Structural Characteristics Of Polysaccharides In Wine And Their Matrix Effect On The Volatility Of Typical Aroma Compounds

Aroma is an important aspect of the wine sensory quality to reflect the wine style and characteristics,which become an important factor for consumers to choose wine products.However,some aroma compounds will be hydrolyzed or lost during wine storage,affecting the quality and shelf life of the product.It was found that polysaccharides from grape and yeast fermentation process can interact with wine aroma compounds,thus delaying the hydrolysis of some aroma compounds and making the aroma more durable.But it’s difficult to explore the mechanism of volatility of aroma compounds by different polysaccharides due to diverse composition of wine substrate and extremely complex structure of polysaccharides.At present,there is no systematic study on the effect of polysaccharides on the volatility of wine aroma.In this study,Pinot noir grapes,RC212 Saccharomyces cerevisiae and Pinot noir wines were used as test materials.Firstly,grape polysaccharides,yeast polysaccharides and wine polysaccharides were extracted and isolated by hot water extraction technology,alkali extraction technology and ultrafiltration membrane separation technology.Then the components of grape polysaccharides and yeast polysaccharides were separated and purified by DEAE-Sephacel anionic column chromatography.Subsequently,the chemical composition and structural characteristics of polysaccharides were analyzed by ultraviolet-visible spectroscopy(UV-Vis),Fourier transform infrared spectroscopy(FT-IR),Raman spectroscopy(Raman),size exclusion chromatography(GPC/SEC),matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF),nuclear magnetic resonance(NMR)and gas chromatography-mass spectrometry(GC-MS).Finally,the matrix effect of the tested polysaccharides(grape polysaccharides,yeast polysaccharides and wine polysaccharides)in wine on the volatility of typical aroma compounds in different solutions(water,water-acid and water-acid-alcohol)was investigated based on the concentration change of aroma compounds(esters,higher alcohols,aldehydes,terpenes,C13-norisoprenoids,volatile phenols,methoxypyrazines,sulfur compounds and lactones)in the headspace detected by gas chromatography-mass spectrometry,and the possible mechanism of its influence was also discussed.The results are helpful to optimize the winemaking technology and provide theoretical basis and data support for improving the flavor quality of wine.The main findings were as follows:(1)Purification,chemical composition and structural characteristics of Pinot noir grape polysaccharides.Grape polysaccharides PNGP1(obtained by hot water extraction method)and PNGP2(obtained by alkali extraction method)had lower intrinsic viscosity,the polydispersity index of PNGP1 was relatively smaller than PNGP2,and the molecular weight distribution of polysaccharides components was more concentrated.PNGP1 had the highest intrinsic viscosity.The purified polysaccharides fractions obtained by gradient elution with water,0.1 mol/L,0.3 mol/L and 0.5 mol/L Na Cl solutions,named f1～f4,and PNGP1-f1 had higher purity(83.4%).The chemical composition of grape polysaccharides varied greatly.The polysaccharides fractions eluted by high concentration Na Cl solution had more uronic acid.The main components of grape polysaccharides were polysaccharides rich in arabinose and galactose and rhamnogalacturonan,followed by glucans and mannoprotein.Grape polysaccharides were heteropolysaccharides and acidic polysaccharides with α-type and β-type glycosidic bonds.There were many branches in the structure of grape polysaccharides,and PNGP1-f1 contained more side chains.In addition,there was no triple helix structure and no starch structure of grape polysaccharides,however,PNGP1-f3 had more pectin structure.(2)Purification,chemical composition and structural characteristics of RC212 Saccharomyces cerevisiae polysaccharides.Yeast polysaccharides SCP1(obtained by hot water extraction method)and SCP2(obtained by alkali extraction method)mainly had pyranose rings.The protein infrared absorption peaks of SCP2 and its purified polysaccharides fractions were much weaker than those of SCP1 and its purified fractions,which was demonstrated in Raman spectra.SCP2 and its purified polysaccharides fractions had smaller polydispersity index,indicating that the molecular weight distribution of polysaccharides components was more concentrated.The main components of SCP2-f1 were mannoprotein and glucans,while the main polysaccharides of other yeast polysaccharides were mannoprotein.The glucoside bond type of yeast polysaccharides was mainly α-type,and the mannose main chain was connected by α-1,6.There were many branches on the main chain,the side chains were connected by α-1,2/α-1,3.Compared with grape polysaccharides and wine polysaccharides,yeast polysaccharides had the best purification effect.Yeast polysaccharides contained O-glucoside bonds,but there was no triple helix structure.(3)Isolation,chemical composition and structural characteristics of Pinot noir wine polysaccharides.Low molecular weight(PNWP-L)and high molecular weight(PNWP-H)wine polysaccharides were acidic polysaccharides with different α-type andβ-type glycosidic bond structures.PNWP-L contained more uronic acid than PNWP-H.More than 72% of the polysaccharides components in PNWP-H were distributed in the range of 25 k Da to 670 k Da,while the molecular weight of all polysaccharides components in PNWP-L was below 25 k Da.PNWP-L was mainly composed of rhamnogalacturonan and polysaccharides rich in arabinose and galactose,and PNWP-H was mainly composed of polysaccharides rich in arabinose and galactose and mannoprotein.In addition,PNWP-L had triple helix structure,PNWP-H contained more pectin structures and branches.The two kinds of wine polysaccharides didn’t contain starch structure,but there were O-glucoside bonds.The results showed that polysaccharides rich in arabinose and galactose and rhamnogalacturonan in wine were mainly derived from grapes,and mannoprotein was mainly derived from Saccharomyces cerevisiae.(4)Matrix effect of polysaccharides in wine on the volatility of aroma compounds.SCP2 and PNGP2 were the most significant polysaccharides that affect the volatility of aroma compounds.The aroma compounds with significant volatile changes were mainly ethyl decanoate,β-ionone and geranyl acetate with strong hydrophobicity and weak polarity,and phenethyl acetate and nonanal with weaker polarity.In water-acid solution,the volatility of ethyl decanoate decreased by 73.2% in the presence of SCP2,and the volatility ofβ-ionone was decreased by 18.1% and 26.1% in the presence of SCP2 and PNGP2,respectively.In water-acid-alcohol solution,the volatility of nonanal was reduced by 21.3%under the influence of PNGP2.However,the volatility of nonanal was reduced by more than40% under the influence of SCP2 in water solution.Compared with other solutions,SCP2 had the greatest effect on the volatility of geranyl acetate in water solution,and its volatility was reduced by more than 20%.SCP1,SCP2,PNGP1 and PNGP2 had the greatest effect on the volatility of phenethyl acetate,and their volatility were all reduced by more than 20% in water-acid-alcohol solution,but they promoted the volatility of phenethyl acetate in other solutions.It was found that matrix solutions,chemical composition and structures of polysaccharides and physicochemical properties of aroma compounds were the factors affecting the volatility of aroma compounds.