Abstract
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.
Highlights
Rice is the most important staple food in the Korean diet
This phenomenon is fairly common in headspace techniques (Sriseadka et al, 2006) and solid-phase microextraction (SPME)-based quantitative studies and is due to the kinetic capacity of an analyte partitioning into the sorbent material on an SPME fiber (Semenov, Koziel, & Pawliszyn, 2000)
The slopes of calibration curves, representing the increase in recovered 2AP per unit increase in the amount of spiked 2AP amount, were consistent (RSD = 2.7%) regardless of the proportion of fragrant rice (FR) in the aseptic-packaged cooked rice (APCR) samples (Figure 3a). These findings suggest that the relative proportions of FR and non-FR do not influence the matrix effects of APCR on quantitative measurements of 2AP
Summary
Rice is the most important staple food in the Korean diet. Its consumption, has rapidly decreased from 142.4 kg per capita in 1986 down to 61.8 kg in 2017 (Korean Statistics Information Service, 2018). Consumption patterns have changed from home-cooked rice to diverse rice-based processed foods such as noodles, cakes, snacks, and drinks (Oh et al, 2010) Among these processed foods, the popularity of aseptic-packaged cooked rice (APCR) is rapidly increasing. Solid-phase microextraction (SPME) coupled to GC-MS has become increasingly popular due to its simplicity, speed, and high sensitivity This method boasts the ability to simultaneously obtain a full profile of the volatile compounds found in rice (Grimm, Bergman, Delgado, & Bryant, 2001; Hinge, Patil, & Nadaf, 2016; Hopfer, Jodari, Negre-Zakharov, Wylie, & Ebeler, 2016; Laguerre, Mestres, Davrieux, Ringuet, & Boulanger, 2007; Maraval et al, 2010; Poonlaphdecha et al, 2012). This report describes a method for quantitating 2AP in FR-based APCR
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