On‐line monitoring of important organoleptic methyl‐branched aldehydes during batch fermentation of starter culture Staphylococcus xylosus reveal new insight into their production in a model fermentation

Abstract

A small fermentor (55 mL) was directly interfaced to a membrane inlet mass spectrometer for continuous on-line monitoring of oxygen and volatile metabolites during batch fermentations of the starter culture Staphylococcus xylosus. Using this technique, we were able to correlate production of the very important flavor compounds 2-methylbutanal, 3-methylbutanal, and 2-methylpropanal with various growth conditions. We found that the aldehydes were present in the culture broth only as transient metabolites. They were produced in the exponential growth phase, reached a maximum concentration when the culture became anaerobic, and then they rapidly disappeared from the culture medium. This general pattern was observed for three different strains of S. xylosus and S. carnosus. Small amounts of inoculum or increased exposure to oxygen were found to favor production of the aldehydes as a result of a longer aerobic growth period. Growing S. xylosus under conditions resembling those in a fermented sausage revealed that NaCl (5%) increased aldehyde production considerably, whereas KNO(3) (0.03%) or NaNO(2) (0.03%) had little effect. A lowering of pH from 7.2 to 6.0 reduced cell density, but had a minor affect on aldehyde production.

In situ determination of total dissolved inorganic carbon by underwater membrane introduction mass spectrometry

“…In support of the observations shown in Fig. 4, the observations of de Vos Petersen et al (2004) indicate that some portion of the transport behavior of PDMS membranes is proportional to analyte fugacity rather than to analyte concentration.…”

“…4 suggest that gas transport through PDMS membranes may be more complicated than has been previously supposed. Further, the work of de Vos Petersen et al (2004) showed that salinity exerted a strong influence on ln ln black. Ion currents against salinity are presented in red (1.27 atm absolute) and blue (184 atm absolute).…”

Branched-chain fatty acid biosynthesis in a branched-chain amino acid aminotransferase mutant ofStaphylococcus carnosus

“…They are used as aroma producers in the production of fermented meat products [7]. During the fermentation process they convert the BCAAs valine, leucine, and isoleucine into flavour important BC aldehydes and short chain carboxylic acids [8,9]. The production of these metabolites is closely linked to the biosynthesis of cellular BCFAs [1,10].…”

Mini‐review: soft sensors as means for PAT in the manufacture of bio‐therapeutics

“…On‐line high‐performance‐liquid‐chromatography, and on‐line mass spectrometry are examples of more expensive stand‐alone instruments with capacity to provide on‐line data for proteins, metabolites or other low‐molecular weight compounds. These methods are more costly to set up in combination with soft sensors, they require significant support and operator surveillance, but could, in many cases, supply reliable and valuable process data with short duration.…”