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Rapid Gas Chromatographic Technique for Quantifying 2-Acetyl-1-Pyrroline and Hexanal in Rice (Oryza sativa, L.)

¹USDA, ARS, Rice Research Unit, 1509 Aggie Drive, Beaumont, TX 77713. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Email address: c-bergman@tamu.edu ³Texas A & M University, Agricultural Experiment Station, 1509 Aggie Drive, Beaumont, TX 77713. ⁴USDA, ARS, Dale Bumpers National Rice Research Center, 2890 Hwy 130 E., Stuttgart, AR 72160. ⁵USDA, ARS, Southern Regional Research Center, P.O. Box 19687, New Orleans, LA 70179. ⁶Mississippi State University, Department of Food Science and Technology, Box 9805, Mississippi State, MS 39762. ⁷USDA, ARS, Rice Research Unit, 1509 Aggie Drive, Beaumont, TX 77713 (retired).

The aroma of rice plays a role in its consumer acceptability. The popcorn-like smell of aromatic rice stemming primarily from its 2- acetyl-1-pyrroline (2-AP) content is considered desirable by many consumers. Conversely, hexanal has been correlated with off odors in rice that develop from lipid oxidation. A rapid method for 2-AP and hexanal quantification suitable for use in breeding programs, large-scale research efforts, and quality assurance programs is needed. While developing such a method, sample preparation (degree of milling, particle size), solvent extraction time and temperature, and gas chromatographic parameters were studied. Particle size had no influence on 2-AP or hexanal recovered. One extraction solubilized ≈80% of the 2-AP and 56% of the hexanal present in milled rice. The optimum extraction method was assessed to require 0.3 g of ground brown or milled rice in methylene chloride held at 85°C for 2.5 hr. The complete gas chromatographic run requires ≈25 min, and 50 samples can be analyzed per day. The optimized method's linear response (R² = 0.99) and reproducibility was demonstrated. The stability of 2-AP and hexanal in frozen milled rice and in refrigerated methylene chloride extracts was excellent for at least six months. Milled and unmilled commercial and breeders' aromatic rice samples contained 10–1,104 ng/g of 2-AP and 148–2,541 ng/g of hexanal. Genotype had the greatest effect on the 2-AP and hexanal content of two lines grown over four years and in four states.