Characterization of Volatile Aroma Compounds in Cooked Black Rice

Abstract

Black rice ( Oryza sativa L.), an aromatic specialty rice popular in Asia, has a unique flavor, the volatile chemistry of which has not been reported. The objectives of this research were to study volatile profiles of cooked black rice and to characterize the odor-active compounds. Thirty-five volatile compounds were identified by gas chromatography-mass spectrometry using a dynamic headspace system with Tenax trapping. Aldehydes and aromatics were quantitatively in the greatest abundance, accounting for 80.1% of total relative concentration of volatiles. The concentration of 2-acetyl-1-pyrroline (2-AP) was high, exceeded only by hexanal, nonanal, and 2-pentylfuran. A total of 25 odor-active compounds, determined by gas chromatography-olfactometry, were applied to principal component analysis, demonstrating significant differences between a black and a traditional white rice cultivar in terms of aroma and explaining 93.0% of the total variation. 2-AP, guaiacol, indole, and p-xylene largely influenced the difference between the aroma in cooked black and white rice. 2-AP and guaiacol were major contributors to the unique character of black rice based on odor thresholds, relative concentrations, and olfactometry.

Comparison of Volatiles in Cooked Rice with Various Amylose Contents

“…The volatiles detected in the cooked rice consisted of aldehydes, ketones, alcohols, heterocyclic volatiles, fatty acids, fatty esters, and phenolic volatiles ( Table 2). The results are consistent with previously reported rice volatiles extracted by different methods (Buttery et al, 1988;Jezussek et al, 2002;Widjaja et al, 1996;Yang et al, 2008aYang et al, , 2008b. One target m/z ion for each volatile was calculated as the method commonly used for metabolite profiling (Ochi et al, 2012), which provided relative levels of the volatiles, and not absolute quantities ( Table 2).…”

Analysis of Volatile Compounds in Shochu Koji, Sake Koji, and Steamed Rice by Gas Chromatography-Mass Spectrometry

“…It is known that hexanal is produced nonenzymatically or by an unknown pathway from linoleic acid in rice 12,19,25 . Moreover, it was previously shown that aldehydes represent the highest percentage of total volatiles in cooked rice 24 , and dimethyl trisulfide has been identified as one of the compounds that make a significant contribution to the odour of rice cakes 3 . Accordingly, it is assumed that these aliphatic aldehydes and sulfide compounds were produced by steam heating, and were then reduced during the koji production process.…”

Characterization of Volatile Compound Profiling of Germinated Brown Rice Revealed by Headspace Solid-phase Micro Extraction Coupled to Gas Chromatography Mass Spectrometry

“…Benzaldehyde showed relatively high contents among the aromatic compounds detected. The relative abundance of 2-pentylfuran was up to 279.58 μg/kg, showing high concentration similar to rice when compared with other volatiles contained in individual samples [7]. Simultaneously, 2-pentyl-furan, benzaldyhyde and 2-Methoxy-4-vinylphenol contributes to the unique roasted and nutty aroma [14].…”

“…A total of nine aldehydes were detected, with the levels ranging from not found to 802.29 μg/kg. The major aldehydes with high concentration included hexanal, heptanal, pentanal, nonanal, decanal, and octanal, which are also the commonly found in different cultivars of polished rice or BR [6], [7], suggesting that GBR retains the qualitatively similar flavor profiles even after germination by soaking in water for a certain duration. It was worth noting that aldehyde compounds often give grass and fresh odor at a sufficiently low concentration in the samples, but high levels of these compounds lead to the sniffing of rancidity.…”