Effects of High Pressure Disintegration of Steeped Maize Grits on the Release of Starch Granules from the Protein Matrix

Abstract

AbstractThe horny endosperm of maize gives the greatest resistance to the mechanical disintegration of the protein matrix during starch extraction. Thus attempts were made to release the starch by wet‐milling of maize grits in the valve of a high‐pressure homogenizer. At the same time, information was gathered on the principles involved in the structural breakdown of the endosperm components. For this purpose the influence of the valve geometry as well as the concentration and flow rate of the suspension on the particle size reduction and disintegration was examined. Using a valve specially constructed for the photographic documentation of this process step, it could be shown that the slit height of the valve predominantly determined the particle size of the wet milled product. Already after a single passage through the valve, set at slit heights between 200 and 600 μm, 70% of the grits were reduced to particles <40 μm. The grits were initially between 250 and 1000 μm in size. Scanning electron microscope photographs showed that a large fraction of the mass existed as free starch granules alongside partly intact particles of the protein matrix. Since the starch granules were of higher purity after raffination, it is assumed that the extent to which disintegration of the endosperm particles results in starch granules and protein particles as separate entities, depends not only on the particle size reduction step, but also on the different visco‐elastic behaviour of the protein matrix and the starch granules under the influence of the large shear forces occuring in the valve.