Formation of volatile components from the thermal interactions of theanine with reducing sugars

Abstract

본 연구에서는 녹차의 umami와 향미성분에 기여하는 아미노산인 theanine (γ-ethylamino-L-glutamic acid)과 환원당 (reducing sugars)인 glucose, fructose의 가열반응 시 생성되는 휘발성 성분들의 형성에 미치는 영향요인에 대해 알아보고자 하였다. 서로 다른 네 가지 질소 급원 (theanine, ethylamine, glutamic acid, and the mixture of ethylamine and glutamic acid)과 두 종류의 환원당에서 생성되는 휘발성 성분들을 비교하기 위하여 glucose와 fructose를 각각 180℃에서 가열 반응하였고, 또한 pH (4, 7, 10)의 영향을 고찰하기 위해 각 조건에서 가열 반응 후 생성된 휘발성 성분들을 비교하였다. 휘발성 성분들은 용매추출을 통해 추출되고 GC/MS를 이용하여 분석하였다. 전체 24개의 model system의 가열반응에서 다양한 furfurals, furans, pyrazines, pyrrols, pyridines이 동정되었다. 특히, pyrazines 중 2,5-dimethyl pyrazine과 trimethyl pyrazine은 glutamic acid와 theanine의 반응물에서 다량으로 생성되었고, pyrroles에서는 1-ethyl-2-formyl pyrrole이 ethylamine, theanine과 glutamic acid, ethylamine 혼합물의 반응에서만 형성되었다. 또한, furfurals는 glutamic acid와 환원당의 반응에서보다 ethylamine과의 반응에서 더 많이 생성되었다. Theanine과 환원당의 반응물은 glutamic acid, ethylamine의 혼합물을 환원당과 반응 시킨 결과와 크게 다르지 않았다. 전반적으로 glutamic acid를 두 환원당과 pH 10에서 반응 시켰을 때, 다양한 종류의 질소원자 함유 성분들이 생성되었으며, theanine과 glutamic acid, ethylamine의 혼합물이 그 뒤를 이었다. 예외적으로 질소원자 함유 성분들 중 pyrroles의 경우 ethylamine에서 많은 양이 생성되었다. 가열반응 시 생성되는 휘발성 질소원자 함유 성분들은 pH가 높아짐에 따라 그 종류와 양이 급격히 증가하는 경향을 보였다. pH 10에서는 pyrazine류, pyridine류, pyrazole류, pyrrole류와 같은 질소원자 함유 성분들이 상당량 검출되었는데, 특히, 2,5-dimethyl pyrazine, trimethyl pyrazine이 다량으로 확인되었다. 반면 pH가 낮아질수록, 산소원자 함유 성분들의 생성량이 증가하였는데, pH 4에서는 furans 및 furfural, 5-methyl furfural 등이 주로 생성되었다. CAMOLA 법을 이용하여 theanine과 환원당의 주요 반응산물인 1-ethyl-2-formyl pyrrole의 생성 기작을 예측해본 결과 C5의 당분해산물과 가열시 theanine으로부터 분리된 ethylamine이 반응하는 것으로 나타났다. 이후 cyclization을 거쳐 최종 pyrrole의 형태로 형성될 것으로 추측된다.;In this study, the formation of volatile components from the thermal interactions of theanine with reducing sugars, such as glucose and fructose, was investigated. The effects of reducing sugars (glucose and fructose), nitrogen sources (theanine, glutamic acid, ethylamine, and a mixture of glutamic acid and ethylamine), and pH (4, 7, 10) on the formation of volatile components were analyzed and compared. The volatile components included diverse furfurals, furans, pyrazines, pyrroles, and pyridines. In particular, a considerable amount of pyrazines, such as 2,3-dimethyl pyrazine and trimethyl pyrazine, were formed from the thermal reactions of theanine and glutamic acid with reducing sugars. However, since ethylamine was the precursors of pyrroles, such as 1-ethyl-2-formyl pyrrole, they were mainly found in the thermal interactions of ethylamine, theanine and the mixture of glutamic acid and ethylamine with reducing sugars. The amount of furfural formed in the reaction of ethylamine with reducing sugars was greater than that of glutamic acid with the reducing sugars. Overall results showed that the effect of glutamic acid on the formation of volatile components was the most significant both qualitatively and quantitatively followed by theanine, the mixture of glutamic acid and ethylamine, and ethylamine. The effect of pH on the numbers and amounts of volatile components formed was also significant. At pH 4, higher contents of furfural and 5-methyl furfural were detected compared to pH 7 and 10. However, the formation of nitrogen-containing compounds, such as pyrazines, pyrroles, pyrazoles and pyridines, considerably enhanced at higher pH. In addition, carbohydrate module labeling study (CAMOLA) was used to elucidate the formation pathway of 1-ethyl-2-formyl-pyrrole, one of the major components from the thermal interaction of theanine with reducing sugars. The first step was the formation of C5 fragmentation from fructose via aldol-condensation. The dicarbonyl compound could react with amino group of ethyl amine to form 1-ethyl-2-formyl pyrrole via the cyclization of dicarbonyl.