Table 2 Functional attributes of dairy and non-dairy kefir

Antimicrobial

Prevents the adhesion of pathogens to the gut epithelium through competitive binding. Produces anti-microbial peptides (bacteriocins, cathelicidin), along with acetaldehyde, CO₂, and H₂O_2, that manifest a bacteriolytic and bacteriostatic impact against a spectrum of pathogens

Produce short chain fatty acids, which decrease the pH and avoid the growth of pH-sensitive pathogenic bacteria in the intestine

[58, 61, 63, 64]

Anti-inflammation

Kefir suppresses the pro-inflammatory cytokines (Th-1, IL-6, IL-1β, TNF-α, NF-kB, and p-MAPK), and elevates the anti-inflammatory cytokines (Th-2, and IL-10), and stimulates TLR-2 proteins

[69,70,71,72,73]

Anti-cancer

Kefir-induced apoptosis is associated with the upregulation of BAX, Cyto-c, Caspase 3, 8, and 9, TGF-β1 mRNA expression and by downregulation of TGF-α and Bcl-2 expression

Furthermore, organic acids produced as secondary metabolites play a pivotal role in fostering cytotoxicity against HepG2 cells

[76,77,78,79]

Antioxidant

The donation of protons from the lactic acid by LAB during the fermentation of kefir scavenges free radicals, thereby augmenting the primary antioxidant property

Lactate ions within kefir can prevent lipid peroxidation by scavenging free radicals

[83,84,85,86]

Anti-diabetic

Promotes the activation of phosphoinositide 3-kinase or other molecules within the insulin signalling pathway, leading to enhanced insulin secretion. It inhibits the activity of pancreatic α-amylase and α-glucosidases, resulting in a significant reduction in postprandial glucose levels in the blood

[92,93,94,95,96,97]