Study of the influence of genes related to muscle oxidative processes on beef color.

The biochemical bases of meat color are determined by the concentration and redox state of myoglobin, hemoglobin, cytochromes, and other pigments. Post-mortem depletion of cellular oxygen results in oxidative stresses that consume NADH and affects reducing activity, while enzymatic detoxification influences the cellular oxidative processes, both affecting meat color. The aim of this work was to study the influence of several genes related to cellular oxidative processes that could affect CIELAB meat color parameters. The study was performed in steers that received a grass-based diet combined with grain, hays and silages. Results suggest a possible link between colorimetric parameters (a*, b* and chroma) and SNPs in the GSTP1 gene (P<0.05). Although the influence of the enzymes, encoded by GSTP1 gene, on meat color has been proposed previously at biochemical level and protein expression level, further association studies in different populations and functional studies of proteins are needed to confirm the genetic determination of that gene on meat color.

Correlation of average hydrophobicity, water/air interface surface rheological properties and foaming properties of proteins.

A comparative study on the behavior in the air-water interface of ß-lactoglobulin, α-lactoalbumin, glycinin and ß-conglycinin was performed. The behavior at the interface was evaluated by equilibrium surface tension and surface rheological properties of adsorbed films. There were significant differences (α ≤ 0.05) in the values of the constants of adsorption to the interface of the four proteins. The glycinin had the slowest rate of adsorption, due to its low average hydrophobicity, low molecular flexibility and large molecular size. Smaller proteins like ß-lactoglobulin and α-lactoalbumin tended to greater equilibrium pressure values than the larger proteins because of its higher rate of adsorption to the interface. The foam capacity of proteins showed a positive correlation with the average hydrophobicity; the maximal retained liquid volume or the initial rate of passage of liquid to foam were significantly lower (α ≤ 0.05) when protein was glycinin. The dilatational modulus of glycinin was the lowest, which implies lowest resistance to disruption of the film. Glycinin protein has lower proportion of gravitational drainage and higher disproportionation having perhaps a less resistant film. In conclusion, ß-conglycinin and whey proteins showed a similar behavior, so ß-conglycinin might be the best soybean protein to replace milk proteins in food formulations.

Genistein effects on Ca2+ handling in human umbilical artery: inhibition of sarcoplasmic reticulum Ca2+ release and of voltage-operated Ca2+ channels.

Isoflavones are a group of natural phytoestrogens including the compound genistein. Health beneficial effects have been attributed to the consumption of this compound, but the fact that it has estrogen-like activity has raised doubts regarding its potential risk in infants, newborns, or in the fetus and placenta during pregnancy. This work is aimed at studying genistein effects on Ca2+ handling by smooth muscle cells of the human umbilical artery (HUA). Using fluorometric techniques, we found that in these cells genistein reduces the intracellular Ca2+ peak produced by serotonin. The same result could be demonstrated in absence of extracellular Ca2+, suggesting that the isoflavone reduces Ca2+ release from the sarcoplasmic reticulum. Force measurement experiments strengthen these results, since genistein reduced the peak force attained by intact HUA rings stimulated by serotonin in a Ca2+-free solution. Moreover, genistein induced the relaxation of HUA rings precontracted either with serotonin or a depolarizing high-extracellular K+ solution, hinting at a reduction of extracellular Ca2+ entry to the cell. This was confirmed by whole-cell patch-clamp experiments where it was shown that the isoflavone inhibits ionic currents through voltage-operated Ca2+ channels. In summary, we show that genistein inhibits two mechanisms that could increase intracellular Ca2+ in human umbilical smooth muscle cells, behaving in this way as a potential vasorelaxing substance of fetal vessels. Taking into account that genistein is able to cross the placental barrier, these data show that isoflavones may have important implications in the regulation of feto-maternal blood flow in pregnant women who consume soy-derived products as part of their meals.

