D-Isocitric acid is an organic acid found in most fruit juices. It is an important marker in multicomponent procedures for the evaluation of authenticity and quality of fruit products; high citric/isocitric acid ratios can be used as an indicator of citric acid addition in some juices.
PRINCIPLE:
D-Isocitric acid is oxidised by nicotinamide-adenine dinucleotide phosphate (NADP+) to 2-oxoglutarate and CO2 in the presence of isocitrate dehydrogenase (ICDH), with the formation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) (1)