Proteins starch granules

After cleaning to remove coarse material, ie, cobs, and fines (broken com, dust, etc), the com is steeped in a sulfurous acid solution to soften the com and render the starch granules separable from the protein matrix that envelopes them. About 7% of the kernel s dry substance is leached out during this step, forming protein-rich steep-water, a valuable feed ingredient and fermentation adjunct. 

Seeds. The seeds are produced in pods containing two or three seeds. The kernels are almost spherical to roughly cylindrical (0.4—1.1 g each) and consist of a thin coat (testa) containing two cotyledons and the embryo. Cotyledons contain protein bodies, Hpid bodies, and starch granules. 

The subsequent advance was rather fortuitous and rested more with serendipity than with scientific logic. A search was made for cheaper more effective replacements for casein hydrolysate. Amongst the tested materials was com steep liquor (CSL). CSL is a by-product of the manufacture of starch from maize kemals. Whole maize is incubated in warm water, at 50°C acidified with SO2. Thermophilic bacteria hydrolyse proteins and other components of the kemals, thereby loosening the starch granules. These are removed, leaving behind the steep liquor which is used to treat further maize kemals. Ultimately, the liquor is too viscous to re-use and the liquor is concentrated and used as cattle feed. It was this material that was used for penicillin fermentation. Surprisingly, the yield of penicillin increased by a further 5-10 fold giving yields of 50-100 ig ml. 

Endosperm constitutes the main part of the corn kernel and consists of 85 to 90% starch, 8 to 10% protein, and a small amount of oil and other compounds. Corn endosperm can be divided into two distinct parts floury and horny endosperm. In floury endosperm, starch particles are round and are dispersed loosely in the protein matrix. In the horny endosperm, the protein matrix is stronger and starch particles are held more firmly. Starch granules are encased in the continuous protein matrix. The tighter setting in horny endosperm gives starch particles a polygonal shape. On average, the amount of horny endosperm in the corn kernel is twice that of the floury endosperm. However, this ratio is a function of the corn kernel protein content (Wolf et al., 1952). 

Meuser, F., Wittig, J., and Huster, H. 1989. Effects of high pressure disintegration of steeped maize grits on the release of starch granules from the protein matrix. Starch/Stdrke 41, 225-232. 

Figure 1. Scanning electron micrograph of Phaseolus vulgaris cotyledon showing protein bodies (P) and starch granules (S). Bar = 10 dm.

Debet, M. R. and Gidley, M. J. (2007). Why do gelatinized starch granules not dissolve completely Roles of amylose, protein, and lipids in granule "ghosP integrity. /. Agric. Food Chem. 55, 4752- 760. 

Lorberth, R., Ritte, G., Willmitzer, L., Kossmann, J. (1998). Inhibition of a starch-granule-bound protein leads to modified stareh and repression of eold sweetening. Nature Biotech., 16, 473 77. 

Solubility and viscosity explains the basic physicochemical nature and the functional behavior of proteins in aqueous solutions. Proteins contribute to the adhesive or cohesive properties of film matrices by the binding of their polypeptides to other components such as starch granules to yield shaped products that, for example, are necessary for trapping gases in breadmaking. 

Figure 13 Map of protein distribution in single wheat starch granules before (left) and after (right) sodium dodecyl sulfate extraction. Granules were scanned after staining with acid fuchsin (from [46]).

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