Efectos de la genisteína en los niveles del Ca2+ citosólico en células musculares de arteria umbilical humana / Genistein effects on Ca2+ handling in human umbilical artery: inhibition of sarcoplasmic reticulum Ca2+ release and of voltage-operated Ca2+ channels

Isoflavones are a group of natural phytoestrogens including the compound genistein.Health beneficial effects have been attributed to the consumption of this compound,but the fact that it has estrogen-like activity has raised doubts regarding itspotential risk in infants, newborns, or in the fetus and placenta during pregnancy.This work is aimed at studying genistein effects on Ca2+ handling by smooth musclecells of the human umbilical artery (HUA). Using fluorometric techniques, we foundthat in these cells genistein reduces the intracellular Ca2+ peak produced by serotonin.The same result could be demonstrated in absence of extracellular Ca2+, suggestingthat the isoflavone reduces Ca2+ release from the sarcoplasmic reticulum.Force measurement experiments strengthen these results, since genistein reduced thepeak force attained by intact HUA rings stimulated by serotonin in a Ca2+-free solution.Moreover, genistein induced the relaxation of HUA rings precontracted eitherwith serotonin or a depolarizing high-extracellular K+ solution, hinting at a reductionof extracellular Ca2+ entry to the cell. This was confirmed by whole-cell patchclampexperiments where it was shown that the isoflavone inhibits ionic currentsthrough voltage-operated Ca2+ channels. In summary, we show that genisteininhibits two mechanisms that could increase intracellular Ca2+ in human umbilical smooth muscle cells, behaving in this way as a potential vasorelaxing substance offetal vessels. Taking into account that genistein is able to cross the placental barrier,these data show that isoflavones may have important implications in the regulationof feto-maternal blood flow in pregnant women who consume soy-derived productsas part of their meals(AU)

Las isoflavonas son un grupo de fitoestrógenosnaturales que incluyen la genisteína. Alconsumo de este compuesto se le han atribuidoefectos beneficiosos para la salud, pero su actividadsimilar a los estrógenos permite pensaren efectos indeseados en niños o en el feto o laplacenta durante el embarazo. En este trabajose estudian los efectos de la genisteína sobre elmanejo de Ca2+ por las células de músculo lisode la arteria umbilical humana (AUH).Mediante la utilización de técnicas fluorométricasse observó que la genisteína reduce elpico de Ca2+ intracelular producido por la serotonina en estas células incluso en ausenciade Ca2+ extracelular, lo que sugiere que la isoflavonareduce la liberación de Ca2+ a partir delretículo sarcoplásmico. Los experimentos demedida de fuerza refuerzan estos resultados, yaque la genisteína redujo la fuerza pico desarrolladapor serotonina en anillos intactos deAUH en una solución libre de Ca2+. Además,la genisteína indujo la relajación de anillos deAUH precontraídos con serotonina o con unasolución despolarizante de alto K+ extracelular,lo que apunta a una reducción de la entradade Ca2+ desde el exterior de la célula. Con latécnica de “patch-clamp” en configuración decélula entera, los resultados confirmaron que laisoflavona inhibe corrientes iónicas a través decanales de Ca2+ operados por el voltaje. Enresumen, mostramos que la genisteína inhibedos mecanismos que incrementan el Ca2+intracelular en células de músculo liso deAUH, comportándose de esta manera comoun potencial vasorrelajante de los vasos fetales.Dado que la genisteína atraviesa la barrera placentaria,estos datos muestran que las isoflavonaspodrían tener consecuencias en la regulacióndel flujo materno-fetal en mujeres embarazadasque incluyan productos derivados de lasoja como parte de sus dietas(AU)

ACE inhibitory tetrapeptides from Amaranthus hypochondriacus 11S globulin.

Amaranth seed is a valuable source of dietary protein with very high nutritional quality, and recently its potential as a nutraceutical has been proposed. The aim of this work was to provide experimental evidence for the presence of anti-hypertensive peptides in globulin 11S, one of the major constituents of the seed, by means of an in-silico based peptide library screening method. A three-dimensional model of globulin 11S was built, upon which anti-hypertensive peptides were mapped via a database-driven method. Solvent accessibility was evaluated for each potential peptide, and two potent and exposed tripeptides were detected: IKP and LEP. An N-terminal extension of these two peptides was built using the globulin 11S primary sequence information, and ACE inhibitory behaviour was simulated by automated ligand-protein docking. The occurrence of two inhibitory tetrapeptides, ALEP and VIKP, was predicted and experimentally validated by an in vitro ACE inhibition assay that showed IC50 values of 6.32 mM and 175 microM, respectively. This study is the first to provide experimental proof of the anti-hypertensive value of Amaranth. Furthermore, this is the first time that a peptide docking approach is used to find ACE-inhibitory peptides from a food protein source.

