Assessment of O2 consumption, a new tool to select bioprotection yeast strains

Abstract

Reduction of sulfur dioxide during winemaking is a request from the wine industry. To replace sulfur dioxide, various alternatives exist, including bioprotection by yeast inoculation. This practice consists in adding non-Saccharomyces yeasts directly on the grapes or must. The antimicrobial properties of non-Saccharomyces yeasts have already been demonstrated due a to niche occupation of the grape must, resulting in a decrease of fungal and acetic bacteria communities. Furthermore, their potential antioxidant properties by consuming oxygen hence reducing the browning of the must and maintaining GSH concentration in white wines has also been described. However, only a few strains of two non-Saccharomyces species were considered in the previous studies while it is known that a significant intra-species genetic diversity exists [1]. In this study, inter and intra species diversity were considered to evaluate O2 consumption by yeast during the prefermentary steps.

First, laboratory assays were optimized and various technological parameters were analyzed such as the O2 concentration, the physiological state of yeasts, the yeast dosages and mixed-combination. Subsequently, 47 yeast strains distributed over 6 enological species and representing their genetic diversity were selected. In order to measure on line dissolved oxygen, a compact FireStingO2 oximeter (Pyroscience, Aix-La-Chappelle, Germany) was used. The kinetics of O2 consumption by yeast in a grape must model medium were evaluated and the consumption rates were calculated and expressed as mg of O2 consumed per liter and per number of living cells (determined by flow cytometry). Thus, an Oxygen Consumption Rate (OCR) per strain was obtained, ranging from 15 to 65 mg/L.

Results show that an interspecific diversity can be highlighted. Indeed, some species consumed significantly more O2 than others. The O2 consumption in grape must by yeasts could be linked to their respiratory metabolism and correlated with a Crabtree effect. Moreover, for some species, intraspecific diversity was obtained revealing a variability which could be interesting to further investigate. These results provide important data for selecting new bioprotection strains in winemaking.

References

1.Masneuf-Pomarede, I.; Bely, M.; Marullo, P.; Albertin, W. The Genetics of Non-Conventional Wine Yeasts: Current Knowledge and Future Challenges. Frontiers in microbiology 2016, 6, 1563.