Determination of γ-Aminobutyric Acid from Developing Bean Sprouts, Active Brown Rice, GABA Tea and GABA Capsules Using High-Performance Liquid Chromatograpgy

Abstract

GABA exists in the brain and medulla spinalis of mammals. A small of amount of GABA is also found in plants. Available natural foods in the market that richly contain GABA include anka, active brown rice, GABA tea and fermented soybean. Literatures indicate forced germination can greatly increase the GABA contents of seeds. This study, therefore, selects such common edibles as adzuki beans, mung beans, soybeans and wheat seeds for experiment. After causing them to sprout, it tests the degree of germination and examines the GABA content of different germination positions in order to identify the seed that has the best GABA production potential. The most frequently employed HPLC method for examining GABA is the precolumn derivatization method. This experiment selects three derivatization reagents, HN, PITC and OPA, to derivatize the samples, analyze the GABA content through HPLC and compare the results. Experiment results indicate the HN derivatization method is not effective for test objects of complicated ingredients, such as gaba tea, germinated brown rice and germinated seed samples. We were unable to identify the GABA peak on the HPLC spectrum. When dealing with samples that contain large amount of amino acid, such as germinated brown rice and sprouted seeds, the PITC derivatization method is prone to disturbance and has the tendency to overestimate the GABA content. The OPA derivatization method effectively isolates the GABA peak of all test samples of this experiment. That its derivatization is simple and speedy makes it suitable for broader applications. Among the seed samples selected for the experiment, adzuki beans have the highest GABA production potential followed by soybeans. So among the experiment samples, the whole grain of Kaohsiung #7 and #8 adzuki beans sprouted to 6 cm and soybeans sprouted to 9 cm have the greatest GABA content per weight unit. Most of the seeds contain almost no GABA before sprouting. Among the sampling lengths (0 - 9 cm), sprouting of 0.5 cm has the lowest GABA content. When the sprouting is greater than 0.5 cm, the GABA content rises significantly as the length of the sprouting increases. Between sprouted adzuki bean and mung bean products, the taste of adzuki bean product is better than mung bean product. Heating enhances the taste. Among sprouted soybean products, soy milk preserves the greatest amount of GABA. Drinking of 531 mL of the soy milk made according to the process of this experiment will result in intake of 18 mg GABA for reduction of blood pressure. Drinking of 338 mL of the soy milk made according to regular process will attain the same effect.

GABA以游離形態存在於哺乳動物的腦和脊髓中，在植物中也有少量GABA的存在，目前市售富含GABA的天然食品有紅麴、發芽糙米、加碼茶及發酵大豆等。 文獻指出種子經過催芽處理可大幅增加GABA含量，因此本實驗選用生活中最常食用的紅豆、綠豆、黃豆、黑豆和小麥種子使其發芽後檢測不同發芽程度及不同發芽部位的GABA含量，找出其中最具GABA生產潛力的種子。 一般最常用於檢測GABA的HPLC方法是柱前衍生化法，本實驗選用HN、PITC以及OPA三種衍生化試劑分別對樣品進行衍生化後以HPLC分析，檢測樣品中的GABA含量，並將檢測結果加以比較。實驗結果顯示HN衍生法對於成分複雜的檢品如茶湯、發芽玄米、發芽種子樣品的分析效果皆不好，在HPLC圖譜上無法辨識GABA peak；PITC衍生法對於含有大量蛋白質胺基酸的樣品如發芽玄米、發芽種子則較易受干擾而可能高估GABA含量；OPA衍生法對於本實驗所有樣品中的GABA peak均有良好的分離效果，且衍生化過程簡單快速是較建議廣泛適用的檢測方法。 實驗所選種子樣品以紅豆最具GABA生產潛力，其次是黃豆。高雄7號、8號紅豆發芽至6 cm，黃豆發芽至9 cm是為實驗取樣中整顆紅豆、黃豆發芽種子單位重量擁有最多GABA的發芽程度。此外大部分種子未發芽時GABA含量幾乎沒有，在取樣長度中( 0 - 9 cm) 發芽至0.5 cm有最低GABA含量，發芽大於0.5 cm GABA含量有隨發芽長度增加而大幅增加的趨勢。在發芽紅、綠豆製品中，紅豆的風味較優於綠豆，且加熱有助於風味提升；發芽黃豆製品中以豆漿保有最多GABA量，如依本實驗的豆漿製程，每天飲用531 mL即可攝取18 mg GABA達到降血壓功效，若依一般製程僅需飲用338 mL即可。