Contribution of the starch, protein, and lipid fractions to the physical, thermal, and structural properties of amaranth (Amaranthus caudatus) flour films.

Amaranth protein-lipid (PL) and protein (P) films were elaborated and compared with amaranth flour films in order to determine the contribution of the interactions between the biopolymer (starch and protein) and the lipids to the film properties. The films were made by the casting method, using the same glycerol concentration (0.9 g glycerol/100 g solution). A separation of the lipid fraction in the PL films and a polymorphic transformation of the corresponding fatty acids were observed by differential scanning calorimetry (DSC) and verified by an analysis of the microstructure by scanning electron microscopy (SEM). The flour films showed no separation of the lipid fraction, evidence that the lipids were strongly associated with the proteins and homogenously distributed throughout the starch network, contributing to the good mechanical properties when compared to the PL films and to the excellent barrier properties when compared to both the PL and P films. The protein-protein interactions also contributed to the mechanical properties of the flour films. The presence of proteins and lipids in the flour films had an important effect on film solubility, and also on the color and opacity of the films. This study showed that the flour film properties depended on the interactions formed by their polymers (starches and proteins) and by the lipid, on the distribution of these interactions within the film matrix and on the concentrations of each component in the film.

Genistein inhibits contractile force, intracellular Ca2+ increase and Ca2+ oscillations induced by serotonin in rat aortic smooth muscle.

The soy-derived isoflavones genistein and daidzein affect the contractile state of different kinds of smooth muscle. We describe acute effects of genistein and daidzein on contractile force and intracellular Ca2+ concentration ([Ca2+]i) in in situ smooth muscle of rat aorta. Serotonin (5-HT) (2 microM) or a depolarizing high K+ solution produced the contraction of aortic rings, which were immediately relaxed by 20 microM genistein and by 20 microM daidzein. Accordingly, both 5-HT and a high K+ solution increased the [Ca2+]i in in situ smooth muscle cells. Genistein strongly inhibited the [Ca2+]i increase evoked by 5-HT (74.0 +/- 7.3%, n = 11, p < 0.05), and had a smaller effect on high K+ induced [Ca2+]i increase (19.9 +/- 4.0%, n = 7, p < 0.05). The K+ channels blocker tetraethylammonium (TEA) (0.5 mM) diminished genistein effects on 5-HT-induced [Ca2+]i increase. Interestingly, during prolonged application of 5-HT, the [Ca2+]i oscillated and a short (90 s) preincubation with genistein (20 microM) significantly diminished the frequency of the oscillations. This effect was totally abolished by TEA. In conclusion, in rat aortic smooth muscle, genistein is capable of diminishing the increase in [Ca2+]i and in force evoked by 5-HT and high K+ solution, and of decreasing the frequency of [Ca2+]i oscillations induced by 5-HT. The short time required by genistein, and the relaxing effect of daidzein suggest that tyrosine kinases inhibition is not involved. The small inhibiting effect of genistein on the [Ca2+]i increase evoked by high K+ and the effect of TEA point to the activation by genistein of calcium-activated K+ channels.

Genistein inhibits contractile force, intracellular Ca2+ increase and Ca2+ oscillations induced by serotonin in rat aortic smooth muscle

The soy-derived isoflavones genistein and daidzein affect the contractile state ofdifferent kinds of smooth muscle. We describe acute effects of genistein and daidzeinon contractile force and intracellular Ca2+ concentration ([Ca2+]i) in in situ smoothmuscle of rat aorta. Serotonin (5-HT) (2 ìM) or a depolarizing high K+ solution producedthe contraction of aortic rings, which were immediately relaxed by 20 ìMgenistein and by 20 ìM daidzein. Accordingly, both 5-HT and a high K+ solutionincreased the [Ca2+]i in in situ smooth muscle cells. Genistein strongly inhibited the[Ca2+]i increase evoked by 5-HT (74.0 ± 7.3%, n=11, p<0.05), and had a smallereffect on high K+ induced [Ca2+]i increase (19.9 ± 4.0%, n=7, p<0.05). The K+ channelsblocker tetraethylammonium (TEA) (0.5 mM) diminished genistein effects on 5-HT-induced [Ca2+]i increase. Interestingly, during prolonged application of 5-HT,the [Ca2+]i oscillated and a short (90 s) preincubation with genistein (20 ìM) significantlydiminished the frequency of the oscillations. This effect was totally abolishedby TEA. In conclusion, in rat aortic smooth muscle, genistein is capable of diminishingthe increase in [Ca2+]i and in force evoked by 5-HT and high K+ solution, andof decreasing the frequency of [Ca2+]i oscillations induced by 5-HT. The short timerequired by genistein, and the relaxing effect of daidzein suggest that tyrosine kinasesinhibition is not involved. The small inhibiting effect of genistein on the [Ca2+]iincrease evoked by high K+ and the effect of TEA point to the activation by genisteinof calcium-activated K+ channels (AU)

