Efficient succinic acid production from high-sugar-content beverages by Actinobacillus succinogenes.

This study presents the production of succinic acid (SA) by Actinobacillus succinogenes using high-sugar-content beverages (HSCBs) as feedstock. The aim of this study was the valorization of a by-product stream from the beverage industry for the production of an important building block chemical, such as SA. Three types of commercial beverages were investigated: fruit juices (pineapple and ace), syrups (almond), and soft drinks (cola and lemon). They contained mainly glucose, fructose, and sucrose at high concentration-between 50 and 1,000 g/L. The batch fermentation tests highlighted that A. succinogenes was able to grow on HSCBs supplemented with yeast extract, but also on the unsupplemented fruit juices. Indeed, the bacteria did not grow on the unsupplemented syrup and soft drinks because of the lack of indispensable nutrients. About 30-40 g/L of SA were obtained, depending on the type of HSCB, with yield ranging between 0.75 and 1.00 gSA /gS . The prehydrolysis step improved the fermentation performance: SA production was improved by 6-24%, depending on the HSCB, and sugar conversion was improved of about 30-50%.

Immobilization of a Pleurotus ostreatus laccase mixture on perlite and its application to dye decolourisation.

In the present study, a crude laccase preparation from Pleurotus ostreatus was successfully immobilized on perlite, a cheap porous silica material, and tested for Remazol Brilliant Blue R (RBBR) decolourisation in a fluidized bed recycle reactor. Results showed that RBBR decolourisation is mainly due to enzyme action despite the occurrence of dye adsorption-related enzyme inhibition. Fine tuning of immobilization conditions allowed balancing the immobilization yield and the resulting rate of decolourisation, with the adsorption capacity of the solid biocatalyst. In the continuous lab scale reactor, a maximum conversion degree of 56.1% was achieved at reactor space-time of 4.2 h. Stability and catalytic parameters of the immobilized laccases were also assessed in comparison with the soluble counterparts, revealing an increase in stability, despite a reduction of the catalytic performances. Both effects are most likely ascribable to the occurrence of multipoint attachment phenomena.

Continuous lactose fermentation by Clostridium acetobutylicum--assessment of energetics and product yields of the acidogenesis.

An assessment of both the growth and the metabolism of acidogenic cells Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a CSTR under controlled pH conditions. Cultures were carried out using a semi-synthetic medium supplemented with lactose as carbon source. Acids and solvents, that represent products of the ABE process, have been purposely added in controlled amounts to the culture medium to investigate their effects on the product yields. The mass fractional yield of biomass and products were expressed as a function of the specific growth rate taking into account the Pirt model. The maximum ATP yield and the maintenance resulted 29.1 g(DM)/mol(ATP) and 0.012 mol(ATP)/g(DM)h, respectively. Quantitative features of the C. acetobutylicum growth model were in good agreement with experimental results. The model proposes as a tool to estimate the mass fractional yield even for fermentations carried out under conditions typical of the solventogenesis.

Strategies for dephenolization of raw olive mill wastewater by means of Pleurotus ostreatus.

The reduction of polyphenols content in olive mill wastewater (OMW) is a major issue in olive oil manufacturing. Although researchers have pointed out the potential of white-rot fungus in dephenolizing OMW, the results available in the literature mainly concern pretreated (sterilized) OMW. This paper deals with the reduction of polyphenols content in untreated OMW by means of a white-rot fungus, Pleurotus ostreatus. Dephenolization was performed both in an airlift bioreactor and in aerated flasks. The process was carried out under controlled non-sterile conditions, with different operating configurations (batch, continuous, biomass recycling) representative of potential industrial operations. Total organic carbon, polyphenols concentration, phenol oxidase activity, dissolved oxygen concentration, oxygen consumption rate, and pH were measured during every run. Tests were carried out with or without added nutrients (potato starch and potato dextrose) and laccases inducers (i.e., CuSO4). OMW endogenous microorganisms were competing with P. ostreatus for oxygen during simultaneous fermentation. Dephenolization of raw OMW by P. ostreatus under single batch was as large as 70%. Dephenolization was still extensive even when biomass was recycled up to six times. OMW pre-aeration had to be provided under continuous operation to avoid oxygen consumption by endogenous microorganisms that might spoil the process. The role of laccases in the dephenolization process has been discussed. Dephenolization under batch conditions with biomass recycling and added nutrients proved to be the most effective configuration for OMW polyphenols reduction in industrial plants (42-68% for five cycles).

Continuous lactose fermentation by Clostridium acetobutylicum--assessment of acidogenesis kinetics.

An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a continuous stirred tank reactor under controlled conditions adopting a complex medium supplemented with lactose as carbon source to mimic cheese whey. The effects of acids (acetic and butyric), solvents (acetone, ethanol and butanol) and pH on the growth rate of acidogenic cells were assessed. The conversion process was characterized under steady-state conditions in terms of concentration of lactose, cells, acids, total organic carbon and pH. The growth kinetics was expressed by means of a multiple product inhibition and interacting model including a novel formulation to account for the role of pH. The model has the potential to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production.