STERILIZATION OF SOYBEAN COTYLEDONS BY BOILING IN LACTIC-ACID SOLUTION

The effect of pH on the heat resistance of Bacillus stearothermophilus spores at 100 degrees C in the presence of 0.11 mol l(-1) lactic acid and 0.2 mol l(-1) sodium phosphate buffer was examined. At pH values of 7.0 and 6.0 spores survived 60 min exposure unharmed but at pH 4.3 and 3.0 they died with decimal reduction times (DRTs) of similar to 27 min and similar to 2.8 min, respectively. Death rates ere similar in the presence or absence of hydrated soybean cotyledons. In the presenc e of phosphate buffer and cotyledons at mean pH 3.6 the DRT was simila r to 118 min but in the presence, in addition, of lactic acid it was s imilar to 11 min. It is suggested that the enhanced death rate nias du e to toxic effects of undissociated lactic acid. Rhizopus oligosporus NRRL 2710 grew well on cotyledons, having pH values from 7.0 to 3.7, p repared by boiling for 60 min in the presence of 0.11 mol l(-1) lactic acid and 0.2 mol l(-1) phosphate buffer.