Degree of hydrolysis of some vegetable proteins used as fining agents and its influence on polyphenol removal from red wine
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The increasing demand for economic and efficient wine fining leads to the search for alternatives to traditionally used proteins, preferably new products with the side effect of non-allergenicity. A comparative fining trial on laboratory scale with equal quantities of vegetable proteins, partly used for the first time as fining agents for wine in Germany, was accomplished. Spectrum of wheat, rice, maize and potato proteins was expanded by enzymatic hydrolysis, additionally to evaluate influence of protein structure on fining effects. Proteins were modified by two different enzymes, proline-specific endopeptidase (PeP) and alcalase. Molecular weight distributions and degree of hydrolysis (DH) were compared to color intensity and HPLC data of phenolic marker substances primarily responsible for bitterness and astringency. With a total of 20 different varieties of fining agents, statistical evaluation was performed for a rapid exploratory analysis of taste improvement without the need for sensorial tests. Overall, influence on phenol composition and color intensity decreased with the degree of proteolysis. The effect of maize proteins and corresponding hydrolyzates was rather low, whereas maize proteins were nearly not influenced by the use of 2 different peptidases. Wheat proteins with highest proline content (about 9–10%) and molecular weight fractions of 14 and 30–45 kDa had a pronounced effect on color intensity. Rice and potato proteins with only half of proline content and molecular weight fractions mainly ranging between 10 and 32 kDa showed less effect on wine color, but preferably on phenolic marker compounds mainly responsible for bitter and astringent taste sensations.