María Cristina Añón

Effect of emulsifier and guar gum on micro structural, rheological and baking performance of frozen bread dough

The influence of mono- and diacylglycerols esterified to mono- and diacetyltartaric acid (DATEM) and guar gum on dynamic rheological behaviour, starch gelatinization, microstructure and bread properties of frozen dough were analysed. The results obtained showed that the dough freezing and storage at −18 °C decreased the bread quality. The dough freezing and frozen storage provoked a decrease in the complex modulus (G∗) and the storage modulus (G′) showing a reduction in dough firmness and elasticity. Structural damage caused on dough ultra structure through frozen storage was observed by scanning electron microscopy. Starch gelatinization was affected by additives and by dough storage at −18 °C. DATEM and gum guar improved volume and texture of bread obtained from non-frozen and frozen dough, but neither DATEM nor gum guar could avoid the effect of dough frozen storage on the dynamic rheological parameters and microstructure damage.

Freezing rate effects on the drip loss of frozen beef

One of the quality parameters of frozen meat is the amount of exudate which arises during thawing. The amount of drip obtained by centrifugation under standard conditions, and the protein composition of the exudate, has been correlated for different thermal histories. The results obtained show that the amount of exudate varies in relation to the time that the sample needs to pass from -1°C to -7°C (characteristic freezing time). On the other hand, pH and concentration of proteins do not show significant differences between frozen and unfrozen samples. Similarly, neither one nor the other varies with the rate of freezing. The proteins were also analysed by electrophoresis in polyacrylamide gel. In this case, no differences were observed either between frozen samples and unfrozen ones or between samples which had been frozen at different rates. Hypotheses on the origin of cellular damage and alternatives which lead to the establishment of a standard of quality for quick frozen meat are presented in relation to the results obtained.

Polyphenoloxidase activity from strawberry fruit (Fragaria ananassa, Duch., cv Selva): characterisation and partial purification

In this work, polyphenoloxidase (PPO) from Selva strawberry fruit (Fragaria × ananassa, Duch) was extracted, characterised and partially purified. The activity of PPO was analysed in crude extracts obtained from either fresh fruits or acetone powder. The presence of NaCl and Triton X-100 in the extraction buffer caused a marked increase in enzyme extractability. The enzyme showed an apparent Km value of 11.2 mM with pyrocatechol as substrate. The maximum enzyme activity was observed at 50 °C and pH 5.3–6.0 without SDS and pH 7.2 in the presence of SDS. The presence of SDS increased PPO activity at pH 7.2 but diminished it at pH 6.0. The enzyme showed high thermal stability and maintained activities equal to or greater than 50% of its maximum activity in the 2.6–9.3 pH range. One polyphenoloxidase isoenzyme was detected in crude extracts of all ripening stages, showing an isoelectric point of 7.3. The specific activity of PPO decreased continuously through fruit ripening. Maximum specific activities were found at the ‘small green’ and ‘large green’ ripening stages. A total enzyme extract was partially purified by means of (NH4)2SO4 precipitation and cationic exchange chromatography in an FPLC system. The purification grade achieved was near 25. The partially purified enzyme showed an isoelectric point equal to 7.3 and a molecular mass of 135 ± 4 kDa for the native protein. © 2000 Society of Chemical Industry

Effects of Yeast Freezing in Frozen Dough

ABSTRACT The effects of freezing and frozen storage of bread dough and compressed yeast on bread quality were studied. Besides, the effects of compressed yeast freezing on cell viability, gas production and release of substances by the yeast cells were examined. Freezing and frozen storage of dough made with fresh yeast had more negative effects on baking quality than the addition of frozen yeast to dough. When the compressed yeast is frozen and stored at -18°C, the CO2 production decreased, while the amount of dead cells, the total protein, and the total reducing substances leached from the yeast increased as the length of yeast frozen storage increased. SDS-PAGE showed that the substances leached from frozen yeast caused an increase in the solubility of some gluten proteins. On the other hand, size-exclusion chromatography (SEC) pointed out that the relative amount of two protein fractions of low molecular weight leached from frozen yeast increased for longer yeast frozen storage periods. The yeast leac...

Effect of exogenous application of gibberellic acid on color change and phenylalanine ammonia-lyase, chlorophyllase, and peroxidase activities during ripening of strawberry fruit (Fragaria x ananassa Duch.)

The effect of exogenously applied gibberellic acid (GA3) on the postharvest color change of strawberry fruit was evaluated through their external color and surface color parameters. A significant delay on color evolution was observed in fruits treated with GA3. The evolution of activities of phenylalanine ammonia-lyase (PAL), chlorophyllase, and peroxidase was also analyzed. PAL activity increased during strawberry ripening, but in fruits treated with GA3 the increase in such activity was slower, and, probably as consequence, the development of red color was delayed. Moreover, the activity of chlorophyllase and peroxidase, enzymes possibly involved in chlorophyll metabolism, decreased during strawberry ripening. However, a delay was observed in the decrease of such activities in GA3-treated fruits.

Dynamic properties of soy globulin adsorbed films at the air-water interface

In this paper we present surface dilatational properties of soy globulins (beta-conglycinin, glycinin, and reduced glycinin with 10 mM of dithiothreitol (DTT)) adsorbed onto the air-water interface, as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (8.0), and ionic strength (0.05 M). The surface rheological parameters were measured as a function of protein concentration (ranging from 1 to 1x10(-3)% wt/wt). We found that the surface dilatational modulus, E, increases, and the phase angle, phi, decreases with time, theta, which may be associated with protein adsorption. These phenomena have been related to protein adsorption, unfolding, and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution. From a rheological point of view, the surface viscoelastic characteristics of soy globulin films adsorbed at the air-water interface are practically elastic. The main conclusion is that the dilatational properties of the adsorbed films depend on the molecular structure of the protein.

Optimization of a competitive ELISA with polyclonal antibodies for quantification of prolamins in foods

The optimization of a sequential competitive ELISA for the quantification of prolamins in foods is described in this article. The assay was developed using polyclonal antibodies obtained by the hyper‐immunization of rabbits with commercial gliadin. The ELISA developed in this way showed a very high degree of detectability (detection limit, 1 ng ml‐1), as well as the ability to discriminate between prolamins harmful to coeliac individuals from non‐toxic prolamins. The influence of the solvent used for extraction of the samples on the detection capability of the test was also studied. The assay proved to be useful for the evaluation of gliadins in processed foods including meat products. The assay was applied to many types of foods and was compared with a commercial kit approved by the Association of Official Analytical Chemists.

Trehalose, a cryoprotectant for Lactobacillus bulgaricus

Abstract The cryoprotective effect of trehalose in the freezing-thawing process was assayed in two strains of Lactobacillus bulgaricus. The viability and acidification properties before and after the process were compared. At a concentration of 0.3 M, trehalose was able to preserve the viability and the acidification power. The degree of protection is dependent on the strain and those compounds present in the medium. This effect is more noticeable in water an culture medium than in milk. However, the milk supplied with trehalose has the highest effectiveness.

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.

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.