Principles of Cereal Science and Technology, Third Edition
Maize is by far the most important source of industrial cereal starch in North America, while wheat is the most important source in Europe and Australia. In comparison, only minor volumes of rice starch are produced industrially. The present chapter discusses the isolation processes for the two main starches as well as their co-products and also briefly deals with rice starch isolation.
The fact that, in North America, maize is the main source of starch is mainly because of the availability of this cereal in this part of the world and the higher yield of high-quality starch from maize than from wheat (see below). In contrast, in Europe and in Australia, relatively little maize is grown, and the obvious raw material for starch isolation is wheat.
Maize is processed into starch, protein, fiber, and oil-rich germ in a process generally referred to as “wet milling.” Indeed, in contrast to what at first sight would seem logical, in industrial practice, the kernel disintegration occurs only following the softening of the kernel by steeping it in water. In contrast, in the production of wheat starch, the raw material is high-extraction flour (typically 78%, see Chapter 8) obtained by dry milling. The flour is subjected to wet processing, which yields starch and gluten as the main products. In industrial rice starch isolation, broken milled rice (see Chapter 10) is subjected to wet processing as well.
Sorghum has been wet milled by essentially the same system as that used for maize. However, sorghum starch isolation is not a very attractive process for the following reasons. First, the presence of pigments (mainly polyphenolics) in the pericarp can give the starch an off-color, particularly if it is placed in an alkaline solution. Second, sorghum bran breaks into small pieces that interfere with the separation of the protein and starch in the process. Finally, its germ is quite small, and the recovery of sorghum oil is hence not worthwhile.