Nephelometry as a Method for Studying the Relations Between Polyphenols and Proteins

Abstract

The conditions to be fulfilled by a nephelometer intended to tackle the problems of the colloidal stability of beers are reviewed in the light of 30 years of original work in the author's laboratory. Emphasis is put on the various methods involving the kinetics of the formation of the proteotannic hazes which can be studied from either the proteinic side or the polyphenolic side. They are all simple, quick, sensitive, inexpensive yet highly discriminant methods some of them being routinely used for many years in the control laboratories of some brewing companies. Experience has lad to the realisation that a universal nephelometer especially developed for the needs of the brewing industry can be applicable to the numerous fields where polyphenolics are involved.

125th Anniversary Review: The Non-Biological Instability of Beer

“…Perhaps of rather more value are tests in which colloidally sensitive materials are forced out of solution. The most famous of these is the Chapon test 30 , in which a sample of beer is chilled to -8°C without freezing (added alcohol prevents freezing) and left for 8 hours before the chill haze is measured. This type of test is especially valuable because any material that displays a tendency to fall out of solution is likely to be detected in this test, which combines the very low temperature and the added precipitant (ethanol).…”

Measurement of HGB beer colloidal ageing and tannoid content development using complex turbidimetric analysis.

“…Je zaměřena na hledání korelace mezi vývojem obsahu tanoidů stanoveným metodou dle Chapona [11] a vývo-jem chladového zákalu během zrychleného stárnutí [12] ředěného a neředěného HGB piva s cílem získat detailnější analytické informace o příčinách koloidní nestability finálně stočeného produktu [13,14]. Pro ilustraci je studie doplněna o výsledky testů obsahu citlivých bílkovin (titrací taninem) a stanovení prahu precipitace bílkovin (titrací nasyceným roztokem síranu amonného) [15].…”

“…Po korekci na hranici rozlišitelnosti stanovení tanoidů (okolo 10 mg PVP/l) [15] jsou počáteční hodnoty obsahu tanoidů ředěného piva v korelaci s ředicím poměrem. Tento výsledek je ve shodě s měřeními McMurrougha [18].…”

Prediction of Colloidal Stability of Highly Stabilized Beers by a Modified Chapon Tannoid Content Test

“…Tannoids include low and medium molecular weight polyphenols, the polymers of catechin and antho-cyanogens. The tannoid content of beer, wort, barley, malt and hop extracts can be determined by precipitation with PVP 7,8 . This polymer, which can be considered as a structural analogue of proteins, binds with tannoids to give rise to haze.…”