Since D-lactate-dehydrogenase is available on the market L- and D-lactic acid can be determined separately.
The enzymatic method for determination of L- and D-lactic acids has been tested as to its validity and reproducibility for products of the sugar industry. A standard deviation of ±3-4 % in juices and molasses was found.
A systematic test programm on the variation of the L- and D-lactic acids content from the beet till to the molasses was run. In the beets, we have found an average 13,8 mg L- and 7,3 mg D-laictic acid/100 g pol-sugar and in the raw juice 35,9 L- and 10,7 mg D-lactic acid/100 g pol-sugar. During the extraction Lrllactic acid is mainly formed by microorganisms. The destruction of invert sugar during the juice purification increases the concentration in the thin juice to 177,6 mg L-lactic acid/100 g pol-sugar and 113,9 mg D-lactic acid/100 g pol-sugar.
In average 489 mg invert sugar produce 245 mg lactic acid. The proportion of L- to D-lactic acid, which is obtained during the juice purification, is not equi- molecular. Further investigations have to find out if by chemical destruction of invert sugar more L-lactic acid than D-lactic acid is obtained, or if during the predefecation L-lactic acid is produced by microorganisms.
No details can be given whether lactic acid is formed during the evaporation or how the concentration changes during crystallisation and curing. In molasses we found up to 6 g total lactic acid per 100 g non sugars.
Proceedings: CITS 1971
pdf download: CITS1971-171-186.pdf