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Yoghurt with increased vitamin-levels

A focus was placed on increasing the vitamin B12 content in yoghurt using selected strains. Propionibacterium and Lactobacillus reuteri are known vitamin B12 producers and the performance of selected strains, obtained from NIZO food research and CERELA, was tested with respect to vitamin B12 production in yoghurt trials. Strains Propionibacterium B374 and B369 from the NIZO strain collection are relatively high folic acid producers (about 20mg/L x OD), but their capacity to produce vitamin B12 is yet unknown. The strains were pre-cultured in skimmed milk + 0.1% (w/v) casiton to support their growth. Yoghurt was prepared at 30 degrees Celsius using the MUH306 yoghurt culture with varying dosages of Propionibacterium B374 and B369 pre-culture. The results show that during yoghurt fermentation no growth occurred of Propionibacterium.

The total vitamin B12 content in prepared yoghurt s was determined by a microbiological assay using Lactobacillus delbrueckii ATCC 7830. Vitamin concentration in milk and yoghurt samples is measured before fermentation (t=0), after fermentation (t= pH4.5) and after 14 days (P+14) storage at 4 degrees Celsius. It is well known that during preparation of yoghurts the vitamin B12 content is reduced because the yoghurt bacteria consume vitamin B12 for growth purposes. In addition, this process of vitamin B12 consumption continues during storage of the yoghurt at 4 degrees Celsius. The results of the reference yoghurt MUH306 confirm these literature reports. Co-cultivation of yoghurt culture with Propionibacterium strains results in an increased level of vitamin B12 in the final product.

The results show that Propionibacterium does not grow during yoghurt fermentation, but is nevertheless able to actively produce vitamin B12. In addition, both Propionibacterium strains were shown to produce vitamin B12 at 4 degrees Celsius and consequently vitamin B12 concentration is enhanced in yoghurt during storage at 4 degrees Celsius for 14 days. In a second series of yoghurt trials we have tested the ability of selected Lactobacillus reuteri strains NIZO B1533 and CRL 1098 to produce vitamin B12 during yoghurt fermentation at 37 degrees Celsius and during subsequent storage for 14 days at 4 degrees Celsius. Lb. reuteri shows a ten-fold increase in cell numbers during yoghurt fermentation, but no growth is observed during storage at 4 0C. Both tested Lb. reuteri strains were able to enhance the vitamin B12 concentration level in yoghurt.

Furthermore, the results clearly show that Lb reuteri strains produce vitamin B12 in yoghurt during storage for 14 days at 4 degrees Celsius. This is the first report that describes the production of vitamin B12 in milk and yoghurt using Lb. reuteri strains. In the literature it has been suggested that Lb.reuteri CRL1098 might be a good candidate to increase vitamin B12 content in fermented food (Taranto, 2003).

However, Taranto and co-workers only describe vitamin B12 production by Lb. reuteri using synthetic laboratory growth media. Furthermore, these authors provide evidence that exogenous added vitamin B12 to the growth medium may repress endogenous vitamin B12 biosynthesis in Lb. reuteri, as has been observed in other micro-organisms. Remarkably, our results clearly show that Lb. reuteri produces vitamin B12 in milk, despite the fact that milk itself also contains vitamin B12. Grading results show that 1% (v/v) inoculum of Lb. reuteri strains produces a mild, sweet flavour to the yoghurt in comparison with reference yoghurt. Similar results were observed for 5% (v/v) inoculum with this exception that strain B1533 in addition produces an extra off-flavour described as "old" and "carton" in the yoghurt.

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