectin.[28]

It is of main interest because fractionation of normal starch to obtain pure amylose or amylopectin is very costly. Waxy endosperm is inherently a defect in metabolism, and its low frequency in most maize populations in the face of recurring mutations indicates that it is acted against by natural selection.[29]

[edit] Genetic drift

Experiments by Sprague[30] have shown that ten to twenty plants are required for adequate representation of genetic diversity in an open-pollinated maize variety. Since the number of ears saved for seed by ancient Asian maize cultivators with only small plots of land at their disposal was often smaller than this and, indeed, since new maize populations are sometimes established by growing the progeny of a single ear, it follows that there must often have been genetic drift – changes in gene frequencies resulting from the creation of small breeding populations.

A striking example of genetic drift in maize is the occurrence in parts of Asia of varieties with waxy endosperm. In maize races of America such a variety is unknown, but the waxy character itself has been discovered in non-waxy varieties: in a New England flint maize[31] and in a South American variety.[32][33]

The fact that waxy maize occurs so commonly in a part of the world that also possesses waxy varieties of rice, sorghum, and millet can be attributed to artificial selection. The people of Asia being familiar with waxy varieties of these cereals and accustomed to using them for special purposes recognised the waxy character in maize after it was introduced into Asia following the discovery of America and purposely isolated varieties purely for waxy endosperm. But the fact that waxy endosperm came to their attention in the first place is probably due to genetic drift. The gene for waxy endosperm, which has a low frequency in American maize, apparently attained a high frequency in certain samples of Asian maize.

Indeed, the practice reported by Stonor and Anderson[34] of growing maize as single plants among other cereals would result in some degree of self-pollination and, in any stock in which the waxy gene was present, would inevitably lead in a very short time to the establishment of pure waxy varieties with special properties that people accustomed to the waxy character in other cereals could hardly fail to recognise.[35]

[edit] Genetics

A single recessive gene (wx), located on the short arm of chromosome 9, codes for the waxy endosperm of the kernel (Wx codes for endosperm with normal starch).[36] This was first shown by Collins[37] and Kempton.[38] The structure of the wildtype waxy (wx+) locus has been determined through DNA sequence analysis.[39] The gene has 3718 bp (14 exons and 13 introns). Waxy endosperm is the counterpart in maize of the “glutinous” character in rice.[40] There is a wide range of species also presenting the waxy mutation, including rice, sorghum, millet, barley and wheat, which were characterised by starch granules staining red with iodine.

In crosses between heterozygous plants for the waxy character, a small but significant deviation from an expected Mendelian ratio in self pollination is produced.[41][42] Bear[43] obtained from 71 segregated ears on the F1 generation 23,77% of waxy kernels and 76,23% of non-waxy kernels. This is evidenced by the two heterozygous types, Wx Wx wx and wx wx Wx. The waxy gene is epistatic[44][45] for all known other starch forming mutants genes like dull (du), sugary-1 (su1 ) and sugary-2 (su2),[46] it increases sugars and water-soluble polysaccharides (WSP) in a su1 background[47] and it causes dramatic increases in sugars and reduction in starch with ae or ae du. The mutation from Wx to wx is not uncommon in Corn Belt varieties, Bear[48] having found three separate mutations to waxy in three consecutive years in a total population of some 100,000 selfed ears.

Mangelsdorf[49] found also many mutants on his trial fields. Argentine waxy (wx-a), an allele at the waxy locus first reported by Andrés and Bascialli,[50] is known to produce small amount of amylose (< 5%) and gives an intermediate staining reaction with iodine. Other mutant alleles at the waxy locus have been reported which possess similar starch properties to those observed with wx.[51][52][53] More than 40 mutant alleles are known for the waxy locus, making up the finest collection of mutations found among higher plants.[54] Some of them are very stable whereas others are very unstable.

The phenotype of the stable mutants remains unchanged whereas the one of unstable mutants changes because of the insertion of transposable elements (5-8).[55] For a listing of all these mutations, the excellent book of Neuffer, Coe et al.[56] is greatly recommended. Because the waxy mutation is expressed in an easy identifiable nonlethal phenotype, it has been the subject of major research during the 20th century. Nelson[57] made a fine structure genetic map of most of these mutations.

