Eva Hierro

Changes in the Components of Dry-Fermented Sausages during Ripening

Several chemical changes occur during the ripening of dry-fermented sausages that determine the flavor and odor of the end product. The phenomena that take place during fermentation, that is, both acidification of the sugars by lactic acid bacteria and reduction of nitrates and nitrites to nitric oxide by micrococci have been known for several years. However, the chemical changes involved in this process, and, particularly, the agents responsible have not yet been established, although they have been attributed to changes in the majority components (proteins and lipids) and to the ingredients added (spices and condiments) in the preparation of the original mixture. The typical flavor and odor of dry-fermented sausages cannot be attributed to volatile substances alone, but to a large number of volatile and nonvolatile compounds present in the product in suitable proportions. Microbial growth in the sausage together with activity of the meat endogenous enzymes are undoubtedly partially responsible for the development of a number of aromatic and sapid compounds. However, lipid autooxidation reactions are also an important source of these substances, and it is not yet known which of these processes is more important in sausage ripening. Much research has focused on the break up of triglycerides into free fatty acids, diglycerides, and monoglycerides during ripening and the progressive increase in the amounts of different carbonyl oxidation products. Carbonyl compounds probably play a significant role in determining the flavor because, in general, these have very low perception thresholds, in the ppm and ppb range. Similarly, the protein breakdown to yield peptides and amino acids has been studied extensively, the latter being substrates of several microbial and chemical reactions that generate many flavor compounds.

Microbial and physicochemical modifications of hake (Merluccius merluccius) steaks stored under carbon dioxide enriched atmospheres

Microbial counts (total viable, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae), biochemical parameters [pH, total volatile nitrogen, nucleotide breakdown products, non-volatile amines, D(−) and L(+) lactic acid and short-chain fatty acids] and sensory attributes (colour and odour) of refrigerated (2 °C) hake (Merluccius merluccius) steaks under carbon dioxide enriched air (CO2 /air, 20/80 v/v and CO2 /air, 40/60 v/v) and air atmospheres were determined. When compared with air, sensory results showed shelf-life extension of 4 and 11 days for 20% and 40% CO2-enriched atmospheres, respectively. Microbial and biochemical results also revealed that the 40% CO2-enriched atmosphere was the most effective packaging type for refrigerated hake. © 2000 Society of Chemical Industry

Inactivation of Salmonella enterica serovar Enteritidis on shell eggs by pulsed light technology

This is a study on the efficacy of pulsed light (PL) technology for the inactivation of Salmonella enterica serovar Enteritidis on shell eggs. In preliminary studies on noble agar, a PL treatment of 0.7 J/cm(2) gave an inactivation of 6.7 log CFU/cm(2). Photoreactivation of Salmonella (0.5-0.7 log CFU/cm(2)) was observed. Different results were obtained in eggs according to the state of the cuticle. When unwashed eggs were pulsed, 24 to 80% of the samples showed the maximum decontamination (3.6 log CFU/egg), depending on the fluence applied. This maximum was not obtained on washed eggs, in which the highest reduction was 1.8 log CFU/egg with a fluence of 12 J/cm(2). PL can be a useful method for egg processing since the integrity of the cuticle is preserved, and requires that the treatment should be applied as soon as possible after laying and on unwashed eggs. As Salmonella has shown the capability of photoreactivation, it is advisable to keep eggs protected from light once they have been pulsed.

Use of carbon dioxide enriched atmospheres in the refrigerated storage [2°C] of salmon (Salmo salar) steaks

Abstract Selected microbial counts (total viable microbiota, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae), biochemical parameters [pH, total volatile nitrogen, nucleotide breakdown products, non-volatile amines, d(–) and l(+)-lactic acids and short-chain fatty acids] and sensory attributes (colour and odour) of refrigerated (2  °C) salmon (Salmo salar) steaks stored under CO2-enriched [CO2/air (20/80, v/v), CO2/air (40/60, v/v)] and air atmospheres were determined. When compared with air, sensory results showed shelf-life extension of 6 days and 15 days for 20% and 40% CO2-enriched atmospheres, respectively. Microbial and biochemical results also revealed that the 40% CO2-enriched atmosphere was the most effective packaging type for refrigerated salmon.

