Paloma Fernández

Application of a frequency distribution model to describe the thermal inactivation of two strains of Bacillus cereus

Abstract Isothermal heat-resistance studies were carried out on two toxin-producing Bacillus cereus strains (AVZ421 and AVTZ415) isolated from foods. Experimental data were analysed using the traditional Bigelow first-order kinetic model and the Weibull distribution model. Semilogarithmic survival curves showed an initial curvature that was more pronounced in the case of the psychrotrophic strain AVTZ415. Regression curves were obtained by means of the traditional Bigelow first-order model and the D values were calculated. Correlation coefficients ranged from 0.983 to 0.989 for the AVZ421 strain and from 0.953 to 0.980 for the AVTZ415 strain. When the Weibull function was applied to experimental data, a good description of the survivor microorganisms was obtained for the two strains considered. Using coefficients describing the survival function, an average of the organisms heat resistance or sensitivity, ‘tc’, at each temperature was estimated. Accuracy factors were obtained for experimental and calculated survivors as predicted by means of the Weibull or the Bigelow model. Results indicated that the accuracy factor was lower when the Weibull model was used (1.10 and 1.10) than when using the Bigelow model (1.20 and 1.30) at 95 and 85°C, respectively.

Characteristics of low- and high-fat beef patties: Effect of high hydrostatic pressure

The purpose of this study was to analyze the consequences of applying high pressures (100 and 300 MPa for 5 or 20 min) on characteristics such as water- and fat-binding properties, texture, color, microstructure, and microbiology of low-fat (9.2%) and high-fat (20.3%) beef patties. In nonpressurized patties, the low-fat product exhibited significantly poorer (P < 0.05) binding properties and higher (P < 0.05) Kramer shear force and Kramer energy than did high-fat patties. Although high pressure did not clearly influence the binding properties of low- and high-fat beef patties, it did produce a rise in the Kramer shear force and energy which were more pronounced at 300 MPa. High pressures altered patty color, the extent of alteration depending on fat content, pressure, and pressurizing time. Pressurizing high- and low-fat beef patties at 300 MPa not only produced a lethal effect (P < 0.05) on microorganisms, but caused sublethal damage as well.

Frozen storage of Bologna sausages as a function of fat content and of levels of added starch and egg white

The effect of freezing and frozen storage on the water holding capacity (WHC) and texture of Bologna sausages formulated with varying fat levels (7.2, 12.8 and 20.1%) and with different proportions of added starch (0, 5 and 10%) and egg white (EW) (0, 1.5 and 3%) was studied. High-fat sausages exhibited better binding properties than low-fat sausages. Freezing and frozen storage caused binding properties to deteriorate, the more so the lower the fat content. In general, addition of starch caused an increase in penetration force and a decrease in elasticity of sausages, and also favoured freeze-thaw stability. Addition of egg white had no influence (p > 0.05) on the WHC of Bologna sausages but did influence texture.

High-pressure-induced changes in the characteristics of low-fat and high-fat sausages

The purpose of this study was to analyse the consequences of applying high pressures (100 and 300 MPa for 5 and 20 min) on characteristics such as water and fat binding properties, texture, colour, microstructure and microbiology of low-fat (90 g kg -1 , LF) and high-fat (247 g kg -1 , HF) meat emulsions. Pressurising of LF and HF samples at 300 MPa caused a decline (P < 0-05) in emulsion stability, which was more pronounced at the higher pressure. The influence of high pressures on emulsion texture varies according to fat content. In HF samples, high pressure caused a decrease (P < 0.05) in Kramer shear force and Kramer energy, regardless of pressure intensity or time. Pressurisation generally caused increase (P < 0.05) in the colour lightness parameter in sausages; the effect on redness and yellowness, however, was dependent on fat content, pressure intensity and pressure time.

Characteristics of High- and Low-Fat Bologna Sausages as Affected by Final Internal Cooking Temperature and Chilling Storage

A study was made of the effect that final internal processing temperature (63, 70 and 78°C) and chilling storage (2°C) exerted on the characteristics (cooking loss, purge loss, colour, Instron texture profile analysis) of high-fat (242 g kg -1 ) and low-fat (100 g kg -1 ) bologna sausage. High-fat sausages were harder and chewier than low-fat sausages. Lower fat contents were accompanied by a significant reduction in the cooking loss and purge loss. Binding properties were not affected (P > 0.05) by final internal cooking temperature. In general, Hunter colour parameter a values were higher in low-fat samples subjected to a high final internal cooking temperature than in those cooked up to only 63°C. High internal temperatures produced harder meat emulsions, an effect which was more pronounced in high-fat than in low-fat sausages. Cohesiveness and springiness of sausages was not affected (P > 0.05) by heat treatment. There were no major variations in textural parameters as a result of chilled storage.

