Margarita Garriga

Functionalty of enterococci in meat products

The presence of enterococci in meat fermentation is a constant as reported in the literature. Despite the concern about pathogenicity of enterococci, recent studies point out that food and meat enterococci, especially Enterococcus faecium have a much lower pathogenicity potential than clinical strains. Enterococci possess a competitive advantage over other microbiota in meat fermentations, and many enterococci isolated from sausages have the ability to produce enterocins harbouring antimicrobial activity against pathogens and spoilage microorganisms of meat concern. The application of enterocins producing enterococci or their purified metabolites, as extra hurdles for preservation in sausage fermentation and in sliced-vacuum packed cooked meat products can be beneficial, preventing the outgrowth of Listeria monocytogenes and slime-producing lactic acid bacteria. Enterocins and bacteriocinogenic enterococci hold considerable promise as alternatives to traditional chemical preservatives and they could be exploited for the control of emergent pathogens in meat products. Their inhibitory effect can be increased when used in conjunction with particular physical and chemical processes, but current regulation is hampering the application of purified bacteriocins.

Biochemical characterization of lactobacilli from dry fermented sausages

The characterization of 254 strains of lactobacilli isolated from dry spontaneously fermented sausages from 15 different producers at two different stages of ripening time is reported. The species identified were Lactobacillus sake 55%, L. curvatus 26%, L. bavaricus 11% and L. plantarum 8%. The main criteria for the identification of isolates to species level were: production of lactic acid isomers, presence of mDpm acid in cell walls, deamination of arginine and fermentation of mannitol and melibiose. The composition of the populations of lactobacilli were the same for the two stages of ripening. The deamination of arginine was tested in aerobic and anaerobic cultures and in different media by checking the production of ammonia and detecting the production of citrulline. In 94% of strains tested both methods gave identical results. In two L. sake strains arginine catabolism was dependent on culture media; for two other L. sake strains the deamination of arginine only occurred when oxygen was scarce.

Inhibition of Listeria monocytogenes and Salmonella by Natural Antimicrobials and High Hydrostatic Pressure in Sliced Cooked Ham

The effectiveness of nisin, lactate salts, and high hydrostatic pressure to inhibit the growth of Listeria monocytogenes and Salmonella in sliced cooked ham was studied through a combination of PCR-based detection methods, most probable number, and classical microbial enumeration techniques (International Organization for Standardization protocols). A synergistic effect to inhibit a cocktail of Listeria monocytogenes CTC1010, CTC1011, and CTC1034 was observed between potassium lactate, high hydrostatic pressure (400 MPa, 17 degrees C, 10 min), and low storage temperature when sliced cooked ham was stored for 84 days at 1 degrees C. The high hydrostatic pressure treatment also proved to be useful to inhibit a cocktail of Salmonella enterica serotypes London CTC1003, Schwarzengrund CTC1015, and Derby CTC1022.

Safety properties and molecular strain typing of lactic acid bacteria from slightly fermented sausages

Aim:  To evaluate the biodiversity of lactobacilli from slightly fermented sausages (chorizo, fuet and salchichon) by molecular typing, while considering their safety aspects.

Application of enterocins as biopreservatives against Listeria innocua in meat products.

The antilisterial effect of enterocins A and B in meat and meat products (cooked ham, minced pork meat, deboned chicken breasts, pâté, and slightly fermented sausages [espetec]) have been shown. An infective dose of 5 to 10 most probable numbers (MPN)/g to simulate the counts of Listeria generally found in meat products was used. Enterocins at 4,800 AU/g reduced the numbers of Listeria innocua by 7.98 log cycles in cooked ham and by 9 log cycles in pâté when stored at 7 degrees C for 37 days. In deboned chicken breasts stored at 70 degrees C for 7 days, 4,800 AU/cm2 of enterocins diminished the L. innocua counts in 5.26 log cycles when compared to the control batch. In minced pork meat held at 7 degrees C for up to 6 days, 1,600 AU/g kept L. innocua counts under 3 MPN/g, while the control batch reached 50 CFU/g. In espetec sausages, 648 AU/g diminished the number of L. innocua under 50 CFU/g from the fifth day until the end of the process (12 days) while the control batch kept the initial counts (3 x 104 CFU/g). This is the first report on enterocins showing an antilisterial effect in different types of meat products.

