Effect of Shortening Replacement with Oatrim on the Physical and Rheological Properties of Cakes

Oatrim (oat β‐glucan amylodextrins) was evaluated as a fat substitute in a cake system. The physical and rheological properties of cakes containing shortening replaced with 20, 40, and 60% by weight of Oatrim were characterized. The increase in the specific gravity of the cakes and the decrease in the viscosity as more shortening was replaced with Oatrim were correlated with the change in the cake volume. The number of air bubbles present in the cake batters varied significantly; however, the size of the observed bubbles did not change. The cakes containing more Oatrim displayed a higher starch gelatinization temperature due to the amylodextrins in the Oatrim. The dynamic rheological properties of the cakes were investigated during baking and correlated with the differential scanning calorimetry results. The oscillatory shear storage moduli decreased upon initial heating, then increased due to starch gelatinization, and finally reached a plateau value that varied based on the sample composition. Moreover, increased replacement of shortening with Oatrim resulted in higher observed oscillatory shear storage moduli. The cakes prepared with up to 20% by weight of Oatrim did not evidence significant changes in softness (P < 0.01) and generally exhibited similar physical properties to the control cake.     

Solution Viscoelastic Properties of OATRIM-10 and Cooked Oat Bran

The solution rheological behaviors of OATRIM-10 and cooked oat bran were investigated. The rheological properties of the materials were investigated using both thixotropic loop and small-amplitude oscillatory shear experiments. The cooked oat bran exhibited shear-thinning behavior during a thixotropic loop experiment over a shear rate range of 0–250/sec. The shear-thinning behavior was reproduced during the measurement of a second thixotropic loop. In contrast, OATRIM-10 exhibited an unexpected region of shear-thickening behavior at 20–80/sec. The shear-thickening and subsequent shear-thinning regions for OATRIM-10 could be described by a transient network model indicating that the shear-thickening behavior is caused by a shear-induced entangled network that is partially disentangled at higher shear rates. Subsequent thixotropic loop experiments displayed the shear-thickening region for OATRIM-10, indicating that the network structure can be reformed during the imposition of a shear field. Small-amplitude oscillatory shear data for cooked oat bran can be described reasonably well using a generalized linear viscoelastic (GLV) model. The oscillatory shear data obtained for OATRIM-10 could not be described by the GLV model. OATRIM-10 exhibited a distinctive plateau centered at 10/sec, and the low frequency response of storage modulus G′ decreased with a much larger slope in frequency than was predicted by the GLV model.     

Effect of Extrusion on Hypocholesterolemic Properties of Rice,Oat, Corn,and Wheat Bran Diets in Hamsters

Brans from rice, oats, corn, and wheat were cooked in a twin-screw extruder at either high or low energy input, and their cholesterol-lowering effects were compared with those of unprocessed brans when fed to four-week-old male golden Syrian hamsters (n = 10 per treatment) for three weeks. Peanut oil was added to oat, corn, and wheat bran during the extrusion process to match the oil content of rice bran. Diets contained 10% total dietary fiber, 10.3% fat, 3% nitrogen, and 0.3% cholesterol. Plasma and liver cholesterol and total liver lipids were significantly lower with low-energy extruded wheat bran compared with unprocessed wheat bran. Extrusion did not alter the hypocholesterolemic effects of rice, oat, or corn brans. Plasma and liver cholesterol levels with corn bran were similar to those with oat bran. Relative cholesterol-lowering effects of the brans, determined with pooled (extruded and unextruded) bran data, were rice bran > oat bran > corn bran > wheat bran. Rice bran diets resulted in significantly lower levels of total plasma cholesterol and very low density lipoprotein cholesterol compared with all other brans. Total liver cholesterol and liver cholesterol concentrations (mg/g) were significantly lower with high-energy extruded rice bran compared with the cellulose control group. Plasma cholesterol and total liver cholesterol values with low-energy extruded wheat bran were similar to those with rice bran (unextruded or extruded) diets. Lowered cholesterol with rice bran diets may result in part from greater lipid and sterol excretion with these diets. Results with low-energy extruded wheat bran suggest that this type of processing may improve the potential for lowering cholesterol with wheat bran products.     

