Microbiological and chemical properties of Norwegian kefir during storage

Five commercial productions of Norwegian kefir were investigated for development in microbiology, volatile compounds, organic acids, carbohydrates and free amino acids during cold storage for 8 weeks. Lactic acid bacteria numbers decreased during the first 4 weeks of storage, whereas yeast numbers increased throughout the storage period. The important yeast metabolites CO2 and ethanol both increased throughout the storage period. The amino acid glutamic acid was reduced during storage, and a consequent increase in its decarboxylation product γ-aminobutyric acid (GABA) was found. GABA has earlier been found to have blood-pressure-lowering effect in mild hypertensives when consumed in fermented milk in amounts of 10 mg daily over a 12-week period.