C. Chemical Composition
1. NIR Proximate Analysis – Sorghum
Proximates are the major components of the grain. For sorghum, the NIR Proximate Analysis includes oil content, protein content, and starch content (or total starch). This procedure is nondestructive to the sorghum. Chemical composition tests for protein, oil, and starch were conducted using approximately a 50-gram sample in a Perten DA 7250 Near-Infrared Reﬂectance (NIR) instrument. The NIR was calibrated to chemical tests, and the standard error of predictions for protein, oil, and starch were about 0.3%, 0.4%, and 0.5%, respectively. Results are reported on a dry basis (percent of non-water material).
Leucoanthocyanidins (catechins) and proanthocyanidins (tannins) are a class of ﬂavonoids known as ﬂavonols that react with vanillin in the presence of mineral acids to produce a red color. Vanillin reacts with the ﬂavonols, but other ﬂavonoid compounds can give specific color development. Values near or below 4.0 mg catechin equivalents (CE) per g sample by this method generally imply absence of condensed tannins. Type III tannin sorghums usually have values greater than 8.0 mg CE/g. The test involves grinding approximately 50 g sound seed using a UDY grinder with 1 mm sieve and accurately weighing 0.30 g of this sample for analysis. Extraction and analysis is performed using the vanillin-HCl test with blank subtraction to remove interference by sorghum pigments. Developed color is measured using a UV-Vis spectrophotometer at 500 nm. Standard curve is run using pure catechin. Tests are run in triplicates and the average value is reported as mg CE/g sample on a dry basis.