Impulse viscoelastic characterization of wheat flour dough during fermentation

A new technique, named impulse viscoelasticity, was introduced and applied to investigate the rheological properties of dough. Specifically, the effects of mixing and fermentation times on the extensional properties of dough were characterized under small extensional strains of short duration. From the stress and strain responses measured, the tensile storage and loss moduli of dough were obtained as a function of mixing and fermentation times. There were significant changes in the tensile moduli of the dough samples over mixing times and in general high extensional properties were measured for the optimally-mixed dough. Fermentation caused the reduction of both tensile storage/loss moduli with a greater decrease in the storage moduli, clearly showing the loss of elasticity of the fermenting dough. The results showed that the short duration of the applied strain allows the impulse viscoelastic technique to be appropriately used in characterizing the rheology of foods which can vary during processing.     

Antioxidative effect of cactus pear fruit (<Emphasis Type="Italic">Opuntia ficus-indica</Emphasis>) extract on lipid peroxidation inhibition in oils and emulsion model systems

The lipid peroxidation inhibitory effects of cactus pear fruit (Opuntia ficus-indica) extracts (CPFE) on fish oil, fish oil-in-water emulsion and linoleic acid were studied using conjugated diene hydroperoxides (CDH), weight gaining, peroxide value (PV), and thiobabituric acid reactive substances (TBARS) assays. A modified DPPH assay was used in the characterization of CPFE antioxidants for their thermal stability. CPFE successfully controlled lipid peroxidation at different stages of the pathway in a dose-dependent manner. Inhibition of the lipid peroxidation in oils and emulsion was successfully improved by increasing the level of CPFE from 0.01 to 0.1%. CPFE controlled conjugated diene formation from lipid radicals, demonstrating lower conjugated diene hydroperoxide values than its control counterpart. Moreover, it controlled the addition of oxygen to conjugated dienes to form lipid peroxyl radicals, resulting in lower weight gain. It also recorded a lower PV than its control counterpart, indicating its inhibitory effect on peroxyl radical formation. Such multiple and integrated effects controlled the overall lipid peroxidation, resulting in lower TBARS values than the control. Characterization of the CPFE antioxidants proved that those antioxidants are heat-resistant, although the color of the CPFE pigments disappeared rapidly.     

A new instrumental setup for determination of small amplitude viscoelastic properties of dough during fermentation

In this study, the working principles and the theoretical background of a new method to measure the viscoelastic properties of dough in the fermentation process are presented. During measurements, the dough sample was placed between a stationary bottom plate and an oscillating top plate and squeezed at random frequencies ranging from 10 to 100,000 rad/s. By measuring the required force and velocity of oscillations, the mechanical impedance of the samples, defined as the ratio of the force to oscillation velocity, was determined during fermentation. The measured mechanical impedance was used to calculate viscoelastic properties such as elastic and loss moduli of the dough samples. The nondestructive quick measurements and data covering a wide range of frequencies are some of the main advantages of the method. Furthermore, the described instrument can be easily affixed to the commonly available texture analyzer type equipments.     

Effect of flour heating on dough rheology

Heating soft wheat flour at 80°C for 15 min has already been shown to improve its bread-making potential. In this study, flour was fractionated to determine the specific effect of heating on its constituents (gluten, starch, lipid, water-soluble). While gluten was easier to extract and its texture was slacker after heating, it significantly increased dough-mixing stability and development time (P<0.01). Heated water-soluble fraction containing pentosans partly decreased stability (P=0.06).     

Monitoring the dynamic density of dough during fermentation using digital imaging method

A simple and new method was developed for monitoring the dynamic density of dough during fermentation process. In this method digital imaging was applied to determine volume of dough sample in actual proofing conditions, i.e., temperature and relative humidity of the fermentation oven. The method resulted that the volume increasing profile affected by temperature and relative humidity conditions of the fermentation oven. As when temperature and relative humidity was increased, volume expansion rate was higher. The data also demonstrated that dough density decrease with the investigated proofing temperatures of 25, 30 and 35 °C more significantly (p < 0.01) than proofing relative humidity of 65%, 75% and 85% (p < 0.05). The new imaging method have the advantage of being low cost and measuring dough density in actual proofing conditions as used in bread making.     