[edit] Genotype and characterisation with iodine

The wx locus is expressed in the endosperm, in the male gametophyte (pollen)[58][59] as well as in the female gametophyte (embryo sac).[60] Amylose and amylopectin have different iodine binding-properties, with maize amylose and amylopectin giving iodine affinity (IA) values of about 19 to 20 and 1%, respectively, depending upon the source. Weatherwax discovered this process in 1922.[61]

The amount of apparent amylose can be determined either by measuring the absorbency of the starch-iodine complex (blue-value) and relating this value to that of pure amylose and amylopectin standards[62] or by measuring the amount of iodine (mg) bound per 100 mg of starch in a potentiometric titration and relating the value to the amount bound by an amylose standard.[63] Values used on the iodine binding, however, are only estimates of amylose content because of differences in the binding abilities (and structure) of amylose and amylopectin among starch types. For example, amylopectin molecules with long external branches bind more iodine than those with short branches do,[64][65] resulting in a small measure of apparent amylose. Chromatographic profiles of wx-containing starches, however, reveal no amylose peak. The wave-length at which a starch-iodine complex has maximum absorbency is referred to as the lambda max.[66]

Plants which are heterozygous on the waxy gene (Wx:wx) can be characterised by staining the pollen with iodine. Half of the pollen will be blue and half brown whereas the kernels will stay blue (very helpful in backcrossing program). If the plant is homozygous recessive (wx:wx) the whole pollen will be brown and the kernel too. Being homozygously dominant (Wx:Wx) the iodine will appear only blue.

[edit] Biochemistry

Normal dent maize has two different pathways for starch formation: one leading to branched chain (amylopectin) and the other to straight-chain polysaccharides (amylose).[67] The amylopectin consists of chain of α-D-(1-4) and α-D-(1-6)-glucosidic linkages that form a branched molecule. Amylose is primarily linear with α-D-(1-4)-linked glucose residues. However the full starch content is the same in both genotypes.[68] The locus wx code for a starch granule-bound nucleotide diphosphate-starch glycosyl transferase (UDPG) responsible for amylose biosynthesis.[69][70] It catalyses the 1–4 linkage from glucose residues to amylose synthesis in the developing endosperm. This enzyme is located in the amyloplasts and is the major component of the starchbound protein in maize.[71] Nelson showed that starch granules from wx wx wx endosperm had very low starch granule-bound glucosyl transferase activity.

When measuring if the activity of the transferase was a function of the Wx dosage in diploid and tetraploid maize, Akatsuka[72] noticed a linear proportionality between a preparation of Wx Wx Wx and Wx Wx Wx Wx Wx Wx . Nevertheless the amylose content was the same in both types suggesting that activity of the transferase is not directly linked to the amylose content.

In maize and some other plants, there is evidence of a starch molecule that is intermediate in size to amylose and amylopectin.[73] The intermediate fraction contains chains of (1–4)-linked alpha-D-anhydroglucose residues, but the average length of these chains and the number of chains per molecule are different from those in either amylopectin or amylose. Several researchers[74][75] demonstrated the presence in normal maize starch of about 5 to 7% intermediate polysaccharides, basing their conclusions on indirect evidence from IA.

As early as in 1956, it was stated that amylopectin contained three different types of chains.[76] In each macromolecule there is one C-chain, which carries the only reducing group. The B-chains are linked to the macromolecules linked by their potential reducing group, and may contain one or more A-chains that are similarly linked. The ratio of A-B chains (1:1 to 1,5:1) is a measure of the degree of multiple branching and is an important property describing amylopectin. Nevertheless the exact arrangement of chains within the amylopectin molecule is still not clear.[77] The aewx starch contain 21% apparent amylose and has a lambda max. of 580 for the iodine-starch complex. The aewx outer chains are longer than those of wx and fewer in number per weight of starch. In general, the aewx starch had a unique structure that is similar to the anomalous amylopectin (intermediate fraction) reported in ae starch.

Increased dosage at the ae locus, regardless of the genotype at the wx locus, resulted in amylopectin with increased linearity. Short-chained amylose (approximately 100 glucose units) was observed in all ae genotypes in a homozygous Wx background.[78] Amylopectin of the aewx mutants had an increased proportion of long B-chains and a decreased proportion of short B-chains compared with wx amylopectin, whereas amylopectin of the duwx mutant had a decreased proportion of long B-chains and an increased proportion of short B-chains, thus confirming the novel nature of aewx and duwx amylopectin.

The A:B chain ratios, however, for amylopectin from aewx, aewxfl2, aewxsu1, aewxsu2, btwx, duwx and su2wx were in the range of 1.1 to 1.4 and all similar to the wx amylopectin.[79] This unique structure of aewx maize was confirmed by Yamada et al. [??] and they termed it ”amylo-waxy“ maize.

