Distribution of phytase activity, total phosphorus and phytate phosphorus in legume seeds, cereals and cereal by-products as influenced by harvest year and cultivar

Abstract

Samples of legume seeds, cereals and cereal by-products ( n = 113) grown in south-western Germany and originating from different cultivars and harvest years were analyzed for phytase activity, total phosphorus (P) and phytate P. Phytase activities determined by means of a direct incubation method were lowest in legume seeds and oats (262–496 U/kg dry matter), intermediate in cereals (except oats) (2323–6016 U/kg DM) and highest in cereal by-products (9241–9945 U/kg DM). However, the application of an extraction procedure for the determination of phytase activities in legume seeds resulted in values below the detection limit of 50 U/kg. On average, about 0.67 of total P in legume seeds, cereals and their by-products is bound to phytate. There was a significant influence (P<0.001) of harvest year (1998–2000) on phytate P contents in wheat. Furthermore, total P and phytate P concentrations differed (P<0.05) between different cultivars of wheat. Moreover, phytase activities differed (P=0.023) between different cultivars of barley. Total P and phytate P concentrations were highly correlated in legume seeds ( r = 0.95) and cereal by-products ( r = 0.96) and, to a smaller extent, in cereals ( r = 0.66). Milling of cereal grains to bran and flour revealed that phytase activity, total P and phytate P are highly concentrated (P<0.001) in the outer grain layers of cereals. The influence of preservation of intact legume seeds with propionic acid over a period of 4, 8 or 12 weeks resulted only in a marginal decrease in phytase activity. Due to high native phytase activities in cereals (except oats) and their by-products these feedstuffs may contribute substantially to the gastrointestinal hydrolysis of phytate in non-ruminant animals, whereas the contribution of native phytases originating from legume seeds in terms of improving the availability of plant P seems to be rather limited.