Encapsulation techniques, action mechanisms, and evaluation models of probiotics: Recent advances and future prospects

The related studies of probiotics-based functional foods have recently attracted increasing interests in developing new types of oral administration systems. Probiotics has various biological functions, including increasing adsorption ability of nutrients, competitively rejecting pathogenic organisms, and regulating the immune system. It is well known that probiotics cannot be worked until their colonies reach the intestine alive, as well as the amount reaches 10⁶–10⁷ colony-forming units/g at the end of product's shelf life. However, the delivery of probiotics to the colon through oral administration is always challenging due to weak viability under exposure to harsh conditions in the presence of ions and small molecules from the upper gastrointestinal tract. Moreover, the low viability of the probiotics due to the lack of resistance to the acidity of food matrices, high temperature during food processing, and oxygen changes during storage also limit the applications of probiotics in food products. Therefore, encapsulation of probiotics could particularly protect the probiotics from degradation and inactivation, resulting in enhanced viability during the transition from consumption to digestion in the gut. Emulsion cross-linking, complex coacervation, microcapsules, spray drying, layer-by-layer self-assembly, electrospinning, hydrogel, and other methods are used to encapsulate probiotics. Herein, this review mainly highlights the gut health functions and encapsulation techniques of probiotics, followed by the current challenges and future development prospects.