Scientific Publications - Work Done by Microbiology Reader Bioscreen C

E. Skyttä, A. Vaari, A. Haikara, E. Saarisalo and S. Jaakkola, Inhibition of aerobic spoilage yeasts in silage by hurdle technology?, VTT Biotechnology Projects, Finland, 2002

INTRODUCTION

In biological ensiling with lactic inoculants spoilage yeasts often tend to dominate the aerobic spoilage flora. Particularly harmful are the spoilage yeasts capable of utilising lactate as the source of energy. Because their growth can not be inhibited by any single environmental parameter hurdle technology could provide an alternative tool for controlling their growth. Preservation by hurdle technology is based on simultaneous application of various antimicrobial factors affecting the target organisms by different mechanisms. In biological ensiling both combination of synergistically working inoculants and combination of an appropriate inoculant and chemical treatment could be considered. In this study we examined in vitro how a combination of a selected lactic inoculant, potassium sorbate and sodium benzoate inhibited the growth of four spoilage yeast strains isolated from grass silage.

RESULTS AND DISCUSSION L. plantarum VTT E-78076 is known for its broadspectrum antimicrobial activity both against gram positive and gram negative bacteria and, furthermore, against Fusarium moulds. However, the results of this study indicated that against the selected spoilage yeasts E76 crude extract was not very efficient (Fig. 1). At the highest concentration level of the crude extract (10%, v/V) a marginal antimicrobial effect was only detected against R. mucilaginosa, a yeast strain not fermenting lactate. Similarly weak was the inhibition effect of sodium benzoate (0,1 g/ml) alone whereas potassium sorbate at the same concentration level to some extent inhibited the growth of all yeast strains, and particularly the growth of R. mucilaginosa. With a combination of E76 and sodium benzoate the hurdle effect could be demonstrated: the growth of P. anomala and R. mucilaginosa was nearly completely inhibited. The combination of E76 and potassium sorbate was similarly effective against P. anomala and R. mucilaginosa, and in addition, to somewhat less extent against T. delbrueckii and P. kluyveri var. kluyveri. The only hurdle combination being able to inhibit nearly completely the growth all target organisms was consisted of E76 crude extract, sodium benzoate and potassium sorbate. Since the pH differences between the sample and control wells was at maximum 0.2 pH units, the inhibition potential detected was not attributable to pH effects.

CONCLUSIONS The results obtained with the combination of E76 and sodium benzoate or potassium sorbate were promising: the inhibition of two yeast isolates was nearly complete. By using a combination of E76, sodium benzoate and potassium sorbate an equally complete growth inhibition of all four isolates was achieved.

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Last modified: May 25, 2005