Biocontrol of Penicillium nordicum growth and ochratoxin A production by native yeasts of dry cured ham

Abstract

Twelve yeast strains isolated from the surface of Italian typical dry-cured hams, belonging to D. hansenii, D. maramus, C. famata, C. zeylanoides and H. burtonii species, and previously selected for their ability to grow in dry-cured ham-like substrates, were screened for antagonistic activity against a toxigenic strain of P. nordicum and inhibition of ochratoxin A (OTA) biosynthesis. On average, yeast inhibitory activity was lowered by increasing fungal inoculum and enhanced by NaCl presence. In the assay conditions, H. burtonii and C. zeylanoides were the most effective, both in inhibiting P. nordicum growth and OTA production. D. hansenii was the species with the lowest inhibitory activity, especially in the absence of salt. OTA production dropped from the range < LOD - 5000 ppb in P. nordicum control plates to the range < LOD - 200 ppb in yeast-added plates. OTA production increased in the presence of NaCl in P. nordicum control plates, while salt enhanced inhibition against OTA production in yeast-added plates.

Keywords: NaCl; Penicillium nordicum; antagonistic yeasts; dry-cured meat product; ochratoxin A.

Figure 1

Growth of P. nordicum (10⁴ conidia/mL) on Yeast Peptone Dextrose (YPD) and YPD +3% NaCl agar (control) for 7 days at 20 °C compared to the growth of P. nordicum (10², 10⁴, 10⁶ conidia/mL) on YPD and YPD +3% NaCl agar containing 10⁸ cfu/mL of selected yeast (yeast-added plates).

Figure 2

Influence of NaCl (0% or 3% in YPD medium) on yeast inhibitory activity against P. nordicum (% diameter reduction at 14 days of incubation at 20 °C).

Figure 3

(a) Ochratoxin A (OTA) distribution in control and yeast treated plates, clustered according to salt presence in growing media (YPD and YPD +3% NaCl); (b) Magnification of yeast treated plate box plots.