M. Pérez-Mateos

Oyster Preservation by High-Pressure Treatment

The purpose of this study was to analyze the effect of 10-min continuous pressure and pulsed pressure in two 5-min steps (400 MPa at 7 degrees C) on the microbial flora, total volatile bases, pH, and texture of purified and unpurified oysters. High-pressure treatment reduced the number of all the target microorganisms (total viable count, H2S-producing microorganisms, lactic acid bacteria, Brochothrix thermosphacta, and coliforms), in some cases by around 5-log units. The difference between the counts in the control and the pressurized oysters remained stable throughout 41 days of storage at 2 degrees C. No Salmonella spp. were detected in either the control batch or the pressurized batches during this storage period. Deterioration of the oyster was accompanied by increased total volatile bases, mainly in the nonpressurized samples. The pH was practically constant in the pressurized oysters and fell slightly in unpressurized samples. As for mechanical properties, shear strength values were higher in pressurized than in unpressurized oysters. Step-pulse pressurizing (400 MPa at 7 degrees C in two 5-min pulses) produced no apparent advantages over continuous pressurizing based on any of the indices used.

Characterization of polyphenoloxidase of prawns (Penaeus japonicus). Alternatives to inhibition: additives and high-pressure treatment

Polyphenoloxidase (PPO) presented different specific activities at different locations in the imperial tiger prawn (Penaeus japonicus), with the highest values in the carapace. The procedure achieved a degree of purification, close to 70 times, increasing relative activity by means of ammonium sulphate (0–40%) saturation. Isoelectric focusing showed two bands around pI 5.0. The optimum temperature for PPO reaction with DOPA was between 40 and 60°C, however thermal stability was greatest at temperatures below 35°C. The enzyme was most active at pH 5 and 8, but most stable at basic pH. Pressurization of the enzymatic extract was assayed within a range of 0.1–400 MPa, for 10 min at <10°C. Pressure-induced inactivation was evident, particularly at 300–400 MPa. Total inhibition of the extract was achieved only with ascorbic acid and citric acid at pH 3.0. 80 μg/ml sulphite, 150 μg/ml of kojic acid, 1 g/l of 4-hexylresorcinol or 0.1 g/l of sodium benzoate was required for 80% inhibition.

Microstructural behaviour and gelling characteristics of myosystem protein gels interacting with hydrocolloids

Hydrocolloids were added to blue whiting mince in order to study their distribution in the gel and obtain more information about how these additives act on gel characteristics. The addition of hydrocolloid in powder significantly reduced puncture test properties with respect to the hydrocolloid-free gels, except in the case of locust bean gum. On the other hand, compression properties were altered to a greater or lesser extent in gels containing anionic hydrocolloids. Light microscopy revealed that the hydrocolloids expanded as inclusions, forming cavities of varying morphology and size. The anionic hydrocolloids were mixed throughout the protein matrix, probably through interaction with the myofibrillar protein. The non-ionic hydrocolloids were dispersed throughout the matrix but did not interact with it and were located simply by inclusion. The thickening hydrocolloids (locust bean gum, guar gum, xanthan gum, carboxymethylcellulose and alginate) formed a mesh of filaments inside the cavities; while the gelling hydrocolloids (carrageenans) that were mainly inside the cavity interiors formed a continuous structure.

Extension of the Shelf Life of Prawns (Penaeus japonicus) by Vacuum Packaging and High-Pressure Treatment

The present study has investigated the application of high pressures (200 and 400 MPa) in chilled prawn tails, both conventionally stored (air) and vacuum packaged. Vacuum packaging and high-pressure treatment did extend the shelf life of the prawn samples, although it did affect muscle color very slightly, giving it a whiter appearance. The viable shelf life of 1 week for the air-stored samples was extended to 21 days in the vacuum-packed samples, 28 days in the samples treated at 200 MPa, and 35 days in the samples pressurized at 400 MPa. Vacuum packaging checked the onset of blackening, whereas high-pressure treatment aggravated the problem. From a microbiological point of view, batches conventionally stored reached about 6 log CFU/g or even higher at 14 days. Similar figures were reached in total number of bacteria in vacuum-packed samples and in pressurized at 200-MPa samples at 21 days. When samples were pressurized at 400 MPa, total numbers of bacteria were below 5.5 log CFU/g at 35 days of storage. Consequently, a combination of vacuum packaging and high-pressure treatment would appear to be beneficial in prolonging freshness and preventing spotting.

