Douglas C. Doehlert

Staling of Bread as Affected by Waxy Wheat Flour Blends

ABSTRACT Crumb softness and improved shelf life of bread is often achieved by incorporating expensive shortenings in the formulation. We hypothesized that similar results could be achieved by blending bread wheat flour with waxy (low amylose) durum wheat flour. White pan bread was baked from 10, 20, and 30% waxy durum wheat flour composites and evaluated for loaf volume and crumb firmness over a period of 0, 3, and 5 days. The loaf volumes were not affected by the waxy flour blends. However, as staling progressed over 3–5 days, significant firming of crumb was observed in the control sample compared with loaves containing waxy flour. The firmness was inversely proportional to the level of waxy flour used in the blend. A 20% waxy wheat flour blend was optimal in retarding staling while producing bread quality comparable with the control. It was further established that bread made with 20% waxy flour gave lower firmness values after 5 days of storage in comparison to bread made with 3% shortening. These res...

Spinach leaf sucrose phosphate synthase: Activation by glucose 6-phosphate and interaction with inorganic phosphate

not received Sucrose phosphate synthase Glucose 6-phosphate Inorganic phosphate Sucrose Spinacea oleracea L. Regulation

Rheological Properties of (1→3),(1→4)-β-d-Glucans from Raw, Roasted, and Steamed Oat Groats

ABSTRACT Effects of hydrothermal treatments (steaming, roasting) of oat grain on β-glucan extractability and rheological properties were tested on oat cultivars with low (Robert) and high (Marion) β-glucan content. Steaming of grain reduced the amount of β-glucan that could be extracted, compared with raw or roasted grain, but the extracts from steamed grain had much greater viscosity. Increased extraction temperatures increased the amount and the average relative molecular mass (M r) value of β-glucan extracted. In boiling water extractions, the average M r values among raw, roasted and steamed oat samples were equivalent, but extracts from steamed oat grain had significantly higher intrinsic viscosity than the extracts from roasted or raw oat grains. β-glucan solutions purified from steamed grain extracts were very viscous and highly pseudoplastic, as described by the power law equation. Oat β-glucan from steamed samples were more viscoelastic than β-glucan from roasted or raw oat samples. Because visco...

Effects of heat stress on enzyme activities and transcript levels in developing maize kernels grown in culture

Abstract Heat stress can cause decreased grain yields and increased susceptibility in maize to the aflatoxin-producing fungus, Aspergillus flavus . We hypothesized that heat stress may affect gene expression in developing kernels, thereby affecting enzyme activities and storage product accumulation. To test this hypothesis, maize ( Zea mays L. hybrid B73xMo17) kernels were cultured in vitro and grown at 25 (control), 30, and 35°C. At 5-day intervals, developing kernels were analyzed for levels of gene expression and enzyme activity. Message levels of all genes evaluated, including Shrunken-1, Shrunken-2, Brittle-2, Aldolase, Waxy, α-Zein, β-Zein , and Opaque-2 were reduced 65 to 80% after 5 days at 35°C. In contrast, of the 17 enzymes assayed, only the activities of adenosine diphosphate glucose (ADP-Glc) pyrophosphorylase, aldolase, aspartate aminotransferase, acid invertase, and acid phosphatase were decreased by heat-stress. Although the decrease in ADP-Glc pyrophosphorylase activity corresponded well with its decreased mRNA, aldolase activity only loosely corresponded to its mRNA levels, and sucrose synthase activity was not affected by growth temperature, although its transcript was reduced by 80%. We suggest that the declines in enzyme activities in the heat-stressed kernels are a result of declines in transcript. The differing responses of enzyme activities to the heat stress may reflect differences in protein turnover. In a subsequent experiment, we tested the hypothesis that heat stress may interfere with the ability of a maize kernel to generate pathogenesis-response proteins. We found that the activity of the pathogenesis-related protein, chitinase, was increased two-fold in cultured kernels grown at 25°C by treatment with salicylic acid. However, the salicylate-induced increase in chitinase activity was inhibited in kernels grown at 35°C. These results suggest that heat stress inhibits the induction of pathogenesis-related proteins in the maize kernel, and may, thereby, interfere with the ability of the kernel to defeat pathogen invasion.

Genotypic and environmental effects on oat milling characteristics and groat hardness.

ABSTRACT The production of oat bran involves the dehulling of oats, inactivation of their enzymes, and the subsequent grinding and sieving of the clean groats to isolate the larger bran particles. The bran yield from the oat groats may be related to their hardness, as it is in wheat. Groat breakage, which occurs during the dehulling process, reduces milling yield and may also be related to groat hardness. This study sought to investigate genotypic and environmental effects on oat dry milling and oat dehulling characteristics, and attempted to define properties associated with oat groat hardness. Significant genotypic differences in bran yield were largely attributed to groat composition, where higher β-glucan and oil concentrations in the groat were associated with higher bran yields. Bran composition was largely dependent on a combination of the bran yield and the groat composition. Although groat breakage was correlated with bran yield and with groat β-glucan concentration, environmental factors appeare...

