GAS-CHROMATOGRAPHIC DETERMINATION OF PROPIONIC-ACID AND SORBIC ACID CONTENTS OF RYE BREAD - INTERLABORATORY STUDY

An interlaboratory study of the gas chromatographic (GC) determination of propionic acid and sorbic acid in rye bread was conducted. Homogen ized test portions were extracted with a diethyl ether-phosphoric acid solution. Extracts were analyzed by capillary GC with flame ionizatio n detection. Valeric acid and heptanoic acid were used as internal sta ndards for propionic acid and sorbic acid, respectively. Six rye bread samples (3 blind duplicates) with propionic acid and sorbic acid at 3 concentration levels varying from 0.09 to 0.41% (w/w) were analyzed s ingly according to the proposed procedure by 11 laboratories. For all samples analyzed, repeatability relative standard deviations varied fr om 3.4 to 3.9% for propionic acid and from 1.7 to 3.0% for sorbic acid . Reproducibility relative standard deviations ranged from 5.0 to 8.0% for propionic acid and from 5.1 to 5.9% for sorbic acid. Average calc ulated recoveries from rye bread prepared from spiked dough were 100-1 01% for propionic acid and 101-106% for sorbic acid for 3 concentratio n levels.