烘烤过程中烟叶脂氧合酶活性与膜脂过氧化的关系

对烘烤过程中烟叶脂氧合酶(LOX)的活性与膜脂过氧化关系的研究结果表明,随着烘烤过程的进展,烟叶水分逐渐散失,脂氧合酶(LOX)活性在0~24h期间缓慢上升,在24~48h期间急剧上升,48h之后明显下降直到完全消失;丙二醛(MDA)含量在0~48h与LOX活性变化同步,48h后MDA对脂氧合酶的反馈抑制作用逐渐增强。叶绿素、不饱和脂肪酸的降解与脂氧合酶活性和MDA的含量密切相关;蛋白质的降解与脂氧合酶活性和MDA含量相关性不明显      

Relationship of polymeric proteins and empirical dough rheology with dynamic rheology of dough and gluten from different wheat varieties

Dynamic rheological properties of dough and gluten were studied and related to the empirical rheology (Farinograph) and the protein fractions of different wheat varieties. The relationship between high molecular weight-glutenin subunits (HMW-GS) and dough strength was evaluated. Dynamic rheology of under-, optimum- and over-mixed dough was also related to the farinograph characteristics and the protein fractions. The moduli (G′ and G″) of over- and optimally-mixed dough were significantly correlated with Farinograph characteristics and SDS-unextractable polymeric protein (UPP) content. The temperature-induced rheology of glutens revealed that the differences in G′ and G″ during heating as well as cooling were related to the UPP content. Principal component analysis revealed wide range of differences in the dynamic rheology among the wheat varieties mainly attributed to UPP.     

An update on products and mechanisms of lipid peroxidation

The free radical reaction of polyunsaturated fatty acids with molecular oxygen leads to hydroperoxides as the first stable products. From linoleic acid the two conjugated diene hydroperoxides at carbons 9 and 13 were considered the only primary products until the recent discovery of the bis‐allylic 11‐hydroperoxide. The 11‐carbon is the site of the initial hydrogen abstraction, and the 11‐hydroperoxide is formed without isomerization of the 9,10 and 12,13 cis double bonds. In the autoxidation reaction, bis‐allylic hydroperoxides are obtained only in the presence of an efficient antioxidant, for example, α‐tocopherol. The antioxidant functions as a hydrogen atom donor, necessary to trap the fleeting bis‐allylic peroxyl radical intermediate as the hydroperoxide. Understanding of the mechanism of formation of bis‐allylic hydroperoxides has led to increased appreciation of the central role of the intermediate peroxyl radical in determining the outcome of lipid peroxidation.     

Effects of Saccharomyces cerevisiae on the structural kinetics of wheat dough during fermentation

As shown in previous studies the application of yeast presents a challenge for rheological measurements. The continuously produced metabolites of this living organism strongly influence the resulting data. In the study on hand, the method for fundamental oscillatory tests was modified to fit the needs of the flow behavior of yeasted dough. The analysis of the pH-value offered a method to indirectly determine the carbon dioxide production, as was proven by a linear correlation with the density (R² = 0.88, p < 0.001). As evidenced by Rheofermentometer measurements, the gas holding capacity of wheat dough was not affected by the kinetics of CO₂-production, whereas the total amount of gas was decisive. Moreover, the method associated density correlated significantly (p < 0.001) with the resistance to extension, the extensibility and the complex shear modulus. Finally, different yeast concentrations provoked up to 57% higher loss factors immediately after kneading. In summary, it was proven that yeasted wheat dough was significantly more plastic and susceptible to pressure than the non-leavened models. In turn, this provides a practical and realistic insight into the structural changes of wheat dough as affected by the metabolism of Saccharomyces cerevisiae.     

Antioxidative activity of nitrite in metmyoglobin induced lipid peroxidation

 The antioxidative activity of nitrite in metmyoglobin (MMb)-initiated lipid peroxidation in linoleic acid emulsions was examined using oxygen consumption measurement. Nitrite decreased MMb-induced lipid peroxidation with increasing concentrations. The antioxidative effect of nitrite was independent of pH in the range 6.3–5.5, and 1% NaCl did not seem to influence the antioxidative activity of nitrite. Furthermore, nitrite reduced MMb denaturation during MMb-induced peroxidation of linoleic acid. Thermal analysis using differential scanning calorimetry showed that nitrite increased the denaturation temperature of MMb. However, direct complexation between nitrite and the iron center of MMb could not be confirmed using chromatographic methods and analysis of UV-visible spectra of mixtures of nitrite and MMb. The observed results can rather be explained by a weak reversible interaction between nitrite and MMb such as binding of nitrite at the entrance to the haem cavity protecting MMb against heat denaturation and protecting both MMb and the fatty acids against oxidative degradation. Received: 8 March 1996     

Antioxidative activity of some vegetable peels determined in vitro by inducing liver lipid peroxidation