Effects of Na+, K+ and Ca2+ on gels formed from fish mince containing a carrageenan or alginate

Abstract The effects of mixtures of added chloride salts (0–1% NaCl plus 0–1% KCl plus 0–1% CaCl 2 ) on the characteristics of blue whiting muscle gel containing different added gelation agent (iota-carrageenan, kappa-carrageenan, or sodium alginate) were studied by response surface methodology (RSM) and factor analysis (principal component analysis). The salts exhibited independent effects on gel properties. NaCl mainly altered breaking strength in the gels made with iota-carrageenan, the yellowness ( b ∗ ) value in the gels made with kappa-carrageenan, and adhesiveness in the gels made with sodium alginate. KCl mainly affected adhesiveness in the gels made with one of the carrageenans, especially iota-carrageenan; it had no apparent effect on the gels made with sodium alginate. The effect of CaCl 2 in all the formulations was mainly to increase elasticity and lightness and decrease the rest of the properties considered. Combined action of the salts did reveal certain significant interactions, such as the interaction between sodium and calcium which affected the folding test value in the gels made with alginate and breaking strength in the gels made with iota-carrageenan, or the interaction between potassium and sodium which affected the redness ( a ∗ ) value in the gels made with iota-carrageenan. Factor analysis showed the main trends in the variables tested, calcium being the salt that exerted the primary influence and contributed to the first two factors in each of the factor analyses. Each of the salts contributed to a separate factor, the only exception being the mixture of CaCl 2 and KCl in the formulations that contained iota-carrageenan, in which both salts contributed to factor 1.

Vitamin C content and sensorial properties of dehydrated carrots blanched conventionally or by ultrasound

Vitamin C content and sensorial properties have been evaluated in air-dried carrots previously subjected to different ultrasound (US) or conventional blanching pretreatments. In addition, mass spectral fingerprints obtained by the Headspace ChemSensor System have been evaluated for the first time for classification of carrots according to their processing. Conventional blanching treatments at high temperature gave rise to carrots with retention of vitamin C in the range 37.5-85%, whereas carrots blanched conventionally at 60°C and by US-probe at temperatures up to 60 and 70°C showed vitamin C retention values lower than 4%. Regarding sensorial analysis of rehydrated carrots, US-pretreated samples presented acceptable quality, and no statistically significant differences with respect to conventionally blanched carrots, were detected. In spite of this, differentiation of samples processed under comparable intensity conditions and/or with similar composition was possible from their mass spectral fingerprints after chemometric data analysis.

Effects of Magnetic Fields on Freezing: Application to Biological Products

Magnetic freezing is nowadays established as a commercial reality mainly oriented towards the food market. According to advertisements, magnetic freezing is able to generate tiny ice crystals throughout the frozen product, prevent cell destruction, and preserve the quality of fresh food intact after thawing. If all these advantages were true, magnetic freezing would represent a significant advance in freezing technology, not only for food preservation, but also for cryopreservation of biological specimens such as cells, tissues, and organs. Magnetic fields (MFs) are supposed to act directly on water by orientating, vibrating, and/or spinning molecules to prevent them from clustering and, thus, to promote supercooling. However, many doubts exist about the real effects of MFs on freezing and the science behind the potential mechanisms involved. To provide a basis for extending the understanding of magnetic freezing, this paper presents a critical review of the materials published in the literature up to now, including both patents and experimental results. After examining the information available, it was not possible to discern whether MFs have an appreciable effect on supercooling, freezing kinetics, ice crystals, quality, and/or viability of the frozen products. Experiments described in the literature frequently fail to identify and/or control all the factors that can play a role in magnetic freezing. Moreover, many of the comparisons between magnetic and conventional freezing are not correctly designed to draw valid conclusions, and wide ranges of MF intensities and frequencies are unexplored. Therefore, more rigorous experimentation and further evidence are needed to confirm or reject the efficacy of MFs in improving the quality of frozen products.

