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Application to the dairy industry of the toluidine blue-membrane filter method for estimating dry mass of bacteria - dissolution of whole milk and cream for filtration

Authors: D.K. O'Toole


Dilution methods were developed to make whole milk and cream filterable through tortuous pore membrane filters so that the toluidine blue-membrane filter method could be applied to these substrates. Bacteria and somatic cells in milk and cream were spread evenly and uniformly over the filter by the addition of 1mL of substrate to 9 mL of either 5% Triton X200 (TX) or a mixture of 2.5% TX and 2.5% Tween 80 (TX-T80) at 60°C, mixing vigorously and followed immediately by the addition of 1 mL of 10% sodium tripolyphosphate before filtration. Some fat remained on the filter but it could be removed by dipping the filter in diethyl ether after filtration. The effects of TX and TX-T80 diluents on four organisms were compared by measuring the absorbance of stained cells. The TX diluent caused a 6% reduction in absorbance values when compared with TX-T80 and the latter is recommended as a consequence. It may be possible to use this procedure with the toluidine blue-membrane filter method to measure somatic cells in milk.

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