Proanthocyanidin-free barley for brewing: progress in breeding for high yield and research tool in polyphenol chemistry.
von Wettstein, D., Nilan, R.A., Ahrenst-Larsen, B., Erdal, K., Ingversen, J., Jende-Strid, B., Kristiansen, K.N., Larsen, J., Outtrup, H. and Ullrich, S.E.
Proanthocyanidins (anthocyanogens) of barley consist mainly of dimers and trimers of (+) catechin (+) gallocatechin units. The biosynthetic pathways have been studied by the use of mutants with genetic blocks in these pathways and by feeding labelled precursors and intermediates to developing caryopses. A large number of chemically induced mutant proanthocyanogen (PA)-free barleys were obtained and the best ones used in breeding programmes. The majority showed more or less severe defects in agronomic characteristics. The mutant "ant 17-148" (Galant) isolated from Triumph yielded almost as well as the parent variety (99.7% in 1982 and 95.4% in 1983). Crosses of the mutant "ant 13-13" from Foma with Rupal and Nordal gave yields comparable with currently grown North American malting barleys. The absence of proanthocyanidins did not result in any increased susceptibility to lodging or disease. Malting quality of PA-free barleys was evaluated by micromalting. Results indicate a more rapid uptake of water and tendency to quicker modification unless steeping time is reduced. When this is done satisfactory analyses are obtained. PA-free barleys showed unimpaired feeding quality in trials. The colloidal stability of beers brewed with PA-free malt was in all cases markedly superior to control beers and taste panels scores were, on average, identical. The use of PA-free hop extracts or of natural hops with a low PA to alpha acid ratio enabled the colloidal stability advantages to be fully realised. A study of the polyphenolic materials associated with proanthocyanidins has begun. These are present in mutants "ant 17" and "ant 18" but are eliminated in mutant "ant 13". They appear to have no significance for colloidal or flavour stability.
Keywords: anthocyanogen barley beer breeding brewing haze malting mutant polyphenol procyanidin