Pressure-induced gel properties of fish mince with ionic and non-ionic gums added

Abstract Various non-ionic gums (locust bean and guar) and anionic gums (xanthan and carboxymethylcellulose) were added to blue whiting mince and subjected to gelling treatments in different combinations of pressure–time–temperature in order to determine their behaviour in mince gel. The treatment of gelation induced more drastic effects that the kind of gums added in the fish mince. Heat treatment at atmospheric pressure generally originated higher adhesiveness and yellowness ( b *). High pressure at cold temperatures induced the highest cohesiveness and breaking deformation (except with xanthan) and the lowest elasticity, and high pressure at moderate heating generally produced the lowest hardness. The organization of the gum generally differed according to the treatment: filamentous structures forming under pressure and aggregates forming with heat (except xanthan). Water holding capacity increased under pressure in gels containing ionic gums. Overall, the combination of hydrocolloid and gelling treatment appeared to offer increased technological possibilities in that it produced a wider range of rheological characteristics, water holding capacity and colour in the gelled product.

Effects of cations on the gelling characteristics of fish mince with added nonionic and ionic gums

Abstract The effects of a mixture of added chloride salts (0–1% NaCl plus 0–1% KCl plus 0–1% CaCl 2 ) on the gelling characteristics of blue whiting muscle containing nonionic (locust bean gum, guar gum) or ionic (xanthan gum, carboxymethylcellulose) gums were studied by response surface methodology and factor analysis (principal component analysis). The salts employed did not display any interaction effects altering the gelling properties of the different formulations; only sodium and calcium sometimes exhibited such effects, depending on the hydrocolloid used. The main trends in the variables tested revealed by principal component analysis showed that calcium yielded elastic gels with lower cohesiveness and higher lightness and that this same salt contributed to the factor(s) that explained the largest proportion of the variance. In contrast, addition of the monovalent salts had a lesser effect on the gelling properties, with intermediate concentrations resulting in the largest increases in the properties. No similar trends were observed with addition of the monovalent cation or the divalent cation or the hydrocolloid charge (nonionic or ionic gums).

A comparative study of the effects of high pressure on proteolytic degradation of sardine and blue whiting muscle

High-pressure technology is used as an alternative to heat processing because of its inactivating effect on microorganisms and enzymes. However, it can also alter the structure of other muscle proteins. The present study compares the effects of high pressure (300 MPa, 7°C, 20 min) on the proteolytic degradation and alterations in the myofibrillar proteins of sardine and blue whiting muscle. Also, muscle homogenates and enzyme extracts were pressurized in order to evaluate the high-pressure effects on unprotected proteolytic enzymes outside the whole muscle structure. Peak proteolytic activity was found to occur at 55°C in both species. The peak activity pH was pH 3 for the sardine and pH 8 for the blue whiting; the main enzyme families being aspartic proteases in the former and alkaline serine proteases in the latter. Pressurization lowered activity levels at the peak activity pH and temperature in the fish muscle (by 30.8% in the sardine and by 9.5% in the blue whiting) and also slightly in the enzyme extracts (by 16.8% in the sardine and by 19.4% in the blue whiting). The electrophoretic profiles disclosed higher protein degradation in the pressurized muscle. Overall, the observed changes in proteolytic activity can be attributed not only to the effect of high pressure on the enzymes, but also and mainly, to the effect on other muscle proteins.