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Type: Conference paper
Title: Black Point of Barley: A Possible Enzymatic Browning Reaction
Author: Hadaway, T.
Collins, H.
Able, A.
Citation: 9th International Barley Genetics Symposium: proceedings, 20-26 June, 2004
Publisher: Czech Journal of Genetics and Plant Breeding
Issue Date: 2004
Conference Name: International Barley Genetics Symposium (9th : 2004 : Brno, Czech Republic)
Abstract: The possibility of an enzymatic browning reaction as the cause of black point in barley was investigated. Black point discolouration appears to be similar to the enzymatic browning characteristic of plant tissues subjected to physical damage, which involves the oxidation of phenolic compounds present in plant tissues by polyphenol oxidase (PPO) or peroxidase (POX) and the transformation of the oxidation products to black or brown pigments. Particularly high levels of oxidative enzymes such as POX and PPO are of particular importance in barley grain, as they are implicated to promote haze, off-flavour and staling of the finished beer. Lipoxygenase (LOX) is widely known to impart cardboard flavour to beer. Activity of the oxidative enzymes PPO, POX and LOX was measured during development of barley varieties differing in susceptibility to black point. The key enzyme for the production of phenolics in plant tissues, phenylalanine ammonia-lyase (PAL), was also measured. In order to determine differences in enzymatic activity of clean and black pointed grains, and hence the suitability of black pointed barley grain for use in malting and brewing, POX, PPO, LOX and PAL was measured during grain development using enzymatic activity assays, isoelectric focusing and Northern blotting for mRNA expression.
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