Germination-Induced Changes in Flavoring Compound Profiles and Phytonutrient Contents in Scented Rice

Although rice has been cultivated as a major food crop for approximately 5,000 years, the interest of customers in 'scented rice' is a recent trend in the Korean market. As a part of developing a germinated scented rice variety, the newly bred scented rice variety 'Cheonjihyang-1 se' was germinated for 24 h, and changes in profiles of flavor-related volatiles, lipophilic phytonutrients, and fatty acids were investigated. The profiling of volatile compounds by using a headspace-gas chromatography-mass spectrometry (HS-GC-MS) revealed a total of 56 odor-active flavoring compounds; 52 at the pre-germination stage, 51 at the post-germination stage, and 47 common at both stages. The major flavoring compounds were nonanol and benzene, which constituted 11.5% and 6.6%, respectively, of the total peak area in pre-germinated rice, and 19.4% and 6.5%, respectively, in post-germinated rice. Germination induced an increase in 13 flavoring compounds, including 3,3,5-trimethylheptane and 1-pentadecene, which increased by 763 and 513%, respectively by germination. However, we observed a germination-induced decrease in most of the other flavoring compounds. Especially, the most important scented rice-specific popcorn-flavoring compound, 2-acetyl-1-pyrroline, showed 89% decrease due to germination. Furthermore, the germination of scented rice induced a decrease in the content of various phytonutrients. For example, the total contents of phytosterols, squalene, and tocols decreased from 207.97, 31.74, and $25.32{\mu}g\;g^{-1}$ at pre-germination stage down to 136.66, 25.12, and $17.76{\mu}g\;g^{-1}$, respectively at post-germination stage. The fatty acid compositions were also affected by germination. The composition of three major fatty acids, linoleic, oleic, and palmitic acids, increased from 36.6, 34.2, and 24.4%, respectively, at the pre-germination stage to 37.9, 36.9, and 20.7%, respectively, at the post-germination stage. All these results suggested significant changes in the flavor-related compounds and phytonutrients of the scented rice variety 'Cheonjihyang-1 se' during the process of germination, and subsequently the need for developing a more precise process of germination to enhance the flavor and nutritional quality of the germinated scented rice products.

향미벼의 발아 전 후 향기 성분 및 기능성 지질성분 함량의 변화

새로운 식품 소재의 개발을 목적으로 향미벼 신품종을 이용하여 발아현미를 제조하고 발아 전 후 종실에 함유된 향기성분과 생리활성 물질, 그리고 지방산 조성의 변화를 관찰한 결과는 다음과 같다. 1. 향기성분은 발아 전 52개, 발아 후 51개 등 총 56개 성분이 동정되었으며 이들은 hydrocarbon(29%)과 alcohol(23%) 및 aldehyde(21%)류로 분류되었으며, 주요 향기성분으로는 nonanal, benzene, 1-octanol, 1-hexanol, furan, decanal 등이 동정되었다. 2. 발아로 인하여 heptane,3,3,5-trimethyl, 1-pentadecene, 2-heptanone 등 13개 성분은 함량이 증가한 반면, 향미벼 특유의 팝콘향을 나타내는 2-acetyl-1-pyrroline을 비롯하여 1-nonanol, 1-heptanol, 1-hexanol 등 39개 성분은 발아로 인하여 함량이 감소하였다. 3. 향기 성분의 함량을 이용한 PLS-DA 분석 시 뚜렷하게 향기 특성에 따라 발아 전과 발아 후의 구별이 가능하였으며, 2-acetyl-1-pyrroline, 2-octanone 등은 발아 전의, 그리고 benzaldehyde, tridecene 등은 발아 후의 특징적인 향기성분으로 나타났다. 4. 발아된 향미벼의 campesterol, stigmasterol, sitosterol 등 phytosterol류와 squalene, 그리고 5종의 tocols 등 생리활성물질 함량은 모두 발아 전에 비해 낮은 것으로 나타났다. 5. 향미벼의 주요 지방산은 linoleic, oleic 및 palmitic acid였으며 발아로 인하여 linoleic acid와 oleic acid는 각각 1.3%, 2.7%의 증가하고 palmitic acid는 3.7%의 조성 비율이 감소하는 것으로 나타났다.