In Vitro Binding of Bile Acids by Rice Bran,Oat Bran,Wheat Bran,and Corn Bran

The in vitro bile acid binding by rice, oat, wheat, and corn brans was determined using a mixture of bile acids normally secreted in human bile at a physiological pH of 6.3. The objective of the study was to relate bile acid binding of cereal brans to health promoting properties. Three experiments were conducted testing substrates on an equal weight (dry matter) basis, an equal total dietary fiber (TDF) basis, and an equal TDF and equal fat basis. Each experiment was repeated to validate the results (for a total of six experiments). The relative in vitro bile acid binding of the cereal brans on an equal TDF basis considering cholestyramine as 100% bound was rice bran 51%, wheat bran 31%, oat bran 26%, and corn bran 5%. The data suggest that cholesterol lowering by rice bran appears to be related to bile acid binding. The primary mechanism of cholesterol lowering by oat bran may not be due to bile acid binding by soluble fiber. Bile acid binding did not appear to be proportional to the soluble fiber content of the cereal brans tested. Bile acid binding by wheat bran may contribute to cancer prevention and other healthful properties.     

超细粉碎辅助提取裸燕麦多糖工艺研究

以燕麦麸皮为原料,研究了超细粉碎辅助提取裸燕麦多糖的工艺技术。对裸燕麦麸皮进行超细粉碎,采用X射线小角散射法检测了麸皮的粒度分布,并通过单因素实验和正交实验优化了裸燕麦多糖的提取条件。确定超细粉碎后的燕麦麸皮的平均粒度为397.6nm,中位粒径为408.9nm,分布散度为134.8nm;裸燕麦多糖的提取条件为:提取时间0.5h,料液比为1:20,提取4次,提取温度60℃;该工艺条件下多糖的得率为0.126 g·g-1。本研究为裸燕麦的精深加工提供了理论依据,并为进一步研究裸燕麦多糖的结构效应关系奠定了基础。     

Nonstarch Polysaccharides from Preprocessed Wheat Bran: Carbohydrate Analysis and Novel Rheological Properties

Wheat preprocessing technology produces a bran fraction rich in both soluble (8.5%) and insoluble (29.2%) fibers. The fraction, prepared by the Tkac and Timm commercial process, contained 9% alkaline extractable nonstarch polysaccharides (NSP). Conditions for extraction of NSP were chosen on the basis of both yield and molecular size of product. The extracted NSP was composed of an arabinoxylan and a mixed linkage(1→3)(1→4)-β-d -glucan. The NSP differed from previously reported wheat pentosans by exhibiting shear-thinning flow behavior at low concentration in water (0.5%, 25°C) and, more importantly, forming a thermally reversible gel upon cooling at 4°C. This unique gelling property is neither the commonly described irreversible gelation brought about by oxidation of wheat endosperm pentosans nor a characteristic property of cereal β-glucan. The low degree of substitution of the xylan chain of the arabinoxylan (xylose-to-arabinose ratio = 3) in this NSP might be responsible for the rheo-logical behavior.     

Reducing Beta-Glucan Solubility in Oat Bran Muffins by Freeze-Thaw Treatment Attenuates Its Hypoglycemic Effect

The viscosity of soluble fibers such as β-glucan depends on their concentration in solution and molecular weight (MW) distribution. We investigated whether freezing treatment of oat bran muffins affected the physicochemical properties of β-glucan, and its physiological effectiveness in lowering postprandial blood glucose response. A controlled range of β-glucan solubility was achieved by subjecting oat bran muffins containing two levels of β-glucan to repeated freeze-thaw temperature cycling. β-Glucan solubilized by in vitro digestion extraction was measured by flow-injection analysis. MW distributions of β-glucan were analyzed using size-exclusion chromatography. β-Glucan solubility decreased as the number of freeze-thaw cycles increased, while MW distribution of β-glucan decreased slightly. Peak blood glucose rise (PBGR) after fresh muffins (8 and 12 g of β-glucan/serving) was significantly lower than that after muffins (8 and 12 g of β-glucan/serving) treated with four freeze-thaw (FT) cycles (1.84 ± 0.2 vs. 2.31 ± 0.1 mmol/L, P = 0.007). Compared with the control whole wheat muffins, the reduction in incremental area under the glucose response curve (AUC) after fresh muffins (8 and 12 g of β-glucan/serving) was nearly twice that after 4 FT cycles (43.3 ± 4.4% vs. 27.0 ± 5.4%, P = 0.016). A significant inverse linear relationship was found between the log [concentration] of extractable β-glucan and PBGR (r² = 0.85, P = 0.01), and AUC (r² = 0.71, P = 0.03). The results show that reduction of β-glucan solubility in foods attenuates its physiological effectiveness in lowering postprandial glycemia.     

