The proportion of amylose and amylopectin, one linear molecule and the other branched, determines the properties of each type of starch.
Starch is a digestible complex carbohydrate (polysaccharide), from the group of glucans. It consists of glucose chains with a linear (amylose) or branched (amylopectin) structure. It constitutes the energy reserve of vegetables. In the kitchen it is valued for being a hydrocolloid: it has the ability to trap water, which causes the formation of gels, or to thicken a liquid or a liquefied product.
Amylose and amylopectin are polysaccharides that can be broken down (digested) by the body through the enzymes amylase and glucosidase present in saliva and pancreatic juice. In 2007, a group of researchers led by George H. Perry of Arizona State University in Tempe and Nathaniel J. Dominy of the University of California at Santa Cruz showed that humans have extra copies of the AMY1 gene (basic for amylase synthesis) and a higher proportion of AMY1 than other primates. There are also differences between human populations, depending on the consumption of starchy products for generations. Starches, rich in calories, could have been crucial for human nutrition and evolution.