Poster (Scientific congresses and symposiums)
Determination of optimum conditions for preservation and reactivation of freeze-dried Acetobacter senegalensis used as vinegar starter
Shafiei, Rasoul; Thonart, Philippe
2011SFGP 2011
 

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Keywords :
Acetobacter, Freeze-drying, Alcohol dehydrogenase, Acetaldehayde dehydrogenase, Vinegar
Abstract :
[en] Availability of efficient starters is one of the most important elements during fermentation technology. Acetic acid bacteria (AAB) face extreme conditions (low pH, high acetic acid concentration (>7%), ethanol and high temperature) during vinegar fermentation. In spite of introduction of broth media contained viable AAB as starter by some companies; traditional methods for initiation of vinegar fermentation are still used even in modern factories, therefore there is a long Lag phase for initiation of fermentation. In recent studies in CWBI, a kind of lyophilized starter has been produced by using an isolated thermotolerant bacterium: Acetobacter senegalensis. The aim of this study is to determine the best media for revitalization and the optimum temperature for preservation of the freeze-dried cells. To produce biomass, glucose was used as carbon source in batch culture under regulated conditions. The cells harvested when they reached to stationary phase. Harvested cells suspended in spent growth medium (final supernatant of fermentation). Maltodextrin (10%), manitol (20%) and spent growth medium were used as protestants. After freeze-drying they were subjected to storage test at -20° C, 4° C and 35° C for six months. The viability of cells determined by using spread plate technique using three different media: YG (yeast extract, glucose) and YGE (yeast extract, glucose, ethanol) and YGEA (yeast extract, glucose, ethanol, acetic acid). According to residual viable cells, manitol and maltodextrin showed higher protective functions rather than spent growth medium (92.3%, 88.2% and 82.1% survival, respectively) during freeze-drying process. Viability of cells during rehydration is completely dependent to the composition of the broth media used for this purpose. Adding ethanol (>0.5%) or acetic acid (>1%) to rehydration medium caused 40-45% reduction in viable cell numbers in comparison to YG broth. The composition of culture media can also influence the growth of bacteria after rehydration. In YG, much higher cell growth (about 1 log unit) was observed in comparison to YGE and YGEA. Addition of glucose (20 g/l) to YGE can neutralize the adverse effect of ethanol considerably but it cannot improve the growth in YGEA. This can be partially explained according to the activity of alcohol dehydrogenase and acetaldehyde dehydrogenase. It was revealed that freeze-dried cells had very low activities for these two enzymes. Analysis of total soluble protein contents of lyophilized cells during storage at different conditions revealed that the soluble protein content of cells reduced by increasing the storage temperature. At 35° C after 15 days, there were 4.87 log units reduction in the viability of cells, and also about 14% less soluble protein was detectable under this condition whereas keeping of cells at -20 or + 4° C had no influences on protein and viability of cells. Storage of cells at +4° C in darkness for six month showed that about 79.2% and 68.3% viability of cells remained for cells protected by manitol and maltodextrin, respectively. To assess the real activity of lyophilized cells as starters, they were introduced to broth media (YGE contained 20g/l of glucose). It was seen that 6 months old lyophilized cells (with maltodextrin or manitol as protectants) were able to grow and consume 5 v/v of ethanol in 48 hr in the presence of initial acetic acid concentration (0.5%) at 30° C. In conclusion, the mentioned methods for preservation and reactivation of freeze-dried Acetobacter senegalensis can provide a promising tool for decreasing the lag phase of vinegar fermentation.
Disciplines :
Biotechnology
Author, co-author :
Shafiei, Rasoul ;  Université de Liège - ULiège > GIGA - Utilisateurs machines
Thonart, Philippe ;  Université de Liège - ULiège > Département des sciences de la vie > Biochimie et microbiologie industrielles
Language :
English
Title :
Determination of optimum conditions for preservation and reactivation of freeze-dried Acetobacter senegalensis used as vinegar starter
Publication date :
November 2011
Event name :
SFGP 2011
Event place :
Lille, France
Event date :
30-11-2011
Audience :
International
Available on ORBi :
since 19 March 2013

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