Luffa sponge offsets the negative effects of aeration on bacterial cellulose production.

AIMS: To offset the negative effects of aeration on bacterial cellulose (BC) production by acetic acid bacteria using enmeshed cellulose microfibrils (CM) on luffa sponge matrices (LSM). METHODS AND RESULTS: The CM were enmeshed on LSM (LSM-CM). The optimal amount of LSM-CM was determined for BC production under aerated conditions. Without LSM-CM, no BC was produced in seven out of nine production cycles at the highest aeration rate (9 l min-1 ). However, with 0·5% LSM-CM and an aeration rate of 3 l min-1 , a satisfactory oxygen transfer coefficient was achieved, and also a good yield of BC (5·24 g l-1 ). Moreover, the LSM-CM was able to be recycled through nine consecutive BC production cycles. The highest BC yields (from 5·8 ± 0·4 to 6·6 ± 0·4 g l-1 ) were associated with high bacterial biomass and this was confirmed by scanning electron microscopy. CONCLUSIONS: We confirm that LSM-CM works well as a starter. Microenvironments low in dissolved oxygen within the matrices of LSM-CM are important for BC production under aeration conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The LSM-CM provides a microenvironment which offsets the negative effects of aeration on BC production. A sustainable, economic process for mass BC production is described using recycled LSM-CM with aeration.

Influence of calcium chloride in the high temperature acetification by strain Acetobacter aceti WK for vinegar.

AIMS: To improve the thermotolerant properties (TTP) of acetic acid bacteria (AAB) cells for high temperature acetification. METHODS AND RESULTS: 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. CONCLUSIONS: The results confirm that changes of the content of lipid, activities of membrane-bound enzymes and cell-wall thickness occurred with added CaCl2. SIGNIFICANCE AND IMPACT OF THE STUDY: 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.

Impact of high initial concentrations of acetic acid and ethanol on acetification rate in an internal Venturi injector bioreactor.

AIMS: To evaluate the comparative impact of high initial concentrations of acetic acid (AAi ) and of ethanol (ETi ) on acetification rate (ETA). METHODS AND RESULTS: Acetic acid bacteria (AAB) were cultivated in a 100-l internal Venturi injector bioreactor. To quantify the oxygen availability, the 1.0 l min(-1) air inflow rate for the start-up phase (25 l) while 3·0 l min(-1) for the operational phase (75 l) achieved a high oxygen transfer coefficient (kL a). Changes in cell wall by TEM images and the remained ADH and ALDH activities confirmed the high acid tolerance ability of AAB. While ETAs using high AAi at 65 g l(-1) could be processed of 9.57 ± 0.19 g l(-1) day(-1) , which is just higher than 9.12 ± 0.12 g l(-1) day(-1) using high ETi at 55 g l(-1) . The average biotransformation yields were at 96.3 ± 0.1% and 94.4 ± 0.1% for high AAi and ETi , respectively. CONCLUSIONS: Results confirm that high oxygenation was generated in the bioreactor. Both high AAi and ETi were important in increasing ETA under stress 100 g l(-1) total concentration. SIGNIFICANCE AND IMPACT OF THE STUDY: High acid-tolerant AAB contains the high ADH and ALDH activities causing higher ETAs in HIA process. It is a competitive commercialized acetification process.

Acetification of rice wine by Acetobacter aceti using loofa sponge in a low-cost reciprocating shaker.

AIMS: To maximize acetification rate (ETA) by adsorption of acetic acid bacteria (AAB) on loofa sponge matrices (LSM). METHODS AND RESULTS: AAB were adsorbed on LSM, and the optimal shaking rate was determined for maximized AAB growth and oxygen availability. Results confirm that the 1 Hz reciprocating shaking rate with 40% working volume (liquid volume 24 l, tank volume 60 l) achieved a high oxygen transfer coefficient (k(L)a). The highest ETA was obtained at 50% (w:v) LSM-AAB:culture medium at 30 ± 2°C (P ≤ 0·05). To test process consistency, nine sequential acetification cycles were run using LSM-AAB and comparing it with no LSM. The highest ETA (1·701-2·401 g l(-1) d(-1)) was with LSM-AAB and was associated with the highest biomass of AAB, confirmed by SEM images. CONCLUSIONS: Results confirm that LSM-AAB works well as an inert substrate for AAB. High oxygenation was maintained by a reciprocating shaker. Both shaking and LSM were important in increasing ETA. SIGNIFICANCE AND IMPACT OF THE STUDY: High cell biomass in LSM-AAB provides good conditions for higher ETAs of quick acetification under adequate oxygen transfer by reciprocating shaker. It is a sustainable process for small-scale vinegar production system requiring minimal set-up cost.