In honour of our American readers celebrating Thanksgiving, the theme of this week’s leaf is the maize plant, Zea mays, and the cover picture is of a corn maze.
Maize was first domesticated in Mexico some 10 millenia ago. It is now the dominant grain crop in North America but also grown widely around the world as one of humankind’s four main food crops. Maize, wheat, rice and soybean together provide about ¾ of our food!
Maize exemplifies C₄ photosynthesis(see Leaf 71, https://lnkd.in/dZieh8Ud). In arid climates, maize has a big advantage over wheat, rice and soybean and other “conventional” C₃ plants, as the C₄ adaptation enables it to get bring in CO₂ with stomata almost closed, thus saving water.
Beside the tall maize plants, the cover picture shows diagrams of two polysaccharides, amylose and amylopectin, the main constituents of starch. Both are polymers of glucose, but whereas amylose has very long chains of glucose linked by α(1→4) bonds, amylopectin is branched at points where a glucose has an additional α(1→6) bond.
Cornstarch is usually about¼ amylose and ¾ amylopectin, similar to other vegetable starches. However, varieties of maize have been identified and bred where the starch is almost entirelyamylopectin (waxy cornstarch, amylose absent) or where the amylose fraction isincreased.
Starch forms gels when heated. While starch with high amylose forms stronger gels, the branching in amylopectinreduces the heat requirement and gel strength. The process is also influenced by the starch-grain structure and handling – all important in food preparation and in industry.
Starch composition also affectsits digestibility. While starch digestion starts with saliva enzymes, high-amylosestarches are “resistant”, much of it passing undigested to the intestines whereit is proposed to have prebiotic effects, encouraging growth of health-promotinggut bacteria. (Harris, 2019).
Cornstarch is usedwidely in cosmetics, notably as an alternative for talc. Quite possible the amylose and amylopectin have prebiotic effects on the microbiome of a baby’s bottom.
Further reading
🌽 Wikipedia(2023). “Starch”. https://en.wikipedia.org/w/index.php?oldid=1178069635
🌽 Wikipedia (2023) “Starch gelatinization” https://en.wikipedia.org/w/index.php?title=Starch_gelatinization&oldid=1176852790
Harris KF (2019). An introductory review of resistant starchtype 2 from high-amylose cereal grains and its effect on glucose and insulinhomeostasis. Nutr. Rev. 77(11), 748–764. https://doi.org/10.1093/nutrit/nuz040
🌽 Cosmetic Ingredients Dictionary, “Zea Mays Starch” https://inci.guide/carbohydrates/zea-mays-starch
