Stability and functionality of freeze-dried probiotic Bifidobacterium cells during storage in juice and milk

We investigated the stability of differently produced (variables being fermentation time, pH during drying, and cryoprotectant) freeze-dried Bifidobacterium animalis subsp. lactis E-2010 (Bb-12) cells in fruit juice and low-fat milk. In addition, the effect of the food matrix on the acid and bile tolerance of the cells was studied. Cells produced in different ways had comparable stability in milk, whereas in juice, sucrose-protected cells survived better than reconstituted skim milk-protected cells. The acid and bile tolerance was better in cells added to milk compared with those in phosphate buffered saline or juice. Despite good culturable stability in milk the acid and bile tolerance of cells decreased during the storage. Apparently, culturable stability data alone do not give an accurate enough prediction of the probiotic functionality in adverse conditions (e.g. survival in acid and bile stress). When choosing a cryoprotectant for a probiotic also the stability in target food applications should be considered.     

Improving the storage stability of Bifidobacterium breve in low pH fruit juice

Bifidobacterial food applications are limited since bifidobacteria are sensitive to e.g. acidic conditions prevalent in many food matrices. The aim of the present study was to investigate whether a low pH selection step alone or combined to UV mutagenesis could improve the viability of an acid sensitive Bifidobacterium strain, B. breve 99, in low pH food matrices. Furthermore, the potential of carriers and an oat fibre preparation to further improve the stability was studied. The best performing low pH tolerant variants in the present study were generated by UV-mutagenesis with 70-700 μJ/cm² followed by incubation in growth medium at pH 4.5. The most promising variants regarding the low pH tolerance showed, in repeated tests with cells grown without pH control, about one Log-value better survival in pH 3.8 fruit juice after one week storage at 4 °C compared to wild-type B. breve 99. Cells grown with pH control, PDX formulated and then frozen showed poorer viability in low pH fruit juice than cells grown with no pH control. For frozen concentrates pH 3.8 was too stressful and no or small differences between the variants and the wild-type strain were seen. The differences detected at pH 3.8 with the cells grown without pH control were also seen with the frozen concentrates at pH 4.5. Some improvement in the stability could be achieved by using a combination of trehalose, vitamin C and PDX as a freezing carrier material, whereas a significant improvement in the stability was seen when oat fibre was added into the fruit juice together with the frozen cells. Due to the initial very poor fruit juice tolerance of B. breve 99 the obtained improvement in the stability was not enough for commercial applications. However, the same methods could be applied to initially better performing strains to further improve their stability in the fruit juice.     

Monitoring of the quality of modified atmosphere packaged broiler chicken cuts stored in different temperature conditions: B. Biogenic amines as quality-indicating metabolites

The formation of biogenic amines was studied in broiler chicken cuts stored in modified atmosphere (MA) packages. Also, the applicability of biogenic amines for the quality control of MA-packaged broiler chicken cuts was evaluated in various constant and variable temperature schemes. It was found that temperature dependent changes took place in the concentrations of tyramine, putrescine and cadaverine. The changes in the concentrations of these amines were in accordance with the microbiological quality of broiler chicken cuts. On the basis of the results it was concluded that tyramine, putrescine and cadaverine could serve as quality indicating tools for MA-stored poultry.     

Acid tolerant mutants of Bifidobacterium animalis subsp. lactis with improved stability in fruit juice

The potential of UV mutagenesis combined with a specific selection step to generate more acid-resistant Bifidobacterium animalis subsp. lactis Bb-12 strains with improved viability in low pH food matrices was investigated in this study. A total of 144 Bb-12 UV-mutants were initially characterised. After prolonged storage in apple juice (pH 3.5) and various pheno- and genotypic tests (acid and bile tolerance, substrate utilisation, antibiotic susceptibility, aerotolerance, RAPD) two mutants (2.20 and 2.56) were chosen for further studies including cell surface morphology, stability of various traits after repeated inoculations, and performance in a fermenter and during down-stream processing. 2.20 and 2.56 showed over two Log-values better viability in pH 3.5 juice compared to Bb-12. Alterations in cell surface structures of 2.20 and 2.56 were detected with AFM, whereas other studied traits remained unchanged.In conclusion, UV mutagenesis and subsequent incubation in acidic medium enabled improving the stability of B. animalis subsp. lactis in low pH juice. Acid tolerance testing (HCl, pH 2.5, 2 h) results did not predict long-term stability of the strains in acidic food matrix (apple juice pH 3.5).