Gonzalo D. García de Fernando

Proteolysis in dry fermented sausages: The effect of selected exogenous proteases

The effect of three commercial proteases (pronase E from Streptomyces griseus, aspartyl proteinase from Aspergillus oryzae and papain) on protein breakdown and the sensory characteristics of dry fermented sausages was investigated. Water soluble, non-protein, 5% phosphotungstic acid soluble, 5% sulphosalicylic acid soluble and total volatile basic nitrogen contents increased during fermentation, stabilizing later until the end of ripening (26th day). Nitrogen values were always greater in the aspartyl proteinase added batch in comparison with the other protease added batches. Total free amino acid changes showed a similar pattern to those observed for the 5% sulphosalicylic acid soluble nitrogen. The electrophoretic studies demonstrated that proteolysis of high molecular weight myofibrillar and sarcoplasmic proteins was more prominent in protease added batches. It was especially intensive in papain one. The dominant amino acids at the end of ripening were similar in all batches. Tyramine and histamine increased throughout ripening. No significant differences in sensory properties were found between control and pronase E and papain added batches, but they were significantly different (p < 0.01) from the sausages containing aspartyl proteinase, due to an excessive softening. The effect of exogenous enzyme addition on the flavour potentiation of dry fermented sausage is discussed.

Effect of Modified Atmosphere Composition on the Metabolism of Glucose by Brochothrix thermosphacta

ABSTRACT The influence of atmosphere composition on the metabolism of Brochothrix thermosphacta was studied by analyzing the consumption of glucose and the production of ethanol, acetic and lactic acids, acetaldehyde, and diacetyl-acetoin under atmospheres containing different combinations of carbon dioxide and oxygen. When glucose was metabolized under oxygen-free atmospheres, lactic acid was one of the main end products, while under atmospheres rich in oxygen mainly acetoin-diacetyl was produced. The proportions of the total consumed glucose used for the production of acetoin (aerobic metabolism) and lactic acid (anaerobic metabolism) were used to decide whether aerobic or anaerobic metabolism predominated at a given atmosphere composition. The boundary conditions between dominantly anaerobic and aerobic metabolisms were determined by logistic regression. The metabolism of glucose by B. thermosphacta was influenced not only by the oxygen content of the atmosphere but also by the carbon dioxide content. At high CO2 percentages, glucose metabolism remained anaerobic under greater oxygen contents.

Effect of the addition of pronase E on the proteolysis in dry fermented sausages

The effect of the addition of pronase E at two different concentrations on protein breakdown during the ripening of dry fermented sausage was studied. In all batches, water-soluble, non-protein and 5% phosphotungstic acid soluble nitrogens increased sharply during the first days of ripening, then became stabilized until the end of the process (26th day), and the total volatile nitrogen consistently increased during ripening. The greater the pronase E added the higher were the values reached for all these fractions. The changes in total free amino acids showed a similar pattern to that observed for the phosphotungstic acid soluble nitrogen. Histamine and tyramine progressively increased throughout the ripening. By sensory evaluation, no significant differences between the control batch and the batch with the lowest amount of added pronase E were found, but both batches were significantly different (P < 0·1) from the batch manufactured with the highest concentration of pronase E, which was classed as objectionable by the panellists because of its excessive softness.

Effect of the Addition of Papain on the Dry Fermented Sausage Proteolysis

The effects of the addition of two different concentrations of papain on the proteolysis development and the sensory characteristics of dry fermented sausage were studied. In all batches, water soluble, non-protein, 50 g litre -1 phosphotungstic acid soluble, 50 g litre -1 sulphosalicylic acid soluble and total volatile basic nitrogens increased during fermentation (first 2 days). The changes were more pronounced and the values greater when the highest level of papain was added. After fermentation, nitrogen levels became stabilised until the end of ripening (26 days). The electrophoretic studies showed that the proteolysis of high molecular weight myofibrillar and sarcoplasmic proteins was more prominent in protease-added batches. A similar pattern was observed for free amino acids compared with that found in 50 g litre -1 sulphosalicylic acid nitrogen. Histamine and tyramine increased through ripening. Although the addition of papain increased the proteolysis phenomena, no improvement of the sausage flavour was observed in the sensory analysis.

Effects of electron beam irradiation on the variability in survivor number and duration of lag phase of four food-borne organisms.

The effect of electron beam irradiation on microbial inactivation and duration of lag time of individual surviving cells of Listeria innocua, Enterococcus faecalis, Pseudomonas fluorescens and Salmonella Enteritidis has been studied. In addition, the data on variability in microbial inactivation and duration of lag phase for surviving microbes have been fitted by normal and gamma distributions, respectively. The standard deviations of survivor number and lag phase duration of individual cells were higher in irradiated batches than in non-irradiated ones. Furthermore, the more intense the irradiation treatment was, the higher the variability in both survivor number and duration of lag phase of survivors. These findings should be considered in predictive models of microbial inactivation, in risk assessment, and in adjusting preserving and/or storage conditions in the food industry.

