Proteins and polyphenols were combined in model systems, and the resulting hazes were measured by light scattering. The amount of haze formed depends both on the concentrations of protein and polyphenol and on their ratio. A conceptual model in which a protein molecule has a fixed number of polyphenol binding sites explains the observed behavior and has implications for turbidimetric methods for estimating haze-active protein and haze-active polyphenol in beverages. The ranking of haze-forming activity of the test polypeptides was different with tannic acid than with catechin; this indicates differences in binding site availability, bridging ability, or specificity for the two polyphenols. More haze was observed when model systems were heated, suggesting that polyphenol binding sites are exposed when protein hydrogen bonds are broken. Freshly formed haze dissolved when dimethylformamide or dioxane was added; this may be useful for recovering compounds from isolated hazes for analysis. Keywords: Haze-active protein; haze-active polyphenol; beverages; model systems; gelatin; tannic acid

The haze-forming activity of a polypeptide depends greatly on its proline content. Haze-forming polyphenols have at least two binding groups, each of which has at least two hydroxy groups on an aromatic ring. The protein/polyphenol ratio has a strong influence on the amount of haze formed; the largest amount occurs when the numbers of polyphenol binding ends and protein binding sites are nearly equal. This has important consequences for turbidimetric methods used to measure haze-active proteins and polyphenols in beverages. The ratio also influences the effectiveness of a number of stabilization procedures.

Protein−polyphenol hazes form in beer, wine, and fruit juices and can limit shelf life. Haze-active protein is higher in beer than the other beverages. Haze-active polyphenol is highest in apple juice and red wines, variable in grape juices, and low in beer and white wine. A systematic study of factors that influence haze formation was carried out in a model system. Pectin, arabinogalactan, and poly(galacturonic acid) led to increased haze while free amino acids and other carbohydrates had no effect. Maximum haze occurred near pH 4 with less haze at higher and lower pH's. As ethanol concentration increased near pH 4, the haze at first declined, but further increases in ethanol led to increased haze. It appears that haze formation is similar in all the beverages examined and may be explained by a single mechanism. This has implications for analysis of haze-active constituents and beverage stabilization. Keywords: Haze-active protein; haze-active polyphenol; pH; alcohol; turbidity; beer; wine; fruit juices

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