QUANTIFICATION OF VARIATION IN TYROSINASE ACTIVITY AMONG DURUM AND COMMON WHEAT CULTIVARS

A quantitative colorimetric microtitre plate assay was developed to me asure levels of tyrosinase and phenol oxidase activity in individual w heat kernels. The kernels were incubated for 2.5 h in a tyrosine solut ion, and the optical density of the soluble pigments was measured spec trophotometrically. The test was performed on 85 durum and 55 common w heat cultivars. The majority of the durum cultivars had low levels of tyrosinase activity, while most hexaploids had high levels of activity . There was an overlap of activity levels between the two, however, so that it was not always possible to distinguish durum wheats from comm on wheats. This assay is simple and non-destructive and would be a sui table test for the screening of material in plant breeding programmes to improve noodle and pasta quality.