|Tipo di tesi||Tesi di laurea magistrale|
|Titolo||La produzione di aceto in sistema sommerso: parametri di processo e microbiologia dell’aceto di alcool in fermentatori pilota|
|Titolo in inglese||Submerged vinegar production: process variables and alcohol vinegar microbiology in pilot fermenters|
|Struttura||Dipartimento di Scienze della Vita|
|Corso di studi||CONTROLLO E SICUREZZA DEGLI ALIMENTI (D.M.270/04) (RE)|
|Data inizio appello||2015-04-15|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
I batteri acetici sono noti nell’industria alimentare come organismi alla base della produzione di aceti. La produzione industriale di aceto da vari substrati di acetificazione (vino, sidro, alcol) avviene mediante processi in sommerso. La fermentazione acetica in sistema sommerso è condotta mediante colture indigene di batteri acetici mantenute in coltivazione in cicli di fermentazione ripetuti. Per tali colture è documentata la difficile coltivazione in terreni di coltura, a causa della bassa capacità di dare origine a colonie e della bassa densità cellulare di colture all’interno dei bioreattori. Vista la non facile gestione delle colture acetiche, la gestione dei parametri di processo risulta di fondamentale importanza per favorire gli organismi e i bioprocessi necessari alla produzione.
Acetic acid bacteria are known in food industry for their role as bacteria responsible for vinegar production. Industrial vinegar production from different substrates (e.g. wine, sider, ethanol) is carried out by submerged processes. Acetic acid fermentation in submerged system is performed by indigenous acetic acid bacteria cultures propagated by repeated cultivation cycles. These bacterial cultures are known to be difficult to cultivate in media due to low ability to form colonies e low cellular density cultures into bioreactors. Due to the difficult handling of acetic acid bacteria cultures, the management of processes parameters is of great importance to favorite suitable bacteria and conditions. Advances in the study of acetic acid bacteria microflora of submerged processes could be of relevance in the light of existing processes optimization. On the basis of these observations, the research work of this thesis was focused on acetic acid bacteria and variables that affect their activity in submerged alcohol vinegar production. The research activity is composed by two parts: 1) training activity in Cetotec GmbH, specialized in services for the vinegar industry; 2) experimental activity performed at the laboratory of Food Microbiology (UNIMORE). The first part of the activity focused the production of alcohol vinegar. Two pilot systems operating in fed-batch and semi-batch, respectively were analyzed. Both systems are based on the use of a part of the fermented product at high cells concentrations as inoculum of the next cycle. Fed-batch system is operated dosing ethanol intermittently to the aim to increase total concentration (sum of ethanol and acetic acid) gradually. Semi-batch system is carried by a single charge phase and the discharge of the end product at a concentration of about 15% of acetic acid. During the training the processes were followed by monitoring processes parameters (acetic acid, ethanol, temperature, oxygen) along cycles to correlate bacteria growth to media composition. The second parts of the thesis activity focused the microbiological study of samples deriving from the aforementioned bioreactors. Strains isolation was carried out on culture media at different composition and bacteria growth was very slow (for some cultures about 15 days). The highest strain recovery was obtained in culture media at multiple carbon sources (glucose, ethanol, acetic acid). In fact, it was possible to carry out tests confirming the occurrence of acetic acid bacteria. However, the very low growth was a limit for further phenotypic assays. Culture independent analysis was performed by genomic DNA extraction from vinegar samples. In this case it was obtained a suitable genomic DNA for further molecular analysis by PCR/DGGGE. This work allowed to investigate submerged processes for alcohol vinegar production, both regarding processes parameters and acetic acid bacteria microflora. Selective pressure due to stringent conditions into bioreactors was detected as the main limit for the ex situ study of bacterial population.