Aumento da vida útil e microbiologia da carne suína embalada em atmosfera modificada

The objective of the present study was to evaluate the effect of modified atmospheres on refrigerated pork meat (Longissimus dorsi). Pork meat was cut into ca. 1cm thick slices of 9cm2, introduced in Cryovac type BB4L bags, characterized by its low gas permeability, and divided into four batches. The bags of each batch were filled with either 1.0 L of air (100%), nitrogen (100%), 20/80 or 40/60 CO2/O2 and finally sealed. Samples were subdivided into two batches and stored in walk-in cold rooms at 1 and 7oC. Samples were taken at different days of storage and pH and gas concentration (CO2/O2/N2) were determined. Likewise, total viable, lactic acid bacteria, Enterobacteriaceae, Brochothrix thermosphacta and Pseudomonas were counted. Bacterial growth parameters were assessed using Gompertz equations. As expected, modified atmosphere packaging extended the pork meat shelf life. However, modified atmospheres enriched with CO2 and at 1oC showed a greater effectiveness. The samples conserved in MAP enriched in CO2, as much to 7 as to 1oC, maintained the constant pH during the period of storage. At 1 and 7oC the lag phases and the duplication times of the total microbiota were progressively larger in the following order: air (100%), N2 (100%), 20/80 and 40/60 CO2/O2. In accordance with the results, it can be concluded that, by as much to 1 as to 7oC, the use of the modified atmospheres slowed the growth of the spoilage bacteria of pork meat, favoring the extension of the useful life, mainly in the MAP enriched with CO2.

Influence of heat treatment on carnosine, anserine and free amino acid composition of beef broth and its role in flavour development

Abstract In an attempt to determine the most important free amino acids (FAAs) in the development of the flavour of beef broths, the amino acid compositions of beef broths prepared at different temperatures and cooking times, with flavours of different intensities, were studied. From our data, broths obtained at temperatures above 75  °C and cooking times longer than 120 min had significantly lower levels of most of the FAAs studied (P<0.05). Statistical analysis of the sensorial and analytical data (principal component analysis, chi-square analysis) permitted the different FAAs to be grouped in relation to the flavour. There was a significant association between elevated levels of glutamic acid, asparagine (P<0.01), lysine and methionine (P<0.05) and the development of beef broth flavour. However, this was inversely related to levels of cysteine, proline, serine, M-histadine, tyrosine, valine, arginine and aspartic acid whereas reduced levels of β-alanine, asparagine, tyrosine, threonine, methionine, cysteine, leucine, isoleucine, tryptophan, glutamic acid, histidine, lysine and phenylalanine were associated with sapid properties not characteristic of beef broths (astringent, warmed-over flavours). A significant correlation (P<0.01) between sensory evaluation and carnosine and anserine levels was also observed.

A comparison of the effects of E-beam irradiation and heat treatment on the variability of Bacillus cereus inactivation and lag phase duration of surviving cells.

The effects of electron beam irradiation and heat treatments on the variability of inactivation of Bacillus cereus spores (CECT 131/ATCC 10876) and of the lag phase of single surviving cells have been studied. In general, dispersion in the number of survivors increased as the stress became more intense. A polynomial relationship was derived between the coefficient of variation of the survivor number and the inactivation achieved. Heat treatments caused wider distributions than irradiation for the same substrate and for a similar degree of microbial inactivation. Increasing the intensity of the inactivation treatment lengthened the lag phase of survivors and increased its variability. Comparison of lag phases of heated and irradiated spores did not show any clear relationship. Heating did not affect the specific growth rate of surviving cells, whereas irradiation lowered the maximum specific growth rate in proportion to the dose applied. These results suggest that the shelf life of irradiated foods is longer than that of heated foods.

Modeling the Listeria innocua micropopulation lag phase and its variability

Listeria innocua micropopulation lag phase and its variability have been modeled as a function of growth temperature, intensity of heat stress, and the number of surviving cells initiating growth. Micropopulation lag phases were found to correlate negatively with inoculum size and growth temperature and positively with heat shock intensity. Validation of the models using experimental milk samples indicated that the average lag phase duration predicted is shorter and more variable than the observed, meaning that they should be considered safe for risk assessment. Our results suggest that the effect of inoculum size on the population lag phase has both stochastic and physiological components.

Analysis and validation of a predictive model for growth and death of Aeromonas hydrophila under modified atmospheres at refrigeration temperatures.

ABSTRACT Specific growth and death rates of Aeromonas hydrophila were measured in laboratory media under various combinations of temperature, pH, and percent CO2 and O2 in the atmosphere. Predictive models were developed from the data and validated by means of observations obtained from (i) seafood experiments set up for this purpose and (ii) the ComBase database (http://www.combase.cc ; http://wyndmoor.arserrc.gov/combase/ ).Two main reasons were identified for the differences between the predicted and observed growth in food: they were the variability of the growth rates in food and the bias of the model predictions when applied to food environments. A statistical method is presented to quantitatively analyze these differences. The method was also used to extend the interpolation region of the model. In this extension, the concept of generalized Z values (C. Pin, G. García de Fernando, J. A. Ordóñez, and J. Baranyi, Food Microbiol. 18:539-545, 2001) played an important role. The extension depended partly on the density of the model-generating observations and partly on the accuracy of extrapolated predictions close to the boundary of the interpolation region. The boundary of the growth region of the organism was also estimated by means of experimental results for growth and death rates.