Effects of Natural Chelating Agents on the Solubility of Some Physiologically Important Mineral Elements in Oat Bran and Oat Flakes

The solubility of mineral elements from oat bran and flake samples was studied by a method using equilibrium dialysis after enzymatic digestion of starch and proteins. The effects of six potential chelating agents common in food were tested on the solubility of mineral elements. The minerals studied were calcium, magnesium, iron, manganese, zinc and potassium, and the chelating agents were citric, lactic, malic, and ascorbic acids, glucose and xylitol. The mineral elements were tightly bound to the dietary fiber of the samples. Bran fiber bound even the zinc and calcium contributed through the enzymes used. Adding citric, malic, or lactic acids increased the solubility of the mineral elements studied, except for potassium which was easily dialyzable as such. Iron was insoluble in all situations. Citric acid was the most efficient chelating agent in solubilizing the mineral elements. The effect of malic and lactic acids on the solubility of minerals was small. No effect was found with glucose, ascorbic acid, and xylitol. Thus, the intestinal availability of mineral elements may be affected by dietary hydroxy acids such as citric and malic acids in high dietary fiber diets.     

Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties

Breads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm³/g). Flour-water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion. However, increasing acetic acid decreased these values. Scanning electron microscope (Cryo-SEM) observation showed that the bread dough made from the same acetic acid-treated flour indicated continuum and no cracks in the dough matrix. Evaluation of mixograms showed the decrease of mixing stability with increased acetic acid levels. Viscosity and water binding capacity of flour-water suspensions were sharply increased by the addition of acetic acid at pH 5.0–3.5.     

Effect of Modified Oat Starch and Protein on Batter Properties and Quality of Cake

Starch and protein separated from oat were chemically modified using cross‐linking and acetylation protocols for starch, and deamidation and succinylation for protein isolate. Cross‐linking decreased swelling power of starch, whereas syneresis increased, but cross‐linking does not have a significant effect on gelatinization temperature. Acetylation increased swelling power, but gelatinization temperature and syneresis diminished. Deamidation and succinylation increased nitrogen solubility index, emulsion activity, foaming capacity, and water and oil binding capacity. Emulsion stability did not change with deamidation and it diminished with succinylation, while foaming stability decreased with both treatments. Acetylated starch and two types of modified proteins were substituted for 5, 10, 15, and 20% of oat flour to bake cake samples and then physical properties of the cakes were measured. Acetylated starch increased batter viscosity, cake volume, and whiteness of cake crust. Increased level of deamidated protein produced cakes with lower batter viscosity, higher volume, and darker color (increase in redness). Application of higher levels of succinylated protein led to higher batter viscosity and lightness, and lower cake volume. Therefore, substitution of deamidated protein and acetylated starch can improve cake properties.     

Effect of Outer Bran Layers from Germinated Wheat Grains on Breadmaking Properties

Wheat grains were germinated in the dark at room temperature (24°C) for 1, 2, 3, 5, and 8 days. Germinated wheat grains were pearled in a Waring blender, and the outer bran layers were separated from the pearled grains. Breadmaking was performed with wheat flour and 10% of the outer bran layer. Breadmaking properties (bread height [mm] and specific volume [cm³/g]) were gradually enhanced by blending the germinated outer bran layers, and maximum specific volume was obtained after 5 days of germination. However, the improvement was lost after 8 days of germination. Rapid ViscoAnalyser (RVA) and Brabender Farinograph profiles of wheat flour and outer bran layers (10%) indicated that the maximum decrease of peak viscosity and increase of angle of tail were obtained after 3 and 5 days of germination, respectively. Those changes are presumed to be due to the action of enzymes found in the outer bran layers. Activities of α‐ and β‐amylase, lipase, protease, and xylanase in the outer bran layers were measured, and correlation coefficients (r) between breadmaking properties and peak viscosity (RVA), angle of tail (farinograph), and enzyme activities were calculated. These data suggest that xylanase and α‐amylase activities in the outer bran layers were highly related to the enhancement of the breadmaking properties.     