Vegetable peels are normally thrown away as kitchen wastes. In order to reveal their possible biological value, an in vitro investigation was performed on the antioxidative potential of some peel extracts such as Luffa cylindrica (Lc), Raphanus sativus (Rs), Daucus carota (Dc), Pisum sativum (Ps) and Trichosanthes dioica (Td) in ferrous sulphate (FeSO₄), hydrogen peroxide (H₂O₂) and carbon tetrachloride (CCl₄) induced lipid peroxidation (LPO) in liver, the major target organ of any drug. Effects were compared with that of a known antioxidant, butylated hydroxy anisole (BHA). A dose dependent inhibition was observed in all three, FeSO₄, H₂O₂ and CCl₄ induced hepatic LPO. However, with respect to one test peel (Rs), the two lower doses (125 and 250 μg/ml) were found to be ineffective. We suggest that the test peels have the potential to inhibit the lipid peroxidation and the observed differential antiperoxidative effects of the test peels could be the result of their poly phenol and flavonoid contents.     

Effect of glucose levels on the rheo-fermentation properties of dough during fermentation

In this study, recombinant dough and simulated dough medium were used to study the effect of different glucose levels on quality of dough. With the increase of glucose levels (3, 6, 9, 12 and 15 g/100 g mixed flour) in recombinant dough, the water absorption and extensibility of the dough decreased significantly. Compared with the sugar-free medium, the maximum height of the dough added with glucose gradually increased, and the CO₂ retention rate decreased slightly. The glucose levels in the dough changed the water mobility and distribution. Compared with 3% glucose levels, yeast produced much more glycerol content and ethanol content in 6% and 15% glucose medium, which affected rheological properties of dough. Different glucose levels affected the fermentation state of yeast and metabolites significantly, 3% glucose medium was more suitable for the dough fermentation and growth of yeast during dough fermentation.     

Purification of glutathione S-transferase from lamb muscle and its effect on lipid peroxidation

Lamb muscle contained 0.4 mg glutathione S-transferase (EC 2.5.1.18) per gram of tissue. On storage at 1°C, 20% of the activity was lost after 3 weeks. Glutathione S-transferase was isolated from lamb muscle by affinity chromatography on S-hexyglutathione Sepharose 6B. One major form of the enzyme was present in the purified preparation, a dimer with subunit molecular weight of 22 900 and isoelectric point of 6.7. This enzyme fits into the Pi class on the basis of substrate specificity. Linoleic acid hydroperoxides and trans, trans-2,4-decadienal, products of linoleate peroxidation, were both substrates (0.11 and 0.24 μmol min^?1 mg^?1 protein respectively). Glutathione S-transferase inhibited copper-stimulated peroxidation of arachidonate in the presence of glutathione. The inhibition was only slightly less efficient in the absence of glutathione. The latter effect probably arises from the presence of enzyme-bound glutathione (4–5 mol mol^?1 enzyme subunit) and also from a small but significant glutathione-independent peroxidase activity. The latter was detected using an HPLC assay which monitors formation of product directly. Reduced glutathione per se showed only a slight inhibition of arachidonate peroxidation.     

Effects of Amelanchier fruit isolates on cyclooxygenase enzymes and lipid peroxidation

Bioassay-directed isolation and purification of the ethyl acetate and methanol extracts of Amelanchier canadensis resulted in 1,3-dilinoleoyl 2-olein (1), 1,3-dioleoyl 2-linolein (2), 5-hydroxymethyl-2-furfural (3), 5-(sorbitoloxymethyl)-furan-2-carboxaldehyde (4), 5-(mannitoloxymethyl)-furan-2-carboxaldehyde (5), and 5-(α-d-glucopyranosyloxymethyl) furan-2-carboxaldehyde (6). Four compounds, oleanolic acid (7), ursolic acid (8), kaempferol-3-O-α-l-rhamnopyranosyl (1 ← 2) rhamnopyranoside (9), and kaempferol-3-O-α-l-rhamnopyranoside (10) were isolated from the ethyl acetate extract of fresh fruits of Amelanchier arborea. The compounds were isolated and purified by various chromatographic techniques and characterized by NMR and GC/MS methods. The isolated compounds inhibited lipid peroxidation (by 85%) at 100 ppm when compared to 89%, 87%, and 98% for the commercial antioxidants butylated hydroxy anisole (BHA), butylated hydroxytoluene (BHT), and tert-butylhydroxyquinone (TBHQ) at 1.67, 2.2, and 1.67 ppm, respectively. Although not selective, some of these compounds inhibited cyclooxygenase (COX)-1 and -2 enzymes. Compounds 3–6 were isolated for the first time from A. canadensis and compounds 7–10 were isolated for the first time from A. arborea fruits.     

