| dc.identifier.citation | Filipčev, B., Đalović, I., Nježić, Z., Šimurina, O., Bekavac, G., & Pojić, M. (2022). Physical and milling properties of maize (Ch. 1). In S.S. Purewal, P. Kaur, S.P. Bangar, K.S. Sandhu, S.K. Singh, M. Kaur (Eds.). Maize:Nutritional composition, processing and industrial uses (pp. 1-37). CRC Press, Taylor&Francis Group, Boca Raton, London, New York. ISBN 9781032127927 (hbk) 9781032156675 (pbk) 9781003245230 (ebk), DOI: 10.1201/9781003245230-1 | en_US |
| dc.description | Maize is widely cultivated all over the world, and each year its production increases more than that of any other grain product. Today, it is mostly grown in the United States of America (about 40%) and China (about 20%); other top producers are Brazil, Argentina, Indonesia, Ukraine, India, Mexico, Indonesia, and France. Maize is mainly used as animal feed, as a raw material in industry, and, to a lesser extent, as human food, especially in developing countries. Grain milling properties are very important from the standpoint of milling efficiency and effectiveness. The milling performance of maize grains is dominantly influenced by endosperm structure i.e. the ratio of vitreous to floury endosperm often referred to as hardness. Kernel hardness affects the grinding power requirements, yields of milling products and their processability into a food. There are great variations in texture and strength of vitreous and floury endosperm, even within one type of maize, that results from differences in ratios of vitreous to starchy parts, pericarp to cell structure thickness, cell wall thickness, compactness of cellular structures, cell sizes within the endosperm. The endosperm structure depends on interactions between starch granules and the protein matrix. In floury endosperm, starch granules are loosely packed and wrapped with a thinner protein matrix, unlike vitreous endosperm. A thin protein matrix easily ruptures during grain drying, weakens the endosperm strength and increases its susceptibility to breakage. The milling performance of maize is indirectly estimated by parameters that describe the physical properties of kernels, such as test weight, density, kernel hardness, pericarp damage, presence of stress cracks, and resistance to grinding or abrasion. The basic industrial maize grain processing technologies are dry and wet milling. Dry milling yields an array of products with different applications in the food and feed industry. The most important products of dry milling are grits, meal and flour, which, alone or in combination with wheat flour, are used to manufacture various food products: bread, porridges, breakfast cereals, instant food, extruded snacks, many of which are staple food items. Dry milling is a complicated processing technology requiring careful management to successfully separate anatomic parts of maize kernel. The most important step is a separation of germ which allows recovery of corn oil as a separate product and yields endosperm with low fat content and longer shelf-life. Wet milling is designed to efficiently separate maize kernel components (starch, proteins, oil and fibres) into relatively pure forms. The process involves steeping in water and multi-step operations for component separation. Wet milling is a fully industrialised technology that cannot be operated at a small scale and yields products that require further industrial processing before being ready for consumption. Different maize quality traits are required depending on the type of milling. Desired grain properties for efficient and effective dry milling are kernels uniform in size, preferably large ones, hard vitreous endosperm, high test weight, low level of stress cracks, minimum breakage, foreign materials and absence of mycotoxins and odours. The grain quality requirements for wet milling are soft grain with highly extractable starch, medium density, low breakage susceptibility, large grains, low stress and pericarp cracks, and pericarp damage. | en_US |
