METHODS FOR THE SEPARATION OF YEAST-CELLS FROM THE SURFACES OF PROCESSED, FROZEN FOODS

More aggressive pre-isolation treatments of samples, such as vigorous shaking, jet-streaming with excess of water and sonication, were applied in sequence to the study of yeast ecology of the surface of several frozen foods. The conventional isolation method based on bland shaking was unable to disengage yeast cells from their substrates in most of the cases, while each more aggressive treatment caused progressive separation of colony-forming units (cfu) along the sequence of application of the three procedures. Altogether, in the majority of cases, a few colony forming units were found on the surface of frozen fish, poultry, vegetables and mushrooms. Conversely, the numerically poor yeast flora is almost constantly represented by many species, always different from those found on the surface of the same foods in nature before processing. The uniformity of the composition of the yeast flora throughout the four different categories of foods excludes any possible occasional origin of the yeast colonization and probably indicates a processing plant origin.