Effect of sausage ingredients and additives on the production of enterocin A and B by Enterococcus faecium CTC492. Optimization of in vitro production and anti‐listerial effect in dry fermented sausages

Enterocin A and B in Enterococcus faecium CTC492 were co‐induced by the different factors assayed in this study (r = 0·93) and followed primary metabolic kinetics. Enterocin production was significantly inhibited by sausage ingredients and additives, with the exception of nitrate. The addition of sodium chloride and pepper decreased production 16‐fold. The temperature and pH influenced enterocin production, with optima between 25 and 35 °C, and from 6·0 to 7·5 of initial pH. The maximum activity was achieved, under favourable growth conditions, with MRS supplemented with sucrose (2%) plus glucose (0·25%) and Tween‐80 (1%). MRS concentration, NaCl plus pepper addition, absence of Tween‐80 in the growth medium, incubation at 45 °C and an initial pH under 5·5 were detrimental to bacteriocin production. Stress conditions did not favour enterocin production. Desadsorption was Tween‐dependent. Enterocin A activity in the crude extracts stored at −80 °C was better preserved than enterocin B (when tested against their specific indicator strain), but anti‐listerial activity remained intact. Applied as anti‐listerial additives in dry fermented sausages, enterocins significantly diminished Listeria counts by 1·13 log (P < 0·001), while Enterococcus faecium CTC492 added as starter culture did not significantly reduce Listeria counts (P > 0·1) compared with the standard starter culture (Bac–). Enterocins A and B could be considered as extra biopreservative hurdles for listeria prevention in dry fermented sausages.

Inhibition of Salmonella sp. Listeria monocytogenes and Staphylococcus aureus in cooked ham by combining antimicrobials, high hydrostatic pressure and refrigeration.

Recontamination of ready-to-eat products such as cooked ham during post-processing may be the cause of outbreaks of food-borne disease. The effectiveness of the combination of high pressure processing (HPP) at 600MPa with the natural antimicrobials nisin and potassium lactate has been evaluated in sliced cooked ham spiked with 4LogCFU/g of Salmonella sp., Listeria monocytogenes and Staphylococcus aureus after 3-months of storage at 1 and 6°C. In non-HPP sliced cooked ham, the addition of nisin plus lactate inhibited the growth of L. monocytogenes during the entire storage period while the refrigerated storage inhibited the growth of Salmonella sp. and S. aureus. The application of an HPP reduced the levels of Salmonella and L. monocytogenes to levels below 10CFU/g. These levels continued until the end of storage at both 1 and 6°C. HPP produced a reduction of less than 1LogCFU/g to S. aureus. The combination of HPP, nisin and refrigeration at 6°C was necessary to decrease the levels of S. aureus by 2.4LogCFU/g after 3-months of storage.

Genetic diversity and safety aspects of enterococci from slightly fermented sausages.

Aims:  To determine the biodiversity of enterococci from slightly fermented sausages (chorizo and fuet) at species and strain level by molecular typing, while considering their safety aspects.

Technologies to shorten the drying period of dry-cured meat products

Dry-cured meat products are well-known for their unique sensory characteristics. However, the traditional process is very time consuming. The process can be shortened especially by accelerating the drying period, which is the most time consuming. This paper deals with some technological, safety and sensorial aspects for producing fermented sausages and dry-cured hams when the process time is shortened. Different techniques, such as temperature increase and thickness reduction, and the effects of some ingredients and additives are discussed. A Quick-Dry-Slice process based on a continuous system that combines both convective and vacuum drying could accelerate the drying of slices after the desired pH is reached in fermented sausages. There are safety concerns when processes are shortened, but possible additional hurdles, such as the introduction of bacteriocin-producing starter cultures and high-pressure treatments at the end of the process, could reduce them. Methods to speed up the development of typical colour, texture and flavour and their limitations are also discussed.

Combined effect of enterocin AS-48 and high hydrostatic pressure to control food-borne pathogens inoculated in low acid fermented sausages

The single and combined effects of enterocin AS-48 and high hydrostatic pressure (HHP) on Listeria monocytogenes, Salmonellaenterica, and Staphylococcus aureus was investigated in fuet (a low acid fermented sausage) during ripening and storage at 7 degrees C or at room temperature. AS-48 (148 AU g(-1)) caused a drastic 5.5 log cfu g(-1) decrease in L. monocytogenes (P<0.001) and a significant (P<0.01) inhibition (1.79 logs) for Salmonella at the end of ripening (10 d). After pressurization (400 MPa) and storage Listeria counts remained below 5 cfu g(-1) in all fuets containing AS-48 (pressurized or not). HHP alone had no anti-Listeria effect. HHP treatment significantly reduced Salmonella counts, with lowest levels in pressurized fuets with AS-48. S. aureus showed similar growth for all treatments and storage conditions. These results indicate that AS-48 can be applied alone to control L. monocytogenes and combined with HHP treatment to control Salmonella in fuets.