2-acetyl-1-pyrroline and n-hexanal

Jasmine rice (Khao Dawk Mali 105) is popular because of its pleasant unique aroma. Milling is an important step in order to produce various types of edible rice. The distribution of volatile aroma compounds in rice especially, endosperm and bran fractions are different. Hence, the purpose of this study was to determine the volatile aroma compounds of low-milled and high-milled Jasmine rice that affect the aroma quality of cooked rice. The new crop of Jasmine paddy was used in this study. Volatile aroma compounds in raw and cooked rice with two degrees of milling, i.e., low-milled rice (2-4% rice bran) and high-milled rice (11-13% rice bran) were investigated. The raw and cooked samples were extracted with dichloromethane and analyzed by gas chromatography-time of flight mass spectrophotometer (GC-TOFMS). The amount of volatile aroma compounds in rice was decreased with high milling. 3-Penten-2-ol (green odor), the most abundant compound in raw rice, was the lowest amount in high-milled rice. On the other hand, the high-milled rice bran had the highest amount of this compound. After cooking, more types of volatile aroma compounds were detected. 2-Acetyl-1-pyrroline (2AP) (pandan-like, popcorn-like) was the most abundant in cooked rice. Meanwhile, hexanal was the highest amount in cooked rice bran. However, 2AP was the potent aroma compound with the highest odor activity values in both raw and cooked rice with low and high milling degree as well as in rice bran.

Topics: Aldehydes; Chromatography, Gas; Cooking; Jasminum; Odorants; Oryza; Pyrroles; Volatile Organic Compounds

The effects of cooling rate (CR) on retrograded nucleation of rice starch-aromatic molecule complexes were evaluated. Six aromatic molecules (hexanal, 1-octen-3-ol, γ-decalactone, guaiacol, 2, 3-butanedione, and 2-acetyl-1-pyrroline) were chosen to represent the typical aromas in cooked rice. Differential scanning calorimetry results showed that increased CR from 0.34 to 3.04 °C/min led to reduced enthalpy change (ΔH) (in 2-acetyl-1-pyrroline from 2.08 to 1.40 J/g), reduced Tp (in 2-acetyl-1-pyrroline 100.91 to 98.29 °C whereas in 2,3-butanedione it remained almost constant) and increased Tc-To (but fluctuating in γ-decalactone) (p < 0.05). These results indicate that the nucleation forming at higher CR were more thermally unstable, less perfect, and more heterogeneous. X-ray diffraction analysis further indicated that nucleation forming at high CR was looser and with lower relative crystallinity (in 2-acetyl-1-pyrroline decreased from 2.18% to 1.00%) (p < 0.05). These results may aid the development of procedures for more effective preservation of aromatic molecules in cooked rice.

Topics: Aldehydes; Calorimetry, Differential Scanning; Cold Temperature; Cooking; Oryza; Pyrroles; Spectroscopy, Fourier Transform Infrared; Starch; X-Ray Diffraction

The solid phase microextraction (SPME) has been the most used technique for the extraction of volatile compounds from rice because of its easy operation and solvent-free. The extraction parameters, sample mass and incubation temperature, were optimized through a central composite rotational design (CCRD), aiming at maximizing the extraction of 2-acetyl-1-pyrroline (2AP), the main compound responsible for the aroma in aromatic rice, and minimizing the generation of hexanal, a marker of lipid oxidation. Besides, the time of sample incubation and fiber exposure for the extraction of the volatile compounds from rice were determined. The optimized conditions for SPME were: 2.5 g of ground rice in a 20 mL vial, sample incubation at 80 °C for 60 min and exposure of the divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) fiber in the headspace for 10 min. The optimized method was sucessfuly applied to 12 varieties of rice and principal component analysis (PCA) was performed to observe similarities in their volatile profile. A total of 152 volatile compounds were identified among the different rice varieties. From these, 42 were identified in arborio rice, 47 in basmati brand A, 43 in basmati brand B, 55 in black rice, 63 in brown rice, 39 in jamine rice, 50 in parboiled brown rice, 43 in parboiled rice, 54 in red rice, 63 in sasanishiki rice, 46 in white rice and 70 in wild rice.

Topics: Aldehydes; Dimethylpolysiloxanes; Hot Temperature; Odorants; Oryza; Polyvinyls; Principal Component Analysis; Pyrroles; Solid Phase Microextraction; Volatile Organic Compounds