Investigation on the Formation of Volatile Components in White and Brown Rice and the Effects of γ–Decalactone Precursors during Fermented by Lactobacillus paracasei

Abstract

본 연구에서는 Lactobacillus paracasei에 의해 발효시킨 현미와 백미의 휘발성 향기성분을 stir bar sorptive extraction (SBSE) 방법과 GC-MS를 통해 분석되었다. 4종의 esters, 17종의 aldehydes, 16종의 ketones, 13종의 alcohols, 4종의 hydrocarbons, 5종의 benzene and benzene derivatives, 3종의 furans, 1종의 phenols, 1종의 sulfur-containing compound, 1종의 nitrogen-containing compound, 그리고 3종의 lactones를 포함하여 총 68개의 휘발성 향기성분이 분석되었다. Methyl ester와 ethyl ester와 같은 esters류의 함량은 백미 발효물보다 현미 발효물에서 더 많은 양이 검출되었다. 몇몇의 aldehydes류와 alcohols류, ketones류 (3-methylbutanal, hexanal, octanal, nonanal, furfural, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol, 1-octen-3-ol)는 현미 발효물에서 더 많은 양이 검출되었다. Dacetyl과 acetoin은 현미 발효물과 백미 발효물에서 모두 검출되었으며, 이들의 양은 발효기간에 따라 증감양상이 반비례하는 결과를 보였다. 또한, γ-nonalactone, γ-decalactone, δ-dodecalactone의 경우에는 발효 기간에 따라 직선적으로 증가하는 양상을 보였다. 이러한 lactones류는 백미 발효물에서 보다 현미 발효물에서 더 많은 양이 검출되었다. 이러한 lactones류는 oleic acid와 linoleic acid 같은 유리지방산으로부터 기인하였음을 유추할 수 있었다. Solid phase extraction (SPE) 방법을 통해 기간별 쌀 발효물에 함유되어있는 유리지방산을 추출하여 GC-MS를 통해 분석한 결과, 발효 기간이 지남에 따라 oleic acid와 linoleic acid 같은 유리지방산은 감소함을 알 수 있었다. 이를 통해 시료에서 분석된 γ-decalactone의에 대하여, 이의 생성에 효과가 있는 전구체 첨가 효과를 규명하였다. Oleic acid로부터 생성되는 γ-decalactone의 생성경로를 통해 중간 생성물인 ricinoleic acid 와 4-hydroxy decanoic acid를 현미발효물의 0일차에 첨가하여 4일간 발효시켰다. 그 결과, 두 전구체 모두 γ-decalactone 생성을 더 증가 시키는 데에 효과가 있었으며, 특히 4-hydroxy decanoic acid가 ricinoleic acid 보다 더 많은 효과가 있었다.;Volatiles of brown and white rice samples fermented by Lactobacillus paracasei were analyzed using GC-MS combined by stir bar sorptive extraction (SBSE). A total of 68 volatiles compounds, including 4 esters, 17 aldehydes, 16 ketones, 13 alcohols, 4 hydrocarbons, 5 benzene and benzene derivatives, 3 furans, 1 phenols, 1 sulfur-containing compound, 1 nitrogen-containing compound, and 3 lactones, were identified. The contents of esters, such as ethyl and methyl esters, were higher in the brown rice samples. The contents of some aldehydes and alcohols (3-methylbutanal, hexanal, octanal, nonanal, furfural, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol, and 1-octen-3-ol) were significantly higher in fermented brown rice containing high amounts of lipids. Also, the amounts of ketones were larger in fermented brown rice. Both diacetyl and acetoin were obtained in fermentation rice samples during fermentation, and their concentrations were inversely proportional to each other. In addition, lactones, which were γ-nonalactone, γ-decalactone, and δ-dodecalactone, were significantly increased according to fermentation periods. Their concentrations were also higher in fermented brown rice samples than white ones. These γ-lactones might be formed from free fatty acids, such as oleic acid and linoleic acid. The levels of free fatty acids were analyzed by GC-MS combined by solid phase extraction (SPE) (full name) and derivatization. These free fatty acids were decreased during fermentation for 4 days. To investigate the effects of precursors for γ-decalactone formation, ricinoleic acid and 4-hydroxy decanoic acid were added into brown rice sample (0 day) as precursors. Both ricinoleic acid and 4-hydroxy decanoic acid could lead to the increase formation of γ-decalactone. However, the addition of 4-hydroxy decanoic acid was much more effective for its formation.