Lactic acid and lactose were estimated by utilizing a Waters high pressure liquid chromatography unit (Waters Instruments, New Milford, Mass.). Propionic acid (HPr) and acetic acid (HAc) were assayed by gas chromatography. A Packard Model 5880A with a capillary column (J & W DX4 column) and a flame ionization detector were used. The column temperature was programmed to begin at 90° C. and increase to 250° C. at a rate of 10°/min., injector and detector temperatures were 275° C. The carrier gas was helium with a flow rate of ml per minute. Samples were prepared by adding 5 ml of broth to 45 ml of 2% H 3 PO 4 containing a valeric acid internal standard. Cells and other suspended solids were removed by filtering through a micron acrodisc (Gillman Scientific). One microliter of the acidified filtrate was injected using a ul Hamilton N701 syringe. Results were calculated from a standard curve.