Optimisation of vitamin B12 and folate production by Propionibacterium freudenreichii strains in kefir

Vitamin B12 and folate deficiencies in poor Southern African communities lead to mandatory fortification of basic foodstuffs. Since folate- and B12-enriched kefir offers a cheaper alternative, regimes to include Propionibacterium freudenreichii (PAB) strains into kefir grains (KG) were investigated: two levels of PAB cell concentrations; freeze-drying KG to preserve PAB activity; and repeated PAB culture additions. Elevated B12 and folate levels and PCR results confirmed inclusion of PAB in all KG. Repeated inoculations with freeze-dried cultures (PAB concentration 1 × 108 cfu mL−1) delivered the highest B12 and folate production rate and concentration after 3 d. The best treatment (freeze-dried inoculum (5 × 107 PAB cfu mL−1) reacted once, followed by freeze-drying) delivered 186% Recommended Dietary Allowance (RDA) (B12) and 19% RDA (folate) per 200 mL serving. Freeze-drying preserved PAB activity in KG.