关键词: 糙米, 挥发性风味化合物, 发芽, 挤压膨化, 气相色谱-质谱, 气相色谱-嗅闻

Abstract:

【Objective】The objective of this study was to investigate the effects of germination and extrusion process on volatile flavor compounds of brown rice by analyzing changes of the volatile flavor compounds of brown rice, so as to provide a reference for evaluating and improving the volatile flavor of brown rice. 【Method】The volatile flavor compounds of raw brown rice (RBR), extruded brown rice (EBR), germinated brown rice (GBR) and extruded germinated brown rice (EGBR) were analyzed by headspace solid phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The qualitative and relative quantitative analyses of the volatile flavor components were carried out by NIST14 database, retention index (RI), and internal standard. Gas chromatography olfactory (GC-O) was used to analyze the composition spectrums of the active odor compounds and their overall flavor profile as well as the volatile flavor characteristics of brown rice samples. 【Result】 A total of 28 volatile flavor compounds were identified, including aldehydes, alcohols, terpenes, esters, heterocycles and arenes. After extrusion, the contents of aldehydes, heterocycles and arenes in brown rice were increased significantly, while the contents of alcohols and terpenes decreased significantly; moreover, new esters were detected after extrusion. After germination treatment, the content of alcohols was increased, while the contents of aldehydes, terpenes, heterocycles and arenes decreased; however, esters were undetected after germination treatment. After extrusion, the content of aldehydes, terpenes, heterocycles and arenes in germinated brown rice were increased, furthermore, while the content of alcohols decreased; moreover, new esters were detected. What’s more, the contents of aldehydes, terpenes, esters and heterocyclic compounds in germinated brown rice were significantly higher than those in brown rice after extrusion. The principal component analysis showed that the increases of the contents of compounds, such as heptanal, nonanal, benzaldehyde, D-limonene, toluene and 2-AP, were highly correlated with extrusion, while the increases in contents of 2-ethyl-1-hexanol and 3-methylbutanol were highly correlated with germination, and the increases in contents of ethyl acetate, butyl acetate, dimethyl sulfide and pyridine were highly correlated with germination-extrusion treatment. GC-O results showed that 19 kinds of active odor compounds were detected, with the odor intensity value (OIV) of some compounds’ over ≥ 3, such as hexanal, heptanal, hexanol, 1-octene-3-ol, 2-acetyl-1-pyrroline and p-xylene. The flavor profile analysis showed that the odor intensity of wax was the highest in brown rice, followed by those of grass and nut, while those of floral and fruity odor were the lowest. After extrusion, the nutty, grassy and fruity odor intensities of brown rice were increased significantly, in contrast, the waxy odor intensity decreased significantly. After germination, the waxy, nutty, grassy and floral odor intensities of brown rice were decreased, however, the fruit odor intensity did not change. After extrusion, the nutty, waxy, grassy and fruity odor intensities of germinated brown rice were increased significantly. 【Conclusion】Germination could improve the production of alcohols in brown rice, while it could decrease the contents of other volatile compounds to some extent, resulting in the decline of overall flavor intensity. However, during the process of germination, brown rice could produce volatile flavor precursors through biochemical action, which could promote the formation of more volatile flavor compounds by extrusion in germinated brown rice. Extrusion could have a positive effect on the formation of aldehydes, terpenes, esters, heterocycles and arenes in brown rice as well as germinated brown rice. Moreover, the volatile flavor compounds content in extruded germinated brown rice were significantly higher than those in extruded brown rice. The overall flavor intensities of both raw brown rice and germinated brown rice were increased after extrusion, with the most significant increase in the nutty and fruity odor intensities.

Key words: brown rice, volatile flavor compounds, germination, extrusion, gas chromatography-mass spectrometry, gas chromatography-olfactory