Quality of Spaghetti Made from Full and Partial Waxy Durum Wheat

ABSTRACT The waxy character is achieved in durum wheat (Triticum turgidum L. var. durum) when the granule-bound starch synthase activity is eliminated. The result is a crop that produces kernels with no amylose in the starch. The presence of two Waxy loci in tetraploid wheat permits the production of two partial waxy wheat genotypes. Advanced full and partial waxy durum wheat genotypes were used to study the effect of waxy null alleles on pasta quality. Semolina from full and partial waxy durum wheats was processed into spaghetti with a semicommercial-scale extruder, and pasta quality was evaluated. Cooked waxy pasta was softer and exhibited more cooking loss than pasta made from traditional durum cultivars. These features were attributed to lower setback of waxy starch as measured with the Rapid Visco Analyser. High cooking loss may be due to the lack of amylose-protein interaction, preventing the formation of a strong protein network and permitting exudates to escape. Waxy pasta cooked faster but was le...

Composition of Oat Bran and Flour Prepared by Three Different Mechanisms of Dry Milling

ABSTRACT Three mechanisms of oat milling were tested for laboratory-scale oat bran production. Oat bran consistent with AACC definition and commercially obtained product was generated with either roller-milling or impact-milling of groats, followed by sieving to retain larger particles. These bran preparations were enriched ≈1.7-fold in β-glucan and ash, 1.4-fold in protein, and 1.1-fold in lipid. Bran finishing made further enrichments in protein, β-glucan, and ash. Tempering oat (to 12% moisture for 20 min) improved bran yield from roller-milling nearly two-fold but had little effect on bran composition. Bran yield from the impact-type mill was significantly affected by grinding screen size. Oat bran obtained from a pearling mill was only slightly enriched in β-glucan and protein, but it was more heavily enriched in ash and oil than brans from roller or impact mills. The pearling mill isolated the outer layers of the groat directly, but because of its low β-glucan composition it did not meet the AACC de...

Starch Characteristics of Waxy and Nonwaxy Tetraploid (Triticum turgidum L. var. durum) Wheats

ABSTRACT Manufacture of pasta products is paramount for durum wheat (Triticum turgidum L. var. durum). The recent development of waxy durum wheat containing starch with essentially 100% amylopectin may provide new food processing applications and present opportunities for value-added crop production. This investigation was conducted to determine differences in some chemical and functional properties of waxy durum starch. Starch was isolated from two waxy endosperm lines and four nonwaxy cultivars of durum wheat. One of the waxy lines (WX-1) was a full waxy durum wheat whereas the other line (WX-0) was heterogeneous, producing both waxy and nonwaxy seed. Effects on starch swelling, solubility, pasting, gelatinization, and retrogradation were examined. The full waxy starch had four times more swelling power than the nonwaxy durum starches at 95°C, and was also more soluble at three of the four temperatures used. Starch pasting occurred earlier and peak viscosities were greater for starches from both waxy li...

Factors Affecting Viscosity of Slurries of Oat Groat Flours

ABSTRACT Oat grain is routinely kilned and steamed before milling to develop flavor and to inactivate lipid-degrading enzymes. Heat treatments can significantly affect viscous properties, which have functional and nutritional importance. Oat flour slurries (23%, w/w, solids dry basis) made from steamed (for 20 min) or autoclaved (at 121°C, 15 psi, for 10 min) grain developed high viscosities, whereas flour slurries made from raw or kilned (105°C for 90 min) oats did not. Flour slurries made from raw groats, surface-sterilized by 1% hypochlorite, were more viscous than untreated raw groat flour slurries, suggesting that β-glucan hydrolases on the surface of the groat caused the viscosity losses observed in raw or kilned groats. However, because viscosities developed by surface-sterilized groats were not as great as in steamed oat-flour slurries and because some roasting treatments also inactivated enzymes without enhancing viscosity, it appears steaming might also affect the β-glucan polymer, resulting in ...

Effects of Oat Grain Hydrothermal Treatments on Wheat-Oat Flour Dough Properties and Breadbaking Quality

ABSTRACT Hydrothermal treatments, which are routine in oat processing, have profound effects on oat flour dough rheological properties. The influence of roasting and steam treatments of oat grain on dough mixing and breadbaking properties was investigated when hydrothermally treated oat flour was blended with wheat flour. Roasting of oat grain (105°C, 2 hr) resulted in oat flours that were highly detrimental to wheat flour dough mixing properties and breadbaking quality. Steaming (105°C, 20 min) or a combination of roasting and steaming of oat grain significantly improved the breadbaking potential of the oat flours. The addition of oat flours increased water absorption and mixing requirements of the wheat flour dough and also decreased bread loaf volume. However, at the 10% substitution level, steamed oat flours exhibited only a gluten dilution effect on bread loaf volume when wheat starch was used as a reference. Oat flour in the breadbaking system decreased the retrogradation rate of bread crumb starch....