Abstract
To improve the thermotolerant properties (TTP) of acetic acid bacteria (AAB) cells for high temperature acetification. At high temperature (36 ± 1°C), the acetification rate (ETA) is usually lower than at 30 ± 1°C. The addition of 0·15% calcium chloride (CaCl2 ) may decrease the negative effect of the increase of temperature from 30 ± 1°C to 36 ± 1°C on the ETA. The effect of CaCl2 on the thermotolerant properties of acetic acid bacteria cells was investigated. The CaCl2 increased the content of phospholipids (phosphotidylcholine and phosphatidylglycerol), fatty acids (cis-vaccenic acid, palmitic acid and myristic acid) and the activities of membrane-bound enzymes involved in acetification, alcohol dehydrogenase and aldehyde dehydrogenase. Transmission electron microscope images revealed a more compact cell wall with CaCl2. Process consistency at 36 ± 1°C was tested in nine sequential acetification cycles using 0·15% (w/v) CaCl2. High ETAs (9·33 ± 0·6; 8·67 ± 0·8 and 9·67 ± 0·7 g l(-1) day(-1)) were obtained during the last three cycles. The results confirm that changes of the content of lipid, activities of membrane-bound enzymes and cell-wall thickness occurred with added CaCl2. High temperature acetification (HTA) with additions of CaCl2 was investigated. Significant reductions in the overall production costs result from lower cooling costs associated with HTA.
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