EFFECT OF DILUENT TYPE ON VIABILITY OF YEASTS ENUMERATED FROM FOODS OR PURE CULTURE

The effects of seven diluent types on the viability of yeasts enumerat ed from foods and in pure culture were studied. The diluents were labo ratory glass distilled water; saline water (0.85% NaCl), sodium phosph ate buffer (0.1 M, pH 7.0), 0.1% peptone, 0.1% yeast extract, 0.1% pep tone in 0.1 M sodium phosphate buffer, pH 7.0, and 0.1% malt extract. For all foods studied, dilution in 0.1% peptone gave the highest count s, with saline and phosphate buffer diluents giving lower counts than those obtained with distilled water. When seven species of yeast were enumerated in pure culture, highest counts were obtained using 0.1% pe ptone as the diluent and, with three exceptions, all species gave high er counts when diluted in diluents other than distilled water. When ye ast suspensions were held in diluents for up to 2 h before plating, ce ll death occurred. The extent of death was highest in distilled water, saline and phosphate buffer diluents. Cell death also occurred in 0.1 % peptone, yeast extract and malt extract, but to a lesser degree. (C) 1997 Elsevier Science B.V.