Microbiota of high-pressure-processed Serrano ham investigated by culture-dependent and culture-independent methods.

The microbiota of Serrano dry-cured ham of different chemical composition, subjected or not to high-pressure processing (HPP), was investigated using culture-dependent and culture-independent methods. Microbial counts were submitted to analysis of variance with physicochemical parameters (aw, NaCl concentration, salt-in-lean ratio and intramuscular fat content) or HPP as main effects. In untreated hams, physicochemical parameters significantly affected counts of aerobic mesophiles, psychrotrophs, and moulds and yeasts. NaCl concentration and fat content influenced the levels of four and three of the five studied microbial groups, respectively, whereas no influence of aw was stated. The HPP treatment had a significant effect on counts of all investigated microbial groups. Culture-independent methods showed the presence of bacteria such as Staphylococcus equorum, Staphylococcus succinus, Bacillus subtilis and Cellulosimicrobium sp., moulds like Penicillium commune, Aspergillus fumigatus, Sclerotinia sclerotiorum, Eurotium athecium and Moniliella mellis, and yeasts like Debaryomyces hansenii and Candida glucosophila. Absence of B. subtilis bands and weaker bands of E. athecium were recorded for HPP-treated hams. The higher microbial levels found in lean ham might result in a quicker deterioration. HPP treatment confirmed its suitability as a procedure to control spoilage microorganisms. DGGE did not seem to be sensitive enough to highlight changes caused by HPP treatment in the microbiota of ham, but contributed to the detection of microbial species not previously found in ham.

Study of the counts, species and characteristics of the yeast population during the manufacture of dry-cured "lacón". Effect of salt level.

The aim of this work was to study the yeast population during the manufacture of dry-cured "lacón" (a Spanish traditional meat product) and the effect of the salting time. For this study, six batches of "lacón" were manufactured with three different salting times (LS (3 days of salting), MS (4 days of salting) and HS (5 days of salting)). Yeast counts increased significantly (P < 0.001) during the whole process from 2.60 to 6.37 log cfu/g. An increased length of salting time did not affect yeast counts throughout the manufacture of dry-cured "lacón", although the highest yeast counts were obtained from LS batches. A total of 226 isolates were obtained from dry-cured "lacón" during drying-ripening stage, of which 151 were yeasts and were identified at the species level using molecular techniques. The total of 151 identified yeasts belonged to 4 different genera: Debaryomyces, Candida, Cryptococcus and Rhodotorula. Debaryomyces hansenii was the most abundant species isolated throughout the whole process as much in the interior as in the exterior of the pieces of three salt levels of "lacón" studied, while Candida zeylanoides was only isolated from the interior of MS and HS batches and from the exterior of LS and HS groups, but at lesser proportion than D. hansenii.

Taxonomical and technological characteristics of Saccharomyces spp. associated with blue veined cheese.

In blue veined cheeses, the dominant yeast species in most cases is Debaryomyces hansenii. Saccharomyces spp. occurs less frequently, but they can be found in some blue veined cheeses. In the present study, the taxonomy of Saccharomyces spp. associated to blue veined cheeses was studied and comparisons made to type strains of Saccharomyces spp. and starter cultures of Saccharomyces spp. used in other food fermentations. Phenotypically, the cheese strains were referred to the Saccharomyces sensu stricto complex and were further identified as S. cerevisiae. Genotypically, the Saccharomyces spp. investigated were similar although chromosomal polymorphism were observed. Concerning the technological characteristics, they were similar in assimilation and fermentation of the residual sugars and organic acids naturally found in cheese. The investigated yeasts were also similar in their lipolytic activity being able to hydrolyse tributyrin and low chain (C:8), but not C:14 fatty acids. However, they differed in their tolerance to NaCl with the blue cheese strains showing a higher tolerance. The cheese strain S. cerevisiae FB 7 was the only yeast capable of degrading casein. It mainly degraded the alpha(s1)-casein and the beta(alpha2)-casein components. It was also the only isolate stimulating the development of Penicillium roqueforti in cheese agar imitating the conditions in blue veined cheese. The stimulation of P. roqueforti was most pronounced for the least proteolytic strain of P. roqueforti examined.

Regulation of the potassium to sodium ratio and of the osmotic potential in relation to salt tolerance in yeasts.

By using the isotope pairs (22)Na-(24)Na and (42)K-(86)Rb, the uptake and retention of Na and K was studied in the salt-tolerant Debaryomyces hansenii and in the less tolerant Saccharomyces cerevisiae at NaCl levels of 4 mm and 0.68, 1.35, and 2.7 m in the medium. The ratio of K to Na is much higher in the cells than in the media, and higher in D. hansenii than in S. cerevisiae under comparable conditions. The difference between the two species is due to a better Na extrusion and a better uptake of K in D. hansenii. The kinetics of ion transport show that at about the time when extrusion of Na could be demonstrated in D. hansenii, K-Rb previously lost to an easily washable compartment of the cells was reabsorbed in both organisms. More H(+) was given off from S. cerevisiae than from D. hansenii in the course of these events. The findings fit the working hypothesis tested, which regards salt tolerance as partly dependent on the ability to mobilize energy to extrude Na from the cells and to take up K. The volume changes in S. cerevisiae are greater and are more slowly overcome than those in D. hansenii. The total salt level of the cells is not sufficient to counteract the osmotic potential of the medium, so that additional osmoregulatory mechanisms must be involved in determining halotolerance.