Gallic acid profiling

Tannins are present in the skins of red grapes and play an important part in the flavor profile of red wine. Tannins in grapes are usually estimated in terms of the content of gallic acid (Amerine and Joslyn 1970). 

Fig. 2 High-performance liquid chromatographic profile of a standard solution at 280, 320, and 350 nm. Separation was achieved with an analytical HPLC unit (Gilson), using a reversed-phase Shepherisorb ODS2 (25.0 x 0.46 cm 5 pm particle size) column. The solvent system used was a gradient of water/formic acid (19 1) (A) and methanol (B). The gradient was as follows 0 min, 30% B 15 min, 30% B 20 min, 40% B 30 min, 45% B 50 min, 60% B 53 min, 100% B and 55 min, 100% B. Detection was accomplished with a DAD. 1—Gallic acid (hydroxybenzoic acid) 2—caffeic acid (hydroxycinnamic acid) 3—mangiferin (xanthone) 4—ferulic acid (hydroxycinnamic acid) 5—eriodictiol (flavanone) 6—hemiarin (coumarine) and 7—quercetin (flavonol).

A simple CZE method, using a borate buffer at pH 9.5 and UVD at 280 nm, was applied for analysis of Spanish red wines. Although the electrophoretic profile was similar for different wines, the quantitative analysis varied much between them. The following phenolic components were identified (—)-epicatechin (2), (+)-catechin (3), (—)-epigallocatechin (74), syringic acid (70), vanillic acid (38), gallic acid (8), protocatechuic... 

Figure 5.12 Release profiles of gallic acid from chitosan-sodium alginate (CSA) microcapsules immersed in phosphate buffer saline (PBS) of pH 5.0 and pH 5.4.

We see an accumulation of 6 peaks (peak 1-6). The non-identified compound at Rt= 19 might be assignable to morroniside (3) according to the UV-spectrum. Peak 6 shows nearly the same UV-profile as gallic acid (1) and could be assigned to a more lipophilic galloylester. 

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