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Genistein inhibits contractile force, intracellularCa2+ increase and Ca2+ oscillations induced byserotonin in rat aortic smooth muscle

The soy-derived isoflavones genistein and daidzein affect the contractile state ofdifferent kinds of smooth muscle. We describe acute effects of genistein and daidzeinon contractile force and intracellular Ca2+ concentration ([Ca2+]i) in in situ smoothmuscle of rat aorta. Serotonin (5-HT) (2 ìM) or a depolarizing high K+ solution producedthe contraction of aortic rings, which were immediately relaxed by 20 ìMgenistein and by 20 ìM daidzein. Accordingly, both 5-HT and a high K+ solutionincreased the [Ca2+]i in in situ smooth muscle cells. Genistein strongly inhibited the[Ca2+]i increase evoked by 5-HT (74.0 ± 7.3%, n=11, p<0.05), and had a smallereffect on high K+ induced [Ca2+]i increase (19.9 ± 4.0%, n=7, p<0.05). The K+ channelsblocker tetraethylammonium (TEA) (0.5 mM) diminished genistein effects on 5-HT-induced [Ca2+]i increase. Interestingly, during prolonged application of 5-HT,the [Ca2+]i oscillated and a short (90 s) preincubation with genistein (20 ìM) significantlydiminished the frequency of the oscillations. This effect was totally abolishedby TEA. In conclusion, in rat aortic smooth muscle, genistein is capable of diminishingthe increase in [Ca2+]i and in force evoked by 5-HT and high K+ solution, andof decreasing the frequency of [Ca2+]i oscillations induced by 5-HT. The short timerequired by genistein, and the relaxing effect of daidzein suggest that tyrosine kinasesinhibition is not involved. The small inhibiting effect of genistein on the [Ca2+]iincrease evoked by high K+ and the effect of TEA point to the activation by genisteinof calcium-activated K+ channels (AU)

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The Na+/Ca2+ exchanger is active and working in the reverse mode in human umbilical artery smooth muscle cells.

The data presented in this work suggest that in human umbilical artery (HUA) smooth muscle cells, the Na(+)/Ca(2+) exchanger (NCX) is active and working in the reverse mode. This supposition is based on the following results: (i) microfluorimetry in HUA smooth muscle cells in situ showed that a Ca(2+)-free extracellular solution diminished intracellular Ca(2+) ([Ca(2+)](i)), and KB-R7943 (5microM), a specific inhibitor of the Ca(2+) entry mode of the exchanger, also decreased [Ca(2+)](i) (40.6+/-4.5% of Ca(2+)-free effect); (ii) KB-R7943 produced the relaxation of HUA rings (-24.7+/-7.3gF/gW, n=8, p<0.05); (iii) stimulation of the NCX by lowering extracellular Na(+) increases basal [Ca(2+)](i) proportionally to Na(+) reduction (Delta fluorescence ratio=0.593+/-0.141 for Na(+)-free solution, n=8) and HUA rings' contraction (peak force=181.5+/-39.7 for 130mM reduction, n=8), both inhibited by KB-R7943 and a Ca(2+)-free extracellular solution. In conclusion, the NCX represents an important Ca(2+) entry route in HUA smooth muscle cells.

High-pressure induced physicochemical and functional modifications of low-density lipoproteins from hen egg yolk.

