Zein: A History of Processing and Use

Cereal Chem. 79(1):1–18 Corn is the largest and most important agricultural commodity in America. Zein, one of the components in corn, has long been investigated for uses other than food and feed. Zein is a unique and complex material, and it is one of the few cereal proteins extracted in a relatively pure form. Today, because of environmental concerns, interest in zein utilization is again growing. Some of the more important research on zein is more than 50 years old. Most of this work has been either forgotten, lost, or difficult to locate. Much of this work was done at the USDA laboratory in Peoria, IL. Since most early zein literature is still easily accessible at that laboratory, this review on zein has been prepared making use of this old literature. This review reexamines the old literature and reconciles it with new zein research to illustrate some of the unique properties of and opportunities for zein. Zein has been examined as a possible raw material for polymer application since the early part of the 20th Century. Gorham (1821) first described zein after isolating the protein from maize. He named the material “zeine”. The description that Gorham gave to zein would easily be recognized today. It resembled bees’ wax and to be soft, ductile, tenacious, and elastic. It had some of the properties of wheat gluten and was analogous to resin. The same material was later described as “maize fibrin” by Ritthausen (1872). Other early work on zein was conducted by Bizzo (1822) and Stepf (1859). Chittenden and Osborne (1891a,b) and Osborne (1897; 1908; 1924) placed zein in its present classification as a prolamin. Osborne (1891b, 1902) also was granted two patents on the extraction of zein. During this same period, there were numerous patents granted relating to the extraction and uses of zein (Rathmann 1954). However, commercial production of zein did not start until the mid-1930s (Anon 1944). For the next 20 years, a number of uses were found for zein in all fields (Rathmann 1954), including the manufacture of buttons, fiber, adhesives, coatings, and binders, etc. Commercial production of zein peaked in the late 1950s, approaching 15 million pounds a year in the United States (Anon 1978). By 1978 the production of zein had dropped to one million pounds a year and has remained fairly constant since then. Renewed interest in zein as a polymeric material has been stimulated, in part, by the perceived negative impact of plastic on solid waste disposal. Zein offers several potential advantages as a raw material for film, coatings, and plastics applications. It is biodegradable and it is annually renewable. The annual surpluses of corn provide a substantial raw material resource. However, there are also some problems with the use of zein as a plastic material. Zein is a biological material and, like most biological materials, it is affected by water. This, coupled with the fact that water is a plasticizer for zein, means that zein’s properties are subject to change with humidity. The cost of zein is also a major limitation in its use as a polymeric raw material. Indeed, cost was one of the reasons for zein’s loss of markets in the late 1950s and early 1960s. Interest in zein utilization is growing again. Zein is a unique and complex material, and it is one of the few cereal proteins extracted in a relatively pure form. This review will reexamine the old literature and reconcile this with the new zein research to illustrate some of the unique properties of and opportunities for zein.