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Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)

Abstract

When acetylmethylcarbinol or diacetyl was added to a tomato bouillon culture of one of the citric acid fermenting streptococci normally present in butter cultures, there was a rapid disappearance of the added reagent and an increase in 2,3-butylene glycol. The amount of the glycol produced accounted, in a general way, for the acetylmethylcarbinol or diacetyl that disappeared. The added reagent did not usually disappear completely. In trials with acetylmethylcarbinol the change of the carbinol to the glycol was delayed when sulfuric acid was added in amounts to yield a pH of from 3.8 to 4.0.

There was also a change of acetylmethylcarbinol or diacetyl to 2,3-butylene glycol when one of these reagents was added to a milk culture of one of the organisms. With the diacetyl there was an increase in the acetylmethylcarbinol as well as in the 2,3-butylene glycol, and the increase in the carbinol was greater than the increase in the glycol. The added reagent did not disappear completely in any of the trials.

When various amounts of sulfuric acid were added to milk cultures of the organisms, acetylmethylcarbinol was not produced at the higher pH values but was produced at the lower values, while 2,3-butylene glycol was produced at both the higher and lower pH values. There was less of the glycol formed at the lower pH values than at the higher ones. The total molarities of acetylmethylcarbinol and 2,3-butylene glycol showed an increase as the pH was lowered, although there were some irregularities in the increase with one of the organisms.

The addition of 0.65 percent citric acid to a milk culture of one of the organisms resulted in an increase in both acetylmethylcarbinol and 2,3-butylene glycol.

The reduction of acetylmethylcarbinol, which had been added to a milk culture of one of the organisms, to 2,3-butylene glycol was not delayed by potassium nitrate in the quantity used but was delayed by the largest amount of hydrogen peroxide employed.

In pure cultures of the citric acid fermenting streptococci which had been acidified with sulfuric acid to a pH of about 3.9, the addition of acetaldehyde or propionaldehyde increased the amount of acetylmethylcarbinol present after 96 hours at 21 °C. but decreased the amount of 2,3-butylene glycol and also commonly decreased the total molarities of the two compounds. These results suggest that the increased production of acetylmethylcarbinol is accounted for by a decrease in the reduction of the carbinol to the corresponding glycol, rather than to an aldehyde condensation involving, in part, the added aldehyde.

In butter cultures the decrease in acetylmethylcarbinol was accompanied by an increase in 2,3-butylene glycol, and there was commonly an increase, from one examination to the next, in the total molarities of the two compounds. When ripened butter cultures were neutralized to a low acidity there was a rapid decrease in the acetylmethylcarbinol, and in some of the trials this was followed by an increase. The decrease in the carbinol was accompanied by a rapid increase in 2,3-butylene glycol, and there was also an increase in the total molarities of the two compounds. Hydrogen peroxide, in certain concentrations, delayed the reduction of acetylmethylcarbinol to 2,3-butylene glycol as did also 1 percent sodium fumarate or 12 percent sodium chloride. Ice water temperatures also delayed the reduction in either neutralized or unneutralized cultures, but the reduction was more rapid with neutralization than without.

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