High-pressure treatment represents a potential method to stabilize microbiologically agricultural raw materials that are sensitive to heat treatments. Low-density lipoproteins (LDL), the main contributors to the exceptional emulsifying properties of yolk, are particularly sensitive to heat treatment. In this study, high-pressure treatments have been performed on LDL, and their impact on LDL physicochemical and emulsifying properties has been assessed. LDL dispersions at two pH levels (pH 3 and 8) were treated at different pressure levels: 200, 400, and 600 MPa at 20 degrees C. LDL dispersion characteristics (solubility, aggregation, and protein denaturation) and LDL emulsifying properties (o/w 30:70 emulsions: droplet size, flocculation, and protein adsorption) of nontreated and high-pressure treated dispersions were compared. Solubility is not altered by high-pressure treatment whatever the pH, whereas aggregation and protein denaturation are drastically enhanced, in particular at pH 8. The effects of these modifications on LDL emulsifying properties are mainly a diminution of the flocculation (depletion and bridging) at this same pH. Finally, it seems that high-pressure treatment combined with an alkaline pH decreases droplet flocculation of LDL dispersions.

Determinaciones analíticas de bebidas no alcohólicas / Analytic determinations of non-alcoholic beverages

El propósito del presente trabajo fue determinar pH intrínseco, determinación de sólidos solubles, efecto buffer a pH 5.5 y pH 7.0 de diferentes bebidas de consumo. Material y método: fueron seleccionados, basándose en estudios de mercado y agrupados por categorías, 78 productos de consumo. En cada uno de los productos se realizaron: 1- determinación de pH. 2- Determinación de sólidos solubles. 3- efecto buffer a pH 5.5. 4- efecto buffer a pH 7.0. Para las mediciones de pH se utilizó un equipo BC-TUGUI-01-CIDCA con resolución de 0,1 unidades de pH y una precisión de +-0.1, con sistema de adquisición de datos con archivos formato ASCII, calibrado a pH 4.0 y 7.0. La determinación de sólidos solubles se realizó mediante medición de Brix directo con refractómetro Abbe, Bellingham-Staney Ltd., England, calibrado con patrones de soluciones de sacarosa p/p. Las determinaciones se realizaron en 3 muestras de cada producto de diferentes partidas. Se calcularon las medias de cada producto y las medias de cada grupo de bebidas. Resultados: las gaseosas, los jugos (naturales, preparados y en polvo), las bebidas a base de soja saborizadas y los yogures presentaron valores de pH ácidos. Las leches y las bebidas a base de soja naturales sus pH resultaron alcalinos o próximos a la alcalinidad. Los sólidos solubles, expresados en grados Brix, variaron de 0 para el agua mineral, hasta 13 en las leches fermentables. Los valores de efecto buffer, expresado en minimoles por litro, resultaron elevados en los jugos naturales (naranja y pomelo) y jugos sin soja, tanto a pH 5 como pH 7 y bajos en el agua mineral. Conclusiones: las bebidas no alcohólicas de consumo frecuente presentaron un pH ácido, incluyendo algunas aguas minerales. Los jugos naturales además de presentar bajo pH presentan elevado efecto buffer. Las leches presentan pH casi alcalinos. Las bebidas a base de soja sin saborizar presentan pH alcalino

Determinaciones analíticas de bebidas no alcohólicas / Analytic determinations of non-alcoholic beverages

El propósito del presente trabajo fue determinar pH intrínseco, determinación de sólidos solubles, efecto buffer a pH 5.5 y pH 7.0 de diferentes bebidas de consumo. Material y método: fueron seleccionados, basándose en estudios de mercado y agrupados por categorías, 78 productos de consumo. En cada uno de los productos se realizaron: 1- determinación de pH. 2- Determinación de sólidos solubles. 3- efecto buffer a pH 5.5. 4- efecto buffer a pH 7.0. Para las mediciones de pH se utilizó un equipo BC-TUGUI-01-CIDCA con resolución de 0,1 unidades de pH y una precisión de +-0.1, con sistema de adquisición de datos con archivos formato ASCII, calibrado a pH 4.0 y 7.0. La determinación de sólidos solubles se realizó mediante medición de Brix directo con refractómetro Abbe, Bellingham-Staney Ltd., England, calibrado con patrones de soluciones de sacarosa p/p. Las determinaciones se realizaron en 3 muestras de cada producto de diferentes partidas. Se calcularon las medias de cada producto y las medias de cada grupo de bebidas. Resultados: las gaseosas, los jugos (naturales, preparados y en polvo), las bebidas a base de soja saborizadas y los yogures presentaron valores de pH ácidos. Las leches y las bebidas a base de soja naturales sus pH resultaron alcalinos o próximos a la alcalinidad. Los sólidos solubles, expresados en grados Brix, variaron de 0 para el agua mineral, hasta 13 en las leches fermentables. Los valores de efecto buffer, expresado en minimoles por litro, resultaron elevados en los jugos naturales (naranja y pomelo) y jugos sin soja, tanto a pH 5 como pH 7 y bajos en el agua mineral. Conclusiones: las bebidas no alcohólicas de consumo frecuente presentaron un pH ácido, incluyendo algunas aguas minerales. Los jugos naturales además de presentar bajo pH presentan elevado efecto buffer. Las leches presentan pH casi alcalinos. Las bebidas a base de soja sin saborizar presentan pH alcalino (AU)

