Investigation of the Wet Extraction of Hydrocarbons from a Heterotrophic Microalga, <i>Aurantiochytrium</i> sp. 18W-13a, by Cell Disruption Using a High-pressure Homogenizer

Abstract

Aurantiochytrium, a heterotrophic microalga, produces hydrocarbons inside its cells and has a higher growth rate than other photosynthetic microalgae. To investigate a possible method of extracting hydrocarbons from wet Aurantiochytrium cells, cell cultures of Aurantiochytrium were treated with a high-pressure homogenizer. The influence of cell disruption and extraction time on the cell morphology, hydrocarbon yield, and energy balance of hydrocarbon extraction was evaluated. The hydrocarbon yield increased with an increase in extraction time regardless of cell disruption. After one round of the homogenizing treatment in which cells were fragmented (one-pass treatment), a second round (two-pass treatment) did not cause any additional morphological change. For the 40-min extraction, the yield of hydrocarbon from disrupted samples was found to be over ten times higher than that of undisrupted ones. In contrast, for the 180-min extraction, the yield of undisrupted samples was almost the same as that of disrupted ones because the cells of Aurantiochytrium were disrupted by extended contact with n-hexane over the longer extraction time. Furthermore, the input energy of the 40-min extraction with cell disruption was 78% lower than that of the 180-min extraction without cell disruption to obtain almost the same hydrocarbon yield. 従 属栄養性の微 細藻類 Aurantiochytrium は細胞内部に炭化 水素を産生し，他種の藻類と比較して増殖速度が大きい。 Aurantiochytrium の湿潤状態の細胞から炭化水素を抽出する方法を検討するため，高圧ホモジナイザーを用いて細胞を破砕した。 細胞の破砕および抽出条件が細胞の形状，炭化水素の抽出率および炭化水素抽出におけるエネルギー収支に及ぼす影響を評価 した。破砕の有無にかかわらず，抽出時間の増加に伴い，炭化水素の抽出率は増加した。また，高圧ホモジナイザーによる破砕処 理では， １回目の処理で細胞は断片化され，２回目の処理では細胞の形状のさらなる変化はなかった。40 min の抽出時間では，破 砕処理をした試料からの炭化水素の抽出率は未処理の試料からの抽出率と比べ 10 倍以上高い。その一方で，180 min の抽出時 間では，破砕処理をした試料および未処理の試料からの抽出率は同程度であった。これは，長時間 n-ヘキサンと接触することで Aurantiochytrium の細胞が破砕されたためである。また，破砕した試料を 40 min 抽出した場合の消費エネルギーは，同程度の抽 出率を得るために未処理の試料を180 min 抽出した場合と比べ 78％削減可能であった。