Polyphenolic substrates of cationic and neutral/anionic peroxidases from barley and malt using a chronometric method for the determination of pod activity

4-methylcatechol, phenolic acids from the benzoic and cinnamic series, flav an 3-ols and L-tyrosine were tested to determine the catalytic behavior of barley peroxidases (POD) at the expense of hydrogen peroxide. A chronometri c assay using L-ascorbic acid was described for determining the peroxidatic activity of basic and neutral/anionic enzymatic fractions. The effects of hydrogen donors H2O2, and Ca++ ion concentrations and pH were studied to se t maximal conditions for POD measurement. The sensitivity to endogenous phe nolic compounds (ferulic and p-coumaric acids, (+) catechin) along with caf feic acid for POD fractions was investigated and compared with their respon se versus guaiacol. Under the conditions tested, syringic and sinapinic aci ds as well as L-tyrosine were very weakly oxidized by POD from barley, wher eas ferulic and caffeic acids were rapidly transformed. Levels of POD activ ity extracted from barley, green malt and kilned malt crude extracts were t hereafter compared.