Chopping temperature effects on the characteristics and chilled storage of low- and high-fat pork Bologna sausages

The object of this study was to investigate the influence of chilled storage (2 °C) and final chopping temperatures (8, 15 and 22 °C) on the characteristics and stability of Bologna sausage containing two levels of fat (8.5 and 23%). When the fat level was reduced there was a significant decrease in penetration force and an increase in both cooking and purge loss. A lower chopping temperature reduced purge loss during chilled storage. In general, an inverse relationship was found between chopping temperature and penetration force. Chopping temperature did not influence total aerobic count, but during chilled storage counts were significantly higher in the low fat sausages.

Rheological changes during thermal processing of low-fat meat emulsions formulated with different texture-modifying ingredients

The rheological behaviour of high-fat (22%) and low-fat (8%) meat emulsions during thermal processing in the presence (3%) of various texture-modifying non-meat ingredients, namely maltodextrin, starch, wheat flour, egg white and apple fibre, was analysed. Rheological properties of emulsions were assessed using non-destructive measurements (thermal scanning rigidity monitor, TSRM). The lower the fat content, the lower were the rigidity values of meat emulsions throughout the temperature range studied. Emulsions made with maltodextrin proved less rigid. Addition of starch and egg white favoured the formation of more rigid structures in low-fat meat emulsions at temperatures over 55 °C. Low-fat meat batters containing wheat flour and apple fibre exhibited the highest rigidity values over the given temperature range. The presence of wheat flour caused variations in the modulus of rigidity at all stages of the thermal gelation process, very similar to those observed in high-fat emulsions.

Involvement of the glucose moiety in the molecular recognition of methyl β-lactoside by ricin: synthesis, conformational analysis, and binding studies of different derivatives at the C-3 region.

Syntheses of the 3-aminodeoxy (4), 3-deoxy-3-methyl (5), and 3-epi (6) derivatives of methyl beta-lactoside (1) have been achieved from 1 in a straightforward way, and their solution conformations in water and dimethyl sulfoxide analysed through molecular mechanics and dynamics calculations and nuclear magnetic resonance data. The overall shape of all the compounds studied is fairly similar and may be described by conformers included in a low energy region with phi = 15 +/- 45 degrees and psi = -25 +/- 30 degrees, that is ca. 5% of the total potential energy surface for the glycosidic linkages of the disaccharides. The binding of the different compounds to ricin, the galactose-specific toxin from Ricinus communis, has been investigated. The results confirm the involvement of the C-3 region in a nonpolar interaction with the protein at the periphery of the combining site.

The conformation of the monomethyl ethers of methyl β-lactoside in D2O and Me2SO-d6 solutions

The solution conformations of all the possible monomethyl ethers of methyl beta-lactoside have been analysed using molecular mechanics and dynamics calculations and nuclear magnetic resonance data (variable temperature and NOE experiments). The overall shape of all the compounds studied is fairly similar and may be described by conformers included in a low-energy region with phi = -100 +/- 40 degrees and psi = -135 +/- 35 degrees, which is ca. 5% of the total potential energy surface for the glycosidic linkages of the disaccharides.

Retail Chilled Display Storage of High- and Reduced-Fat Sliced Bologna

This study examined the influence of light (1,900 lux) and dark display conditions on purge loss, color, residual nitrite, rancidity, texture, and microbiological changes of sliced vacuum packaged high-fat (24.7%) and reduced-fat (9.4%) bologna during chilled storage at 2 and 7°C. Color stability was more dependent upon photochemical action than upon temperature. The rate of color fading was greater at a lower fat content. Residual nitrite depletion varied according to fat content, chill temperature, and display conditions. High-fat sausages were harder and chewier (P < 0.05) than reduced-fat sausages. Texture parameters were not appreciably influenced by storage temperature or exposure to light. Microbiological counts were higher in reduced-fat samples than in high-fat samples. Temperature influenced the growth of microflora in sliced bologna sausage, but light had no important effect.