“…Potential causes of the "black ring" defect include a boron deficiency during beet root development (Halbrooks, 1981), the presence of oxygen in the can headspace (Vilece et al, 1955), microbial activity (Cameron et al, 1936), nonenzymic browning (Parkin and Im, 1990) or the action of oxidative enzymes (Stevenson, 1925;Boscan et al, 1962: Lee andSmith, 1979).…”