Physical properties, water absorption rate, equilibrium moisture content, and NIR composition of yellow, white, and specialty type maize hybrids

Corn hybrids posses particular attributes that make them suitable for specific food, industrial or fuel applications. However, there is a lack of information about which corn hybrids have characteristics that could be valuable for processors, and in turn, that farmers can grow to maximize their profits or ensure a market for their crops. The purpose of this study was to determine and quantify the physical properties and chemical composition of Yellow, White, and Specialty corn hybrids commonly grown in the Midwestern United States, and to relate them to conditioning and processing characteristics including water absorption rate and equilibrium moisture content. All corn hybrid samples were screened to remove small and round kernels, and then conditioned with air at a relative humidity between 70 and 77%. After conditioning, the Yellow and White hybrids had an average moisture content of 13.64±0.61% and 13.92±0.96%, respectively. The variation in physical properties within the Specialty hybrids was greater than that within the Yellow and White hybrids. These two groups of hybrids had similar kernel dimensions, kernel weights, kernel volumes, face areas, sphericities, and thousand kernel weights, but differed in kernel and bulk densities, germ to endosperm ratios, and Stenvert hardness. Additionally, the pericarp of White hybrids was significantly thicker than that of Yellow hybrids on the middle of both the germinal and abgerminal sides of the kernels. The NIR protein content was greater for White than for Yellow hybrids, but the contents of the other constituents were similar. In general, for the Specialty hybrids the minor diameter, kernel volume, face area, and fat (oil) content were significantly (P\u3c0.05) greater than comparable values for either Yellow or White hybrids. Compared to the Yellow hybrids, the differences in the thousand kernel weight, kernel and bulk density, and pericarp thickness of the Specialty hybrids were not statistically significant. However, they were significantly less (P\u3c0.05) than the corresponding values for the White hybrids. The Specialty hybrids had an intermediate value of Stenvert hardness, and a significantly (P \u3c 0.05) lower starch content compared to Yellow and White hybrids. The water absorption rate of Yellow and White corn hybrids was correlated to the thickness of the pericarp, especially at the top (r=0.60, P\u3c0.0001) and middle abgerminal side (r=0.41, P\u3c0.0001), to the ash (r= -0.68, P\u3c0.0001), protein (r= -0.37, P\u3c0.05), and starch contents (r=0.28, P\u3c0.05), and to the following physical properties: major diameter (r=0.31, P\u3c0.05), volume (r=0.27, P\u3c0.05), face area (r=0.31, P\u3c0.05), kernel density (r= -0.26, P\u3c0.05) and bulk density (r= -0.30, P\u3c0.05). Scanning Electron Microscopy studies on eleven of the hybrids revealed that the internal porosity of the kernel may have influenced the water absorption rate. The EMC of Yellow and White hybrids was significantly correlated to protein (r= -0.56, P\u3c0.0001) and ash content (r= -0.39, P\u3c0.0008), and the following physical properties: kernel density (r= -0.47, P\u3c0.0001), bulk density (r= -0.57, P\u3c0.0001), thousand kernel weight (r= -0.32, P\u3c0.0075), kernel weight (r= -0.34, P\u3c0.0043), and Stenvert hardness (r= -0.56, P\u3c0.0001). For the Specialty hybrids, fat content had a great influence on EMC. High Amylose hybrids had a dramatically higher EMC than White corn, High Protein High Oil, Highly Extractable Starch and Waxy hybrids over the relative humidity range of 50-90%. The effects of high temperature drying on EMC, hardness, and germ viability were also studied. In general, high temperature drying lowered the EMC and germination of kernels, but it increased their hardness. The magnitude of these changes was different for each of the hybrids tested. Possible explanations of these differences are discussed