Influence of Roasting Process on the Chemical Profile of Aquilaria malaccensis Lam. Tea

The study was carried out as an initial evaluation of the effect of the roasting process on the chemical profile of Aquilaria malaccensis, which reportedly possessed astringency and bitter taste and is used as leaf tea. The study intended also to evaluate the required roasting temperature to enhance the chemical properties of Aquilaria leaf tea. The sample was collected, cleaned, and dehydrated for 48 h. Then, it was ground and sieved prior to roasting. For the roasting process, a conventional oven was used and samples were subjected to increasing temperatures such as small fire (SF) at 120–130 °C for 30 min, medium fire (MF) at 130–140 °C for 3.5 h, high fire (HF) at 145–155 °C for 3.5 h, and higher fire (H2F) at 145–155 °C for 4 h. After roasting, samples were then infused with boiling water to simulate the traditional method of brewing tea. To determine the effect of the roasting process, the following parameters were used: color hue, pH, odor, moisture content, water extract, total sugars, total phenolics, DPPH, and CUPRAC antioxidant activities. In addition, green tea, black tea, and oolong tea were used as reference teas. The results revealed that roasting temperature greatly affected the parameters. The color hue, as well as the acidity level of all roasted samples, were changed but still acceptable to the range value of a typical tea. The % moisture content and % water extract of A. malaccensis were significantly lowered in HF and H2F compared to that of unroasted samples. In terms of total sugars, the values of A. malaccensis at both SF and MF roasting temperatures were comparable to the values of reference teas. However, the total phenolic content (TPC) and antioxidant activities of A. malaccensis in all roasting temperatures were lowered compared to that of reference standards. Interestingly, there was an observable trend that as the roasting temperature increased, the TPCs and antioxidant activities of Aquilaria tea decreased. This is probably due to the degradation of some polyphenols or other compounds responsible for antioxidant activity. Based on the findings, it is recommended to roast A. malaccensis using SF and MF conditions in which their compounds are not greatly degraded. The results of this study will be used in the optimization of the manufacturing process of Aquilaria leaf tea.