Biosurfactant Production from Lactobacilli: an Insight on the Interpretation of Prevailing Assessment Methods.

Biosurfactants constitute amphiphilic molecules, receiving increased attention as environmentally benign, biodegradable alternatives to substitute for the petroleum derived counterparts in food, pharmaceutical and cosmetics applications. However, their high production cost hinders industrial production. In this study, fifty GRAS lactobacilli strains were screened for their ability to produce biosurfactants, implementing different substrates. Cheese whey permeate (CWP) was also assessed as a low-cost and inherent lactobacilli substrate, aiming to mitigate its polluting impact, expand valorization strategies, alleviate costs deriving from commercial supplements and enhance overall sustainability. Surface tension, emulsification activity (E24) and oil displacement were deployed to identify the most promising candidates. Results reveal surface tension as the most robust method and underline the effect of substrate on biosurfactant synthesis. Likewise, this study indicates the fundamental role of including the final fermentation substrate (CWP) during strain selection to avoid misinterpretation of results and enhance subsequent bioprocess integration.

In vitro fermentation properties of pectins and enzymatic-modified pectins obtained from different renewable bioresources.

The suitability of artichoke and sunflower by-products as renewable sources of pectic compounds with prebiotic potential was evaluated by studying their ability to modulate the human faecal microbiota in vitro. Bacterial populations and short-chain fatty acid (SCFA) production were measured. Reduction of the molecular weight of artichoke pectin resulted in greater stimulation of the growth of Bifidobacterium, Lactobacillus and Bacteroides/Prevotella, whilst this effect was observed only in Bacteroides/Prevotella for sunflower samples. In contrast, the degree of methoxylation did not have any impact on fermentability properties or SCFA production, regardless of the origin of pectic compounds. Although further in vivo studies should be conducted, either pectin or enzymatically-modified pectin from sunflower and artichoke by-products might be considered as prebiotic candidates for human consumption showing similar ability to promote the in vitro growth of beneficial gut bacteria as compared to well-recognized prebiotics such as inulin or fructo-oligosaccharides.

Valorization of By-Products from Palm Oil Mills for the Production of Generic Fermentation Media for Microbial Oil Synthesis.

This study demonstrates the production of a generic nutrient-rich feedstock using by-product streams from palm oil production that could be used as a substitute for commercial fermentation supplements. Solid-state fermentations of palm kernel cake (PKC) and palm-pressed fiber (PPF) were conducted in tray bioreactors and a rotating drum bioreactor by the fungal strain Aspergillus oryzae for the production of crude enzymes. The production of protease was optimized (319.3 U/g) at an initial moisture content of 55 %, when PKC was used as the sole substrate. The highest free amino nitrogen (FAN) production (5.6 mg/g) obtained via PKC hydrolysis using the crude enzymes produced via solid-state fermentation was achieved at 50 °C. Three initial PKC concentrations (48.7, 73.7, and 98.7 g/L) were tested in hydrolysis experiments, leading to total Kjeldahl nitrogen to FAN conversion yields up to 27.9 %. Sequential solid-state fermentation followed by hydrolysis was carried out in the same rotating drum bioreactor, leading to the production of 136.7 U/g of protease activity during fermentation and 196.5 mg/L of FAN during hydrolysis. Microbial oil production was successfully achieved with the oleaginous yeast strain Lipomyces starkeyi DSM 70296 cultivated on the produced PKC hydrolysate mixed with commercial carbon sources, including glucose, xylose, mannose, galactose, and arabinose.

Biorefinery development through utilization of biodiesel industry by-products as sole fermentation feedstock for 1,3-propanediol production.

Rapeseed meal (RSM) hydrolysate was evaluated as substitute for commercial nutrient supplements in 1,3-propanediol (PDO) fermentation using the strain Clostridium butyricum VPI 1718. RSM was enzymatically converted into a generic fermentation feedstock, enriched in amino acids, peptides and various micro-nutrients, using crude enzyme consortia produced via solid state fermentation by a fungal strain of Aspergillus oryzae. Initial free amino nitrogen concentration influenced PDO production in batch cultures. RSM hydrolysates were compared with commercial nutrient supplements regarding PDO production in fed-batch cultures carried out in a bench-scale bioreactor. The utilization of RSM hydrolysates in repeated batch cultivation resulted in a PDO concentration of 65.5 g/L with an overall productivity of 1.15 g/L/h that was almost 2 times higher than the productivity achieved when yeast extract was used as nutrient supplement.