Studio di metodi analitici per il controllo delle cessioni colloidali dalle cellule di lievito durante l'affinamento dei vini bianchi sur lies

The ageing of wine on the yeast lees, a traditional practice adepted in Burgundy for the production of Chardonnay, is actually carried out in many wineries. The composition of the lees is mainly represented by yeasts that release in the wine wall polysaccharides as β- glucans and mannoproteins. These macromulecoses can improve the sensorial and the technological profile of the wine. In particular, mannoproteins can improve the tartaric, protein and phenolic stability, promote the development of lactic bacteria, adsorb ochratoxin A and ethilphenols, reduce the tannins astringency and improve the sensation of some aromatic molecules. The rapidity and the entity of the macromulecoses release from the yeast depends on biochemical reactions that happen during the ageing which are linked to the conditions of the ageing like the frequency of the batonnage. The quantification of colloids and mannoproteins can be carried out by affinity chromatography. Ion exchange and size exclusion can be used to quantify different polysaccharide fractions. Gas chromatography can instead be used to quantify and characterize the wine monosaccharides. At present there is not an easy and approachable method that consent to follow, directly in the winery, the mannoproteins cession during the ageing of wine on the lees . This study has been done to test and develop some analytical methods to find an easy, reliable and repeteable method that allow to follow the mannoproteins cession. During this study we tried the Lowry method to quantify proteins, the phenol and the gravimetric method for colloids (after precipitation with ethanol), and the enzymatic method for the mannose after acid hydrolysis. Some of these tried procedures were expencive, time-consuming, dangerous for the laboratory technician, and unsuitable to follow the cession. The enzymatic method showed accuracy but the analysis is very affected by the way to prepare the sample. In this study we tried many differents method to prepare the sample before the acid hydrolysis. After the tries we chose to use the method with ultrafiltration and concentration before the acid hydrolysys and the enzimatic method. We also tried the ruggedness and the repeability of the method which gave us good results. During these tries the method has been tested on white wines. To see if it could also give good responses with red wines we added a red grape extract to a white wine and we use the method to quantify the mannose before and after the addiction. The results showed a good response for mannose. In conclusion we can say that the method studied showed reliability, repeteability and it is also easy to realize. These characteristics make it applicable in the winery to follow the cession of mannoproteins to the wine during the ageing on the lees.