Effect of Storage Time and Temperature on Rheological and Microstructural Properties of Gluten

To investigate the effects of frozen storage on the rheological and microstructural properties of gluten, two model systems were investigated: System A, gluten and water; System B, gluten, water, and NaCl. The storage time was varied from 1 to 16 weeks and the storage temperature was varied from ‐5 to ‐30°C. After thawing, uniaxial and biaxial deformations, and stress relaxation measurements were performed on gluten. In System A, the major effects were noticed when the gluten was stored at ‐5°C. Frozen storage induced a decrease in stress and in strain at breaking, but an increase in modulus (stress/strain) under uniaxial deformation. In System B, only stress relaxation measurements showed differences between the fresh gluten and the gluten stored at ‐18°C. These results suggest that at ‐5°C, gluten strands form more entanglements. Microscopic analyses of frozen gluten showed that, during the freezing step, ice crystals compressed the gluten. A significant phase separation was observed between gluten and ice but no difference was observed between the storage time and storage temperature. However, after thawing, gluten microstructure exhibited a structure similar to the fresh gluten, and the structure looks like a sponge (a fine gluten structure with tiny water pockets).     

Serum Lipids in Hypercholesterolemic Men and Women Consuming Oat Bran and Amaranth Products

One hundred‐eighty hypercholesterolemic subjects following the National Cholesterol Education Program Step One Diet were randomly divided into six groups (30 ± 2/group). Group 1 served as the control and received no fiber supplements. The fiber supplemented groups received 50 g/day of oat bran or amaranth from various sources: Group 2 (oat bran muffins); Group 3 (amaranth muffins); Group 4 (Oat Bran O's); Group 5 (Oat Bran Flakes); and Group 6 (a variety of oat bran products). Fasting serum total cholesterol (FSTC), low density‐, very low density‐, and high density‐lipoprotein cholesterol (LDL‐C, VLDL‐C, and HDL‐C) and serum triacylglycerols were measured before and after the 28‐day intervention. Three‐day diet records were completed before and after intervention. Subjects reduced (P < 0.05) the mean intake of total and saturated fat, and cholesterol. FSTC dropped more than twice as much (P < 0.05) as was observed with fat modification alone (Group 1 = ‐0.31 mmol/L), when oat bran was provided as flakes (Group 5 = ‐0.86 mmol/L) or in a variety of forms (Group 6 = ‐0.75 mmol/L). If the initial ratio of HDL‐C to FSTC was low, then supplementation did not decrease FSTC to the extent observed when the initial ratio was high. Compliance with the dietary interventions was best when the subjects gave the product a rating of ≤2.0 (on a 1–4 hedonic scale, with 1 being excellent). We can conclude from these data that fiber supplementation to reduce serum cholesterol is most effective in hypercholesterolemic individuals that have a greater proportion of HDL‐C. In addition, not all the oat bran products evaluated were able to lower cholesterol to the same extent, indicating that the ability of soluble fiber to reduce FSTC can be compromised by other dietary factors such as insoluble fiber.     

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

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 definition of oat bran, indicating a relatively uniform distribution of β-glucan in the groat.     

Structure and Pasting Properties of Oat Starch

Following a period of declining food use, oats are now increasing in importance because of perceived nutritional benefits. The pasting properties of oat starch were regarded as similar to those of other cereal starches until the development of instruments with a more rapid mixing system than the amylograph showed characteristic differences in oats. These differences in pasting properties offer opportunities for novel products in both food and industrial areas. The structure, composition, and pasting properties of oat starch are reviewed, with particular emphasis on methods of measurement. Future directions of research in this area are suggested.     

