Abstract
Volatile compounds in raw and cooked black rice (cv. Sintoheugmi) samples with different degrees of milling (step 0, 0%; step 1, 4.2%; and step 2, 10.5%, w/w) were investigated by headspace solid-phase microextraction and gas chromatography–mass spectrometry. A total of 101 volatile compounds were found. Among them, 44 compounds found in raw black rice were absent in cooked black rice and 20 compounds were newly formed in cooked black rice. The 8 identified major odor-active volatile compounds in raw and cooked black rice included 3 phenols (guaiacol, 4-vinylphenol, and 2-methoxy-4-vinylphenol), 2 benzenes (benzaldehyde and p-xylene), 2 furans (2-butylfuran and 2-pentylfuran), and 1 terpene (calamenene). Additionally, fatty acid oxidation products such as hexanal, 2-nonenal, octanal, and 2-pentylfuran were found in raw and cooked black rice samples. The relative concentrations of these volatile compounds were significantly higher in step 0 than in step 2 of raw and cooked black rice (p < 0.05). Partially milled cooked black rice (i.e., step 1) contained ~ 80% guaiacol (a favorable unique black rice flavor) of unpolished rice (step 0), with similar levels of several lipid oxidation indicator volatile products (e.g., 2-nonenal and 2-pentyl furan) of fully milled rice (step 2). Thus, partially milled black rice should be consumed rather than fully milled black rice.
Highlights
Black rice has received attention from the food industry and researchers because of its high levels of anthocyanins such as cyanidin-3-O-glucoside and peonidin-3-O-glucoside [1]
Black rice has a relatively intense flavor that is distinctly different from that of white rice. 2-Acetyl-1-pyrroline, guaiacol, indole, and p-xylene are unique volatile compounds found in cooked black rice but not in cooked white rice [2]
The objectives of this study were to (1) identify and quantify the volatile compounds in raw black rice varying in degree of milling and (2) observe changes in volatile composition according to milling degrees by the cooking process by using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS)
Summary
Black rice has received attention from the food industry and researchers because of its high levels of anthocyanins such as cyanidin-3-O-glucoside and peonidin-3-O-glucoside [1]. Black rice has a relatively intense flavor that is distinctly different from that of white rice. 2-Acetyl-1-pyrroline, guaiacol, indole, and p-xylene are unique volatile compounds found in cooked black rice but not in cooked white rice [2]. Guaiacol is responsible for a smoky flavor, making cooked black rice acceptable to customers. Guaiacol and its derivatives have been used as flavor agents in the food and perfume industries. The smoky flavor imparts a roasted flavor to processed foods including bacon. Guaiacol can be used as a starter compound for vanillin synthesis [3]
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