ReviewmiRNAs: The hidden bioactive component of milk

- Milk is enriched with miRNAs present in its whey, lipids and exosomes fraction.
- They are more abundant in colostrum compared with mature milk.
- The abundant milk miRNAs are identified as immune related.
- Exosomal milk miRNAs are stable, tolerating harsh degradative conditions.
- Being bioavailable, they may function to effect the physiology.

BackgroundmiRNAs are the non-coding ribonucleic acid species around 22 nucleotides in length that are involved in various biological processes via regulating gene expression. They are abundantly present in the milk and have been identified in the various fractions of milk.Scope and approachMilk miRNAs are emerging as the new bioactive component of milk. miRNAs have been identified in whey, lipid as well as the exosomal fraction of milk of different species. But they are majorly present as encapsulated in the lipid bilayered nano-vesicles called exosomes, which confers stability and functionality to the milk miRNAs. They are stable even under harsh conditions, including high temperature, enzymatic treatments and low pH, indicating their physiological significance. Most of the abundant milk miRNAs are having immune-related functions, inclining the attention towards the role of milk miRNAs in providing immunity as well as nutrition. These milk exosomes not only participate in the intercellular communication but also, facilitate encapsulating cellular component including miRNAs to perform cellular functions. Overall, the stability of exosomes along with their potential to communicate with the target cells strengthens the view of encapsulated milk miRNAs as a bioactive component of milk.Key findings and conclusionsMilk miRNAs are stable against degradative conditions, may be bioavailable, may enter into the blood circulation and may affect the gene expression of target genes in recipient cells, influencing the immunity of infants and adult consumer of bovine milk. However, more studies are needed to be done to discover their physiological stability and bioactive potential.