Search

Introduction. Ochratoxin A was recently reported in dry cured pork meat as caused by Penicillim nordicum contamination. The ecological needs of the fungus are limitedly known. This study wishes to assess the role of temperature, aw and incubation time on P. nordicum growth in a dry-cured pork-like medium (DPM). Methods. A Penicillium nordicum strain isolated from dry cured pork during ripening, able to produce OTA in vitro (1, 2), was selected. Thirty g of lyophilised dry-cured pork (4% moisture, 11% NaCl, 67% proteins, 18% fat) were added to 1 l of bidistilled water, maintained 1 h in a thermostatic bath, shaken, filtered and added with 15 g of agar to prepare DPM. The original aw (0.97) was modified by glycerol. Then the DPM was poured into 9 cm  Petri dishes (10 ml/ plate) for inoculation. A blocked Central Composite Design (CCD) was organized on three independent factors at 5 levels: temperature (7, 10, 15, 20, 23°C), aw (0.83, 0.86, 0.90, 0.94, 0.97), and incubation time (2, 7, 14, 21, 26 days). Each condition was quadruplicated (a total of 112 Petri dishes). Fungal growth rate (mm/d) was the measured response. The CCD was generated by TRIAL RUN (TRIAL RUN 1.0, SPSS Inc. Chicago, IL), and a fitting model was calculated according to a polynomial multiple regression (MLR). Results. Mycelial growth occurred in all the assayed experimental region. The diameter of P. nordicum colonies was maximum at 20°C and 0.94 aw, after 3 weeks ( = 67.9 mm). In the CCD central point (15°C, 0.90 aw and 14 days of incubation time), the average  = 22.1 mm was measured. The model calculated to explain the measured response (fungal growth) was (sdz coeff.): mm/day = 0.645 temperature + 0.073incubation time + 0.771aw - 0.087temperature×incubation time + 0.363 temperature×aw - 0.037incubation time×aw - 0.136temperature2 + 0.051incubation time2 - 0.006aw2 (R2 = 0.913). The coefficients of the MLR model showed temperature, aw and their two-way interaction as positively affecting the gr

Dry-cured hams during the ripening stages are commonly covered by moulds and yeasts whose type and extension depends on ecological conditions in the maturing rooms. The microbial community is important as it determines the characteristics of final products, like flavour and aroma. Nevertheless, some microorganisms can produce undesirable metabolites, as P. nordicum, a fungus able to synthesise ochratoxin A (OTA), a nephrotoxin with negative effects on human and animal health . Different approaches can be applied to reduce fungal growth, but the application of biological control agents (BACs), never taken in consideration to reduce mould contamination on proteinaceous food, could represent a suitable opportunity. The aim of this work was to evaluate in vitro the ability of selected authochtonous yeasts (Debaryomyces spp., Candida zeylanoides and Hyphopichia burtonii), isolated from the ham surface, to compete with P. nordicum in the perspective of being used as starter inoculum to prevent or minimize OTA contamination. P. nordicum growth was drastically reduced in co-presence of all yeasts, with C. zeylanoides and D. hansenii as the most and the least efficient, respectively. The efficacy of yeasts in reducing P. nordicum growth decreased with increasing fungal inoculum concentration. OTA production was also considerably influenced by yeasts and sodium chloride in the media; all species tested reduced significantly OTA production, irrespective of the concentration of fungal inoculum. This approach gave promising results and the application of natural yeasts microflora as starter inoculum can be of interest to inhibit P. nordicum contamination of dry-cured hams. Further studies are ongoing to define and check the application method in vivo.