Studies on Cucumber Softening under Commercial Salt - Stock Conditions in Ontario 1 II . Pectolytic Microorganisms Isolated

The investigation of cutcumber softening can be traced back to the turn of the centuiry when Aderhold (1899) described a sporeforming organism, which he called Bacterium coli, as the cauise of this spoilage. Kossowicz (1908), however, implicated the genus Bacillus and further work by Rahn (1913), LeFevre (1919), and Joslyn (1929) confirmed and extended this theory. Fabian and Johnson (1938) contiinuied the study of the aerobic, sporeforming, mesophilic bacteria and were successful in isolating Bacillus mesentericus futscus (Bacillus subtilis) from brine containing soft cucumbers. It was shown that this organism grew readily in 9 per cent salt, 0.2 per cent acetic acid, and 0.3 per cent lactic acid. In addition, it was shown that the cultural filtrate of this organism, after growth in beet molasses medium, caused spoilage of firm desalted cucumbers in 24 hr. Despite the evidence implicating the genus Bacillus, it is generally considered that this group probably plays a very minor role in softening under normal curing conditions. Fabian and Johnson (1938) were probably the first to cast doubt on this theory wvhen they found the pectic enzymes of B. subtilis were inhibited by 2 per cent salt. They were able to increase the salt tolerance of the enzymes to 7 per cent salt by continuous culture at high concentrations of salt, but as softening occurs at much higher levels, it was concluded that spoilage by this organism was unlikely. More recently Nortje and Vaughn (1953) carried ouit qualitative studies with B. subtilis and Bacillus pumilis in relation to cucumber softening and indicated further doubt as to the importance of bacterial spore-formers as causal agents. The pectolytic enzyme complex of B. subtilis, similar to polygalacturonase, was found to be most active at pH 8.6 and reasonably stable in an alkaline environment, but lost its activity under acid conditions. Vaughn et al. (1954) concluded that species of Bacillus would carry out softening of brined cucumbers only if