Quantitation of 2-acetyl-1-pyrroline in aseptic-packaged cooked fragrant rice by HS-SPME/GC-MS

Aseptic-packaged cooked rice (APCR) is a rice-based food product with a rapidly increasing market size, and APCR made of fragrant rice (FR) has recently appeared on the market. The fragrance of FR is produced by a combination of odoriferous compounds, among which 2-acetyl-1-pyrroline (2AP) has been identified as the most important contributor to overall aroma. This study describes the development of a method to quantify 2AP in FR-based APCR using headspace solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS). The recovery of 2AP spiked into APCR was lower than 10%, which suggests significant matrix effects and inappropriateness of external standard-based calibration. For standard addition calibration method, up to 1,000 ng of 2AP were spiked into APCR containing 0% to 100% FR. Subsequent regression analyses of recovered peak area (Y) as a function of the amount of 2AP spiked (X) yielded highly linear calibration curves (R ² > 0.9917) with consistent slopes (RSD = 2.7%), regardless of FR composition. Y-intercepts, however, which represent the amount of 2AP in APCR without spiking, increased linearly (R ² = 0.9898) in proportion to the composition of FR in the APCR. The amount of 2AP in APCR, determined by extrapolating the standard addition calibration curves, also increased linearly (R ² = 0.9963) as a function of FR composition. Practicality of developed method was tested by monitoring 2AP contents in APCR under realistic storage conditions, which successfully demonstrated 38% and 60% 2AP reductions in APCR of 20% FR after 1 and 2 months of storage at 25°C, respectively. The present study demonstrates that a standard addition method, whereby up to 1,000 ng of 2AP standard is spiked into 4 g of APCR containing 5%-100% FR in a 20-mL headspace vial followed by SPME/GC-MS, may serve as an effective means of quantitating 2AP in fragrant rice-based APCR.