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Cereal Chem. 79(6):819-825Resistant starches (RS) were prepared by phosphorylation of wheat, waxy wheat, corn, waxy corn, high-amylose corn, oat, rice, tapioca, mung bean, banana, and potato starches in aqueous slurry ( 33% starch solids, w/w) with 1-19% (starch basis) of a 99:1 (w/w) mixture of sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) at pH 10.5-12.3 and 25-70°C for 0.5-24 hr with sodium sulfate or sodium chloride at 0-20% (starch basis). The RS 4 products contain 100% dietary fiber when assayed with the total dietary fiber method of the Association of Official Analytical Chemists (AOAC). In vitro digestion of four RS 4 wheat starches showed they contained 13-22% slowly digestible starch (SDS) and 36-66% RS. However after gelatinization, RS levels fell by 7-25% of ungelatinized levels, while SDS levels remained nearly the same. The cross-linked RS 4 starches were distinguished from native starches by elevated phosphorus levels, low swelling powers ( 3 g/g) at 95°C, insolubilities (<1%) in 1M potassium hydroxide or 95% dimethyl sulfoxide, and increased temperatures and decreased enthalpies of gelatinization measured by differential scanning calorimetry.Starch is consumed in a variety of foods and serves as a major source of energy for humans. The digestion of starch is mediated by salivary and pancreatic a-amylases that release oligosaccharides and dextrins into the lumen of the small intestine. The latter are further hydrolyzed to glucose by glucoamylase and a-glucosidase in the brush border region of the small intestine.Starch sometimes resists digestion by a-amylase. Englyst et al (1992) classified ingested starch based on its probable digestive fate in vivo. They proposed three classes of dietary starch: 1) rapidly digestible starch (RDS), which is likely to be digested in the human intestine; 2) slowly digestible starch (SDS), which is likely to be slowly yet completely digested in the small intestine; and 3) resistant starch (RS), which is likely to resist digestion in the small intestine.RS is defined as the sum of starch and starch degradation products not digested in the small intestine of healthy individuals. It is subdivided into four categories depending on the cause of resistance (Englyst et al 1992;Eerlingen et al 1993): RS 1 , physically inaccessible starch due to entrapment in a nondigestible matrix; RS 2 , raw starch granules with crystallinity; RS 3 , retrograded amylose; and RS 4 , chemically modified starch.SDS and RS are of particular interest because of possible potential health benefits for humans. A high proportion of SDS relative to RDS in a starchy food indicates a food with a low glycemic index.

Starches were isolated from grains of waxy, heterowaxy, and normal sorghum. To study the relationship between starch structure and functionality and guide applications of these starches, amylose content, amylopectin chain-length distributions, gelatinization and retrogradation, pasting properties, dynamic rheological properties, and in vitro enzyme digestion of raw starches were analyzed. Heterowaxy sorghum starch had intermediate amylose content, pasting properties, and dynamic rheological properties. Stress relaxation was a useful indicator of cooked starch cohesiveness. Cooked heterowaxy sorghum starch (10% solids) had a viscoelastic-solid type of character, whereas cooked waxy sorghum starch behaved like a viscoelastic liquid. Amylopectin of normal sorghum starch had a slightly higher proportion of chains with degree of polymerization (DP) of 6-15 (45.5%) compared with amylopectin of heterowaxy starch (44.1%), which had a gelatinization peak temperature 2 degrees C higher than normal sorghum starch. Heterowaxy sorghum starch contained significantly lower rapidly digestible starch (RDS) and higher resistant starch (RS) than waxy sorghum starch.

Poly(lactic acid) (PLA) is a biodegradable polymer, but its applications are limited by its high cost. Blending granular starch with PLA reduces the cost, but the blend has poor strength properties. In this study, a 55/45 (w/w) mixture of PLA (weight-average molecular weight ϭ 120,000 Da) and dried wheat starch was blended thermally in an intensive mixer with or without a low level of methylenediphenyl diisocyanate (MDI). Blends with MDI had enhanced mechanical properties that could be explained by the in situ formation of a block copolymer acting as a compatibilizer. Scanning electron micrographs showed reduced interfacial tension between the two phases. The presence of MDI also enhanced the mechanical properties of the blend at temperatures above the glass-transition temperature. Water uptakes by the PLA/ starch blends with and without MDI did not differ.

Cereal Chem. 84(2):130-136The goal of this research is to understand the key factors affecting ethanol production from grain sorghum. Seventy genotypes and elite hybrids with a range of chemical compositions and physical properties selected from ≈1,200 sorghum lines were evaluated for ethanol production and were used to study the relationships of composition, grain structure, and physical features that affect ethanol yield and fermentation efficiency. Variations of 22% in ethanol yield and 9% in fermentation efficiency were observed among the 70 sorghum samples. Genotypes with high and low conversion efficiencies were associated with attributes that may be manipulated to improve fermentation efficiency. Major characteristics of the elite sorghum genotypes for ethanol production by the drygrind method include high starch content, rapid liquefaction, low viscosity during liquefaction, high fermentation speed, and high fermentation efficiency. Major factors adversely affecting the bioconversion process are tannin content, low protein digestibility, high mash viscosity, and an elevated concentration of amylose-lipid complex in the mash.