葡萄酒釀造科學(xué)英文資料：WINE202_Protein Stabilisation_Bin

1、Stabilization,Bin Tian, PhD in Wine Science WINE202, 2015,Stabilization,The process of treating a wine to make it stable and clear for years after bottling, including heat (protein) stability and cold stability. Protein stabilization: process used in white wine production to remove the excess protei

2、ns to avoid any potential protein haze formation after bottling Cold stabilization: process which involves chilling below 0C to promote formation and precipitation of salt crystals (tartrates) and then racking/filtering to remove them,Protein stability,White wine only issue! What about red wine? Phe

3、nolic compounds extracted from skin could interact with proteins, and lead to precipitation Protein stability is not an issue in red wine,Where are proteins from?,Major of proteins are from grape berries During crushing: soluble proteins dissolve in juice and insoluble ones precipitate in lees Littl

4、e proteins are from yeast autolysis,How much of proteins in white juice and wine?,In the range of 30-700 mg/L in juice and 10-250 mg/L in wine, which could be influenced by: The season Variety of grape Grape growing region Ripeness Crop yield,Protein structure,Primary structure sequence of amino aci

5、ds Secondary structure alpha helix or beta sheet Hydrogen bonds Tertiary structure Weak interactions: Hydrogen bonds and Van der Waals interactions Ionic bonds: + and charged amino acid side-chain groups Disulphide bonds Quaternary structure two or more polypeptide chains to form a complex,Isoelectr

6、ic point (pI),The ionisable side-chain groups. A protein with more + than ionised side-chain groups would have a net + charge, and vice versa. If there is no net charge the protein is neutral and becomes insoluble. The pI of a protein is the pH at which the net charge of a protein is zero. For a pro

7、tein, when pH condition below its isoelectric point, the protein will carry net positive charge; when pH condition above its isoelectric point, the protein will carry a net negative charge. Most of proteins in wine have their pI above the wine pH, thus they are positive charged,Wine pH,If the pI of

8、the protein above wine pH, it is + charged,If the pI of the protein below wine pH, it is - charged,+ + + + + + + + + + - - - - - - - - - -,Issue of unstable proteins,No hazard to health of consumers BUT Potential to form haze, which is considered as wine fault SO Have to achieve protein stability be

9、fore bottling,Unstable proteins in wine,Pathogenesis-related (PR) proteins: main soluble proteins in wine Thaumatin-like proteins (TLPs) Chitinases PR proteins in grapes increase during grape ripening PR proteins in grapes increase under stress of fungal infection One exception: Botrytis (grey mold)

10、 decrease the level of PR proteins in grapes Winemaking processes also affect the level of PR proteins in juice,Downy mildew,Powdery mildew,Grey Mold,Formation of protein haze,Hypothesis: the first step in protein haze formation in wines is protein denaturation, a process accelerated by heating, and

11、 then the denatured proteins aggregate into large enough particles to be visually detected as haze, a process that may be affected either positively or negatively by non-protein wine components.,A,B,Wine A was depleted of its own proteins,Proteins from wine B were added into wine A,(Mesquita et al.

12、2001. AJEV. 52, 4: 324-330),Non-protein factors,pH: the heat stability increases as the pH rises from 2.5 to 7.5 (Mesquita et al. 2001. American Journal of Enology and Viticulture. 52, 4: 324-330) Polysaccharides: e.g. manoproteins Metal ions, such as copper ions Phenolic compounds Sulphate,(Pocock

13、et al. 2007. J. Agric. Food Chem. 55, 1799-1807),Protein removal techniques,Bentonite fining Enzyme addition Flash pasteurization Phenolic compounds Alternative adsorbents,Bentonite fining,Bentonite clay: a sedimentary clay composed of weathered and aged volcanic ash.,Disadvantages: Lees formation R

14、emoval of aroma and flavor compounds Time and labor consuming,Bentonite types,Sodium bentonite high swelling capacity but large amount of lees, most often used in NZ Calcium bentonite platelets dont separate as well as Na less exposed surface area but less lees Na-Ca bentonites medium swelling less

15、lees,Bentonite fining trial,Hot/cold test Prepare bentonite slurry Add bentonite slurry at different rates into portions of wine samples, e.g. 0-5 g/L Mixed and centrifuged Heating wine samples at 80C for 6 hours Chilling in the fridge overnight Check the turbidity by nephelometer, if the difference

16、 in turbidity between heated samples and unheated samples is greater than 2 NTU, the wine is not protein stabilised,Adding minimum amount of bentonite required for stabilization!,Heating and enzyme addition,(Maragon et al. 2012. Food Chemistry 135: 11571165),Ultrafiltration,Phenolics and polysaccharides,Addition of tannin e.g. Proanthocyanidins immobilized on a rigid inert surface. The immobilized tannin removes protein from white wine in the same way as grape tannin in red wine prod