Chemical Composition of Milled Products

The efficiency of the various milling procedures is usually determined by the analysis of moisture, ash, fat, and color of refined products. The most common way to determine milling efficiency is by the quantification of ash (AACC Methods 08-03 and 08-12), because the degree of refining is inversely related to the mineral content. This is because bran contains 20 times more ash than the endosperm. Ash is determined gravimetrically after burning or incinerating a sample at temperatures of 600°C. There are other less accurate methods that can predict ash content. The most popular used today is the NIRA. 

The fat (AACC method 30-10) and fiber (AACC method 32-10) analyses are also used for the same purposes as ash determination. However, these methods are less common because they are more complicated to perform. Crude fiber is quantified after acid and alkaline hydrolyses, while fat is gravimetrically determined after extraction with solvents (usually petroleum ether). 

The color of refined wheat flour (AACC Method 14-30) or semolina is generally performed in an Agtion colorimeter operating in the green mode (546 nm). The sample (20 g) is mixed with 25 mL distilled water for 2 min in order to enhance color formation. Next, the slurry is read in the colorimeter that was previously calibrated with disc standards 0, 63, 85, and 100. Similar assays (AACC Methods 14-21 and 14-22) are also used to measure pasta and noodle color. The NIRA can be also calibrated to determine color. 

For durum wheats, the rapid quautitatiou of caroteues is performed using a spectrophotometer or colorimeter (AACC Method 14-50). The yellow pigmentation can be quantified by overnight extraction in aqueous n-butauol followed by measurement of absorbance at 435.8 nm (Dexter and Matsuo 1978). More frequently, the color of semolina is judged visually or with refractive light colorimeters (Allen et al. 1989, Symons and Dexter 1991). 

Many different analytical and functional methods are extensively used to determine the chemical, physical, and functional properties of starches obtained from the various wet-milling processes covered in Chapter 8 and from physically and chemically modified starches described in Chapter 13. 

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