Microbiota of Tayohounta, a fermented baobab flavour food of Benin

The present work provides data on the microbial composition of Tayohounta, a product of natural fermentation of baobab seed kernels. Samples were collected from 3 different small scale producers from Benin at the end of the fermentation process. Microorganisms were enumerated and identified using phenotypic and molecular approaches. Tayohounta was also investigated using culture independent techniques, direct DNA extraction, polymerase chain reaction - denaturing gradient gel electrophoresis (PCR-DGGE) and cloning. Isolated microorganisms were tested for their functionality in baobab seed kernels fermentation. Total viable counts were around 9 log cfu/g representing mainly Bacillus spp., whereas lactic acid bacteria (LAB) (8 log cfu/g), yeasts and moulds represent a smaller part of the total flora in all Tayohounta samples. Sequencing of clones of polymerase chain reaction (PCR) products of bacterial DNA directly extracted from Tayohounta revealed large differences between the products made by different producers. In all products, Bacillus licheniformis, B. pumilus, B. subtilis, B. thermoamylovorans and Lactobacillus fermentum were present. Other microorganisms (B. thuringiensis, Brevibacterium borstelensis, Enterococcus casseliflavus, E. durans, Lb. agilis, Pediococcus pentosaceus, Streptococcus equinus and Weissella confusa) were present occasionally. In experimental pure culture fermentations, B. subtilis showed little effect on pH, but degraded protein and caused a typical pungent smell typical of Tayohounta

Functional implications of the microbial community structure of undefined mesophilic starter cultures

This review describes the recent advances made in the studies of the microbial community of complex and undefined cheese starter cultures. We report on work related to the composition of the cultures at the level of genetic lineages, on the presence and activity of bacteriophages and on the population dynamics during cheese making and during starter culture propagation. Furthermore, the link between starter composition and starter functionality will be discussed. Finally, recent advances in predictive metabolic modelling of the multi-strain cultures will be discussed in the context of microbe-microbe interactions

Microbiological aspects of processing and storage of edible insects

Growing pressure on the worlds’ livestock production sector and enduring protein undernourishment, persuade the search for alternative protein sources. Insects are widely consumed in many parts of the world and are evaluated as food or supplement. Nevertheless, little attention has been given to the food safety and shelf-life of food insects. An exploratory evaluation of the microbiological content of fresh, processed and stored edible insects was carried out, with focus on farmed mealworm larvae (Tenebrio molitor) and house crickets (Acheta domesticus). A short heating step was sufficient to eliminate Enterobacteriaceae, however some sporeforming bacteria will survive in cooked insects. Simple preservation methods such as drying/acidifying without use of a refrigerator were tested and considered promising. Lactic fermentation of composite flour/water mixtures containing 10, or 20% powdered roasted mealworm larvae resulted in successful acidification and was demonstrated effective in safeguarding shelf-life and safety by the control of Enterobacteria and bacterial spores

Microbial diversity and dynamics of microbial communities during black-slop soaking of soybeans as determined by PCR-DGGE and molecular cloning

Tempe is a traditional fermented food in Indonesia. The manufacture process is quite complex, which comprises two stages, preparatory soaking of soybeans and fungal solid state fermentation. Daily addition of previous soak water (back-slopping) during the soybean soaking step is considered to be crucial in the manufacture of high quality tempe. The microbial diversity and dynamics of the microbial communities evolving during back-slop soaking of soybeans for tempe making was investigated by culture-independent PCR–DGGE and molecular cloning. Both DNA and total RNA were isolated and included in this study, to obtain a view on the succession of total and viable bacteria in the complex microbiota. DGGE profiles indicated that Enterobacter sp., Enterococcus sp., Pseudomonas putida, Leuconostoc fallax, Pediococcus pentosaceus, and Weissella cibaria, were the predominant bacteria. Their occurrence shifted dramatically during the back-slop soaking procedure. This study combined with previous culture-dependent studies could gain a better understanding of the complex microbiota of traditional fermented food and give useful information for its quality control

Bacterial concentration and diversity in fresh tropical shrimps (Penaeus notialis) and the surrounding brackish waters and sediment

