Abstract

Fungal growth is the most frequent cause of spoilage in baked goods determining great economic losses. Lactic acid bacteria (LAB) are applied in the process of several bakery products since they significantly contribute to technological and nutritional properties, influence the food flavour and prevent spoilage by producing organic acids, hydrogen peroxide, cyclic dipeptides, bacteriocins, fatty acids, carbon dioxide, ethanol and diacetyl. Among organic acids, lactic, acetic, phenyllactic (PLA) and p-OH-phenyllactic acids (OH-PLA) play a role in inhibiting fungal and bacterial growth [1]. In particular, the inhibitory properties of PLA have been demonstrated against several fungal species. Recently, the research has been moved towards the application of biotechnology aimed to improve PLA production by microorganisms (bacteria and yeast). PLA is a by-product of phenylalanine (Phe) metabolism and its production can be significantly improved by the addition of precursors such as Phe, phenylpyruvic acid (PPA) and ?-ketoglutaric acid to the growth medium. The aim of the current study was to improve the antifungal activity of eight lactic acid bacterial (LAB) strains by the addition of PPA to a defined growth medium (DM) [2]. The effect of PPA addition on the LABs antifungal activity related to the production of organic acids (PLA, D-lactic, L-lactic, acetic, citric, formic and 4-hydroxy-phenyllactic acids) and of other phenylpyruvic-derived molecules, was investigated. In the presence of PPA the inhibitory activity (expressed as growth inhibition percentage) against fungal bread contaminants Aspergillus niger and Penicillium roqueforti significantly increased and was, even if not completely, associated to PLA increase (from a mean value of 0.44 to 0.93 mM).While the inhibitory activity against the yeast Endomyces fibuliger was mainly correlated to the low pH and to lactic, acetic and p-OH-PLA acids. When the Principal Component Analysis (PCA) analysis based on data of growth inhibition percentage and organic acid concentrations was performed, strains grown in DM + PPA separated from those grown in DM and the most active strains Lactobacillus plantarum 21B, Lactobacillus fermentum 18B and Lactobacillus brevis 18F grouped together. The antifungal activity resulted to be strain-related, based on a different mechanism of action for filamentous fungi and the yeast and was not exclusively associated to the increase of PLA. Therefore, a further investigation on the unique unidentified peak in HPLC-UV chromatograms was performed by LC- MS/MS analysis. Full scan mass spectra (negative ion mode) recorded at the retention time of the unknown compound, showed a main peak of m/z 291.0 which was consistent with the nominal mass of the molecular ion [M-H]- of polyporic acid, a PPA derivative whose antifungal activity has been previously reported against 12 species of fungi [3]. Actually, in microorganisms different from LAB, as fungi and lichens, PPA is a precursor

Autore Pugliese

• Valerio Francesca , Lavermicocca Paola , Lattanzio Veronica Maria Teresa , Di Biase Mariaelena

Tutti gli autori

• F. Valerio; M. Di Biase; V.M.T. Lattanzio; P. Lavermicocca

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Anno di pubblicazione

2016

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Settori ERC

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