Micro-scale strategy to detect spermine and spermidine by MALDI–TOF MS in foods and identification of apoptosis-related proteins by nano-flow UPLC–MS/MS after treatment with spermine and spermidine

• A simple MALDI–TOF MS method of detecting spermine and spermidine was established.
• Spermine and spermidine were easily extracted by micro-liquid–liquid extraction.
• The proposed MALDI–TOF MS method was used to detect spermine and spermidine in foods.
• An LTQ Orbitrap was used to identify apoptosis-related proteins.

Spermine and spermidine are multiple-nitrogen compounds found in many foods. Both compounds are essential for cell growth and human health. This study established a simple and fast method of detecting spermine and spermidine in food samples by matrix-assisted laser desorption/ionization combined with time-of-flight mass spectrometry (MALDI–TOF MS). After a simple sample preparation procedure, spermine and spermidine were directly detected by MALDI–TOF MS with no additional purification procedure. The calibration curves for spermine and spermidine ranged from 0.1 to 10 μg/mL. In intra- and inter-batch assays of three different concentrations of spermine and spermidine, all relative standard deviations and relative errors were below 18.9%. These experimental results confirmed the practicability and effectiveness of the proposed MALDI–TOF MS method for fast determination of spermine and spermidine in food samples. Furthermore, since spermine and spermidine have important roles in apoptosis, up-regulation and down-regulation of spermine and spermidine during apoptosis were analyzed. After treating NRK-52E cells with spermine and spermidine, the cells were lysed, and cell proteins were collected, and digested. Apoptosis-related proteins were then identified by tandem MS.