Enhancing vitamin B₁₂ in lupin tempeh by in situ fortification

Tempeh is a traditional, fungal fermented Indonesian product, usually made from soybeans. Tempeh is known to contain vitamin B12 which is essential for a healthy human diet. Therefore, tempeh is of particular interest for vegan diets since B12 is normally found only in animal derived products. The vitamin B12 in tempeh is associated with the presence of opportunistic pathogens like Klebsiella pneumoniae. Levels of B12 in tempeh do not sustain the recommended daily intake though. In addition, the use of a food-grade bacterium instead of K. pneumoniae is preferred. Lupin can serve as alternative substrate for soybeans due to its similar protein content, resulting in ‘lupin tempeh’. In this study, Propionibacterium freudenreichii, a food-grade, vitamin B12 producing bacterium, was used in co-culture with Rhizopus oryzae to produce B12-enriched lupin tempeh. A significant increase of vitamin B12 content (up to 0.97 μg/100 g) was achieved by fermenting lupin using a mixed starter of R. oryzae and P. freudenreichii. Other parameters, such as texture and volatile organic compounds, were not affected by the bacterial co-inoculation. Therefore, these results are promising for in situ vitamin B12 fortification of lupin tempeh making it a sustainable protein source for a healthy human diet.</p

Fecal Bacterial Communities in Insectivorous Bats from the Netherlands and Their Role as a Possible Vector for Foodborne Diseases

Bats are commonly regarded as vectors for viruses, but little is known about bacterial communities in bats and the possible role of bats in the transmission cycle of foodborne diseases. To gain more insight, microbial communities in fecal samples from 37 insectivorous bats of different species from the Netherlands were investigated by polymerase chain reaction and denaturant gradient gel electrophoresis (PCR-DGGE). Subsequently, 10 samples from the following bat species: common pipistrelle (Pipistrellus pipistrellus; n = 3), Daubenton's bat (Myotis daubentonii; n = 3), serotine bat (Eptesicus serotinus; n = 1), whiskered bat (Myotis mystacinus; n = 1), Geoffroy's bat (Myotis emarginatus; n = 1) and Natterer's bat (Myotis nattereri; n = 1) were selected and used in bacterial 16S rDNA cloning and sequencing. The fecal microbiota in bats was found to be diverse with predominant bacterial genera Carnobacterium, Serratia, Pseudomonas, Enterococcus and Yersinia. The presence of opportunistic pathogens Citrobacter freundii, Escherichia coli, Enterococcus faecalis, Serratia fonticola and Rahnella aquatilis was also recorded. Based on cloning results, we found no proof that bats in the Netherlands are a major vector for the transmission of bacterial zoonotic diseases, although previous findings in literature reported isolation of foodborne pathogens from bats.</p

Performance of non-conventional yeasts in co-culture with brewers’ yeast for steering ethanol and aroma production

Increasing interest in new beer types has stimulated the search for approaches to extend the metabolic variation of brewers’ yeast. Therefore, we tested two approaches using non-conventional yeast to create a beer with lower ethanol content and a complex aroma bouquet. First, the mono-culture performance was monitored of 49 wild yeast isolates of Saccharomyces cerevisiae (16 strains), Cyberlindnera fabianii (9 strains) and Pichia kudriavzevii (24 strains). Interestingly, both C. fabianii and P. kudriavzevii isolates produced relatively more esters compared with S. cerevisiae isolates, despite their limited fermentation capacity. Next, one representative strain of each species (Sc131, Cf65 and Pk129) was applied as co-culture with brewers’ yeast (ratio 1:1). Co-cultures with Cf65 and Pk129 resulted in a beer with lower alcohol content (3.5, 3.8 compared with 4.2% v/v) and relatively more esters. At higher inoculum ratios of Cf65 over brewers’ yeast, growth inhibition of brewers’ yeast was observed, most likely caused by competition for oxygen between brewers’ yeast and Cf65 resulting in a reduced level of ethanol and altered aroma profiles. With this study, we demonstrate the feasibility of using non-conventional yeast species in co-cultivation with traditional brewers’ yeast to tailor aroma profiles as well as the final ethanol content of beer.</p

Performance of non-conventional yeasts in co-culture with brewers’ yeast for steering ethanol and aroma production

Increasing interest in new beer types has stimulated the search for approaches to extend the metabolic variation of brewers’ yeast. Therefore, we tested two approaches using non-conventional yeast to create a beer with lower ethanol content and a complex aroma bouquet. First, the mono-culture performance was monitored of 49 wild yeast isolates of Saccharomyces cerevisiae (16 strains), Cyberlindnera fabianii (9 strains) and Pichia kudriavzevii (24 strains). Interestingly, both C. fabianii and P. kudriavzevii isolates produced relatively more esters compared with S. cerevisiae isolates, despite their limited fermentation capacity. Next, one representative strain of each species (Sc131, Cf65 and Pk129) was applied as co-culture with brewers’ yeast (ratio 1:1). Co-cultures with Cf65 and Pk129 resulted in a beer with lower alcohol content (3.5, 3.8 compared with 4.2% v/v) and relatively more esters. At higher inoculum ratios of Cf65 over brewers’ yeast, growth inhibition of brewers’ yeast was observed, most likely caused by competition for oxygen between brewers’ yeast and Cf65 resulting in a reduced level of ethanol and altered aroma profiles. With this study, we demonstrate the feasibility of using non-conventional yeast species in co-cultivation with traditional brewers’ yeast to tailor aroma profiles as well as the final ethanol content of beer.</p

Dynamic modelling of brewers’ yeast and Cyberlindnera fabianii co-culture behaviour for steering fermentation performance

Co-cultivation of brewers' yeast (Saccharomyces cerevisiae) with Cyberlindnera fabianii makes it possible to steer aroma and alcohol levels by changing the inoculation ratio of the two yeasts. A dynamic model was developed based on mono-culture performance of brewers' yeast and C. fabianii in controlled bioreactors with aerated wort as medium, describing growth rate, carbohydrate utilization, ethanol production, maintenance, oxygen consumption and ergosterol biosynthesis/use for cell membrane synthesis (the last one only for brewers' yeast). The parameters were estimated by fitting models to experimental data of both mono-cultivations. To predict the fermentation outcome of brewers' yeast and C. fabianii in co-cultivation, the two models were combined and the same parameter settings were used. The co-cultivation model was experimentally validated for the inoculum ratios 1:10 and 1:100 brewers' yeast over C. fabianii. The use of predictive modelling supported the hypothesis that performance of brewers' yeast in co-cultivation is inhibited by oxygen depletion which is required for the biosynthesis of ergosterol. This dynamic modelling approach and the parameters involved may also be used to predict the performance of brewers’ yeast in the co-cultivation with other yeast species and to give guidance to optimize the fermentation outcome.</p