Protein analysis, tannins used

Sami-Manchado, P. et al.. Analysis and characterization of wine condensed tannins precipitated by proteins used as fining agent in enology. Am. J. Enol. Viticult., 50, 81, 1999. 

Quantitative Analysis of Tannins. Beginning with determinations for total phenolic compounds, all attempts to isolate compounds related to tannins—i.e., those forming stable compounds with proteins—have been unsatisfactory. Hence, one cannot use this as the basis for an analytical method. 

Analysis of vegetable tannins is used to determine the tannin content in the extract solution from the raw or spent materials. The tannin analysis method set up by the American Leather Chemists Association (ALCA, 1954a) is based on the absorption of materials from the extract by hide protein. It is not based on chemical analysis of a true tannin molecule. 

One reason that precise and quantitative assays for tannin determinations have been difficult to develop is that tannins encompass a heterogeneous group of compounds and polymers. However, several assays have been developed to estimate tannin levels in extracts, and an excellent review is available (18). Many of these assays are based on either the reduction capabilities of polyphenols or the propensity of tannins to form precipitates with various proteins. The following two assays are best used as a qualitative analysis for the presence or absence of particular tannins, but can be used with standards for approximate tannin determinations. 

Of the tree nuts, only the almond and hazelnut kits have been evaluated in independent studies. In December 2004 the Veratox Almond kit completed a full evaluation in seven laboratories that met the criteria for it to be added to Health Canada s Compendium of Food Allergen Methodologies (Health Canada, 2004). Although this evaluation does not confer endorsement of the method, the consistent approach adopted means that the methods can be used for enforcement in Canada should it be required. The study required 630 samples to be analyzed by the laboratories 10 replicates at each of three levels (0, 6.25, and 15.63 ppm) in cookies and in milk and plain chocolate. The kit produced satisfactory results for the matrices and at the levels tested. Analysis of plain chocolate produced the lowest recoveries, as expected, due to the presence of tannins and other phenolic compounds that interfere with the extraction of proteins. 

Protein binding has been used in various guises as a method for analysis of tannins and tannin-containing extracts. The hide powder method has been used for decades in the leather industry. More recently, methods based on the residual absorbance of unprecipitated hemoglobin (10), radiometric titration with labelled bovine serum albumin (BSA) (51), and the ferric chloride induced color of protein-tannin complexes resolubilized in alkali (50) have all been suggested as methods of tannin analysis. 

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