Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
TABLE 8.1
Proximate Analysis of No. 2 Yellow Dent Corn and Maize of French Origin
Yellow Dent Corn Maize of French Origin
Component
(% Dry Basis)
(% Dry Basis)
Moisture 15.0 ± 1.0 10.1
Starch 71.8 ± 1.5 71.8
Protein 9.6 ± 1.1 10.2
Lipids 4.6 ± 0.5 4.6
Crude fiber 2.9 ± 0.5 1.93
Minerals 1.4 ± 0.2 n.d. a
Soluble Carbohydrates
a n.d.: Not determined.
2.0 ± 0.4 n.d.
Source: For No. 2 yellow dent corn from Blanchard, P.H., Technology of Corn Wet Milling and
Associated Processes, Elsevier Science, Amsterdam, 1992, chaps. 1 and 3 and for maize of French
origin from Kempf, W., Starch/Staerke, 24, 269, 1972
the grain being undamaged and properly dried. Because of the much higher kernel
moisture content under European harvesting conditions (a maximum of 40% moisture
at harvest), only carefully controlled drying conditions, in particular avoiding
damage by heated air drying, provide undamaged starch and protein bodies with
proper density differences, which are prerequisites for successful separation in the
gravity field during centrifugal separation. 5,6
8.2.3 PROCESSES
Typical in wet milling of corn/maize is the physical breakdown of kernel firmness
after chemical and biological treatments. Kernels enter processing by an initial
steeping procedure that is designed to soften the kernel tissue texture by soaking
to optimum hydration. Furthermore, low-molecular-weight compounds, such as
carbohydrates, peptides and amino acids, and mineral substances, are solved in
this state. Addition of sulfur dioxide (SO 2) or sulfurous acid solution supports
chemical and biological processes in this controlled environment. The dominant
reaction of reduction of sulfur bridges loosens the protein matrix within endosperm
cells, where at the beginning starch granules lie tightly packed and glued to one
another. The differences in intensity of packing can be seen in kernel sections
having horny or floury endosperm. Both the starch granules and protein matrix
contribute to the specific property profiles of these sections. The horny endosperm
represents a structure formed mainly by small-size polygonal starch granules
embedded in a protein matrix that becomes fortified by protein corpuscles. The
floury endosperm, in contrast, contains the large and more spherical starch granules.
Its protein matrix is less dense because of enclosed air and the lack of protein
corpuscles. 3–5