Gelatin index

The procedure consists of adding 5 ml of cold-soluble gelatin solntion (70 g/1) to 50 ml of red wine. After three days, the wine is centrifuged and the tannins (LA) in the supernatant diluted to 1/50 are assayed to determine the tannin concentration Cl (g/1). Co is the tannin concentration of the control, prior to the addition of gelatin. The gelatin index is given by the equation ... 

Making objective measurements of these basic sensations is particularly complex. However, the gelatin index provides an estimate of reactivity to proteins. The intensity of the polyphenol-gelatin reaction depends on conditions in the medium. Acidity is a favorable factor, unlike alcohol content, which inhibits the reaction and gives a sweet taste. The reaction is independent of the tannin concentration at values above 50 mg/1 (Glories, 1983). Under given reaction conditions, it is thus possible to classify the various polyphenols according to their aptitude to combine. 

Table 6.9. Influence of the structure of different groups of phenolic compounds on the reactivity of the molecules (gelatin index) and the tasting qualities, in wines of different ages (Glories, 1992, unpublished)...

Table 6.10. Effect of terroir (soil and microclimate) on the reactivity to proteins of tannins in wine gelatin index and tannic strength (TS) (Merlot from Saint-Emilion, 1992 vintage) (de Freitas, 1995)...

Vineyard Tannins (g/1) Gelatin index Tannic strength (NTU) Tasting notes... 

It is difficult for tasters to distinguish between astringency and bitterness. Mirabel (2000) demonstrated that the gelatin index was preferentially... 

OD 280 Tannins (g/1) Anthocyanins (mg/1) Polysaccharides (mg/1) Dialysis index Gelatin index... 

It is therefore possible to modulate the organoleptic impact of oak barrels on wine (not only aromatic character but also overall structure) by choosing a different toasting level. The HCl value and gelatin index decrease with heating intensity, indicating a softening of the tannins (Chatonnet,... 

Coacervate drops were quite unstable to pH alterations of the system. The stability of coacervate systems to pH variations was evaluated by measuring the turbidity of systems adjusted to various pH values since turbidity of the mixture serves as an index of the degree of coacervation (17). The coacervate systems formed with gum arabic and protein consisting of 10% kappa-casein and 90% gelatin, at pH 3.8, were most stable at pH 3.8. Some of the coacervates persisted when the pH was varied one pH unit, but were completely dissolved at pH 2.0 and below, and pH 6.0 and above, as shown in Table IV. 

Dichromated gelatin is an attractive material because of its large index change and its usefulness in the visible, particularly with an argon laser (488, 514.5 nm). Its major disadvantages are some sensitivity to humidity, the requirement for wet processing, and the fact that it cannot be used in very thick films. 

---