Detection and identification of a soy protein component that cross-reacts with caseins from cow's milk.

Soy-based formulas are the most employed cow's milk substitutes in the treatment of cow's milk allergy in our country. Since adverse reactions have been reported in allergic patients as a consequence of exposure to soy proteins, we have investigated the possible cross-reactivity between components from soybean and cow's milk. A cow's milk specific polyclonal antiserum and casein specific monoclonal antibodies were used in immunoblotting and competitive ELISA studies to identify a 30-kD component from soybean that cross-reacts with cow's milk caseins. Its IgE binding capacity was tested by EAST, employing sera from cow's milk allergic patients, not previously exposed to soy proteins. The 30 kD protein was isolated and partially sequenced. It is constituted by two polypeptides (A5 and B3) linked by a disulphide bond. The protein's capacity to bind to the different antibodies relies on the B3 poly-peptide. These results indicate that soy-based formula, which contains the A5-B3 glycinin molecule, could be involved in allergic reactions observed in cow's milk allergic patients exposed to soy-containing foods.

Structure characterization of human serum proteins in solution and dry state.

The present report describes application of advanced analytical methods to establish correlation between changes in human serum proteins of patients with coronary atherosclerosis (protein metabolism) before and after moderate beer consumption. Intrinsic fluorescence, circular dichroism (CD), differential scanning calorimetry and hydrophobicity (So) were used to study human serum proteins. Globulin and albumin from human serum (HSG and HSA, respectively) were denatured with 8 m urea as the maximal concentration. The results obtained provided evidence of differences in their secondary and tertiary structures. The thermal denaturation of HSA and HSG expressed in temperature of denaturation (Td, degrees C), enthalpy (DeltaH, kcal/mol) and entropy (DeltaS kcal/mol K) showed qualitative changes in these protein fractions, which were characterized and compared with fluorescence and CD. Number of hydrogen bonds (n) ruptured during this process was calculated from these thermodynamic parameters and then used for determination of the degree of denaturation (%D). Unfolding of HSA and HSG fractions is a result of promoted interactions between exposed functional groups, which involve conformational changes of alpha-helix, beta-sheet and aperiodic structure. Here evidence is provided that the loosening of the human serum protein structure takes place primarily in various concentrations of urea before and after beer consumption (BC). Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption. In summary, thermal denaturation parameters, fluorescence, So and the content of secondary structure have shown that HSG is more stable fraction than HSA.

Analysis of the effects of heat treatment on gliadin immunochemical quantification using a panel of anti-prolamin antibodies.

Antigen-labeled capture enzyme-linked immunosorbent assay with four different anti-gliadin monoclonal antibodies and an anti-gliadin serum and two different sample systems (purified gliadin fractions heat-treated in soluble phase and a model of dough simulating a baking process) were employed to study the effects of heat treatment on gliadin quantification. The analysis of purified gliadins showed that there is no particularly heat stable fraction. Remarkably, omega-gliadin did not present a differential heat stability. Reactivity varied depending on the time-temperature conditions of the treatment, the antibody employed, and the fraction analyzed. Heated dough samples showed an impairment of protein extraction depending on the intensity of the treatment. Capillary electrophoresis analysis of extracts showed that each gliadin group is affected to a different extent; omega-gliadin is less modified. Immunochemical analysis of the heat-treated samples using either of the five antibodies showed a decrease in the quantified gliadin, in concordance to the loss in the extracted proteins. Among the different sources of error in gliadin immunochemical quantification, the impairment in extraction efficiency in heat-treated samples appears as a major drawback to be overcome.

