Water Kefir: A Review of its Microbiological Profile, Antioxidant Potential and Sensory Quality

Abstract

Water kefir is a traditional beverage made from the symbiotic fermentation of kefir grains with sweetened water. Fruits such as apples, figs and kiwifruits can be used as flavouring agent or as source of fermentable sugars. Vegetables like pumpkin work similarly as fermentation substrate. This process is carried out at 25 - 30°C in anaerobic conditions, leading to a pH of 3.5 - 4.5 and alcohol content below 1%. The yeast strains mainly belong to Kluyveromyces and Saccharomyces. It is particularly rich in probiotics, such as the lactic acid bacteria Acetobacter spp., Lactobacillus acidophilus, brevis, casei, fermentum, helveticus, kefiri, kefiranofaciens parakefiri, lactis and Leuconostoc mesenteroides. In addition, yeast strains of Kluyveromyces lactis and Saccharomyces cerevisiae are typically present. These microorganisms are embedded in a matrix of kefiran, soluble fibre with hypocholesterolemic and hepatoprotective activities. Fermentation operated by kefir grains on fruit releases glutathione, organic acids and phenolic compounds, all of which act as antioxidants. Water kefir owes its distinctive sour aroma and flavour to lactic acid and alcoholic fermentation. Fruits and vegetables can provide nutrients such as amino acid, vitamins and minerals. Fermentation-induced hydrolysis of fibre releases sugars that lower kefir sourness in favour of sweeter notes