[edit] Agronomic features

Growing maize with pure amylopectin starch is not easy. The waxy gene being recessive, the waxy maize has to be isolated from any nearby normal maize field by at least 200 meters. In maize mono-cropping, volunteers are not uncommon in regions without severe frost. A few volunteers in a waxy field will be enough to contaminate the whole field even if it is isolated [19]. One alternative to this is to use the outside 15 to 20 rows of the field as a buffer strip. They can be fed to cattle. The necessity of detecting some contamination from normal maize type could support the creation of a waxy variety with white kernels. This would allow to select the kernels with a photoelectric cell and to reject the contaminated seeds [30].

No information could be found about the eventual application of this great idea. Responses to fertilisers, diseases, insects, environmental stresses, etc. . . theoretically should not differ between waxy hybrids and their dent counterparts because no physical or chemical differences should exist between these two grain types, except in the kernel. Sucrose is the sugar of transport, but it is not normally converted into starch until it is translocated to the maize endosperm.

[edit] Yield

The production quality and disease resistance of waxy maize appears to be identical to normal types. Kiesselbach indicated that the weight of waxy kernel is slightly higher. Collins obtained an increase of 16% in kernel weight of waxy maize outcrossed by dent maize. Schopmeyer [57] reported that waxy maize starch has approximately 1% higher moisture equilibrium than ordinary maize starch at various moisture and temperatures. Gallais reported a 2 to 3% higher moisture content than normal maize at harvest [30]. The observation that the waxy character may result in approximately 3% less translocation from the stalk to the grain suggests that two hybrids, identical in all genes except waxy, would differ about 3% in yield of grain per ha [37].

[edit] Breeding

The waxy locus is easy to introduce through back-crossing, but this causes a loss of productivity of about 3 to 10% [30]. From the onset of many waxy inbreds development programs, the back-cross method has probably been the most popular. There is one compelling reason to choose this breeding method for waxy hybrid improvement. Competition between the seed companies to provide better hybrids as fast as possible encouraged many breeders to choose the backcross breeding method. Conversion of elite dent lines provide the fastest and most positive result [24]. However, the new hybrids are only expected to have equal but not to exceed the performance of their counterparts. And meanwhile, there are newer and better dent hybrid developments. That is the reason why another breeding method is wished. Initially, most private waxy breeding programs did not have adequate reserves of waxy converted germplasm to permit their utilisation in more complex breeding schemes. Nowadays, enough germplasm material exists and a recurrent selection program would be possible. But due to the limited resources and markets for waxy maize, no long-term program has yet been conducted. Actually, it does not seem that long-term recurrent selection programs are really necessary for waxy maize breeding [60]. In a pedigree-selection scheme performed within a breeding population derived from crossing two elite inbred sources, it is necessary that only one of the two inbred lines contributes the waxy gene to the population.

[edit] Companies

Most maize seed companies do not have a waxy maize breeding program, or if they do, it is apparently a small and insignificant part of their total breeding effort. In the U.S., in 1994, there were fewer than six private seed companies devoting any significant breeding efforts to the development of waxy maize hybrids. They were about 12 to offer waxy hybrids for retail sales. Most of these companies offer fewer than five waxy hybrids covering a very narrow range in relative maturity. There was only one exception offering 20 waxy hybrids ranging in relative maturity from 83 to 122 days.

Unlike the complexities associated with hybrid improvement of high amylose maize, waxy maize breeding programs are generally more conventional and less laborious. This phenomenon is due to the unique expressivity of the waxy gene in maize germplasm and the ease with which it can be transferred between and within breeding populations [24]. A majority of the commercially produced waxy grain is produced under contract to wet milling companies. The contract agreements, in addition to specifying certain grain quality standards, also have waxy purity requirements of waxy grain. Premiums are paid to the waxy grain producer by the wet miller or the waxy grain exporter as compensation for the extra quality control procedures that must be followed [24].

[edit] Utilization

[edit] The amylopectin: industrial uses

Starch is the reserve carbohydrate in the plant kingdom. Although starch occurs throughout the plant world, there are only a few plants used to produce it commercially, and maize is the major source of starch produced world-wide [73]. At the second range comes potato, then wheat and to a lesser extent rice. Maize starch was first produced in the U.S. in 1844 at the plant owned by William Colgate in Jersey City, New Jersey [72].

The amylopectin yield of the kernel ranges from 58,5 to 69% (of dry solid mass) [59]. Wet-milling waxy maize results in starch yields that are only 90% of those of dent maize [73]. The wx starch is relatively easy to gelatinise and produces a clear viscous paste with a sticky or tacky surface, rather than one with sharp edges. This paste resembles pastes of root or tuber starches, such as potato or tapioca. Most starches in their native or unmodified form have limited use in various industries. Therefore, most starches including waxy maize starch are modified either to improve or repress their inherent properties as may be required for special use applications. Many types of modified waxy starches have a multitude of applications in the paper, textile, corrugating, and adhesive industries in addition to an enormous array of application in the food industry [47].

