Qualitative and quantitative determination of trace aldehydes and ketones in food preservative propionic acid for quality improvement†
Aiming at the difficulty in qualitative and quantitative analysis of trace compositions in food preservative propionic acid, the trace compositions and the key components influencing the total aldehyde content in propionic acid were analyzed by gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC) and gas chromatography (GC) in this paper. The results show that the food preservative propionic acid contains 18 trace compositions. The main compositions affecting the total aldehyde content in propionic acid are acetaldehyde, propionaldehyde, 1-cyclopropyl-1-propanone and 2-methyl-2-pentenal, which account for ∼90% of the total aldehyde content in propionic acid. The total aldehyde content in propionic acid can be quickly determined by iodometric titration. However, the impurity compositions, solution oxygen content and pH value of propionic acid may affect the stability of NaHSO3, which lead to a higher titration value of the aldehyde content. The total aldehyde contents in propionic acid determined by GC (148.535–337.890 mg L−1) and HPLC (157.730–335.780 mg L−1) are close and reliable with a relative deviation of 0.31–3.00%. The volatile low-carbon aldehydes and ketones including formaldehyde, acetaldehyde and acetone have a weak response and a high detection limit in GC. The derivation conditions of all aldehydes and ketones in propionic acid should affect the determination results of HPLC. It provides the basic data for quality improvement and ultra-deep purification of food-grade propionic acid.