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Breeding maize with high amylose content

Genotypic material

High-amylopectin corn

Waxy corn contains only amylopectin and no amylase starch molecule in opposition to normal dent maize varieties that contain both. Amylopectin or waxy starch is mainly used in food products, but also in the textile, adhesive, corrugating and paper industry.

Amylopectin or waxy cornstarch is relatively easy to gelatinise, produces a clear viscous paste with a sticky or tacky surface. The paste resembles pastes of root or tuber starches, such as potato starch or tapioca starch (made form cassava). Amylopectine starch has also a lower tendency to retro gradate and is thus more viscosity stable. Modified waxy maize starches are used to improvement of uniformity, stability, and texture in various food products. The clarity and viscous 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

Waxy maize yield about 3.5% less than their dent counterparts and has to be isolated from any nearby normal maize field by at least 200 meters

High-amylose corn

Maize grain is high in starch, accounting to 70% of the total weight of grain. Common maize starch is a mixture of 28% amylose and 72% amylopectin. High-amylose starch has been mainly used as an ingredient in gum candies and as an adhesive for corrugated cardboard. Further, starch based biodegradable thermo plastics were developed. High amylose maize is also a source of resistant starch, a type of starch that resists digestion. As a food additive, consumers can benefit from added resistant starch since it will lower the glycemic index and the risk of colon cancer (Wu et al., 2008).

With wet-milling corn material is steeped in water, with or without sulphur dioxide, to soften the seed kernel in order to help separate the kernel’s various components. Separation of high-quality amylose from common maize is expensive, thus limiting industrial use. High-amylose corn with starch containing 50-80% amlyose can be wet-milled, with some modification in processing conditions, to produce a starch of slightly higher protein content, and in somewhat lesser yield, than usually is obtained from ordinary corn (Anderson et al., 1960). Amylase content can be determined by the iodine sorption method of Bates (Anderson et al., 1960; Wu et al., 2008). Alternatively amylase content can be measured by near infrared spectroscopy (Campbell et al., 1997). The traditional method of cultivating high-amylose maize cultivars is screening by phenotypic selection using backcross and alternate selfing with long breeding cycles. The amylase extender (ae) recessive mutant alleles in maize are an important genetic resource for the development of high-amylose cultivars (Chen et al., 2010). Further genes involved in kernel starch biosynthesis are brittle endosperm 2 (bt2), shrunken 1 and 2 (sh1, sh2), sugary1 and waxy1 (Wilson et al., 2004). The development of stable molecular markers for those alleles would facilitate the identification of promising genotypes. Further, it was suggested that variation in amylase content of RILs was environmentally induced, which was not approved (Fergason and Zuber, 1962). Thus, a specific area for high-amylose production to the development and selection of high-amylose hybrids would usually of secondary importance to the development and selection of high amylase hybrids adapted to a given area. Nevertheless, air temperatures were negatively related to amylase synthesis.

Literature

Anderson, R.A., C. Vojnovich, and E.L. Griffin. 1960. Wet-milling high-amylose corn containing 49- and 57-percent amylose starch. Cereal Chem 37: 334-342.

Campbell, M.R., T.J. Brumm, and D.V. Glover. 1997. Whole Grain Amylose Analysis in Maize Using Near-Infrared Transmittance Spectroscopy. Cereal Chem 74(3): 300-303.

Chen, F., S.W. Zhu, Y. Xiang, H.Y. Jiang, and B.J. Cheng. 2010. Molecular marker-assisted selection of the ae alleles in maize. Genetics and molecular research 9(2): 1074-84.

Fergason, V.L., and M.S. Zuber. 1962. Influence of Environment on Amylose Content of Maize Endosperm. Crop Science 2: 209-211.

Wilson, L.M., S.R. Whitt, A.M. Ibanez, T.R. Rocheford, M.M. Goodman, and E.S. Buckler. 2004. Dissection of Maize Kernel Composition and Starch Production by Candidate Gene Association. The Plant Cell 16: 2719-2733.

Wu, Y., M. Campbell, Y. Yen, Z. Wicks, and A.M.H. Ibrahim. 2008. Genetic analysis of high amylose content in maize (Zea mays L.) using a triploid endosperm model. Euphytica 166(2): 155-164.

April 29th, 2012
Topic: Crop Science, Plant breeding Tags: None

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