Impact of feeding and rearing systems of Iberian pigs on volatile profile and sensory characteristics of dry-cured loin

The effect of growing pigs on free-range (FR) or in confinement with three different diets [acorn (A), acorn and grass (A-G) and formulated diet (FD)] on composition, volatile profile and sensory characteristics of dry-cured loin was studied. The FR, A and A-G diets, in comparison with FD, induce a higher α- and γ-tocopherol concentration, which limits the TBARs values at 24h of air exposure. Sixty volatile compounds were identified in the headspace, including 14 aldehydes, 10 hydrocarbons, eight alcohols, five ketones, four furans, four pyrazines, four sulphur compounds, three acids, three esters, three phenols, one pyridine and one pyrrole. Volatiles from amino acid catabolism stressed the difference among batches FR being the batch with the highest level of these compounds. Products from FD showed the lowest fat content and L(∗) value. FR loins obtained the highest scores for appearance, odour and flavour in the rank order test sensory analysis.

Pulsed light treatment for the inactivation of selected pathogens and the shelf-life extension of beef and tuna carpaccio

The efficacy of pulsed light to improve the safety of carpaccio has been investigated. Beef and tuna slices were superficially inoculated with approximately 3 log cfu/cm2 of Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium and Vibrio parahaemolyticus. Fluences of 0.7, 2.1, 4.2, 8.4 and 11.9 J/cm2 were assayed. Colour, sensory and shelf-life studies were carried out. Treatments at 8.4 and 11.9 J/cm2 inactivated the selected pathogens approximately by 1 log cfu/cm2, although they modified the colour parameters and had a negative effect on the sensory quality of the product. The raw attributes were not affected by fluences of 2.1 and 4.2J/cm2 immediately after the treatment, although changes were observed during storage. The inactivation obtained with these fluences was lower than 1 log cfu/cm2, which may not be negligible in case of cross-contamination at a food plant or at a food service facility. Pulsed light showed a greater impact on the sensory quality of tuna carpaccio compared to beef. None of the fluences assayed extended the shelf-life of either product.

Survival of Listeria innocua in dry fermented sausages and changes in the typical microbiota and volatile profile as affected by the concentration of nitrate and nitrite

The involvement of nitrate and nitrite in the formation of N-nitrosamines in foods is a matter of great concern. This situation has led to revise the real amount of nitrate and nitrite needed in meat products to exert proper technological and safety activities, and also to extensive research to find alternatives to their use. The present study addresses the possibility of reducing the ingoing amounts of these additives below the legal limits established by the current European regulations. Different concentrations of nitrate and nitrite were tested on Spanish salchichón-type dry fermented sausages concerning their role in the microbiota and volatile profile. Sausages were manufactured with the maximum ingoing amounts established by the EU regulations (150 ppm NaNO(3) and 150 ppm NaNO(2)), a 25% reduction and a 50% reduction; control sausages with no nitrate/nitrite addition were also prepared. The mixtures were inoculated with 5 log cfu/g of Listeria innocua as a surrogate for Listeria monocytogenes. L. innocua numbers in the final product were approximately 1.5 log cfu/g lower in the batch with the maximum nitrate/nitrite concentration when compared to 25 and 50% reduced batches, and about 2 log cfu/g in comparison to the control sausages. The final numbers of catalase-positive cocci were 1 log cfu/g higher in the 50% nitrate/nitrite reduced batch and 2 log cfu/g higher in the control sausages, compared to products manufactured with the maximum nitrate/nitrite concentration. This increase was related to a higher amount of volatile compounds derived from carbohydrate fermentation and amino acid degradation. Sausages with no addition of nitrate/nitrite showed higher amount of volatiles from lipid oxidation. Enterobacteriaceae counts reached detectable values (1-2 log cfu/g) in both nitrate/nitrite reduced sausages and in the control batch, while these organisms were not detected in the batch with the maximum ingoing amount. Nitrate and nitrite exerted a significant effect on the typical microbiota of dry fermented sausages and effectively contributed to control Listeria. These considerations should be taken into account in view of a future restriction in the use of these curing additives.

