烘焙方法對茶葉中咖啡因含量之影響

Abstract

茶葉中的咖啡因(caffeine)含量約佔乾重之2％~5％，由於高劑量攝取咖啡因有礙人體健康，因此，本研究利用烘焙方式，希望能有效降低茶葉中的咖啡因含量。 茶葉烘焙之目的在降低含水率，改善茶葉品質，及提高茶葉之香氣。然而，不同之烘焙方式，會使茶葉內之化學成分發生變化，進而影響茶葉之品質。本研究分為二部份，第一部分是觀察茶葉內之咖啡因，在傳統烘焙下的動態變化，第二部份是分析減壓低溫烘焙對茶葉咖啡因含量之影響。 首先探討傳統烘焙方式對臺茶十三號包種茶茶葉咖啡因及兒茶素類之影響，實驗操作變因有烘焙溫度(80、100、120℃)、時間(1、3、6、9、12 hr)以及次數(1、2、3、4次)。茶葉中的咖啡因含量，會隨烘焙溫度的升高而增加，兒茶素類則隨烘焙時間增長，而略為增加，之後隨烘焙溫度及次數增加，而有減少之趨勢。茶葉品質則會隨溫度的提高及烘焙時間的增長而變劣，茶葉色澤變暗沉焦黑，香氣由清香轉為烘焙味，滋味則帶有焦味及火味。 第二部份則基於咖啡因所具有的昇華性質，以炒青綠茶及包種茶茶葉為材料，以減壓低溫烘焙，探討在不同的溫度、壓力、處理時間、茶葉含水率、茶葉顆粒度等條件處理下，對茶葉咖啡因含量的影響。茶葉經減壓昇華處理後，在溫度高於60℃，咖啡因的含量會增加，推測其可能原因為茶葉在加熱後，其組織內部的咖啡因易於溶出，或是咖啡因與其他多元酚類結合產生的複合物(caffeine-tannate complexes)，受加熱影響，而破壞其中之氫鍵和疏水鍵之作用力，使咖啡因分離出來。研究結果發現，在60 ℃、-550 mm Hg、含水率為5 %條件下，處理12小時後，可使綠茶茶葉之咖啡因脫除率達到26 %。顯示藉減壓昇華法可有效降低茶葉中的咖啡因，應可發展出一安全經濟的去咖啡因方法。

The caffeine content in tea leaves varies between 2 and 5 % by dry weight. Due to the adverse effects of caffeine, many methods have been explored for decaffeination, in efforts to remove or reduce the caffeine contained in plant materials. These methods included the traditional methods such as solvent extraction, water decaffeination, adsorption separating and supercritical carbon dioxide extraction. The recent developmental microbial and enzymatic degradation and breeding low caffeine tea varieties are also developed for removal of caffeine. Roasting methods profoundly influence the chemical composition of Paochung tea. In this study, Paochung tea were produced from TTES No.13. The processing parameters under investigation included temperature (80℃, 100℃, 120℃), duration (1, 3, 6, 9, 12 hr) and the number of times. Summer tea of 2008 was used and first roasting was done in autumn of 2008. Second and third roasting were done in 2009. The last roasting were in 2010. After roasting, caffeine and catechins were analyzed by HPLC. Caffeine content increased after roasting. Catechins content of tea increased slightly and then decreased with increasing of roasting duration and times. This study is based on the sublimation of the nature of caffeine. The technique of decompression sublimation was developed to decrease caffeine content of steamed green tea and paochung tea. The influence of temperature, pressure, time, moisture and granularity of tea leaves on decaffeination was investigated. At 60℃, - 600mm Hg and the water content of 5 wt %, after 12 hours, the decaffeination rate was 26 %. Caffeine can be effectively removed from tea leaves by decompression sublimation. It is a safe and inexpensive method for decaffeinating tea.