Effect of Schiff base formation and Aldol condensation on the determination of aldehydes in rice wine using GC-MS

Abstract

In this study, it is proved that the reason of reduction of aldehydes in makgeolli, Korean traditional alcoholic beverage. Four different sample preparation method including centrifugation, adjusting pH, solid phase extraction (SPE), and adding amino acid were prepared to verify effects of schiff base reaction and aldol condensation on reduction of aldehydes. The contents of aldehydes were decreased whereas those of hydroxy carbonyl compounds were increased by increasing pH. Acetaldehyde, 2-methylpropanal, 2-methylbutanal, 3- methylbutanal, and benzeneacetaldehyde were decreased 18 %, 57 %, 75 %, 69 %, 75 %, respectively, compared control with basic state. Methional and 5-methyl-2- furancarboxaldehyde were not determined at basic state. The results could be explained by aldol condensation and also could explain as effect of Schiff base reaction because it is accelerated by base catalysis. Although there are many aldehydes in most alcoholic beverages, especially, aldehydes in makgeolli is more reduced than in other alcoholic beverages, which is deduced that amino acids in makgeolli affect to determining aldehydes. The amount of aldehydes in makgeolli with added amino acid was reduced according to increasing the amount of amino acid. Acetaldehyde, 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, benzeneacetaldehyde, methional, 5-merhyl-2-furancarboxaldehyde were decreased 44 %, 50 %, 57 %, 37 %, 48 %, 31 %, and 69 % respectively. Reduction of aldehydes could result from reaction of aldehydes with added amino acid which is known as Schiff base reaction. The amount of hydroxyl carbonyl compounds are reduced by 50 mg/L of alanine than control. 3-hydroxy-2- butanone, 1-hydroxy-2-propanone, hydroxyl acetaldehyde, 1-hydroxy-2-butanone, and 2-hydroxyl-2-cyclopenten-1-one were reduced 36 %, 45 %, 18 %, 33 %, and 15 %, respectively. However, they are increased by 100 mg/L alanine than sample added 50 mg/L except hydroxy acetaldehyde and 2-hydroxy-2-cyclopenten-1-one. 1-hydroxy-2-propanone, and 1-hydroxy-2-butanone were decreased 33%, 11 %, and 50 %, respectively. The reason of reduction of hydroxy carbonyl compounds can be regarded that aldehydes react added amino acid, and aldol condensation is delayed. The content of hydroxy carbonyl compounds is increased by 100 mg/L of alanine because Schiff bases are equilibrium by high amount of amino acids. Therefore, in makgeolli, the main reason of reduction aldehydes is Schiff base reaction and additionally aldol condensation affect the reduction. It is proposed that pH of makgeolli is adjusted to neutral to identify and quantify aldehydes, which is affected by schiff base and aldol condensation, more accurately,;본 연구는 막걸리 내 알데하이드류 재현성 문제를 해결하기 위하여 문제 발생 원인에 대해 규명하고 전처리 법에 따른 알데하이드류와 향기성분의 정성, 정량적 차이를 제시하여 최적화된 기기분석법을 확립하고자 진행하였다. 재현성 문제의 발생 요인은 탁주 내 아미노산과 알데하이드류가 반응하여 schiff base를 형성하는 것과 알데하이드류 간 반응에 의한 aldol condensation으로 가정하고 원심분리, pH 조절, Solid Phase Extraction (SPE), 아미노산 첨가의 전처리법을 통해 세운 가정의 성립 여부를 확인하였다. pH가 증가에 따른 알데하이드류의 감소와 hydroxy carbonyl compounds의 양의 증가로 막걸리 내 알데하이드류가 aldol condensation에 영향을 받는 것을 확인하였다. 또한, pH 증가에 따른 알데하이드류 감소는 염기성 촉매에 의해 촉진되는 schiff base formation으로도 설명할 수 있다. SPE를 이용한 전처리법에서는 control에 비해 RSD가 감소하였으며, 이를 통해, 아미노산이 알데하이드류의 정성적 분석에 영향을 미친다고 할 수 있다. 막걸리 내 주요 아미노산인 alanine 첨가실험에서는 alanine 함량이 증가할수록 알데하이드류의 양은 감소하였으며, hydroxyl carbonyl compounds의 양은 감소하다가 다시 증가하였다. 이를 통해, 막걸리 내에서 schiff base reaction이 발생한다는 것을 알 수 있었다. 또한, 아미노산 첨가에 따라 hydroxy carbonyl compounds의 양이 감소하는 것은 schiff base formation에 따라 aldol condensation이 지연되었기 때문이며, 이후 schiff base formation이 평형되면서 aldol condensation이 촉진되었다고 할 수 있다. 따라서, 막걸리 내 알데하이드 감소는 schiff base formation과 aldol condensation으로 설명할 수 있다. pH에 영향을 받는 schiff base와 aldol condensation에 의한 알데하이드류의 정확한 정성, 정량을 위해서 막걸리의 pH를 중성으로 조절한 후 분석하는 것이 필요하다.