Pulsed Light Inactivation of Listeria monocytogenes Through Different Plastic Films

The efficacy of decontamination by pulsed light technology through different plastic films has been assayed using Listeria monocytogenes Scott A as target microorganism. A 12-mum polyethylene film, a 48-mum polyamide/polyethylene/vinyl acetate-based copolymer, and a 60-mum polyamide/polyethylene copolymer were tested. Noble agar plates were surface inoculated and wrapped with different films. Unwrapped plates were also analyzed as control. Fluences of 0.175 and 0.35 J/cm(2) were applied. Pulsed light treatment achieved the same degree of inactivation (5-5.5 log cfu/cm(2)) in either wrapped or unwrapped samples. All the polymers showed the same behavior. These results indicate that pulsed light technology could be suitable for decontamination of packaged foods.

Use of Lactococcus lactis subsp. cremoris NCDO 763 and α-ketoglutarate to improve the sensory quality of dry fermented sausages.

The aim of the present work was to enhance the degradation of free amino acids in dry fermented sausages as precursors of volatile compounds responsible for the ripened flavour. For this purpose, Lactococcus lactis subsp. cremoris NCDO 763, its intracellular cell free extract (ICFE) and α-ketoglutarate were added to sausages. Papain was also used to increase the amount of free amino acids. When L. lactis was inoculated in sausages, an increase in the proteolytic phenomena was observed. The addition of α-ketoglutarate increased transamination phenomena in batches where it was added. The enhancement of these phenomena determined a noticeable rise in the content of glutamic acid (the main final product in transamination reactions) and a decrease, among other amino acids, of valine and leucine, with the formation of high amounts of their derivatives 2-methylpropanal and 3-methylbutanal. These aldehydes are responsible for the ripened flavour of dry fermented sausages. Sensory analysis showed an improvement of odour and flavour when L. lactis and α-ketoglutarate were combined. On the other hand, the intracellular cell free extract of L. lactis did not show any important activity in relation to amino acid breakdown even when used together with α-ketoglutarate and/or papain.

A study on the toxigenesis by Clostridium botulinum in nitrate and nitrite-reduced dry fermented sausages.

Nitrite has been traditionally used to control Clostridium botulinum in cured meat products. However, in the case of dry fermented sausages, environmental factors such as pH, aw and the competitive microbiota may exert a more relevant role than nitrite in the inhibition of the growth and toxin production by C. botulinum. In this challenge test study, two varieties of Mediterranean dry sausages (salchichón and fuet) were inoculated with spores of C. botulinum Group I (proteolytic) and C. botulinum Group II (nonproteolytic). Sausages were prepared with 150 mg/kg of NaNO3 and 150 mg/kg of NaNO2 (maximum ingoing amounts allowed by the European Union regulation), with a 25% and 50% reduction, and without nitrate/nitrite. The initial pH in both products was 5.6, and decreased to values below 5.0 in salchichón and to 5.2 in fuet. Lactic acid bacteria counts reached 8-9 log cfu/g after fermentation. The aw decreased from initial values of 0.96 to about 0.88-0.90 at the end of ripening. Botulinum neurotoxin was not detected in any of the sausages, including those manufactured without nitrate and nitrite. Despite the environmental conditions were within the range for germination and growth of C. botulinum Group I during the first 8 days of the ripening process in fuet and 10-12 days in salchichón, acidity, aw and incubation temperature combined to inhibit the production of toxin, independently of the concentration of curing agents. Although decreasing or even removing nitrate/nitrite from the formula did not compromise safety regarding C. botulinum in the conditions tested in this study, their antimicrobial role should not be underestimated in the case that other hurdles could fail or other ripening conditions were used, and also considering the effect of nitrite on other pathogens.