Altering operational conditions during protein fermentation to volatile fatty acids modifies the associated bacterial community.

In recent years, the production of volatile fatty acids (VFA) through mixed culture fermentation (MCF) has been gaining attention. Most authors have focused on the fermentation of carbohydrates, while other possible substrates, such as proteins, have not been considered. Moreover, there is little information about how operational parameters affect the microbial communities involved in these processes, even though they are strongly related to reactor performance and VFA selectivity. Hence, this study aims to evaluate how microbial composition changes according to three different parameters (pH, type of protein and micronutrient addition) during anaerobic fermentation of protein-rich side streams. For this, two continuous stirred tank reactors (CSTR) were fed with two different proteins (casein and gelatine) and operated at different conditions: three pH values (5.0, 7.0 and 9.0) with only macronutrients supplementation and two pH values (5.0 and 7.0) with micronutrients' supplementation as well. Firmicutes, Proteobacteria and Bacteroidetes were the dominant phyla in the two reactors at all operational conditions, but their relative abundance varied with the parameters studied. At pH 7.0 and 9.0, the microbial composition was mainly affected by protein type, while at acidic conditions the driving force was the pH. The influence of micronutrients was dependent on the pH and the protein type, with a special effect on Clostridiales and Bacteroidales populations. Overall, this study shows that the acidogenic microbial community is affected by the three parameters studied and the changes in the microbial community can partially explain the macroscopic results, especially the process selectivity.

Protein composition determines the preferential consumption of amino acids during anaerobic mixed-culture fermentation.

The valorisation of protein-rich residual streams by anaerobic mixed-culture fermentation (MCF) has been barely studied in contrast to carbohydrate-rich wastes. The aim of this work was, therefore, to investigate how protein composition, i.e. the amino acid (AA) profile, affects the individual consumption of amino acids and, consequently, the outcome of the process. Mixed-culture fermentations were performed with two model proteins (casein and gelatin) using continuous and batch reactors at neutral pH values and 25 °C. The acidification was incomplete for both proteins, with casein achieving a higher value than gelatin. Albeit dominated by acetic acid, product spectra were different as well, with n-butyric acid as the second major product for casein and propionic acid for gelatin. The preferential consumption of amino acids was demonstrated, which interestingly depends on protein composition. The previously accepted stoichiometry accurately describes iso and n-butyric acid production, but it fails for propionic, iso and n-valeric acid generation. Overall, this study offers a better understanding of protein fermentation mechanisms, which will help to improve degradation models and to design fermentation processes, based on optimal substrate selection.

A metabolic model for targeted volatile fatty acids production by cofermentation of carbohydrates and proteins.

Anaerobic mixed-culture fermentations are interesting processes to valorise organic wastes by converting them to volatile fatty acids. One of the main issues is that certain operational conditions (e.g. pH or different substrate concentrations) can vary significantly the product spectrum. So far, there are no tools that take into the account the characteristic features of cofermentation processes, which hinders the possibility of designing processes that use real wastes as substrates. In this work a mathematical model was developed for the production of volatile fatty acids from organic wastes with a high concentration of carbohydrates and proteins. The model reproduces satisfactorily experimental results and is also able of giving mechanistic insight into the interactions between carbohydrates and proteins that explain the observed changes in the product spectrum. We envision this model as the core of an early-stage design tool for anaerobic cofermentation processes, as shown in this work with different examples.

Ultrasound-guided compression repair of femoral pseudoaneurysms complicating cardiac catheterization.

BACKGROUND: Femoral pseudoaneurysms complicate cardiac catheterizations in up to 3.2% of cases. Ultrasound-guided compression repair (UGCR) is a known valid alternative therapy to surgical and percutaneous repair. We evaluated its safety and efficacy in a series of patients. METHODS: Patients with clinical findings suggesting pseudoaneurysm after cardiac catheterization, underwent echo-color and duplex studies. When a pseudoaneurysm was diagnosed, the patient underwent UGCR until closure or for 50 min. A groin compression bandage was applied after the procedure and patients were put on bed rest for 12-18 hours; a new ultrasound study was performed the day after the procedure: when the UGCR procedure failed, patients were referred to a vascular surgeon or interventional radiologist. When possible, a third ultrasound study was performed 1 month after the procedure. RESULTS: Between January 2001 and June 2003, 15 pseudoaneurysms were diagnosed and treated by means of UGCR. The UGCR procedure (UGCR followed by groin bandage) was successful in 13 cases (87%); 1 patient underwent surgical repair and 1 patient underwent percutaneous repair. No local or systemic complications were observed following UGCR. CONCLUSIONS: Pseudoaneurysm UGCR constitutes a safe and valid procedure; it is less invasive and easier to perform than percutaneous and surgical repair.