Evaluation of Methods for Determination of Spore-Formers Responsible for the Late Gas-Blowing Defect in Cheese

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Abstract
Late gas-blowing is a defect of European specialty cheeses caused by certain spore-forming bacteria of the genus Clostridium. Five most probable number methods for detecting spores were evaluated: a modified Weinzirl, NIZO-Ede, Fryer/Halligan, BB-lactate, and the BB-lactate with modification using pure cultures of C. butyricum, C. sporogenes and C. tyrobutyricum inoculated into sterile homogenized milk. Tubes containing media of the different methods were incubated for 14 d at 32.degree. C for C. butyricum and 37.degree. C for C. sporogenes and C. tyrobutyricum. The modified Weinzirl and NIZO-Ede methods took the longest time to indicate gas formation (blowing) and detected the spore-formers less frequently. The Fryer/Halligan and BB-lactate methods, which contain lactate, detected spores quicker. No apparent differences were observed between the Fryer/Halligan and BB-lactate methods. The BB-lactate method was modified by making the medium semisolid by addition of 0.2% agar, eliminating the use of Durham tubes, and using an agar plug rather than paraffin. These modifications resulted in a simpler, more sensitive method.