1. email : marco.licalzi@purpan.fr
MINIMIZING THE WILD MICROFLORA ON WINEGRAPES BY MICROWAVES AND OZONATED WATER
Marco LI CALZI1, Marielle PAGES1, Christel COUDERC1 and Frédéric VIOLLEAU1
1- Université de Toulouse ; INP EI-PURPAN, Laboratoire Sciences agronomiques et agroalimentaire, 75, voie du TOEC, BP 57611, F Toulouse cedex 3, France.
Abstract
The majority of wine faults are induced by undesirable microorganisms, present in the vineyard and/or established in the cellar, leading to the production of off-aromas.
Sulfites are used in the winemaking process for their three activities: antimicrobial, anti-PPO (PolyPhenolOxidases) and antioxidant. However, sulfites have been shown to be responsible for severe allergic reactions in 1% of the population and legislation imposes producers to declare on the label their presence [1].
With the objective of finding alternatives to the use of sulfites, microwaves and ozonated water treatments have been tested on Cabernet sauvignon grapes before crush and alcoholic fermentation. The hypothesis is that both techniques will minimize the microbial population on the grapes. In addition, the microwaves treatment will maximize the extraction of anthocyanins.
Results showed that microwaves (5 minutes) and ozone (20 minutes) treatments decreased the yeast population by a logarithmic factor of 1.6 and 0.8 respectively. Both treatments seemed to be more effective on wild yeasts and molds than on bacteria.
In addition, the microwave treatment showed an inhibitory effect on PPO. This can be easily explained by a denaturing effect of the enzyme by the heat generated by the microwave treatment.
Sensory analysis as well as color intensity measurements of the micro-vinified wines are underway.
If these preliminary results will be confirmed at a larger scale, the two techniques could provide a valid replacement to the use of sulfites in the early stages of the winemaking process.
Materials and Methods
Hand harvested Cabernet Sauvingon grapes, donated by the Cave the Rabastens (Vinovalie) were submitted to various treatments (see tables below). Juice was collected after homogenizing winegrapes in ziplocks bags with a stomacher and subjected to 10 fold dilutions. Treatment efficency was evaluated by counting the total viable flora on PCA medium (plate count agar), yeasts and molds on OGA (oxytetracycline glucose agar ). Two repetitions were performed per treatment. Microvinifications were conducted in Bodum-style coffee makers provided with pistons according two A. L. Carew et al [2]. Two punch downs/day were performed throughout the end of alcoholic fermentation.
Treatment
Time of contact
Concentration of water ozoned
Weight of grapes
Ozone
5 minutes
6 ppm
800 grams
20 minutes
Treatment
Time of treatment
Power
Weight of grapes
Microwaves
2 minutes
1150 Watts
1000 grams
5 minutes
Results
Effect of microwave and ozonated water treaments on total microbial population – Effect of microwave treatment on PPO
Fig. 2 Microvinifications
Conclusion
Five minutes microwaves treatment seems more efficient than the 20 minutes ozone treatment on yeasts. The decrease in viable population count resulted in 1,6 log and 0,8 log respectively (Fig. 1).
As for the molds, the 5 minutes microwave treatment had the same effect as the 20 minutes ozonated water, resulting in a 0.8 log decrease in viable population count (Fig. 1).
Ozone and microwaves treatments seem to have a negligible impact on the total microbial population.
Control values between the two treatements (ozone and microwave) are different. This can be explained by the fact that the analysis were not performed on the same day: J=0 ( at the time of receiving the grapes) for ozone treatment and J+1 for microwave treatment. As expected, the microwave treatment partially inhibits the PPO activity. However, this happened only with the 5 minutes treatment and for some unclear reason only with one of the two replicates. If these preliminary results will be confirmed at a larger scale, the two techniques could provide a valid replacement to the use of sulfites in the early stages of the winemaking process.
These preliminary results need to be confirmed at a larger scale. The two techniques could provide a valid replacement to the use of sulfites in the early stages of the winemaking process.
References
[1] Robert K. Bush, Steve L. Taylor, William Busse. “A critical evaluation of clinical trials in reactions to sulfites”. Journal of Allergy and Clinical Immunology. Volume 78, Issue 1 Pages
[2] A. L. Carew, A. M. Sparrow, C. D. Curtin, D. C. Close, and R. G. Dambergs, “Microwave Maceration of Pinot Noir Grape Must : Sanitation and Extraction Effects and Wine Phenolics Outcomes,” Food Bioprocess Technol, vol. 7, pp. 954–963, 2014.