Effect of Added Fat on the Rheological Properties of Wheat Flour Doughs

The effect of added fat content on the rheological properties of wheat flour doughs was determined for three different added fat contents (2.5, 5.0, and 7.5%) at 25°C using dynamic mechanical analysis (DMA) and stress relaxation (SR) tests. Frequency sweeps indicated that added fat had a plasticizing effect on G′ and G″ in the rubbery region. SR results were parameterized using a Maxwell model and a Williams-Watts (WW) model. The WW model indicated that each dough could be characterized by just two major relaxation modes, while four elements were needed for the Maxwell model. The average relaxation time for the shorter process was <1 sec and was not affected by added fat. However, the average relaxation time for the longer WW process actually increased from 107 to 261 sec with added fat up to 5%, and then decreased again. Taken together, these results suggest that added fat actually delayed the onset of viscous flow, while simultaneously attenuating the short-time elastic properties of the gluten fraction of the dough. Furthermore, rheological testing over a wide time (frequency) scale was needed to observe the effect of added fat on both the short-time elastic and longer-time viscous behavior of these doughs.     

Effect of Oxidation on the Dynamic Rheological Properties of Wheat Flour-Water Doughs

Oxidation increased the strength of the dough. Addition of ascorbic acid or azodicabonamide (ADA) to dough increased both elastic modulus (G′) and viscous modulus (G″), while addition of cysteine decreased both values. Hydrogen peroxide, from either calcium peroxide or glucose oxidase, increased G′ and G″ and decreased tan δ (G″/G′) values. In addition to strengthening the dough, hydrogen peroxide dried the dough, but ADA did not. The absorption of doughs containing 20 GU of glucose oxidase (source of hydrogen peroxide) could be increased by ≈5% without altering the rheological properties. Presumably, the mobility of water in the gel formed by oxidative gelation decreased, thereby causing a drying of the dough.     

Effect of l-Ascorbic Acid on the Rheological Properties of Wheat Flour-Water Dough

L-Ascorbic acid (AsA) and its related compounds play an important role as improvers in bread production. Addition of AsA and its related compounds, such as dehydro-L-AsA (DHA) and 2,3-diketo-L-gulonic acid (DKG), affected the rheological properties of flour-water dough during mixing, especially hardness. Addition of 10 or 100 ppm AsA increased the dough hardness of samples as compared with the control dough. Addition of DHA or DKG to dough only slightly increased hardness. Addition of p-quinone significantly increased the hardness. Both glutathione (GSH) and its oxidized form (GSSG) drastically decreased the hardness. Contents of AsA in the treated dough decreased and contents of DHA increased during mixing, suggesting that oxidation occurred. The oxidation rate of AsA was influenced by the concentration of AsA added. The improving effect of AsA on the rheological properties of flour-water dough seemed to be mostly dependent on reactive intermediate oxidation products such as O₂^-, while the contribution of DHA was rather limited.     

Effect of Stabilized Rice Bran Fractions on the Formation of Rice Flour Pasting Properties

Rice flour composition played a key role in determining the changes in pasting properties of rice flour. The influence of incorporating defatted rice bran (DFRB), rice bran fiber (RBF), rice bran protein (RBP), and stabilized rice bran (SRB) fractions on the mechanism of rice flour pasting viscosities was investigated. Pasting properties of long‐ and medium‐grain rice flour substituted with 5, 10, 15, 20, and 100% bran fractions resulted in a significant decrease (P < 0.05) in rice flour pasting property values. Flour substituted with RBP had the lowest pasting property measurements compared with other fractions, and the greater the percentage substituted, the lower the pasting property values. DFRB and RBF were least affected properties when used as a replacement. Results were attributed to the contribution of rice starch in the mechanism of rice paste formation, in which decreasing starch in a rice flour sample, as a result of substituting with fractions of SRB, may have resulted in faster swelling of starch granules to the maximum extent and increased their susceptibility to be disrupted by shear, resulting in low paste viscosities. Results also suggested that protein structural integrity and the nature of starch–protein bonding affected rice flour pasting mechanism formation.