Relationship between lipid peroxidation and fat content in Japanese Black beef Longissimus muscle during storage

We examined the relationship of crude fat content to lipid peroxidation of beef during storage. Longissimus muscle samples (fat content; 6.5–39.4%) from 27 Japanese Black beef steers were stored for 1, 4, 7 and 10 days, and thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxides (LOOH) were determined. TBARS values increased significantly (P<0.05), but LOOH did not change during the 10- day storage period. TBARS values were negatively correlated (P<0.05) with fat content in samples stored for 1, 4, 7 and 10 days. LOOH values, however, were not significantly correlated with fat content except on day 1. Phospholipid contents were correlated (P< 0.01) with LOOH values on each measurement day, but not significantly correlated with TBARS values except on day 1. These findings indicated that: (1) high-fat beef had high preservative properties, and that; (2) TBARS formation was correlated with LOOH derived from phospholipid oxidation in the initial period of storage, and was correlated directly with fat content in a later period.     

The effect of ginger on diabetic nephropathy,plasma antioxidant capacity and lipid peroxidation in rats

Oxidative stress is a major factor in the pathogenesis of diabetic complications. We studied the effects of ginger powder on nephropathy induced by diabetes, and measured changes in plasma antioxidant capacity and lipid peroxidation.     

Structural modification of soy protein by the lipid peroxidation product acrolein

Acrolein was selected as a representative secondary byproduct of lipid peroxidation to investigate the effect of oxidative modification of reactive aldehyde on soy protein structure. Acrolein reacted with histidine, lysine and cysteine residues in soy protein to form covalent adducts, leading to protein carbonylation and degradation of sulfhydryl groups. Circular dichroism spectra showed that soy protein modification by acrolein was related to loss of α-helix and increase of β-sheet structure. The decrease in solubility, surface hydrophobicity and intrinsic fluorescence indirectly implied that acrolein induced soy protein aggregation, and results obtained by size-exclusion chromatography directly showed that gradual aggregation of soy protein was induced by increasing concentration of acrolein. Results of sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that acrolein caused soy protein cross-linking which non-disulphide covalent bonds were involved in the formation of cross-linking, and subunits of β-conglycinin were more vulnerable to acrolein than that of glycinin.     

Effects of hydroperoxide in breads on IgE antibody responses

The effect of hydroperoxide in breads on antigen-antibody reaction against IgE was examined. We compared the antigen-antibody reaction against IgE between dough including hydroperoxide and that not including hydroperoxide. Crude proteins extracted from the dough including hydroperoxide showed weak antigen-antibody reaction on allergic tests such as ring precipitin test with human-specific IgE, and the IgE binding activity on ELISA. In contrast, the dough without hydroperoxide showed antigen-antibody reaction. The crude proteins extracted from the dough with hydroperoxide or without hydroperoxide were applied by affinity chromatography of trypsin-immobilized chitin. Then proteins having affinity were recovered. The recovered proteins were separated by SDS-PAGE. Each protein was examined for the IgE binding activity on ELISA. The IgE binding activity of baked bread was studied as well. Crude proteins of baked bread made from dough including hydroperoxide showed weaker IgE binding activity on ELISA than proteins of baked bread made from dough without hydroperoxide. Those results suggested that addition of hydroperoxide into dough affects on antigen activation.     

Lipid peroxidation inhibition capacity assay for antioxidants based on liposomal membranes

An in vitro antioxidant assay has been developed to better reflect the in vivo conditions of antioxidants interacting with membrane and lipid surfaces. The lipid peroxidation inhibition capacity (LPIC) method measures the ability of both lipophilic and hydrophilic antioxidants to protect a lipophilic fluorescent probe 4, 4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid, incorporated in the membrane, from 2,2'-azobis(2-amidinopropane)hydrochloride generated radicals in the surrounding aqueous solution. Antioxidant activities of test compounds were measured either after they were mixed with preformed liposomes (LPIC(Mixed)) or after they were incorporated into liposomes (LPIC(Inco)) as they were made. The results were analysed to determine how the method of mixing and the structures of the antioxidants influenced their protection of the membrane from free radical attack. The LPIC(Mixed) values were larger than the LPIC(Inco) values for a range of 12 structurally diverse antioxidant compounds. However, there was no linear correlation between the lipophilicities, as measured by their partition coefficient, log P and either LPIC(Inco) or LPIC(Mixed) values. A strong correlation was found between LPIC(Inco) and LPIC(Mixed) values.