Susceptibility of dairy associated molds towards microbial metabolites with focus on the response to diacetyl

Food spoilage may cause food waste, economic losses and even brand image deterioration. In fermented dairy products, spoilage by molds is frequently occurring and the molds are commonly being introduced at the consumer stage after opening. Diverse molds may be involved with the main genera being Penicillium, Mucor, and Cladosporium. Fungal growth may be inhibited by bioprotective cultures by competition and/or production of inhibitive compounds. Several compounds produced by a range of lactic acid bacteria have been reported as having an antifungal activity against certain fungi. Susceptibility tests of a panel of dairy associated molds towards twelve of these pure compounds were performed using microtiter plate well method. Diacetyl was the most potent antifungal among the compounds followed by octanoic acid. Large variations were seen within the Penicillium strains tested with P. commune being more sensitive than P. roquefortii, and two Mucor strains generally exhibiting high tolerance. The growth of two susceptible Penicillium strains in yoghurt serum with pH 4.6 with increasing amounts of diacetyl added were followed. Susceptibility varied but at 64 mu g/mL, both strains were completely inhibited on yoghurt regardless of temperature. At higher pH (5.6) in malt extract agar (MEA), growth was faster but inhibition was still observed. Upon exposure to diacetyl, the level of cytoplasmic reactive oxygen species (ROS) increased and impairment of membrane integrity and leakage of cellular materials were observed. These findings provide new knowledge of the activity of diacetyl against molds.

Automated summary

Food spoilage by molds can lead to waste and economic losses. Bioprotective cultures can inhibit fungal growth through competition and production of inhibitive compounds, with diacetyl being the most potent antifungal.