This study aimed at determining bacterial concentration and diversity in fresh tropical shrimps (. Penaeus notialis) and their surrounding brackish waters and sediment. Freshly caught shrimp, water and sediment samples were collected in Lakes Nokoue and Aheme in Benin (West Africa) during two periods with different water salinity and temperature. We used complementary culture-dependent and culture-independent methods for microbiota analysis. During both sampling periods, total mesophilic aerobic counts in shrimp samples ranged between 4.4 and 5.9 log CFU/g and were significantly higher than in water or sediment samples. In contrast, bacterial diversity was higher in sediment or water than in shrimps. The dominant phyla were Firmicutes and Proteobacteria in shrimps, Firmicutes, Proteobacteria, and Actinobacteria in water, and Proteobacteria and Chloroflexi in sediment. At species level, distinct bacterial communities were associated with sediment, water and shrimps sampled at the same site the same day. The study suggests that the bacterial community of tropical brackish water shrimps cannot be predicted from the microbiota of their aquatic environment. Thus, monitoring of microbiological quality of aquatic environments might not reflect shrimp microbiological quality

Effect of soybean processing on content and bioaccessibility of folate, vitamin B12 and isoflavones in tofu and tempe

Purpose - To compare the content of bioaccessible folate, vitamin B12, and isoflavones in tofu and tempe, as influenced by soybean variety and food processing, particularly fermentation. Principal results - Raw soybeans contained 2207–2671 µg/kg (dry matter) folate, cooked tempe 1493–4143, and cooked tofu 968–1273 µg/kg, the difference was attributed to the fermentation in tempe. Vitamin B12 was detected only in tempe (0.16–0.72 µg/kg). Isoflavone aglycones were formed during soaking of soybeans, with only minor differences between the contents in cooked tempe (average 1922–2968 µg/kg) or tofu (1667–2782 µg/kg) but strongly depending on bean variety. Conclusions - Folate and vitamin B12 contents were mainly influenced by microbial activity during fermentation, whereas isoflavone aglycone content was determined by bean variety. Tofu had lower folate and vitamin B12, but equal isoflavone contents as tempe. Bioaccessibility of folate (80–100%) and isoflavone aglycones (100%) were hig

Contribution of Eat1 and other alcohol acyltransferases to ester production in Saccharomyces cerevisiae

Esters are essential for the flavor and aroma of fermented products, and are mainly produced by alcohol acyl transferases (AATs). A recently discovered AAT family named Eat (Ethanol acetyltransferase) contributes to ethyl acetate synthesis in yeast. However, its effect on the synthesis of other esters is unknown. In this study, the role of the Eat family in ester synthesis was compared to that of other Saccharomyces cerevisiae AATs (Atf1p, Atf2p, Eht1p, and Eeb1p) in silico and in vivo. A genomic study in a collection of industrial S. cerevisiae strains showed that variation of the primary sequence of the AATs did not correlate with ester production. Fifteen members of the EAT family from nine yeast species were overexpressed in S. cerevisiae CEN.PK2-1D and were able to increase the production of acetate and propanoate esters. The role of Eat1p was then studied in more detail in S. cerevisiae CEN.PK2-1D by deleting EAT1 in various combinations with other known S. cerevisiae AATs. Between 6 and 11 esters were produced under three cultivation conditions. Contrary to our expectations, a strain where all known AATs were disrupted could still produce, e.g., ethyl acetate and isoamyl acetate. This study has expanded our understanding of ester synthesis in yeast but also showed that some unknown ester-producing mechanisms still exist

Contribution of Eat1 and other alcohol acyltransferases to ester production in Saccharomyces cerevisiae

Esters are essential for the flavor and aroma of fermented products, and are mainly produced by alcohol acyl transferases (AATs). A recently discovered AAT family named Eat (Ethanol acetyltransferase) contributes to ethyl acetate synthesis in yeast. However, its effect on the synthesis of other esters is unknown. In this study, the role of the Eat family in ester synthesis was compared to that of other Saccharomyces cerevisiae AATs (Atf1p, Atf2p, Eht1p, and Eeb1p) in silico and in vivo. A genomic study in a collection of industrial S. cerevisiae strains showed that variation of the primary sequence of the AATs did not correlate with ester production. Fifteen members of the EAT family from nine yeast species were overexpressed in S. cerevisiae CEN.PK2-1D and were able to increase the production of acetate and propanoate esters. The role of Eat1p was then studied in more detail in S. cerevisiae CEN.PK2-1D by deleting EAT1 in various combinations with other known S. cerevisiae AATs. Between 6 and 11 esters were produced under three cultivation conditions. Contrary to our expectations, a strain where all known AATs were disrupted could still produce, e.g., ethyl acetate and isoamyl acetate. This study has expanded our understanding of ester synthesis in yeast but also showed that some unknown ester-producing mechanisms still exist