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130 PROCEEDINGS OF INTERNATIONAL SCIENTIFIC CONFERENCE ON APPLIED BIOTECHNOLOGY2. MATERIALS AND METHODS 2.1. Plant materialBlack pepper (Piper nigrum L.) used in this study was obtained from local farmer in Dak Lak province of Vietnam. There were two kinds of black pepper seeds including naturally dried and fresh ones with the moisture of 1.15% and 33.30%, respectively. Most of investigation experiments used dried black pepper seeds with the initial mass of 300 g (equivalent to 296.55 g DM).2.2. Experimental setupThe general process of experimental set up is described in Figure 1. Black pepper seeds were ground into small pieces by a blender (MJ-BC300GS, China). Then the raw material was sieved with a mesh to get the selected size. The prepared material was balanced by Ohaus Digital Scale (Model SPX6201, China). To determine the material moisture content, the black pepper was dried at 85 oC in the oven for 48 hours until the mass remaining unchanged. On the other hand, the sieved raw material after balancing was loaded into the 10 L hydro-distillation unit (Model TX05-02, China) and added with RO (reverse omosis) water at the designed ratio of raw material mass and water volume. In all experiments, the mass of dried black pepper was fixed at 300 g for each batch. Heating of the hydro-distillation reactor system was performed by an induction or electric heater (Bluestone, ICB-6728, China) at the medium heat mode for hours. The water vapor containing oil was condensed and drained into another glass funnel to separate water and essential oil layers. The black pepper essential oil was recovered from the condensed liquid by gravitationnal decantation method. The yellow essential oil extract was then collected, weighed and measured the volume of the crude oil. The crude oil can be dried by anhydrous Na2SO4 to