Paul A. Seib

The structure of four waxy starches related to gelatinization and retrogradation

Abstract Starches from two waxy rices, a waxy maize, a waxy barley showed onset temperatures ( T o ) of gelatinization in excess of water of 349.2, 340.5, 339.1, and 331.1 K, respectively, as determined by differential scanning calorimetry. The T o values, as well as peak ( T p ) and final ( T c ) transition temperatures, decreased in the same order as their X-ray crystallinity. Annealing the starches increased T o and T p , but the differences remained the same. After lintnerization in 2.2 m HCl at 30°, the acid-resistant fractions from the four starches gave the same d.s.c. thermograms and the same constitutive molecular dextrins before and after debranching, as determined by high-performance anion-exchange chromatography with pulsed amperometric detection. Gels (50% water) of the four starches all had the same, but reduced T o values after retrogradation. These results indicate that the molecular structure of the microcrystalline region is the same in the four granular starches, and that T o is controlled indirectly by the surrounding amorphous regions. The retrogradation of the four waxy starches appeared to be directly proportional to the mole fraction of unit chains with d.p. 14–24 and inversely proportional to the mole fraction of unit chains with d.p. 6–9.

Cross-linked resistant starch: Preparation and properties

ABSTRACT Resistant 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 RS4 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 RS4 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 RS4 starches were distinguished from native starches by elevated phosphorus levels, low swelling powers (≈3g/g) at 95°C, insolubilities (<1%) in 1M potassi...

Fine structure of maize starches from four wx-containing genotypes of the W64A inbred line in relation to gelatinization and retrogradation

Maize starches from four wx-containing genotypes (wx, du wx, ae wx, and ae du wx) of the W64A inbred line were examined to determine their gelatinization and retrogradation properties and the fine structure of their amylopectins (AP). Chain-length distribution profiles of the APs showed distinct patterns according to genotype. The wx and du wx starches had a large proportion of short chains and showed A-type X-ray patterns, whereas the ae wx and ae du wx starches had a large proportion of long chains and showed B-type X-ray patterns. The ae wx starch had the highest values of onset melting temperature (To) and heat uptake (ΔH), both for gelatinization and after retrogradation, which were attributed to a greater proportion of long chains (degree of polymerization > 16) in the AP. Debranching of β-limit dextrins also revealed that the interior chain-length distribution of AP from the ae wx genotype constituted a large proportion of long chains. The extent of retrogradation increased in the order wx, du wx, ae wx and ae du wx starches and appeared to be proportional to the level of unit chains with DP 16–30 and inversely proportional to the level of short chains with DP 6–11.

Structure and Functional Properties of Sorghum Starches Differing in Amylose Content

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.

Cross-linking of wheat starch and hydroxypropylated wheat starch in alkaline slurry with sodium trimetaphosphate

Abstract Wheat starch was cross-linked at 40 °C and pH 11.0 by slurrying the starch (30% solids) in a solution of sodium trimetaphosphate (STMP), sodium hydroxide, and sodium sulfate. The extent of cross-linking was determined by an increase in alkaline fluidity or by a decrease in alkaline clarity. Response surface analysis showed that cross-linking increased with increasing levels of STMP (0.5-1.5%, based on starch, bos) and sodium sulfate (0–4.0%, bos) over a reaction period of 120–720 min. A regression equation with first and second order terms showed that STMP and sodium sulfate concentrations and the reaction time accounted for 99% of the variability in alkaline fluidity. Wheat starch (37% slurry) was hydroxypropylated by reaction with propylene oxide (8%, bos) for 24h at 45 °C in alkali (pH 11.5) containing 16.0% sodium sulfate (bos). The hydroxypropylated (4.5wt%) wheat starch (DS 0.12-0.13) was not isolated but was cross-linked with STMP (0.1-0.5%, bos) over a 10–40 min reaction period. A comparison of pasting curves at pH 3.5 showed that some of the cross-links produced by STMP were less stable than those produced by phosphoryl chloride, indicating a low level of pyrophosphate as well as monophosphate cross-links. The less stable cross-links were diminished by changing reaction conditions with STMP.

Factors impacting ethanol production from grain sorghum in the dry-grind process.

ABSTRACT The 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 dry-grind 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, l...

Biosynthesis and metabolism of ascorbic acid in plants

The biosynthesis of L‐ascorbic acid in plants differs from that encountered in ascorbic acid‐synthesizing animals. Enzymic details are sparse, but in vivo studies with tracers clearly establish the stereochemical detail of both processes. Examples of each process are found in separate classes of algae. Plants utilize L‐ascorbic acid as the carbon source for the biosynthesis of two important plant acids, oxalic acid and L‐tartaric acid. Here, cleavage of L‐ascorbic acid between carbons 2 and 3 releases the 2 and 4 carbon intermediates. A second L‐tartaric acid‐synthesizing process peculiar to vitaceous plants, i.e., grape, cleaves ascorbic acid between carbons 4 and 5. The physiological significance of these metabolic interconversions is discussed. Other metabolic processes such as the oxidation/reduction properties of L‐ascorbic acid are also considered.

Measurement of Wheat Starch Granule Size Distribution Using Image Analysis and Laser Diffraction Technology

ABSTRACT Starch was isolated from flour of four wheats representing hard red winter (Karl), hard red spring (Gunner), durum (Belfield 3), and spelt (WK 86035-8) wheat classes. Digital image analysis (IA) coupled with light microscopy was used to determine starch size distributions where the volume of granules was calculated as spherical particles or oblate spheroids. Starch granules were classified into three size ranges: A-type granules (> 15 μm), B-type granules (5–15 μm), and C-type granules (<5 μm). An error was noted in using digital image analysis because the perimeter of some granules touch the edge (PTE) of the field being analyzed. To correct for this error, the PTE granules were manually replaced into the field by measuring their diameters and entering them into the database. The results showed differences in the starch size distributions between the classes of wheat evaluated, as well as the method of analysis. Four laser diffraction sizing (LDS) instruments were used to measure granule distrib...

Ethanol and lactic acid production as affected by sorghum genotype and location

Genotype, environment, location, and their interactions have a significant effect on end-use quality characteristics of grain sorghum (Sorghum biocolor (L.) Moench ). The objective of this research was to study the effect of sorghum genotype and production environment on ethanol and lactic acid production. Eight sorghum varieties from two locations were used. Whole sorghum grain was ground, liquefied, saccharified, and fermented to ethanol using Saccharomyces cerevisiae (S. cerevisae , ATCC 24860). For lactic acid fermentation, whole ground sorghum grain was liquefied and fermented to lactic acid with Rhizopus oryzae NRRL 395; saccharification depended upon native gluco- amylase. Results with this limited number of sorghum varieties and locations showed that both sorghum genotype and location had a significant effect on ethanol and lactic acid yields. Variations of 5 and 15% in ethanol and lactic acid yields were observed among the 16 sorghum samples. The effect of location on the fermentation yields was as much as 5% for ethanol and 10% for lactic acid. The effects of variety and location on ethanol and lactic acid production are strongly related to chemical composition and physical properties of grain sorghum samples. Ethanol and lactic acid production increased as starch content increased, whereas the ethanol and lactic acid production decreased as protein content increased. Chemical composition had a greater effect on the ethanol and lactic acid yields than physical properties of the sorghum kernels. The effect of physical properties on ethanol and lactic acid yields was not significant (P /0.05).

Chemistry of L-ascorbic acid related to foods

A review of reactions of L-ascorbic acid related to its antioxidant property in foods, preservation of vitamin C activity, removal of oxygen in headspace of containers, browning reaction, formation of combined forms of vitamin C, and anaerobic loss.