Long-chain polyphosphates inhibit growth of Clostridium tyrobutyricum in processed cheese spreads

The effect of novel food-grade long-chain polyphosphate formulations (JOHA HBS sodium polyphosphate glassy, 69 +/- 1% P2O5, and two similar salts (HBS-1 and HBS-9) on the growth of Clostridium tyrobutyricum ATCC 25755 in liquid culture and in pasteurized, processed cheese spreads was evaluated. In broth, 0.1% polyphosphate was sufficient to inhibit vegetative growth of the organism. In addition, a panel of 21 other gram-positive and 11 gram-negative bacteria were tested for their sensitivity against the polyphosphates. Whereas 17 of the gram-positives could be inhibited by 0.05 to 0.3% polyphosphate, none of the tested gram-negatives were affected. Two different cheese spread formulations (cheese blend A: 55% moisture, 47.2% fat in dry matter; cheese blend B: 55% moisture, 57% fat in dry matter) were fortified with 0.1% to 1.0% polyphosphates, inoculated with 5 x 10(5) (cheese blend A) or 2.5 x 10(6) (cheese blend B) C. tyrobutyricum spores per gram, and incubated at 35 degrees C for up to 7 weeks. Determination of viable cell counts was carried out at days 1, 9, 19, and 49 (cheese blend A) and 8, 16, 27, 35, and 50 (cheese blend B). While 0.1% polyphosphate had little effect, higher concentrations were increasingly inhibitory to growth from a spore inoculum, to cell multiplication, and to gas formation. With 0.5% polyphosphate, onset of growth was delayed for about 3 weeks in cheese blend A, while this concentration was able to inhibit the organism in cheese blend B. In view of the experimental parameters selected (high initial contamination level; intrinsic and extrinsic parameters optimized for growth of clostridia), 0.5% polyphosphate may be sufficient to control C. tyrobutyricum growth under ''normal'' conditions, where initial spore counts are rather low, and storage temperatures are usually at or below 20 degrees C. Moreover, clostridia were completely inhibited by 1.0% polyphosphate, which clearly indicated the usefulness of these polyphosphates for prevention of butyric blowing in pasteurized processed cheese spreads.