An Innovative Optical Sensor for the Online Monitoring and Control of Biomass Concentration in a Membrane Bioreactor System for Lactic Acid Production

Citation: Fan, R.; Ebrahimi, M.; Quitmann, H.; Aden, M.; Czermak, P. An Innovative Optical Sensor for the Online Monitoring and Control of Biomass Concentration in a Membrane Bioreactor System for Lactic Acid Production. Sensors 2016, 16, 411.Accurate real-time process control is necessary to increase process efficiency, and optical sensors offer a competitive solution because they provide diverse system information in a noninvasive manner. We used an innovative scattered light sensor for the online monitoring of biomass during lactic acid production in a membrane bioreactor system because biomass determines productivity in this type of process. The upper limit of the measurement range in fermentation broth containing Bacillus coagulans was ~2.2 g·L?1. The specific cell growth rate (µ) during the exponential phase was calculated using data representing the linear range (cell density ? 0.5 g·L?1). The results were consistently and reproducibly more accurate than offline measurements of optical density and cell dry weight, because more data were gathered in real-time over a shorter duration. Furthermore, µmax was measured under different filtration conditions (transmembrane pressure 0.3–1.2 bar, crossflow velocity 0.5–1.5 m·s?1), showing that energy input had no significant impact on cell growth. Cell density was monitored using the sensor during filtration and was maintained at a constant level by feeding with glucose according to the fermentation kinetics. Our novel sensor is therefore suitable for integration into control strategies for continuous fermentation in membrane bioreactor systems

Process Parameters Affecting the Synthesis of Natural Flavors by Shiitake (Lentinula edodes) during the Production of a Non-Alcoholic Beverage

A novel alcohol-free beverage with a fruity, slightly sour, sweetish, fresh, and plum-like flavor was produced by incorporating the edible mushroom shiitake (Lentinula edodes) into the fermentation process. Shiitake pellets were used as a biocatalyst to promote the synthesis of the fruity esters methyl 2-methylbutanoate and 2-phenylethanol from amino acids and an organic acid present in the wort. We investigated the impact of two critical process parameters (volumetric power input and inoculum concentration) on the morphology of, and flavor production by, the shiitake pellets in a 1 L stirred bioreactor. Increasing the volumetric power input and biomass concentration influenced the morphology of the pellets and promoted the production of the most important flavor compound methyl 2-methylbutanoate in the beverage. Furthermore the worty off-flavor methional was degraded during the cultivation in stirred bioreactor by shiitake pellets. These findings provide useful information to facilitate the scale-up of the biotransformation and fermentation process in bioreactors

Identification of Potent Odorants in a Novel Nonalcoholic Beverage Produced by Fermentation of Wort with Shiitake (Lentinula edodes)

Novel refreshments with pleasant flavors were developed by fermentation of wort with basidiomycetes. Among 31 screened fungi, shiitake (Lentinula edodes) produced the most pleasant flavor. It was perceived as fruity, slightly sour, and plum-like. Flavor compounds were isolated by liquid–liquid extraction (LLE) and by headspace solid phase microextraction (HS-SPME). The key odor-active compounds were analyzed by a gas chromatography system equipped with a tandem mass spectrometry detector and an olfactory detection port (GC-MS/MS-O) and aroma extract dilution analysis (AEDA). For HS-SPME, a revised method of increasing the GC inlet split ratio was used. Most of the key odor-active compounds (e.g., 2-acetylpyrrole, β-damascenone, (<i>E</i>)-2-nonenal, and 2-phenylethanol) were detected with both extraction techniques. However, distinct differences between these two methods were observed