Relationships between different hydration properties of commercial and laboratory soybean isolates.

Functional properties related to water protein interactions of soy protein isolates depend on the structural and aggregation characteristics of their major components (storage globulins 7S and 11S) that could be modified by the preparation procedure, thermal and/or chemical treatments, and drying methods. Commercial and laboratory isolates with different functionalities resulting from their structural modifications were compared. Isolates with high solubility or excessive thermally induced insolubilization or compact calcium-induced aggregates caused low water-imbibing capacity (WIC) values. The highest WIC results from the balance between intermediate solubility and the formation of aggregates with good hydration properties. The apparent viscosity of dispersions of commercial (spray dried) and laboratory (lyophilized) isolates depends on the WIC, the morphology and size of the particles, and the interaction of the hydrated particles. The hydration properties and viscosity of protein isolate suspensions were strongly determined by the amount and properties of the insoluble fraction.

Characterization of peroxidase-mediated chlorophyll bleaching in strawberry fruit.

Peroxidase (POX) from strawberry fruits was analyzed for its capacity to bleach chlorophyll. The partially purified enzyme preperation catalyzed the bleaching of chlorophylls and their derivatives in the presence of H(2)O(2) and phenolic compounds. The optimal reaction conditions were 35 degrees C, pH 5.2 and ionic strength equal to 0.2. The maximum activity was observed at 1 mM of H(2)O(2), while higher concentrations inhibited enzyme activity. Compounds with a high affinity to the heme group, radical scavengers and reducing agents, showed an inhibitory effect. Phenolic compounds such as umbelliferone, naringenin and p-substituted monophenols acted as cofactors. Instead, other phenolic compounds tested such as caffeic acid, catechin, ellagic acid, esculin and quercetin inhibited the activity of POX on chlorophylls. Phenolic compounds extracted from strawberry fruits showed an inhibitory effect on POX-chlorophyll bleaching activity, although this effect decreased markedly during ripening. POX showed higher affinity for compounds derived from chlorophyll a than from chlorophyll b, and the enzyme preferentially degraded chlorophyll derivatives with the Mg(2+) ion present and the phytol group removed. The POX-chlorophyll bleaching activity was found in all ripening stages from small green to ripe, the highest activity corresponding to large green fruits.

Effect of freezing and frozen storage of doughs on bread quality.

The effects of freezing and storage in frozen conditions on bread quality, crumb properties, and aggregative behavior of glutenins were analyzed. The effect of different additives on bread quality was also studied. The results obtained showed that freezing and storage at -18 degrees C decreased the bread quality. Samples stored in frozen conditions supplemented with diacetyl-tartaric acid ester of monoglycerides, gluten, and guar gum produced breads of greater volume and more open crumb structure than those prepared with the base formulation (without additives). All additives analyzed increased the proof time. Crumb firmness increased with dough frozen storage and bread aging time at 4 degrees C. A decrease in the amount of glutenin subunits of high molecular mass was observed by electrophoresis analysis of the SDS-soluble proteins aggregates extracted from the frozen dough. This result suggested that the protein matrix of bread underwent depolymerization during storage in frozen conditions.

Amaranth globulin structure modifications induced by enzymatic proteolysis.

Globulin-P was partially hydrolyzed with papain under specific conditions to study the resulting structural modifications. Under mild hydrolytic conditions, globulin-P polymers were cleaved to render their unitary constituents (280 kDa molecules). Under stronger hydrolytic conditions these unitary molecules were 13% smaller than those from nonhydrolyzed globulin. Moreover, these molecules remained assembled even though they contained degraded polypeptides. The monomeric (M) subunit and the A chains were preferentially cleaved under mild and intermediate hydrolytic conditions, whereas B chains remained with the same size. These results suggest that the M and A polypeptides might be located at an exposed site of the molecules resembling the structure of the legumins. The M subunit may be participating in the stabilization of globulin-P polymers, on the basis that these two species disappeared under the same hydrolytic conditions. Similar events such as those described in this paper might be taking place on globulin-P during germination of amaranth grain.