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SECTION I: MOLECULAR GENETIC ENGINEERING AND BIOCHEMICAL TECHNOLOGY 137Figure 5. Effect of m/V ratio of raw material and water on essential oil recovery yield ; (A) Oil volume (mL); (B) Oil yield (%). * indicates statistically significant differenceIt was observed that increasing volume of water from 3 to 5 L for 300 g material loading resulted in reduction of oil volume from 7.6 to 4.7 mL (Figure 5A). Accordingly, the highest total yield of essential oil production reached 2.18% with material to water ratio of 1/10 (100 g/L) which were statistically higher than that of the 1/15 and 1/12 ratios, yielding 1.35% and 1.53%, respectively (p< 0.05), but insignificantly different from the ratio of 1/7 (p > 0.05) (Figure 5B). This data implies that the water volume loaded into the distillation system should be chosen at the optimal ratio with material loading to simultaneously maximizing oil yield and save time and energy. 3.5. Biochemical analysis of black pepper essential oil by GC-MS GC-MS chromatographic peaks detected in black pepper essential oils from Dak Lak province of Vietnam are shown in Figure 6. The mass compositions of bioactive substances in the plant essential oil is presented in Table 1.