[edit] Food products

Modified waxy maize starches serve essential functions in foods, including the improvement of uniformity, stability, and texture in various food products. The clarity and stability of amylopectin starch make it especially suitable for thickening fruit pies. It improves smoothness and creaminess of canned food and dairy products as well as freeze-thaw stability of frozen foods. It gives a more desirable texture and appearance to dry foods and mixes [24]. Waxy maize starch is also the preferred starting material for the production of maltodextrins because of improved water solubility after drying and greater solution stability and clarity [59]. As of recent, the dietary supplement industry has seen an increase in the usage of Swedish Waxy Maize Starch. It does have a moderate Glycemic Index[citation needed], however, it is it's unique osmolity that allows it to pass through the digestive system relatively quickly and help pull other nutrients with it into the bloodstream[citation needed]. It's purported effect is assumed to be a greater insulin release and having a higher amount of desired materials reach the blood stream in a smaller time frame[citation needed].

[edit] Textile industry

Waxy starch is of interest for the textile industry because of its ability to make transparent films [38].6.1.3 Adhesive industry Starch from waxy maize differs from regular maize starch in both molecular structure and pasting characteristics. According to Watson [67], pastes made from waxy starch are long and cohesive; whereas, pastes made from regular maize starch are short and heavy bodied. Waxy maize starch is a major starch component in adhesives used for making bottle labels. This waxy starch based adhesive imparts resolubilizing resistance to the labels which prevents their soaking off the bottle if immersed in water or being subjected to very high humidity conditions. Moreover, waxy maize starches are commonly used in the manufacture of gummed tapes and envelope adhesives.

[edit] Papermaking

Major advancements in papermaking technology are in part related to the availability of new types of modified waxy starches. These starches essentially provide binding or bonding qualities to the papermaking process, as well as adding other essential features, including improved sizing for greater paper strength and printing properties [24;42]. Papermaking is a highly technical science and the writer cannot cover this more thoroughly because it would be a major theme by itself. For more details about papermaking consult the chap. 13 of the book of Wurzburg [42].

[edit] Starches

Although there is already a large array of available modified starch from normal or waxy maize, there is a growing interest in producing all-natural starches. In fact, consumers prefer it and the rules for regulatory approval of chemical processes are more and more restrictive, thus encouraging the finding of native natural materials to partly replace the chemically modified ones [73]. Several patents have been deposed on double mutant of maize. Two patents have been deposed on the wxsu2 maize genotype, one to use starch as thickener with improved low-temperate stability [74], and the other as an antistalent in bread [77]. In the second case, the bread was said to have a softer, moisture crumb after baking and a fresh texture and appearance after storage than bread made without it. Several patents from the American Maize-products Company are based on new starches that can replace chemically modified ones, all of them containing the wx gene [25–28]. These starches all present a modified viscosity, clarity, paste appearance or freeze-thaw stability.

[edit] Livestock, dairy and poultry feeding

The feeding of waxy maize began in the 1940s. Beginning with a research report in 1944, waxy maize seemed to have the potential to increase feed conversion efficiencies [48]. Manyother feeding trials involving swine, beef and dairy cattle, lambs and poultry were designed to compare the feeding value of waxy to normal dent grain [11;32;46;54]. Generally, the trials indicated an advantage for feeding waxy grain. Seldom have the investigations shown any negative or adverse effects from feeding waxy grains. Increases of both milk production and butterfat content are not uncommon when waxy maize is fed to lactating dairy cattle [24]. Increases of more than 20% in average daily weight gains in fattening lambs were observed when waxy grain was compared with normal dent [46]. In addition, a 14% increase in feed efficiency was noted in favor of waxy grain. Likewise an increase in feed efficiency approaching 10% was obtained in trials where waxy grain was compared with the dent counterparts when fed to finishing beef cattle. The pancreatic digestibility of starches was analysed for several genotypes [56]. They noticed that ae has very low value. We could come to the conclusion that high amylose content is correlated with bad digestibility, but we see that du and su2, also characterised by a high amylose content, present an excellent digestibility. Thus, it cannot be linked. Sandsted [56] suggested that digestibility could lie in the structure of starch granule, in differences in bonding of the starch molecules and in possible anomalous linkages between molecules.

[edit] References

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