A COLLABORATIVE STUDY ON MEDIA FOR THE ENUMERATION OF YEASTS IN FOODS

A collaborative study was made to evaluate the effectivity of a genera l purpose medium, tryptone glucose yeast extract (TGY) agar on the det ection and enumeration of yeasts from food. Nine laboratories particip ated in the study and compared five media (four kinds of TGY with diff erent concentrations of glucose, one of them without tryptone, and, fo r comparison, dichloran rose bengal chlormaphenicol (DRBC) agar). Six food samples were investigated by each laboratory and 23 additional fo od samples were investigated individually by different laboratories. N o difference was found in the performance of media with either the sam ples common to all laboratories or the various samples tested in diffe rent ones. A medium consisting of tryptone, glucose and yeast extract, at any concentration of glucose tested, appeared reliable for the det ection and enumeration of yeasts from foods, and its performance did n ot differ from that of DRBC. Omission of tryptone as recommended by IS O provided an even simpler medium of equally good performance. TGY wit hout chloramphenicol may result in higher total counts due to the deve lopment of bacteria. DRBC incubated in light results in lower counts c ompared to that incubated in the dark. (C) 1998 Elsevier Science B.V. All rights reserved.