Cereal starch content

Starch, a reserve polysaccharide widely distributed in plants, is the most important carbohydrate in the human diet. In plants, starch is present in the chloroplasts in leaves, as well as in fruits, seeds, and tubers. The starch content is especially high in cereal grains (up to 75% of the dry weight), potato tubers (approximately 65%), and in other plant storage organs. 

Iodometric assay of amylose on cereal starches is most often done on lipid-extracted starch, and the amylose content from that assay is termed apparent amylose 145 or total amylose. 123 When the iodometric assay is performed on a lipid-extracted starch and the amylose content is corrected for interference from extra-long chains on amylopectin, the assay gives absolute amylose or real amylose. 145 Iodometric assay of starch that has not been lipid-extracted gives lipid-free (uncomplexed) amylose. Subtraction of total amylose from lipid-free amylose gives lipid-complexed amylose.123 The use of the term apparent amylose to designate lipid-free amylose is avoided in this chapter. All amylose percentages are calculated based on starch. 

Swinkels29 collected published characterization data for tapioca starch and compared it to that for other starches of commercial significance (Table 12.4). Tapioca starch is differentiated from other starches by its low level of residual materials (fat, protein, ash), lower amylose content than for other amylose-containing starches, and high molecular weights of amylose and amylopectin. The small amount of phosphorus in tapioca starch is partially removable30 and, therefore, not bound as the phosphate ester as in potato starch. It is also common to find protein and lipid values of zero, as reported by Hicks.31 The very low protein and lipid content is an important factor which differentiates tapioca starch from the cereal starches. 

Rye starch gives an A-type x-ray diffraction pattern,25 as would be expected for a cereal starch. A content of 6-9% B-type also has been suggested for rye starch.2 The degree of crystallinity was estimated at 15-17%.2... 

The x-ray diffraction pattern of oat starch is the A-type, as expected for a cereal starch.22 33 36 The crystallinity of oat starch was reported to be higher than that of wheat starch when determined at the same moisture content.22 A relative crystallinity in the range of 28.0-36.5% was reported for starch from six different Canadian oat varieties.33 Heat-moisture treatment caused the intensity of d-spacings in the x-ray diffraction pattern to increase.16... 

Cereal starches contain low levels of lipids (0.5-1%), which are generally polar lipids requiring polar solvents such as methanol-water for extraction. Lipid content increases with amylose content, and unless the granule integrity is disrupted, the lipids remain inaccessible to normal fat solvents, suggesting that they are present as an amylose inclusion complex. Noncereal starches contain essentially no lipids. 

X-ray analysis can be used to differentiate between native starches or to detect changes brought about by physical or chemical treatment of granular starch. Cereal starches give the A pattern, with the exception of amylomaizes, which have an amylose content greater than 40 or 45%. Starch precipitated from pastes by evaporation exhibit different patterns depending on the temperature of evaporation, B if below 50°C, B or C if above 50°C. 

The choice of the main cereal component used is based on the lowest cereal cost on a starch content basis, since the sugar ultimately available for fermentation depends on the amount of starch hydrolyzed. Small amounts of a particular cereal, for example, rye for rye whiskey, corn for bourbon, may still be employed to provide the desired flavor element in the final beverage. Rye is used extensively by distillers in the areas where it is plentiful. Corn, wheat, millet (65-68% starch), rice, and potatoes also provide supplementary sources of starch for spirits production, depending on local cost, usage, and availability. Small amounts of hydrolyzed rye are sometimes used to favor initial yeast propagation (about 2% of the total starch input). 

Lewandowicz et al. (1997) conducted experiments to study the effect of microwave processing on the physicochemical properties of cereal starches. They used corn, wheat, and waxy corn at an intermediate moisture content of 30%. Brabender rheological method, light microscopy, x-ray diffractometry (XRD), and differential scanning calorimetry (DSC) methods were used to test different properties of starches, both before and after microwave processing. The experimental results are shown in Figures 3.2 and 3.3. Corn and wheat had pronounced changes in their molecular structure compared to waxy corn. 

---