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 × 105 (cheese blend A) or 2.5 × 106 (cheese blend B) C. tyrobutyricum spores per gram, and incubated at 35°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°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.
Keywords: cheese spread; inhibition; polyphosphate.